TY - JOUR
AU - Wilson, Blake, K
AB - Abstract Cotton byproducts can be an economical source of protein, fat, and fiber in cattle finishing diets. The objectives of this study were 1) to assess the effects of including whole cottonseed (WCS) and cotton gin trash (CGT) in finishing diets on in situ ruminal degradability and 2) to determine the effects of including cotton byproducts in a finishing diet on rumen fluid pH, lactate, and volatile fatty acid concentrations. Six ruminally cannulated steers were used in a crossover design. Treatments included a control diet (CON; 7% prairie hay [PH], 15% Sweet Bran, 67.25% rolled corn, and 5% liquid supplement) and a cotton byproduct diet (CTN; 7% CGT, 15% WCS, 72.25% rolled corn, and 5% water). Both diets included 0.75% urea and 5% dry supplement. In situ bags containing individual diet ingredients and whole diet samples were incubated in the rumen for up to 96 h. Rumen fluid samples were collected over a 24-h period. No treatment × substrate interactions were detected for any fraction of dry matter (DM) or organic matter (OM) degradability for individual ingredients or whole diets (P ≥ 0.14). The A, B, and C fractions, disappearance rate (Kd), and effective degradability of DM and OM differed between diet ingredients (P ≤ 0.04) but were not different between CON and CTN substrates (P ≥ 0.25). A treatment × substrate interaction (P = 0.04) was detected for the effective degradability of neutral detergent fiber (NDF) of CGT and PH but there was no interaction for other fractions (P ≥ 0.27). The A fraction of NDF was greater (P < 0.001) for CGT than PH; however, the B fraction of NDF tended to be greater (P = 0.08) for PH than CGT. No differences (P ≥ 0.37) were detected for the % NDF disappearance at 48 h between CON and CTN substrates. A tendency for a treatment × substrate interaction (P = 0.10) was observed for the effective degradability of starch among diets; however, when the CON substrate was incubated in steers consuming the CON diet, effective degradability of starch was not different (P = 0.84) from when the CTN diet was incubated in steers consuming the CTN diet. There was no treatment × time interaction or treatment effect for rumen pH; however, there was a time effect (P = 0.03). Steers consuming the CTN diet had greater molar proportions of acetate and decreased molar proportions of propionate compared with CON steers (P < 0.01). This experiment suggests that there are minimal differences between the digestibility of finishing diets containing cotton byproducts and those comprised of traditional finishing diet ingredients. Introduction A recent upsurge in cotton production in the Southwestern United States has increased the availability of cotton byproducts for use in cattle diets (USDA, 2018). Cotton gin trash (CGT) consists of the leaves, sticks, burrs, stems, and soil remaining after the ginning process and can be an inexpensive source of physically effective fiber compared with other medium- to low-quality forages in feedlot diets (Meyer, 2007). Whole cottonseed (WCS) is unique in that WCS provides a substantial amount of protein and fat to the diet while also providing additional physically effective fiber. Previous experiments have been conducted to determine the effects of including cotton byproducts in finishing feedlot diets on cattle performance and carcass characteristics. Cranston et al. (2006) included various levels and sources of WCS and cottonseed meal in feedlot finishing diets and reported little to no adverse effects on performance or carcass characteristics. Warner et al. (2020) supplied protein, fat, and fiber in the finishing diet using WCS and CGT. Steers consuming the cotton byproduct-based diet (CTN) had increased dry matter (DM) intakes, average daily gains, and heavier final body weights compared with steers fed a control diet (CON) without cotton byproducts. Additionally, Warner et al. (2020) reported that steers consuming the CTN diet had heavier hot carcass weights, greater dressing percentages, back fat thicknesses, USDA Yield Grades, and kidney, pelvic, and heart fat percentages compared with steers consuming the CON diet. Understanding the digestion kinetics of cotton byproducts and common feed ingredients could help to explain the results of previous feeding trials. Therefore, the objectives of this experiment were 1) to assess in situ ruminal degradability of DM, organic matter (OM), neutral detergent fiber (NDF), and starch of traditional diet ingredients, cotton byproducts, and whole diets and 2) to determine the effects of including cotton byproducts in a finishing diet on rumen metabolism, including pH, lactate, and volatile fatty acid (VFA) concentrations. Materials and Methods All procedures were approved by the Institutional Animal Care and Use Committee at Oklahoma State University (Animal Care and Use protocol number: AG-16–17). Cattle and diets Six ruminally cannulated crossbred beef steers (initial body weight = 898 ± 21.6 kg) were used in this experiment. Steers were individually housed in partially covered, soil surfaced 6.1 × 10.9 m feedlot pens with a shared 76-liters concrete water tank between adjacent pens (model J 360-F; Johnson Concrete, Hastings, NE). Treatment diets (Table 1) included a CON finishing diet that consisted of 7% prairie hay (PH), 15% Sweet Bran (SB; Cargill Inc., Dalhart, TX), 67.25% dry-rolled corn (DRC), and 5% of a corn steep and molasses-based fat supplement or a CTN diet that contained 7% CGT, 15% WCS, 72.25% DRC, and 5% water to condition the diet. Both diets contained 0.75% urea and 5% dry supplement. Feeding occurred once daily at 0800 hours and steers had ad libitum access to feed and water throughout the experiment. Table 1. Ingredient and nutrient composition of treatment diets . Diet1 . . Ingredient, % of DM . CON . CTN . Rolled corn 67.25 72.25 PH 7.0 — CGT — 7.0 WCS — 15.0 SB2 15.0 — Liquid supplement3 5.0 — Dry supplement4 5.0 5.0 Urea 0.75 0.75 Nutrient composition, DM basis  DM, % 80.70 84.34  Crude protein, % 14.16 14.13  NDF, % 25.15 27.33  Acid detergent fiber, % 8.59 15.28  peNDF5, % 8.80 9.82  TDN, % 79.306 78.206  Fat, % 3.25 5.82  NEm, Mcal/kg 1.727 1.697  NEg, Mcal/kg 1.107 1.077  Ca8, % 0.62 0.85  P, % 0.57 0.46  K, % 1.00 0.84  S, % 0.22 0.19  Na, % 0.11 0.05  Mg, % 0.29 0.28  Cu, mg/L 20.00 24.60  Fe, mg/L 144.57 165.93  Zn, mg/L 161.03 145.97  Mn, mg/L 58.32 57.86 . Diet1 . . Ingredient, % of DM . CON . CTN . Rolled corn 67.25 72.25 PH 7.0 — CGT — 7.0 WCS — 15.0 SB2 15.0 — Liquid supplement3 5.0 — Dry supplement4 5.0 5.0 Urea 0.75 0.75 Nutrient composition, DM basis  DM, % 80.70 84.34  Crude protein, % 14.16 14.13  NDF, % 25.15 27.33  Acid detergent fiber, % 8.59 15.28  peNDF5, % 8.80 9.82  TDN, % 79.306 78.206  Fat, % 3.25 5.82  NEm, Mcal/kg 1.727 1.697  NEg, Mcal/kg 1.107 1.077  Ca8, % 0.62 0.85  P, % 0.57 0.46  K, % 1.00 0.84  S, % 0.22 0.19  Na, % 0.11 0.05  Mg, % 0.29 0.28  Cu, mg/L 20.00 24.60  Fe, mg/L 144.57 165.93  Zn, mg/L 161.03 145.97  Mn, mg/L 58.32 57.86 1Prior to the start of the experiment, cattle were fed a common receiving diet consisting of 12.7% rolled corn, 22.5% PH, 60.7% SB, and 4.1% dry supplement. 2Cargill Inc., Dalhart, TX. 3Liquid supplement was formulated to contain (% DM basis) 45.86% corn steep, 36.17% cane molasses, 6.00% hydrolyzed vegetable oil, 5.46% 80/20 vegetable oil blend, 5.20% water, 1.23% urea (55% solution), and 0.10% xanthan gum. 4Dry supplement was formulated to contain (% DM basis) 40.0% ground corn, 29.6% limestone, 20.0% wheat middlings, 7.0% urea, 1.0 % salt, 0.53% magnesium oxide, 0.51% zinc sulfate, 0.17% manganese oxide, 0.13% copper sulfate, 0.08% selenium premix (0.6%), 0.0037% cobalt carbonate, 0.32% vitamin A (30,000 IU/g), 0.10% vitamin E (500 IU/g), 0.009% vitamin D (30,000 IU/g), 0.20 % tylosin (Tylan-40, Elanco Animal Health, Greenfield, IN), and 0.33% monensin (Rumensin-90; Elanco Animal Health). 5Physically effective NDF provided by the roughage and byproducts in the diet. 6Calculated according to Weiss et al. (1992). 7Calculated according to NASEM (2016). 