TY - JOUR
AU - Long, N. M.
AB - Abstract The objective of this study was to determine if supplementation with a rumen undegradable unsaturated fatty acids (FA) source improved marbling deposition in early-weaned steers. All steers (Angus, n = 23; Angus × Hereford, n = 24) were weaned at 150 ± 5 d of age. Steers were blocked by BW and breed and then randomly assigned to either control (CON; average 1.5 kg of corn gluten feed [CGF], n = 23) or isocaloric supplementation containing a rumen undegradable fat source (RUF; 200 g of Megalac-R added to an average of 1.06 kg of CGF, n = 24) offered 5 d/wk for 110 d. All steers had ad libitum access to pastures throughout treatment and received supplements individually. Steer BW and blood samples were collected at 0, 55, and 110 d of supplementation, and real-time ultrasound measurements were collected at d 110. Following treatment, steers were transported to Oklahoma State University for finishing and subsequent harvesting at a commercial plant. All data were analyzed using the PROC MIXED procedure of SAS either as repeated measures or ANOVA depending on parameters. There were no significant changes in BW from the beginning of treatment to harvest due to treatment. Ultrasound data showed that RUF steers tended (P = 0.08) to have more i.m. fat than CON at d 110. Serum concentrations of FA showed a treatment × day interaction (P < 0.02) for 16:0, 18:0, 18:1c-9, 18:2, 20:4, and total FA. These specific FA concentrations slightly increased in CON steers, but there was a more pronounced increase in the concentration of these FA across the supplementation period in RUF steers. Serum triglyceride and cholesterol concentrations were increased (P < 0.01) on d 55 and 110 in RUF steers compared with those in CON steers. Serum leptin concentration in RUF steers was greater (P < 0.01) than CON steers at d 110. After harvest, RUF carcasses had greater (P = 0.01) marbling scores than those of CON carcasses. All other carcass measures were similar between treatments. The percentage of total lipids was increased (P = 0.011) in steaks from RUF compared to CON. There was a decrease (P < 0.05) in adipocyte diameter in i.m. fat depot of RUF steers compared to CON. There was also a tendency (P = 0.06) for RUF steers to have a greater percentage of 20 to 30 μm adipocytes in their i.m. depot than CON steers. This study indicates that supplementation of unsaturated FA can positively impact marbling deposition in early-weaned steers without impacting other carcass measures. INTRODUCTION Currently, one of the interests of the beef industry is finding methods to improve the quality of carcasses. A common way to increase carcass quality is by increasing the amount of i.m. fat, also known as marbling. By increasing marbling, one increases palatability traits (Jost et al., 1983) and carcass value (USDA, 1997). Early-weaning has been shown to improve carcass quality by increasing marbling scores (Harvey et al., 1975; Scheffler et al., 2014) and by decreasing the Warner-Bratzler shear force values (Meyer et al., 2005). Early weaning (weaning between 100 and 177 d of age) is also often associated with early grain feeding, which may lead to metabolic imprinting (Myers et al.; 1999; Fluharty et al., 2000). Accordingly, it has becoming evident that adipogenesis is active within the muscle much earlier than is evident by marbling deposition (Wegner et al., 1998). Although early weaning and high-concentrate feeding have been investigated by several groups, the use of lipid supplements has not been investigated. Fat supplementation to cattle has also been investigated for many years, but the focus has predominately been on reproduction (Ashes et al., 1992; Moallem et al., 1997; Staples et al., 1998). Researchers have begun to expand their investigation of fat supplementation from reproduction to the influence on fatty acid (FA) content within the meat (Duckett et al., 2002; Hess et al., 2007). Calcium salts have been fed to cattle because they decrease FA biohydrogenation