8Minerals analyzed by the Oklahoma State University Soil, Water and Forage Analytical Laboratory (Stillwater, OK). Open in new tab Table 1. Ingredient and nutrient composition of treatment diets . Diet1 . . Ingredient, % of DM . CON . CTN . Rolled corn 67.25 72.25 PH 7.0 — CGT — 7.0 WCS — 15.0 SB2 15.0 — Liquid supplement3 5.0 — Dry supplement4 5.0 5.0 Urea 0.75 0.75 Nutrient composition, DM basis  DM, % 80.70 84.34  Crude protein, % 14.16 14.13  NDF, % 25.15 27.33  Acid detergent fiber, % 8.59 15.28  peNDF5, % 8.80 9.82  TDN, % 79.306 78.206  Fat, % 3.25 5.82  NEm, Mcal/kg 1.727 1.697  NEg, Mcal/kg 1.107 1.077  Ca8, % 0.62 0.85  P, % 0.57 0.46  K, % 1.00 0.84  S, % 0.22 0.19  Na, % 0.11 0.05  Mg, % 0.29 0.28  Cu, mg/L 20.00 24.60  Fe, mg/L 144.57 165.93  Zn, mg/L 161.03 145.97  Mn, mg/L 58.32 57.86 . Diet1 . . Ingredient, % of DM . CON . CTN . Rolled corn 67.25 72.25 PH 7.0 — CGT — 7.0 WCS — 15.0 SB2 15.0 — Liquid supplement3 5.0 — Dry supplement4 5.0 5.0 Urea 0.75 0.75 Nutrient composition, DM basis  DM, % 80.70 84.34  Crude protein, % 14.16 14.13  NDF, % 25.15 27.33  Acid detergent fiber, % 8.59 15.28  peNDF5, % 8.80 9.82  TDN, % 79.306 78.206  Fat, % 3.25 5.82  NEm, Mcal/kg 1.727 1.697  NEg, Mcal/kg 1.107 1.077  Ca8, % 0.62 0.85  P, % 0.57 0.46  K, % 1.00 0.84  S, % 0.22 0.19  Na, % 0.11 0.05  Mg, % 0.29 0.28  Cu, mg/L 20.00 24.60  Fe, mg/L 144.57 165.93  Zn, mg/L 161.03 145.97  Mn, mg/L 58.32 57.86 1Prior to the start of the experiment, cattle were fed a common receiving diet consisting of 12.7% rolled corn, 22.5% PH, 60.7% SB, and 4.1% dry supplement. 2Cargill Inc., Dalhart, TX. 3Liquid supplement was formulated to contain (% DM basis) 45.86% corn steep, 36.17% cane molasses, 6.00% hydrolyzed vegetable oil, 5.46% 80/20 vegetable oil blend, 5.20% water, 1.23% urea (55% solution), and 0.10% xanthan gum. 4Dry supplement was formulated to contain (% DM basis) 40.0% ground corn, 29.6% limestone, 20.0% wheat middlings, 7.0% urea, 1.0 % salt, 0.53% magnesium oxide, 0.51% zinc sulfate, 0.17% manganese oxide, 0.13% copper sulfate, 0.08% selenium premix (0.6%), 0.0037% cobalt carbonate, 0.32% vitamin A (30,000 IU/g), 0.10% vitamin E (500 IU/g), 0.009% vitamin D (30,000 IU/g), 0.20 % tylosin (Tylan-40, Elanco Animal Health, Greenfield, IN), and 0.33% monensin (Rumensin-90; Elanco Animal Health). 5Physically effective NDF provided by the roughage and byproducts in the diet. 6Calculated according to Weiss et al. (1992). 7Calculated according to NASEM (2016). 8Minerals analyzed by the Oklahoma State University Soil, Water and Forage Analytical Laboratory (Stillwater, OK). Open in new tab This experiment was conducted as a crossover design; steers were randomly assigned to one of the two treatment diets for period 1 and were transitioned to the opposite diet for period 2. On day 0, steers began a 14-d transition from a receiving diet (12.7% rolled corn, 22.5% PH, 60.7% SB, and 4.1% dry supplement) to the respective treatment diet by increasing the amount of treatment diet delivered by 4% to 5% each day. Once steers were consuming 100% of the treatment diet, a 21-d acclimation period was allowed for the rumen environment to fully adapt to the diet. Once steers were acclimated to the treatment diets, a 96-h in situ incubation and a 24-h rumen fluid collection were completed. After the period 1 incubation and collection were completed, steers were transitioned from the period 1 diet to the period 2 diet over 14 d by increasing the amount of the new diet delivered by 4% to 5% each day. Steers were again allowed 21 d for the rumen environment to adapt before period 2 in situ incubations and rumen fluid collections were completed. Sample preparation and collection In situ procedures for this experiment were adapted from Vanzant et al. (1998). Throughout this manuscript, the term “substrate” refers to the feedstuff item placed into the in situ bags for incubation. The seven substrates used for in situ incubation included the diet components (PH, CGT, WCS, SB, and DRC), as well as whole ration samples for both the CON and CTN diets. Each substrate was ground to pass through a 6-mm screen (Wiley Cutting Mill Model 4; Thomas Scientific, Swedesboro, NJ) and dried for 48 h at 55 °C in a convection oven. Substrates were then placed into a benchtop desiccator and allowed to equilibrate to room temperature before being weighed into woven nylon in situ bags (10 × 20 cm R1020 Forage Bag; 50-µm pore size, ANKOM Technology, Macedon, NY). Each bag contained 4.0 g of substrate on a DM basis to achieve a sample size:bag surface area ratio of 10 mg/cm2, based on the recommendations from Vanzant et al. (1998). After each substrate was weighed into the in situ bag, a tabletop impulse sealer (ULINE, Pleasant Prairie, WI) was used to seal the bag. In situ bags that were to be incubated for 0, 3, 6, 12, and 24 h were made in triplicate, while bags that were to be incubated for 48, 72, and 96 h were made in quadruplicate in an attempt to ensure adequate substrate was available for analysis. All seven substrates were incubated in each steer for both periods, regardless of treatment. For each time point, all in situ bags were placed into a mesh bag with a string attached for ease of removal. In situ bags were inserted into the ventral sac of the rumen at 96, 72, 48, 24, 12, 6, and 3 h prior to simultaneous removal. Immediately upon removal, bags were shocked in an ice bath and gently rinsed until rinse water ran clear. Hour 0 bags were also rinsed to estimate the immediately soluble fraction of each substrate. After rinsing, bags were placed into a forced air oven at 55 °C for a minimum of 168 h and were rotated daily to ensure all bags received direct airflow. Rumen fluid samples were collected 2 d after the in situ incubation was completed during each period. Sampling began at 0730 hours to represent a 24 h postprandial sample. Following the hour 24 rumen fluid collection, steers were returned to home pens and fed at approximately 0800 hours. Rumen fluid was collected at 2, 4, 6, 8, 10, and 12 h post-feeding. A 50-mL sample was collected from each steer through the rumen cannula using a suction strainer. Immediately after collection, pH was measured using a portable pH meter (pH 6+ Meter; Oakton Instruments, Vernon Hills, IL), aliquoted, and stored at −20 °C until analysis was completed. The aliquot designated for VFA analysis included 100 µL of a 50% (w/v) solution meta-phosphoric acid (Acros Organics, Fair Lawn, NJ) and 100 µL of an 85 mM 2-ethyl butyrate (Thermo Fisher Scientific, Waltham, MA) internal standard. Laboratory analysis Upon removal of in situ bags from the drying ovens, bags were placed into a tabletop desiccator and allowed to equilibrate to room temperature. Bags were individually removed from the desiccator, and the weight of each bag was recorded. Substrates were composited by period, animal, and hour and stored at room temperature for further analysis. All post-incubation in situ substrates were ground to pass a 2-mm screen (Wiley Mini-Mill; Thomas Scientific, Swedesboro, NJ) prior to analysis. All in situ samples were analyzed for DM and OM in duplicate (AOAC, 1990). NDF was analyzed in duplicate for the CGT, PH, CON, and CTN in situ samples post-incubation. For analysis, a 0.45 to 0.50 g sample was placed into a filter bag (F57 filter bag; ANKOM Technology, Macedon, NY) and sealed using an impulse heat sealer (ULINE, Pleasant Prairie, WI). Samples were then placed into an ANKOM 2000 automated fiber analyzer (ANKOM Technology, Macedon, NY). After the NDF solution filled the vessel and agitation began, 4.0 mL of alpha-amylase (ANKOM Technology, Macedon, NY) and 20.0 g of sodium sulfite were manually added, and an additional 8.0 mL of alpha-amylase was added to the dispenser to be automatically added to the vessel during rinsing. After the NDF extraction was complete, sample bags were removed from the vessel, soaked in acetone for 3 to 5 min, and allowed 30 min to air-dry in a ventilated hood. Then, sample bags were transferred to a 100 °C convection oven for 2 to 4 h to dry. Samples were then removed from the oven, places in a desiccant pouch, and individually weighed for the determination of NDF. Starch was analyzed for all post-incubation DRC, CON, and CTN samples using methods adapted from the acetate buffer method described by Hall (2009). Samples weighing 0.17 g were weighed into glass screw-top tubes and 30 mL of acetate buffer and 100 µL of heat-stable alpha-amylase (ANKOM Technology, Macedon, NY) were added to each tube. The glass tubes were then incubated for 1 h in a 100 °C water bath and vortexed at 10, 30, and 50 min of incubation. After tubes were removed from the water bath and cooled, 50 µL of amyloglucosidase (Megazyme; Bray, Ireland) was added to the tubes, the tubes were vortexed, placed into a 60 °C water bath, and vortexed again after 1 h of incubation. After removal from the water bath, 20 mL of water was added to the tubes and vortexed. Then, 1.5 mL of liquid from each tube was transferred into a microcentrifuge tube, centrifuged at 12,000 × g for 10 min, and the supernatant was transferred to a 96-well plate for glucose to be determined using an immobilized enzyme system (YSI Model 2950 D; YSI Inc., Yellow Springs, OH). Substrates that were incubated were assumed to contain no free glucose, and, therefore, enzyme blank tubes were only included for initial diet samples and substrates analyzed for the 0-h incubation. For l-lactate analysis, rumen fluid was centrifuged at 21,100 × g for 15 min at 20 °C (Sorvall Legend Microcentrifuge; Thermo Scientific, Hampton, NH). The supernatant was analyzed using an immobilized enzyme system (YSI Model 2950 D; YSI Inc., Yellow Springs, OH). The VFA concentrations of rumen fluid were analyzed at the University of Kentucky Ruminant Nutrition Laboratory using gas chromatography with a flame ionization detector as described by Foote et al. (2013). Calculations The following were calculated for each substrate post-incubation. DM remaining was calculated as 100 × (total dry weight – empty bag weight) ÷ initial sample weight. Percent DM disappearance was calculated as 100 – DM remaining. OM remaining was calculated as 100 × (dry sample weight × OM of incubated sample) ÷ (initial sample weight × OM of original sample). Percent OM disappearance was calculated as 100 – OM remaining. NDF remaining was calculated as 100 × (dry sample weight × NDF of incubated sample) ÷ (initial sample weight × NDF of original sample). Percent NDF disappearance was calculated as 100 – NDF remaining. Percent starch remaining was calculated as 100 × (dry sample weight × starch of incubated sample) ÷ (initial sample weight × starch of original sample). Percent starch disappearance was calculated as 100 – % starch remaining. Fractions of DM, OM, NDF, and starch in this experiment were defined according to Orskov and McDonald (1979). The A fraction is defined as the immediately soluble fraction, disappearing at a rapid rate upon insertion into the rumen. The B fraction is defined as the amount of DM, OM, NDF, or starch that disappears at a measurable rate. The C fraction is defined as undegradable, or the amount, which did not disappear over the period of observation. The A fraction was determined by the calculation 100 – (B + C). The B and C fractions, disappearance rate (Kd), and lag time were determined using nonlinear regression described below. The effective degradability of DM, OM, NDF, and starch was calculated by the Ørskov and McDonald (1979) equation A + {B × [Kd/(Kd + Kp)]}, where passage rate (Kp) was assumed to be 4%/h, an average passage rate for feed particles in beef cattle diets (NASEM, 2016). Statistical analysis In situ disappearance curves for each steer and substrate were analyzed by nonlinear regression using the NLIN procedure of SAS 9.4. The parameters for each fraction were defined as follows: B fraction: 20 to 50 by 2, Kd: 0 to 0.2 by 0.1, L: 0 to 10 by 1, and C fraction: 10 to 40 by 2. Bounds for the model were specified as follows: B fraction: 0 to 100, C fraction: 0 to 100, Kd: 0 to 30%/h, and L: 0 to 48 h. If the undegradable fraction initially violated the C bound, the undegradable fraction was manually set to be the percent remaining at 96 h for the substrate. The undegradable fraction of starch was assumed to be 0 and was manually set as such for all substrates in which starch was measured. The degradable fractions of DM, OM, NDF, and starch, and the % NDF remaining at 48 h for each substrate, were compared using the MIXED procedure of SAS 9.4. The model included substrate, treatment, and substrate × treatment as main effects, and animal × period was included in the random statement. Rumen fluid pH, lactate, and VFA data were analyzed using the MIXED procedure of SAS 9.4 (SAS Institute Inc., Cary, NC). The fixed effects of treatment, time, period, and treatment × time were used in the model to evaluate the data. Time within period was included as a repeated measure with autoregressive covariance structure and individual animal was the subject. The autoregressive covariance structure was determined to provide the best fit (i.e., lowest Akaike information criterion) for the pH, lactate, and VFA data in the current experiment. For all data, results were considered significant when P ≤ 0.05, and tendencies were considered when 0.05 < P ≤ 0.10. Results and Discussion This experiment was conducted to further assess the differences in performance, intake, and carcass characteristics observed in cattle consuming the same experimental diets by Warner et al. (2020). It is important to note that while the primary roughages and byproducts were included at the same rate in the experimental diets, the objective of Warner et al. (2020) was not to replace a specific diet ingredient for another (i.e., SB with WCS), but rather to determine if cotton byproducts could successfully provide the majority of macronutrients in a finishing diet for beef cattle. Therefore, when discussing the degradability of individual diet ingredients in the current experiment, the primary aim was to assess the potential differences in the metabolism of both the individual ingredients and experimental diets from Warner et al. (2020). In situ DM disappearance There was no treatment × substrate interaction (P ≥ 0.14; Table 2) or main effect of treatment (P ≥ 0.62) for DM disappearance of any fraction; therefore, only the main effect of substrate is reported. The greatest A fraction was observed for SB, with 48.2% of the DM considered immediately soluble. It is well documented that wet corn gluten feed (WCGF) is rapidly and extensively degraded in the rumen due to the considerable amount of soluble steep liquor (McCoy, 1997). However, the observed A fraction of SB in this experiment was greater than the A fraction of WCGF reported by Sindt et al. (2003) who reported that 31.2% of the DM in WCGF was immediately soluble. It is important to note that not all the previously reported research clarifies the source of WCGF used in the experiment. SB has an increased DM (NASEM, 2016) and can vary in nutrient composition compared with unbranded WCGF sources. This variation in the nutrient composition may explain the variation between results reported in the current experiment and results reported in previous literature. Table 2. In situ DM disappearance of diet ingredients1 . A2 . B3 . C4 . L5 . K6 . EDeg7 . Item . % of DM . . . . . .  PH 10.8 ± 0.66e 15.6 ± 2.83e 73.6 ± 2.81a 6.4 ± 2.92ab 2.6 ± 0.70c 14.7 ± 1.43e  Gin trash 25.0 ± 0.63b 15.7 ± 2.70de 59.3 ± 2.67b 12.5 ± 2.38a 3.2 ± 0.67bc 29.4 ± 1.39d  Corn 16.1 ± 0.63cd 77.4 ± 2.70a 6.8 ± 2.67e 6.0 ± 2.13b 5.2 ± 0.67a 58.7 ± 1.39b  SB8 48.2 ± 0.66a 34.4 ± 2.83c 18.5 ± 2.81d 2.0 ± 3.07b 4.1 ± 0.70ab 64.8 ± 1.43a  WCS 15.6 ± 0.63d 37.4 ± 2.70bc 47.0 ± 2.67c 1.7 ± 2.38b 4.9 ± 0.67ab 34.8 ± 1.39c . A2 . B3 . C4 . L5 . K6 . EDeg7 . Item . % of DM . . . . . .  PH 10.8 ± 0.66e 15.6 ± 2.83e 73.6 ± 2.81a 6.4 ± 2.92ab 2.6 ± 0.70c 14.7 ± 1.43e  Gin trash 25.0 ± 0.63b 15.7 ± 2.70de 59.3 ± 2.67b 12.5 ± 2.38a 3.2 ± 0.67bc 29.4 ± 1.39d  Corn 16.1 ± 0.63cd 77.4 ± 2.70a 6.8 ± 2.67e 6.0 ± 2.13b 5.2 ± 0.67a 58.7 ± 1.39b  SB8 48.2 ± 0.66a 34.4 ± 2.83c 18.5 ± 2.81d 2.0 ± 3.07b 4.1 ± 0.70ab 64.8 ± 1.43a  WCS 15.6 ± 0.63d 37.4 ± 2.70bc 47.0 ± 2.67c 1.7 ± 2.38b 4.9 ± 0.67ab 34.8 ± 1.39c 1No treatment × substrate interaction or treatment effect was observed for any fraction (P ≥ 0.14); therefore, only substrate differences are reported. 