within the rumen, which increases the amount of unsaturated fats available for post-ruminal absorption (Zinn et al., 2000; Huang et al., 2009). Our hypothesis is that supplementing rumen-protected essential FA to early-weaned steers on pasture will improve the marbling and quality grade of the carcasses. For this study, the objective was to investigate the effects of supplemental rumen undegradable unsaturated FA on marbling in early-weaned beef steers. MATERIALS AND METHODS All procedures were approved by Clemson University's Institutional Animal Care and Use Committee (AUP 2013-013). Animals, Treatments, and Sampling Forty-seven steer calves with an average weaning BW of 210.5 ± 6.1 kg were utilized for this experiment. All steers had been castrated within 24 h of birth. All steers were Angus sired out of an Angus (AN) or an Angus × Hereford (AN/HP) dam between 2 and 17 yr of age. Steers were out of 6 AN sires, and sires were equally distributed between treatments. Steers were weaned at 150 ± 5 d and were stratified into 6 blocks according to time of weaning. Following weaning, the steers underwent a 14-d adaptation period in a pen separated from their dams. Seven days postweaning, the steers were introduced to individual feeding in 1 of 15 individual feeding stations using a 20:80 ration of corn gluten feed (CGF) and oats. Immediately after the adaptation period, the steers began treatment. Steers were assigned to 1 of 2 treatment groups, balanced for BW and breed, for 110 d. The treatments were either the control group (CON; n = 23) fed 1 kg of CGF (91.7% DM, 20.1% CP, 74.0% TDN, 2.9% ether extract, and 1.78 Mcal/kg of NEm) or the rumen undegradable fat group (RUF; n = 24) fed 0.56 kg of CGF plus 0.2 kg of Megalac-R (Church & Dwight Co., Inc., Princeton, NJ; 0% CP, 163.5% TDN, and 3.95 Mcal/kg of NEm). These supplements were offered individually to steers 5 d/wk (Monday to Friday) by allowing ∼25 min for a group of 15 steers to eat in individual stations before the next group was brought in, and this process was repeated as many times as necessary. Supplement intake was formulated to be isocaloric (provided 1.78 Mcal/d fed of NEm) but were not isonitrogenous (201 and 113 g/d of CP fed to CON and RUF, respectively). The FA profile and composition of the RUF source is shown in Table 1. At d 55 of treatment, CON steers received 1.5 kg of CGF, and RUF steers received 1.06 kg CGF plus the 0.2 kg of Megalac-R per supplementation event, which increased energy provided to 2.67 Mcal/d fed of NEm to both treatments. With 18 d left on treatment, all supplement availability was increased; CON steers received 2.0 kg of CGF while RUF steers received 1.56 kg CGF plus 0.2 kg Megalac-R per supplementation event, which increased energy provided to 3.56 Mcal/d fed of NEm to both treatments. Throughout the treatment period (d 0 to 110), the steers had ad libitum access to a bermudagrass, novel endophyte tall fescue, and wild-type endophyte-infected tall fescue pasture (average of 8,000 kg/ha at turn out onto pasture, 10% CP, 4.3% ether extract, 55.7% TDN, 1.3 Mcal/kg of NEm, ADF of 37.9%, and NDF of 71.6%). When forage availability was <5,500 kg/ha, steers were offered ad libitum supplemental bahia/bermudagrass hay (average of 9.4% CP, 4.0% ether extract, 54.4 TDN, 1.3 Mcal/kg of NEm, ADF of 39.3%, and NDF of 74.6%). Table 1. Nutrient profile and fatty acid composition of Megalac-R, rumen undegradable unsaturated fatty acid source offered to early-weaned steers Item  Contents  DM, %  97.0  Ca, % DM  9.0  Ether Extract, % DM  84.5  C12:0, % DM  0.0  C14:0, % DM  0.0  C16:0, % DM  21.9  C16:1, % DM  0.0  C18:0, % DM  3.0  C18:1 t, % DM  0.0  C18:1 c, % DM  27.8  C18:2, % DM  26.8  C18:3, % DM  4.0  Other LCFA2, % DM  1.0  Item  Contents  DM, %  97.0  Ca, % DM  9.0  Ether Extract, % DM  84.5  C12:0, % DM  0.0  C14:0, % DM  0.0  C16:0, % DM  21.9  C16:1, % DM  0.0  C18:0, % DM  3.0  C18:1 t, % DM  0.0  C18:1 c, % DM  27.8  C18:2, % DM  26.8  C18:3, % DM  4.0  Other LCFA2, % DM  1.0  