2A fraction is defined as the immediately soluble fraction (100 – (B + C)). 3B fraction is defined as the fraction disappeared at a measurable rate. 4C fraction is defined as the fraction undegradable in the rumen. 5Lag time, h. 6Rate of disappearance, % per h. 7Effective degradability calculated as A + {B × [Kd/(Kd + Kp)]}, with Kp assumed to be 4%/h. 8Cargill Inc., Dalhart, TX. a–eWithin column, values with varying superscripts differ by P ≤ 0.05. Open in new tab Table 2. In situ DM disappearance of diet ingredients1 . A2 . B3 . C4 . L5 . K6 . EDeg7 . Item . % of DM . . . . . .  PH 10.8 ± 0.66e 15.6 ± 2.83e 73.6 ± 2.81a 6.4 ± 2.92ab 2.6 ± 0.70c 14.7 ± 1.43e  Gin trash 25.0 ± 0.63b 15.7 ± 2.70de 59.3 ± 2.67b 12.5 ± 2.38a 3.2 ± 0.67bc 29.4 ± 1.39d  Corn 16.1 ± 0.63cd 77.4 ± 2.70a 6.8 ± 2.67e 6.0 ± 2.13b 5.2 ± 0.67a 58.7 ± 1.39b  SB8 48.2 ± 0.66a 34.4 ± 2.83c 18.5 ± 2.81d 2.0 ± 3.07b 4.1 ± 0.70ab 64.8 ± 1.43a  WCS 15.6 ± 0.63d 37.4 ± 2.70bc 47.0 ± 2.67c 1.7 ± 2.38b 4.9 ± 0.67ab 34.8 ± 1.39c . A2 . B3 . C4 . L5 . K6 . EDeg7 . Item . % of DM . . . . . .  PH 10.8 ± 0.66e 15.6 ± 2.83e 73.6 ± 2.81a 6.4 ± 2.92ab 2.6 ± 0.70c 14.7 ± 1.43e  Gin trash 25.0 ± 0.63b 15.7 ± 2.70de 59.3 ± 2.67b 12.5 ± 2.38a 3.2 ± 0.67bc 29.4 ± 1.39d  Corn 16.1 ± 0.63cd 77.4 ± 2.70a 6.8 ± 2.67e 6.0 ± 2.13b 5.2 ± 0.67a 58.7 ± 1.39b  SB8 48.2 ± 0.66a 34.4 ± 2.83c 18.5 ± 2.81d 2.0 ± 3.07b 4.1 ± 0.70ab 64.8 ± 1.43a  WCS 15.6 ± 0.63d 37.4 ± 2.70bc 47.0 ± 2.67c 1.7 ± 2.38b 4.9 ± 0.67ab 34.8 ± 1.39c 1No treatment × substrate interaction or treatment effect was observed for any fraction (P ≥ 0.14); therefore, only substrate differences are reported. 2A fraction is defined as the immediately soluble fraction (100 – (B + C)). 3B fraction is defined as the fraction disappeared at a measurable rate. 4C fraction is defined as the fraction undegradable in the rumen. 5Lag time, h. 6Rate of disappearance, % per h. 7Effective degradability calculated as A + {B × [Kd/(Kd + Kp)]}, with Kp assumed to be 4%/h. 8Cargill Inc., Dalhart, TX. a–eWithin column, values with varying superscripts differ by P ≤ 0.05. Open in new tab The A fraction of WCS in this experiment (15.6%) was reduced compared with the results from Aierli et al. (1989) who reported that 36.6% of the DM in WCS was immediately soluble, which could be due to a difference in substrate processing prior to incubation. Aierli et al. (1989) used WCS that was ground to pass through a 1-mm screen instead of a 6-mm screen. Decreasing particle size could have increased the amount of small particles that were able to escape the in situ bag immediately. The C fraction of WCS was over twice that of SB (47.0% vs. 18.5%, respectively; P < 0.001), which was likely attributed to the increased fiber content (35.7% vs. 40.0% for SB and WCS, respectively) of the WCS as well as the greater A fraction of the SB (P < 0.001). Despite the differences observed among the A and C fractions of the byproducts, there was no difference (P = 0.43) in the B fraction between SB and WCS. The CGT had an increased A fraction compared with PH by approximately 14% (P < 0.001). The C fraction, or the percent of DM undegradable in the rumen, was greatest for PH at 73.6% of DM, while the CGT had a decreased (P < 0.001) C fraction of 59.3% of DM. The observed difference between the C fraction of PH and CGT was likely associated with the greater (P < 0.001) A fraction of the CGT compared with the PH. Despite the differences observed in both the A and C fractions among primary roughage sources, the amount of DM that disappeared at a measurable rate was almost identical between the CGT and PH (15.7% vs. 15.6%, respectively; P = 0.98). As expected, the Kd of DM was the slowest for the primary roughage sources, CGT, and PH. The Kd of DM did not differ between CGT and PH (2.6% vs. 3.2%/h, respectively; P = 0.47). The SB, DRC, and WCS also had similar Kd (4.1, 5.2, and 4.9%/h, respectively; P ≥ 0.20). Sindt et al. (2003) reported a similar Kd of 4.3%/h for WCGF in cattle consuming a diet comprised of alfalfa hay, WCGF, and steam-flaked corn. However, Firkins et al. (1985) reported a slightly faster Kd of 4.9% per h for WCGF in steers consuming a diet comprised of corn silage, soybean meal, WCGF, and dry distiller’s grains. The lag time observed for DM was similar (P = 0.11) between CGT and PH. However, CGT had a greater lag time than any of the other substrates (P ≤ 0.05) The lag times observed among all other substrates ranged from 1.7 to 5.6 h and were not found to be different from each other (P ≥ 0.11), which is likely due to the variance observed in the data for this fraction of DM. The effective degradability of DM was different among all substrates (P ≤ 0.05). As predicted, SB had the greatest effective degradability of DM (64.8%) among substrates. The WCS had an effective degradability of 34.8% of DM in the current experiment, which was decreased compared with the value reported by Arieli et al. (1989), who reported 48.4% effective degradability. The effective degradability of DRC was observed to be 58.7% of DM and is consistent with in situ DM digestibility results previously reported in the literature (56.8%; Lee et al., 2002). The primary roughage sources displayed the least effective degradability of DM among substrates. Among roughage sources, the PH had the smallest effective degradability compared with CGT (14.7% vs. 29.4% of DM, respectively). The observed difference of effective degradability among primary roughage sources was likely a result of the increased A fraction associated with the CGT compared with the PH, as the B fraction and Kd were similar among the two substrates. The effective degradability of CGT in this experiment was decreased compared with the results previously reported in the literature; however, the difference in observed results may possibly be due to the variance of particle size among experiments. Pordesimo et al. (2005) investigated the effects of particle size of CGT on in vitro DM digestibility and reported that CGT with a larger particle size had a decreased percentage of in vitro DM digestibility. Gin trash ground to pass a screen size of 2.0 mm had only a 33.8% in vitro DM digestibility, while CGT ground to pass a 0.5-mm screen had an in vitro DM digestibility of 47.8% (Pordesimo et al., 2005). In the current experiment, CGT was ground to pass a 6.0-mm screen, which could be a source of variation between the DM disappearance observed between this experiment and the results from previous literature. Other low- to medium-quality roughages have had varied results concerning the effective degradability of DM. For example, rice straw was reported to have a DM effective degradability of 20.2% in cannulated steers consuming a basal diet comprised primarily of corn, alfalfa meal, and rice straw (Li et al., 2018). This value was greater than the results of PH and less than the CGT in the current experiment. In situ OM disappearance There was no treatment × substrate interaction (P ≥ 0.21) or main effect of treatment (P ≥ 0.25) for OM disappearance for any fraction; therefore, only the main effect of substrate is reported (Table 3). In contrast to the DM lag time results, the lag time observed for OM for the primary roughage sources was greater for PH than CGT (10.6 vs. 6.0 h, respectively; P = 0.05). Aside from lag time, the observed patterns regarding OM in situ disappearance results were similar to the patterns observed regarding DM in situ disappearance results for all fractions. Table 3. In situ OM disappearance of diet ingredients1 . A2 . B3 . C4 . L5 . K6 . ED7 . Item . % of OM . . . . . .  PH 8.9 ± 0.72a 14.1 ± 1.57a 77.0 ± 1.36a 10.6 ± 1.45a 2.7 ±0.69by 13.0 ± 1.46e  Gin trash 17.9 ± 0.79c 12.0 ± 1.74a 70.1 ± 1.50b 6.0 ± 1.73b 2.4 ± 0.77b 20.6 ± 1.56c  Corn 15.4 ± 0.69b 77.8 ± 1.50c 6.8 ± 1.31e 5.7 ± 1.20b 5.2 ± 0.66a 57.9 ± 1.41b   SB8 45.0 ± 0.69d 35.7 ± 1.50b 19.3 ± 1.31c 1.3 ± 1.73c 4.3 ± 0.66ax 63.1 ± 1.42a   WCS 14.4 ± 0.69b 37.6 ± 1.50b 47.9 ± 1.31d 1.8 ± 1.34c 4.8 ± 0.66a 33.4 ± 1.42d . A2 . B3 . C4 . L5 . K6 . ED7 . Item . % of OM . . . . . .  PH 8.9 ± 0.72a 14.1 ± 1.57a 77.0 ± 1.36a 10.6 ± 1.45a 2.7 ±0.69by 13.0 ± 1.46e  Gin trash 17.9 ± 0.79c 12.0 ± 1.74a 70.1 ± 1.50b 6.0 ± 1.73b 2.4 ± 0.77b 20.6 ± 1.56c  Corn 15.4 ± 0.69b 77.8 ± 1.50c 6.8 ± 1.31e 5.7 ± 1.20b 5.2 ± 0.66a 57.9 ± 1.41b   SB8 45.0 ± 0.69d 35.7 ± 1.50b 19.3 ± 1.31c 1.3 ± 1.73c 4.3 ± 0.66ax 63.1 ± 1.42a   WCS 14.4 ± 0.69b 37.6 ± 1.50b 47.9 ± 1.31d 1.8 ± 1.34c 4.8 ± 0.66a 33.4 ± 1.42d 1No treatment × substrate interaction or treatment effect was observed for any fraction (P ≥ 0.21); therefore, only substrate differences are reported. 2A fraction is defined as the immediately soluble fraction (100 – (B + C)). 3B fraction is defined as the fraction disappeared at a measurable rate. 4C fraction is defined as the fraction undegradable in the rumen. 5Lag time, h. 6Rate of disappearance, % per h. 7Effective degradability calculated as A + {B × [Kd/(Kd + Kp)]}, with Kp assumed to be 4%/h. 8Cargill Inc., Dalhart, TX. a–eWithin column, values with varying superscripts differ by P ≤ 0.05. x,yWithin column, values tend to differ by 0.05 < P ≤ 0.10. Open in new tab Table 3. In situ OM disappearance of diet ingredients1 . A2 . B3 . C4 . L5 . K6 . ED7 . Item . % of OM . . . . . .  PH 8.9 ± 0.72a 14.1 ± 1.57a 77.0 ± 1.36a 10.6 ± 1.45a 2.7 ±0.69by 13.0 ± 1.46e  Gin trash 17.9 ± 0.79c 12.0 ± 1.74a 70.1 ± 1.50b 6.0 ± 1.73b 2.4 ± 0.77b 20.6 ± 1.56c  Corn 15.4 ± 0.69b 77.8 ± 1.50c 6.8 ± 1.31e 5.7 ± 1.20b 5.2 ± 0.66a 57.9 ± 1.41b   SB8 45.0 ± 0.69d 35.7 ± 1.50b 19.3 ± 1.31c 1.3 ± 1.73c 4.3 ± 0.66ax 63.1 ± 1.42a   WCS 14.4 ± 0.69b 37.6 ± 1.50b 47.9 ± 1.31d 1.8 ± 1.34c 4.8 ± 0.66a 33.4 ± 1.42d . A2 . B3 . C4 . L5 . K6 . ED7 . Item . % of OM . . . . . .  PH 8.9 ± 0.72a 14.1 ± 1.57a 77.0 ± 1.36a 10.6 ± 1.45a 2.7 ±0.69by 13.0 ± 1.46e  Gin trash 17.9 ± 0.79c 12.0 ± 1.74a 70.1 ± 1.50b 6.0 ± 1.73b 2.4 ± 0.77b 20.6 ± 1.56c  Corn 15.4 ± 0.69b 77.8 ± 1.50c 6.8 ± 1.31e 5.7 ± 1.20b 5.2 ± 0.66a 57.9 ± 1.41b   SB8 45.0 ± 0.69d 35.7 ± 1.50b 19.3 ± 1.31c 1.3 ± 1.73c 4.3 ± 0.66ax 63.1 ± 1.42a   WCS 14.4 ± 0.69b 37.6 ± 1.50b 47.9 ± 1.31d 1.8 ± 1.34c 4.8 ± 0.66a 33.4 ± 1.42d 1No treatment × substrate interaction or treatment effect was observed for any fraction (P ≥ 0.21); therefore, only substrate differences are reported. 2A fraction is defined as the immediately soluble fraction (100 – (B + C)). 3B fraction is defined as the fraction disappeared at a measurable rate. 4C fraction is defined as the fraction undegradable in the rumen. 5Lag time, h. 6Rate of disappearance, % per h. 7Effective degradability calculated as A + {B × [Kd/(Kd + Kp)]}, with Kp assumed to be 4%/h. 8Cargill Inc., Dalhart, TX. a–eWithin column, values with varying superscripts differ by P ≤ 0.05. x,yWithin column, values tend to differ by 0.05 < P ≤ 0.10. Open in new tab In situ NDF disappearance No treatment × substrate interaction (P ≥ 0.27) or main effect of treatment (P ≥ 0.42) was observed for the A, B, and C fractions, Kd, or lag time variables; therefore, only substrate differences are reported (Table 4). Similar to DM and OM results, the A fraction of NDF was greater for CGT than PH (12.7% vs. 6.0%, respectively; P < 0.001). However, the B fraction tended to be greater for PH than CGT (P = 0.08), and the C fraction of the primary roughage sources were similar (P = 0.81). The calculated Kd of NDF for PH was not different than the Kd of NDF for CGT (4.3 vs. 3.5%/h, respectively; P = 0.70), and lag time did not differ between PH and CGT (P = 0.46). Table 4. In situ NDF disappearance of diet roughage ingredients1 . A2 . B3 . C4 . L5 . K6 . Item . % of NDF . . . . .  PH 6.0 ± 0.79b 16.2 ± 2.62x 77.9 ± 2.71a 11.9 ± 5.74a 4.3 ± 1.95a  Gin trash 12.7 ± 0.76a 10.2 ± 2.48y 77.1 ± 2.56a 17.8 ± 6.14a 3.5 ± 1.86a . A2 . B3 . C4 . L5 . K6 . Item . % of NDF . . . . .  PH 6.0 ± 0.79b 16.2 ± 2.62x 77.9 ± 2.71a 11.9 ± 5.74a 4.3 ± 1.95a  Gin trash 12.7 ± 0.76a 10.2 ± 2.48y 77.1 ± 2.56a 17.8 ± 6.14a 3.5 ± 1.86a 1No treatment × substrate interaction or treatment effect was observed for any reported fraction (P ≥ 0.27); therefore, only differences in the main effect of substrate are reported. 2A fraction is defined as the immediately soluble fraction (100 – (B + C)). 3B fraction is defined as the fraction disappeared at a measurable rate. 4C fraction is defined as the fraction undegradable in the rumen. 5Lag time, h. 6Rate of disappearance, % per h. a,bWithin column, values with varying superscripts differ by P ≤ 0.05. x,yWithin column, values tend to differ by 0.05 < P ≤ 0.10. Open in new tab Table 4. In situ NDF disappearance of diet roughage ingredients1 . A2 . B3 . C4 . L5 . K6 . Item . % of NDF . . . . .  PH 6.0 ± 0.79b 16.2 ± 2.62x 77.9 ± 2.71a 11.9 ± 5.74a 4.3 ± 1.95a  Gin trash 12.7 ± 0.76a 10.2 ± 2.48y 77.1 ± 2.56a 17.8 ± 6.14a 3.5 ± 1.86a . A2 . B3 . C4 . L5 . K6 . Item . % of NDF . . . . .  PH 6.0 ± 0.79b 16.2 ± 2.62x 77.9 ± 2.71a 11.9 ± 5.74a 4.3 ± 1.95a  Gin trash 12.7 ± 0.76a 10.2 ± 2.48y 77.1 ± 2.56a 17.8 ± 6.14a 3.5 ± 1.86a 1No treatment × substrate interaction or treatment effect was observed for any reported fraction (P ≥ 0.27); therefore, only differences in the main effect of substrate are reported. 2A fraction is defined as the immediately soluble fraction (100 – (B + C)). 3B fraction is defined as the fraction disappeared at a measurable rate. 4C fraction is defined as the fraction undegradable in the rumen. 5Lag time, h. 6Rate of disappearance, % per h. a,bWithin column, values with varying superscripts differ by P ≤ 0.05. x,yWithin column, values tend to differ by 0.05 < P ≤ 0.10. Open in new tab A treatment × substrate interaction (Figure 1; P = 0.04) was observed for the effective degradability of NDF of primary roughage sources in the treatment diets. The interaction for effective degradability of NDF was due to the CGT having a greater effective degradability when incubated in CTN steers when compared with the effective degradability of PH when incubated in CON steers (P = 0.02). Overall, the CGT had a greater (P < 0.001) effective degradability than the PH by approximately 5.6% regardless of treatment. The ruminal NDF degradability of CGT observed in this experiment (15.9%) is increased in comparison to other commonly used roughages such as alfalfa hay and wheat straw. Poore et al. (1990) reported that alfalfa hay had a ruminal NDF digestibility of 10.7%, while wheat straw was reported to have a ruminal NDF digestibility of 6.0% in steers fed a 90% concentrate diet. The ruminal NDF degradability of PH observed in this experiment (10.3%) was similar to alfalfa hay and greater than wheat straw as reported by Poore et al. (1990). Figure 1. Open in new tabDownload slide Effective degradability of NDF of PH and CGT in steers consuming a CON (7% hay, 15% Sweet Bran [Cargill Inc., Dalhart, TX], 67.25% dry-rolled corn, 5% liquid supplement, 5% dry supplement, 0.75% urea) or a CTN (7% cotton gin trash, 15% whole cottonseed, 72.25% dry-rolled corn, 5% dry supplement, 0.75% urea) diet. A treatment × substrate interaction (P = 0.04) was observed. A main effect of substrate (P < 0.001) was also observed. Substrates with varying superscripts differ by P ≤ 0.05. Regardless of treatment, the ruminal degradability of NDF was greater for CGT (P < 0.02). Figure 1. Open in new tabDownload slide Effective degradability of NDF of PH and CGT in steers consuming a CON (7% hay, 15% Sweet Bran [Cargill Inc., Dalhart, TX], 67.25% dry-rolled corn, 5% liquid supplement, 5% dry supplement, 0.75% urea) or a CTN (7% cotton gin trash, 15% whole cottonseed, 72.25% dry-rolled corn, 5% dry supplement, 0.75% urea) diet. A treatment × substrate interaction (P = 0.04) was observed. A main effect of substrate (P < 0.001) was also observed. Substrates with varying superscripts differ by P ≤ 0.05. Regardless of treatment, the ruminal degradability of NDF was greater for CGT (P < 0.02). In situ starch disappearance of DRC Based on the results from substrates incubated in the rumen for 96 h, the undegradable fraction of starch for the DRC, CON, and CTN substrates were estimated to be 0. In practice, it is unlikely that DRC would remain in the rumen for an extended amount of time if steers were consuming a high concentrate ration. Karr et al. (1966) reported that only 63.0% of starch was digested in the rumen of steers consuming a diet comprised of 80% ground corn. The value reported