1Data provided by Church & Dwight Co., Inc., Princeton, NJ. 2LCFA = long chain fatty acids. View Large Table 1. Nutrient profile and fatty acid composition of Megalac-R, rumen undegradable unsaturated fatty acid source offered to early-weaned steers Item  Contents  DM, %  97.0  Ca, % DM  9.0  Ether Extract, % DM  84.5  C12:0, % DM  0.0  C14:0, % DM  0.0  C16:0, % DM  21.9  C16:1, % DM  0.0  C18:0, % DM  3.0  C18:1 t, % DM  0.0  C18:1 c, % DM  27.8  C18:2, % DM  26.8  C18:3, % DM  4.0  Other LCFA2, % DM  1.0  Item  Contents  DM, %  97.0  Ca, % DM  9.0  Ether Extract, % DM  84.5  C12:0, % DM  0.0  C14:0, % DM  0.0  C16:0, % DM  21.9  C16:1, % DM  0.0  C18:0, % DM  3.0  C18:1 t, % DM  0.0  C18:1 c, % DM  27.8  C18:2, % DM  26.8  C18:3, % DM  4.0  Other LCFA2, % DM  1.0  1Data provided by Church & Dwight Co., Inc., Princeton, NJ. 2LCFA = long chain fatty acids. View Large All steers remained at Edisto Research and Education Center (Blackville, SC) through the duration of treatment (d 0 to 110). Blood samples and BW were collected at 0, 55, and 110 d of treatment. Blood was collected via jugular venipuncture using Serum Z/9-mL Luer Monovette collection tubes (Sarstedt Inc., Newton, NC). The blood was allowed to clot and then refrigerated at 4°C for 24 h and was then centrifuged at 1,200 × g for 30 min. Serum was collected and stored at −20°C until analysis. Real-time ultrasound carcass measurements were collected on d 110 of treatment to assess i.m. fat, muscle depth, and backfat thickness. Longitudinal scans for i.m. fat content, muscle depth, and backfat thickness were obtained between the 11th and 13th rib using an Aloka 500 V ultrasound machine with a 17 cm, 3.5 MHz linear probe (Corometrics Medical Systems, Wallingford, CT). Images were interpreted using BioSoft Toolbox (Biotronics Inc., Ames, IA) by a trained individual. Upon completion of treatment, all steers were transported by a commercial hauler for 1,700 km to Oklahoma State University's Willard Sparks Beef Research Center to begin the finishing phase. Steers were blocked into 4 pens per treatment based on BW. The diet composition provided to the steers during the finishing period is provided in Table 2. The total feed consumed per pen and refusal was measured daily. Subsequently, pen DMI and individual ADG on a pen basis were calculated. After 176 d of finishing, the steers were hauled 118 km to a commercial packing plant for harvest. Carcass measurements, including HCW and ribeye area, backfat thickness, and KPH were collected by trained personnel at harvest or 48 h postmortem, respectively. Additionally, the right rib section of each carcass (112A Rib, Ribeye Roll, Lip-On; NAMP, 1988) was collected, vacuum-packed, put on ice, and transported to the Clemson University Meat Laboratory. Once at the meat laboratory, the rib sections were stored at 3.5°C for 3 d. From each rib section, 2 steaks approximately 2.54 cm thick were obtained, 1 for proximate analysis and 1 for cell size and distribution analysis. Steaks for proximate analysis had all external fat and connective tissue removed. The steaks were then chopped into cubes and were frozen at −20°C until analysis. Steaks for cell size and distribution were maintained at 4°C until analysis. Table 2. Composition of diets (DM basis) fed to steers during feedlot period Ingredient  Percentage of diet  Dry rolled corn  42.21  Sweet Bran1  20.60  Dried corn distillers grain  13.53  Prairie hay  8.58  Synergy 19-142  10.08  Dry supplement, B-2733  5.00  Nutrient, % DM basis        DM, %  79.8      NDF, %  22.23      Crude fat, %  7.28      CP, %  17.75      Ca, %  0.79      P, %  0.57      K, %  0.97  Ingredient  Percentage of diet  Dry rolled corn  42.21  Sweet Bran1  20.60  Dried corn distillers grain  13.53  Prairie hay  8.58  Synergy 19-142  10.08  Dry supplement, B-2733  5.00  Nutrient, % DM basis        DM, %  79.8      NDF, %  22.23      Crude fat, %  7.28      CP, %  17.75      Ca, %  0.79      P, %  0.57      K, %  0.97  1Sweet Bran; Cargill, Inc., Minneapolis, MN. 