by Karr et al. (1966) is slightly less than the value reported in a review completed by Theurer (1986), which suggests that the ruminal digestion of starch of DRC is approximately 70%. Results from this experiment determined that 95.5% of the starch in DRC disappeared at a measurable rate, and only 4.5% of the starch was immediately soluble. The effective degradability of starch in DRC was similar, regardless of treatment (51.2% and 53.0%; P = 0.71). In situ disappearance of whole diets When comparing the in situ DM degradability of the CON and CTN substrates, the CON had a greater A fraction than the CTN (P < 0.001; Table 5). The greater A fraction in the CON substrate is likely due to the greater A fraction of SB in the CON diet. Interestingly, the differences observed between the A fraction of PH and CGT would suggest that the CTN sample would have a greater A fraction than the CON sample. However, since the primary roughage sources were only included in the diets at 7% of DM, the A fraction of the roughages likely did not influence the A fraction of the whole diets. The differences among the A fraction of individual ingredients were not reflected in the effective degradability of the DM of the whole diets (P = 0.32). No differences were observed between the B or C fractions, lag time, or Kd of DM between whole diets (P ≥ 0.24). Table 5. In situ DM, OM, and starch disappearance of treatment diets1 . A2 . B3 . C4 . L5 . K6 . ED7 . DM  Control diet 26.9 (± 0.63)a 57.0 (± 2.70)a 16.2 (± 2.67)a 4.5 (± 2.38)a 4.5 (± 0.67)a 56.0 (± 1.39)a  Cotton diet 20.4 (± 0.63)b 61.4 (± 2.70)a 18.2 (± 2.67)a 1.4 (± 2.91)a 5.5 (± 0.67)a 54.6 (± 1.39)a OM  Control diet 25.4 (± 0.69)a 59.1 (± 1.50)a 15.5 (± 1.31)a 4.7 (± 1.34)x 4.5 (± 0.66)a 55.5 (± 1.42)a  Cotton diet 18.7 (± 0.69)b 63.8 (± 1.50)a 17.5 (± 1.31)a 1.3 (± 1.39)y 5.5 (± 0.66)a 54.0 (± 1.42)a Starch  Control diet 14.4 (± 2.05)a 85.6 (± 2.05)a 0.08 4.5 (± 0.94)a 4.6 (± 0.44)a — 9  Cotton diet 14.4 (± 2.38)a 85.6 (± 2.38)a 0.08 2.8 (± 1.10)a 6.3 (± 0.50)b — 9 . A2 . B3 . C4 . L5 . K6 . ED7 . DM  Control diet 26.9 (± 0.63)a 57.0 (± 2.70)a 16.2 (± 2.67)a 4.5 (± 2.38)a 4.5 (± 0.67)a 56.0 (± 1.39)a  Cotton diet 20.4 (± 0.63)b 61.4 (± 2.70)a 18.2 (± 2.67)a 1.4 (± 2.91)a 5.5 (± 0.67)a 54.6 (± 1.39)a OM  Control diet 25.4 (± 0.69)a 59.1 (± 1.50)a 15.5 (± 1.31)a 4.7 (± 1.34)x 4.5 (± 0.66)a 55.5 (± 1.42)a  Cotton diet 18.7 (± 0.69)b 63.8 (± 1.50)a 17.5 (± 1.31)a 1.3 (± 1.39)y 5.5 (± 0.66)a 54.0 (± 1.42)a Starch  Control diet 14.4 (± 2.05)a 85.6 (± 2.05)a 0.08 4.5 (± 0.94)a 4.6 (± 0.44)a — 9  Cotton diet 14.4 (± 2.38)a 85.6 (± 2.38)a 0.08 2.8 (± 1.10)a 6.3 (± 0.50)b — 9 1Control diet = 7% prairie hay, 15% Sweet Bran (Cargill Inc., Dalhart, TX), 67.25% rolled corn, 5% liquid supplement, or Cotton diet = 7% cotton gin trash, 15% whole cottonseed, 72.25% rolled corn; both rations contained 5% dry supplement and 0.75% urea. No treatment × substrate interaction or main effect of treatment was observed for any reported fraction (P ≥ 0.14); therefore, only differences in the main effect of substrate are reported. 2A fraction is defined as the immediately soluble fraction (100 – (B + C)). 3B fraction is defined as the fraction disappeared at a measurable rate. 4C fraction is defined as the fraction undegradable in the rumen. 5Lag time, h. 6 Rate of disappearance, % per h. 7Effective degradability calculated as A + {B × [Kd/(Kd + Kp)]}, with Kp assumed to be 4% per h. 8The undegradable fraction of starch was assumed to be 0%. 9The main effect of substrate is not presented in the table due to a treatment × substrate interaction. a,bWithin column and variable (DM, OM, and Starch), values with varying superscripts differ by P ≤ 0.05.x,yWithin column and variable (DM, OM, and Starch), values with varying superscripts tend to differ by 0.05 < P ≤ 0.10. Open in new tab Table 5. In situ DM, OM, and starch disappearance of treatment diets1 . A2 . B3 . C4 . L5 . K6 . ED7 . DM  Control diet 26.9 (± 0.63)a 57.0 (± 2.70)a 16.2 (± 2.67)a 4.5 (± 2.38)a 4.5 (± 0.67)a 56.0 (± 1.39)a  Cotton diet 20.4 (± 0.63)b 61.4 (± 2.70)a 18.2 (± 2.67)a 1.4 (± 2.91)a 5.5 (± 0.67)a 54.6 (± 1.39)a OM  Control diet 25.4 (± 0.69)a 59.1 (± 1.50)a 15.5 (± 1.31)a 4.7 (± 1.34)x 4.5 (± 0.66)a 55.5 (± 1.42)a  Cotton diet 18.7 (± 0.69)b 63.8 (± 1.50)a 17.5 (± 1.31)a 1.3 (± 1.39)y 5.5 (± 0.66)a 54.0 (± 1.42)a Starch  Control diet 14.4 (± 2.05)a 85.6 (± 2.05)a 0.08 4.5 (± 0.94)a 4.6 (± 0.44)a — 9  Cotton diet 14.4 (± 2.38)a 85.6 (± 2.38)a 0.08 2.8 (± 1.10)a 6.3 (± 0.50)b — 9 . A2 . B3 . C4 . L5 . K6 . ED7 . DM  Control diet 26.9 (± 0.63)a 57.0 (± 2.70)a 16.2 (± 2.67)a 4.5 (± 2.38)a 4.5 (± 0.67)a 56.0 (± 1.39)a  Cotton diet 20.4 (± 0.63)b 61.4 (± 2.70)a 18.2 (± 2.67)a 1.4 (± 2.91)a 5.5 (± 0.67)a 54.6 (± 1.39)a OM  Control diet 25.4 (± 0.69)a 59.1 (± 1.50)a 15.5 (± 1.31)a 4.7 (± 1.34)x 4.5 (± 0.66)a 55.5 (± 1.42)a  Cotton diet 18.7 (± 0.69)b 63.8 (± 1.50)a 17.5 (± 1.31)a 1.3 (± 1.39)y 5.5 (± 0.66)a 54.0 (± 1.42)a Starch  Control diet 14.4 (± 2.05)a 85.6 (± 2.05)a 0.08 4.5 (± 0.94)a 4.6 (± 0.44)a — 9  Cotton diet 14.4 (± 2.38)a 85.6 (± 2.38)a 0.08 2.8 (± 1.10)a 6.3 (± 0.50)b — 9 1Control diet = 7% prairie hay, 15% Sweet Bran (Cargill Inc., Dalhart, TX), 67.25% rolled corn, 5% liquid supplement, or Cotton diet = 7% cotton gin trash, 15% whole cottonseed, 72.25% rolled corn; both rations contained 5% dry supplement and 0.75% urea. No treatment × substrate interaction or main effect of treatment was observed for any reported fraction (P ≥ 0.14); therefore, only differences in the main effect of substrate are reported. 2A fraction is defined as the immediately soluble fraction (100 – (B + C)). 3B fraction is defined as the fraction disappeared at a measurable rate. 4C fraction is defined as the fraction undegradable in the rumen. 5Lag time, h. 6 Rate of disappearance, % per h. 7Effective degradability calculated as A + {B × [Kd/(Kd + Kp)]}, with Kp assumed to be 4% per h. 8The undegradable fraction of starch was assumed to be 0%. 9The main effect of substrate is not presented in the table due to a treatment × substrate interaction. a,bWithin column and variable (DM, OM, and Starch), values with varying superscripts differ by P ≤ 0.05.x,yWithin column and variable (DM, OM, and Starch), values with varying superscripts tend to differ by 0.05 < P ≤ 0.10. Open in new tab Following in situ incubation, there was inadequate substrate for the 72 and 96 h sampling times to complete all analyses for the CON and CTN substrates; therefore, NDF was only analyzed for the CON and CTN substrates through 48 h of incubation. When creating the disappearance curves for NDF disappearance of CON and CTN, data did not fit the nonlinear model as expected due to the low NDF disappearance observed and missing data from the 72 and 96 h incubations. As a result, the mean percentage of NDF disappearance at 48 h was analyzed for the CON and CTN substrates. There was no treatment × substrate interaction (P = 0.38) or main effects of substrate (P = 0.37) or treatment (P = 0.51) observed for the % NDF disappearance of whole diets after 48 h of ruminal incubation (Figure 2). The mean percentage of NDF disappeared at 48 h was 33.4% for the CON diet and 36.1% for the CTN diet (P = 0.37). Figure 2. Open in new tabDownload slide Percent NDF disappearance of whole diets after 48 h of ruminal incubation in steers consuming a CON (7% hay, 15% Sweet Bran [Cargill Inc., Dalhart, TX], 67.25% dry-rolled corn, 5% liquid supplement, 5% dry supplement, 0.75% urea) or a CTN (7% cotton gin trash, 15% whole cottonseed, 72.25% dry-rolled corn, 5% dry supplement, 0.75% urea) diet. No treatment × substrate interaction or main effects of substrate or treatment were observed (P ≥ 0.37). Therefore, only substrate means are presented in this figure. Figure 2. Open in new tabDownload slide Percent NDF disappearance of whole diets after 48 h of ruminal incubation in steers consuming a CON (7% hay, 15% Sweet Bran [Cargill Inc., Dalhart, TX], 67.25% dry-rolled corn, 5% liquid supplement, 5% dry supplement, 0.75% urea) or a CTN (7% cotton gin trash, 15% whole cottonseed, 72.25% dry-rolled corn, 5% dry supplement, 0.75% urea) diet. No treatment × substrate interaction or main effects of substrate or treatment were observed (P ≥ 0.37). Therefore, only substrate means are presented in this figure. No treatment × substrate interaction (P ≥ 0.21) or main effect of treatment was observed for the A or B fractions, or Kd of starch for the whole diets. Therefore, only substrate differences will be discussed. Identical values were reported for the A (14.4%) and B (85.6%) fractions of CON and CTN (P ≥ 0.99) when the C fraction of starch was assumed to be 0%. The Kd of starch was determined to be more rapid (P < 0.01) for the CTN diet compared with the CON diet (6.3 vs. 4.6%/h, respectively). No treatment × substrate interaction (P = 0.44) or main effect of substrate (P = 0.23) was observed for lag time. However, a main effect of treatment (P = 0.03) was observed for the lag time of starch disappearance between the CON and CTN treatment (2.8 vs. 5.5 h, respectively). A tendency for a treatment × substrate interaction was observed for the effective degradability of starch (P = 0.10; Figure 3). This interaction is likely a result of the different Kd among substrates, as the A and B fractions of starch did not differ between whole diets. When the CON substrate was incubated in steers consuming the CTN treatment diet, the effective degradability was less than when the CON substrate was incubated in steers consuming the CON treatment diet (P = 0.05). The effective degradability of starch was increased when substrates were incubated in steers consuming the same treatment diet as the substrate, indicating that microorganisms in the rumen adapted to the treatment diet and influenced the differential digestibility of the alternative treatment diets and ingredients. The observed interaction is likely of minimal importance because when the CON substrate was incubated in steers consuming the CON treatment diet, effective degradability of starch did not differ (P = 0.84) from the CTN substrate when incubated in steers consuming the CTN diet. In summary, the ruminal starch degradability was similar between the CON and CTN, despite the observed differences in Kd. Figure 3. Open in new tabDownload slide Effective degradability of starch in whole diets in steers consuming a CON (7% hay, 15% Sweet Bran [Cargill Inc., Dalhart, TX], 67.25% dry-rolled corn, 5% liquid supplement, 5% dry supplement, 0.75% urea) or a CTN (7% cotton gin trash, 15% whole cottonseed, 72.25% dry-rolled corn, 5% dry supplement, 0.75% urea) diet. A tendency for a treatment × substrate interaction (P = 0.10) and main effect of substrate (P < 0.01) were observed. Substrates with varying superscripts differ by P ≤ 0.05. No main effect of treatment (P = 0.15) was detected. Although the interaction tended to be significant, it should be noted that when each substrate was incubated in the rumen of a steer consuming the same diet, the effective degradability of starch was not different between treatments (P = 0.84). Figure 3. Open in new tabDownload slide Effective degradability of starch in whole diets in steers consuming a CON (7% hay, 15% Sweet Bran [Cargill Inc., Dalhart, TX], 67.25% dry-rolled corn, 5% liquid supplement, 5% dry supplement, 0.75% urea) or a CTN (7% cotton gin trash, 15% whole cottonseed, 72.25% dry-rolled corn, 5% dry supplement, 0.75% urea) diet. A tendency for a treatment × substrate interaction (P = 0.10) and main effect of substrate (P < 0.01) were observed. Substrates with varying superscripts differ by P ≤ 0.05. No main effect of treatment (P = 0.15) was detected. Although the interaction tended to be significant, it should be noted that when each substrate was incubated in the rumen of a steer consuming the same diet, the effective degradability of starch was not different between treatments (P = 0.84). The reason for the similar effective degradability observed for DM, OM, and starch among the treatment diets is likely because DRC is the primary ingredient in both diets. Although some differences were observed between individual substrates that were included in the diet, it appears that the inclusion of byproducts at 15% of diet DM and roughages at 7% of diet DM is not great enough to cause an overall difference in total diet degradability of any measured component. Rumen fluid pH There was no treatment × time interaction (P = 0.47) or treatment effect (P = 0.35) for rumen fluid pH; however, there was a main effect of time (P = 0.03; Table 6). Rumen fluid samples collected at hours 2 and 24 post feeding had the greatest pH values (6.06 and 6.07, respectively). The lowest rumen fluid pH value (5.82) was observed 12 h after feeding. This result is similar to Robles et al. (2007), who also reported a decrease in rumen fluid pH 12 h post feeding for heifers fed a high concentrate diet once daily. Although differences among hours post feeding were detected in the current study, pH values over time were relatively constant with an average range of 5.82 to 6.07 in a 24-h period. This is within the range of the average ruminal pH of feedlot cattle consuming high concentrate diets, which has been reported to be between 5.6 and 6.2 (Schwartzkopf-Genswein et al., 2003). Table 6. Effects of including cotton byproducts in a finishing ration on rumen fluid pH values and lactate concentrations over time . Treatment1 . . . . Time2 . . . . . . . . . Variable . CON . CTN . SEM . P-value . 2 . 4 . 6 . 8 . 10 . 12 . 24 . SEM . P-value . pH 5.90 5.99 0.073 0.35 6.06a 5.94abc 5.87bc 5.91abc 5.93abc 5.82c 6.07ab 0.082 0.03 Lactate, g/L 0.78 0.72 0.076 0.84 0.80 0.71 0.62 0.76 0.95 0.73 0.67 0.134 0.98 . Treatment1 . . . . Time2 . . . . . . . . . Variable . CON . CTN . SEM . P-value . 2 . 4 . 6 . 8 . 10 . 12 . 24 . SEM . P-value . pH 5.90 5.99 0.073 0.35 6.06a 5.94abc 5.87bc 5.91abc 5.93abc 5.82c 6.07ab 0.082 0.03 Lactate, g/L 0.78 0.72 0.076 0.84 0.80 0.71 0.62 0.76 0.95 0.73 0.67 0.134 0.98 1Treatments included (DM basis): CON = 7% prairie hay, 15% Sweet Bran (Cargill Inc., Dalhart, TX), 67.25% rolled corn, 5% liquid supplement, or CTN = 7% cotton gin trash, 15% whole cottonseed, 72.25% rolled corn; both rations contained 5% dry supplement and 0.75% urea. 2Time refers to hour post-feeding. a–cWithin row, values with unlike superscripts are different (P < 0.05). Open in new tab Table 6. Effects of including cotton byproducts in a finishing ration on rumen fluid pH values and lactate concentrations over time . Treatment1 . . . . Time2 . . . . . . . . . Variable . CON . CTN . SEM . P-value . 2 . 4 . 6 . 8 . 10 . 12 . 24 . SEM . P-value . pH 5.90 5.99 0.073 0.35 6.06a 5.94abc 5.87bc 5.91abc 5.93abc 5.82c 6.07ab 0.082 0.03 Lactate, g/L 0.78 0.72 0.076 0.84 0.80 0.71 0.62 0.76 0.95 0.73 0.67 0.134 0.98 . Treatment1 . . . . Time2 . . . . . . . . . Variable . CON . CTN . SEM . P-value . 2 . 4 . 6 . 8 . 10 . 12 . 24 . SEM . P-value . pH 5.90 5.99 0.073 0.35 6.06a 5.94abc 5.87bc 5.91abc 5.93abc 5.82c 6.07ab 0.082 0.03 Lactate, g/L 0.78 0.72 0.076 0.84 0.80 0.71 0.62 0.76 0.95 0.73 0.67 0.134 0.98 1Treatments included (DM basis): CON = 7% prairie hay, 15% Sweet Bran (Cargill Inc., Dalhart, TX), 67.25% rolled corn, 5% liquid supplement, or CTN = 7% cotton gin trash, 15% whole cottonseed, 72.25% rolled corn; both rations contained 5% dry supplement and 0.75% urea. 2Time refers to hour post-feeding. a–cWithin row, values with unlike superscripts are different (P < 0.05). Open in new tab Rumen fluid lactate There was no treatment × time interaction (P = 0.32), main effect of treatment (P = 0.84), or main effect of time (P = 0.98) for concentration of rumen fluid lactate (Table 6). These results were expected, as the pH results were not indicative of steers experiencing acidosis. Generally, lactate concentration decreased from feeding through hour 6, increased and peaked at hour 10, and decreased again through hour 24. The mean value of lactate in the rumen fluid was 0.78 g/L for CON steers and 0.72 g/L for CTN steers. These values are greater than the mean l-lactate concentration in the rumen fluid of steers consuming a 70% concentrate diet as reported by Harmon et al. (1984) of 0.18 g/L. Although observed lactate concentrations in this experiment are increased compared with Harmon et al. (1984), observed lactate concentrations were not above the acidosis threshold of 4.5 g/L as reported by Nagaraja and Titgemeyer (2007). Rumen fluid VFA concentrations There was no treatment × time interaction for any VFA (P ≥ 0.71; Table 7); therefore, only the main effects of treatment and time will be discussed. Diets had similar (P = 0.91) total VFA concentrations of approximately 112 mM, which is within the expected normal range of 70 to 130 mM as reported by NASEM (2016). However, there were differences among specific VFA proportions observed between treatments. The acetate to propionate ratio was greater (P < 0.001) for the CTN steers compared with the CON steers, due to an increased proportion of acetate (P ≤ 0.002) and a decreased proportion of propionate (P < 0.0001) in the CTN steers. Because the starch values of the CON and CTN treatment diets were similar (40.65% vs. 39.76%, respectively), the increased acetate to propionate ratio observed in the CTN steers is likely due to the increased physically effective NDF content of the CTN diet compared with the CON diet. Increased fiber in the diet promotes the production of acetate, while increased starch in the diet promotes propionate production at the expense of acetate (Rumsey et al., 1970). Beauchemin and Yang (2005) also reported decreases in propionate and increases in acetate in the rumen fluid of dairy cows as the levels of physically effective NDF in the total mixed ration were increased. Table 7. Effects of including cotton byproducts in a finishing ration on rumen fluid VFA total concentration and molar proportions . Treatment1 . . . VFA2 . CON . CTN . P-value .  Total, mM 112.8 ± 4.76 112.1 ± 1.34 0.91 Proportion, mol/100 mol  Acetate:Propionate 2.02 ± 0.311 2.68 ± 0.306 <0.001  Acetate 51.1 ± 1.78 56.2 ± 1.69 <0.01  Propionate 27.0 ± 1.91 22.6 ± 1.89 <0.001  Butyrate 14.6 ± 1.17 13.8 ± 1.12 0.34  Isobutyrate 0.99 ± 0.062 1.08 ± 0.057 0.23  Valerate 2.22 ± 0.521 1.65 ± 0.502 0.13  Isovalerate 4.19 ± 0.823 4.63 ± 0.815 0.14 . Treatment1 . . . VFA2 . CON . CTN . P-value .  Total, mM 112.8 ± 4.76 112.1 ± 1.34 0.91 Proportion, mol/100 mol  Acetate:Propionate 2.02 ± 0.311 2.68 ± 0.306 <0.001  Acetate 51.1 ± 1.78 56.2 ± 1.69 <0.01  Propionate 27.0 ± 1.91 22.6 ± 1.89 <0.001  Butyrate 14.6 ± 1.17 13.8 ± 1.12 0.34  Isobutyrate 0.99 ± 0.062 1.08 ± 0.057 0.23  Valerate 2.22 ± 0.521 1.65 ± 0.502 0.13  Isovalerate 4.19 ± 0.823 4.63 ± 0.815 0.14 1Treatments included (DM basis): CON = 7% prairie hay, 15% Sweet Bran (Cargill Inc., Dalhart, TX), 67.25% rolled corn, 5% liquid supplement, or CTN = 7% cotton gin trash, 15% whole cottonseed, 72.25% rolled corn; both rations contained 5% dry supplement and 0.75% urea. 2No treatment × time interaction was observed for any VFA (P ≥ 0.71). Open in new tab Table 7. Effects of including cotton byproducts in a finishing ration on rumen fluid VFA total concentration and molar proportions . Treatment1 . . . VFA2 . CON . CTN . P-value .  Total, mM 112.8 ± 4.76 112.1 ± 1.34 0.91 Proportion, mol/100 mol  Acetate:Propionate 2.02 ± 0.311 2.68 ± 0.306 <0.001  Acetate 51.1 ± 1.78 56.2 ± 1.69 <0.01  Propionate 27.0 ± 1.91 22.6 ± 1.89 <0.001  Butyrate 14.6 ± 1.17 13.8 ± 1.12 0.34  Isobutyrate 0.99 ± 0.062 1.08 ± 0.057 0.23  Valerate 2.22 ± 0.521 1.65 ± 0.502 0.13  Isovalerate 4.19 ± 0.823 4.63 ± 0.815 0.14 . Treatment1 . . . VFA2 . CON . CTN . P-value .  Total, mM 112.8 ± 4.76 112.1 ± 1.34 0.91 Proportion, mol/100 mol  Acetate:Propionate 2.02 ± 0.311 2.68 ± 0.306 <0.001  Acetate 51.1 ± 1.78 56.2 ± 1.69 <0.01  Propionate 27.0 ± 1.91 22.6 ± 1.89 <0.001  Butyrate 14.6 ± 1.17 13.8 ± 1.12 0.34  Isobutyrate 0.99 ± 0.062 1.08 ± 0.057 0.23  Valerate 2.22 ± 0.521 1.65 ± 0.502 0.13  Isovalerate 4.19 ± 0.823 4.63 ± 0.815 0.14 1Treatments included (DM basis): CON = 7% prairie hay, 15% Sweet Bran (Cargill Inc., Dalhart, TX), 67.25% rolled corn, 5% liquid supplement, or CTN = 7% cotton gin trash, 15% whole cottonseed, 72.25% rolled corn; both rations contained 5% dry supplement and 0.75% urea. 2No treatment × time interaction was observed for any VFA (P ≥ 0.71). Open in new tab Warner et al. (2020) reported an increase in carcass fat in steers consuming the CTN diet compared with the CON diet without increasing intramuscular fat. The increase of ruminal acetate proportions observed in steers consuming the CTN diet in this experiment could help explain the increase in back fat, USDA Yield Grade, and kidney, pelvic, and heart fat percentage observed by Warner et al. (2020), as acetate is the primary substrate for the synthesis of fatty acids in ruminants (Hanson and Ballard, 1967). Acetate primarily increases the deposition of subcutaneous adipose tissue compared with intramuscular adipose tissue (Rhoades et al., 2007), thus supporting the results of increased back fat in CTN carcasses compared with CON carcasses with no change in marbling among treatments as reported by Warner et al. (2020). No other VFA proportions differed between treatments (P ≥ 0.13), and no time effect was observed for total VFA concentrations (P = 0.15). These results are likely due to the ad libitum feeding strategy, creating variable amounts of VFA in the rumen depending upon time and amount of feed consumption. If cattle are limit-fed, the concentration of VFA has been reported to rapidly increase immediately following feed consumption and steadily decline beginning approximately 4 h after consumption until the next feeding event (Church, 1988). A time effect (P < 0.01) was observed for the molar proportion of isobutyrate. In general, isobutyrate proportions were increased at hour 2, decreased through hour 12, and were greatest at hour 24. No time effects (P = 0.24) were observed for any other proportion of VFA. Conclusions Although differences were observed among individual diet components for ruminal degradability of DM, OM, NDF, and starch, it does not appear that ruminal degradability differed between the total diets. Additionally, there were no differences between the diets concerning rumen fluid pH or lactate concentration. Although total VFA concentrations were not different between treatments, the molar proportion of propionate was greater, while the molar proportion of acetate was less in steers consuming the CON diet compared with steers consuming the CTN diet. These differences in VFA are likely attributed to the greater amount of physically effective NDF in the CTN diet compared with the CON diet. The increase in acetate in the rumen fluid of CTN steers helps to explain the increase in fat on the carcasses of steers consuming the CTN diet as reported by Warner et al. (2020). Results from this experiment suggest that the performance results reported by Warner et al. (2020) are likely due to the increased DM intake and energy intakes and no concomitant alterations in ruminal degradability or fermentation of the treatment diets. In conclusion, this experiment suggests that WCS and CGT can be included in a finishing diet without negatively impacting the ruminal degradability of the diet or the rumen environment. Abbreviations Abbreviations CGT cotton gin trash CON control diet CTN cotton byproduct diet DM dry matter DRC dry-rolled corn Kd rate of disappearance Kp passage rate NDF neutral detergent fiber OM organic matter PH prairie hay SB Sweet Bran VFA volatile fatty acid WCGF wet corn gluten feed WCS whole cottonseed Acknowledgments The authors wish to thank the employees of the Willard Sparks Beef Research Center for assisting with this experiment. This experiment was funded in part by the USDA National Institute of Food and Agriculture Hatch project, the Oklahoma Agricultural Experiment Station of the Division of Agricultural Sciences and Natural Resources at Oklahoma State University, and the Dennis and Marta White Endowed Chair in Animal Science. 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TI - Evaluation of ruminal degradability and metabolism of feedlot finishing diets with or without cotton byproducts
JF - Journal of Animal Science
DO - 10.1093/jas/skaa257
DA - 2020-09-01
UR - https://www.deepdyve.com/lp/oxford-university-press/evaluation-of-ruminal-degradability-and-metabolism-of-feedlot-jHs1niu3iw
VL - 98
IS - 9
DP - DeepDyve
ER -