2Liquid feed supplement; Westway Feed Products, New Orleans, LA. Formulated to contain (DM basis): 63.2% DM, 30.1% CP, 22.2% EE, 109.8 TDN, and 2.90 Mcal/kg of NEm. 3Formulated to contain (DM basis): 6.92% urea, 30.36% limestone, 1.03% MgO, 0.38% salt, 0.119% copper sulfate, 0.116% MnO, 0.05% selenium premix (0.6% Se), 0.618% ZnSO4, 0.311% vitamin A (30 IU/mg), 0.085% vitamin E (500 IU/g), 0.317% Rumensin 90, 0.195% Tylan 40, 38.46% ground corn, and 21.04% wheat middlings. View Large Table 2. Composition of diets (DM basis) fed to steers during feedlot period Ingredient  Percentage of diet  Dry rolled corn  42.21  Sweet Bran1  20.60  Dried corn distillers grain  13.53  Prairie hay  8.58  Synergy 19-142  10.08  Dry supplement, B-2733  5.00  Nutrient, % DM basis        DM, %  79.8      NDF, %  22.23      Crude fat, %  7.28      CP, %  17.75      Ca, %  0.79      P, %  0.57      K, %  0.97  Ingredient  Percentage of diet  Dry rolled corn  42.21  Sweet Bran1  20.60  Dried corn distillers grain  13.53  Prairie hay  8.58  Synergy 19-142  10.08  Dry supplement, B-2733  5.00  Nutrient, % DM basis        DM, %  79.8      NDF, %  22.23      Crude fat, %  7.28      CP, %  17.75      Ca, %  0.79      P, %  0.57      K, %  0.97  1Sweet Bran; Cargill, Inc., Minneapolis, MN. 2Liquid feed supplement; Westway Feed Products, New Orleans, LA. Formulated to contain (DM basis): 63.2% DM, 30.1% CP, 22.2% EE, 109.8 TDN, and 2.90 Mcal/kg of NEm. 3Formulated to contain (DM basis): 6.92% urea, 30.36% limestone, 1.03% MgO, 0.38% salt, 0.119% copper sulfate, 0.116% MnO, 0.05% selenium premix (0.6% Se), 0.618% ZnSO4, 0.311% vitamin A (30 IU/mg), 0.085% vitamin E (500 IU/g), 0.317% Rumensin 90, 0.195% Tylan 40, 38.46% ground corn, and 21.04% wheat middlings. View Large Forage and Supplement Analysis Samples of available forages and subsamples of CGF and hay were collected for nutritional analysis. Forage samples were collected monthly or as the steers were moved to different pastures. Using a 0.09-m2 frame and cutting 2.54 cm from the soil, random pasture samples were collected in triplicate. Hay subsamples were collected before being fed ad libitum and were then composited. Each pasture sample was weighed after collection and reweighed after drying at 60°C for 48 h to determine DM. The 3 forage samples from each cutting, the hay subsamples, and CGF subsamples were pooled and ground using a Wiley Mill (Model 4; Thomas Scientific, Swedesboro, NJ) to pass a 1-mm screen. According to the procedures of Goering and Van Soest (1970), NDF and ADF were determined using Ankom Fiber Analyzer F200 (Ankom Technologies, Fairport, NY). The concentration of CP was determined by the combustion method using a Leco FP528 nitrogen combustion analyzer (Leco Corp., St. Joseph, MI). Proximate Analysis of Steaks Steaks were allowed to thaw partially and were then pulverized in a Blixer 3 Series D (Robot Coupe USA Inc., Ridgeland, MS). The samples were then stored and maintained at −20°C. The percentage of moisture and the percentage of total lipid of each sample were determined in triplicate and in duplicate, respectively, according to Method 950.46 and Method 960.39 (AOAC, 1990). Total lipid extraction was performed by washing samples with petroleum ether (EMD Millipore Corporation, Billerica, MA) in a Soxhlet extract apparatus for approximately 24 h. The intra-assay CV for the percentage of moisture and total lipids were 0.9 and 1.9%, respectively. Cell Size and Distribution One steak per animal was used to determine adipocyte cell size of both the s.c. and i.m. adipose depots according to Etherton et al. (1977). Duplicate slice samples of s.c. adipose tissue from the exterior of the ribeye (approximately 2 cm2) and duplicate samples of i.m. adipose tissue that had been dissected from the ribeye steak (approximately 1 g) were used for determination of adipocyte cell size. All samples were rinsed twice with 0.154 M NaCl to remove any free lipid from ruptured adipocytes. Adipocytes from each deport were fixed in 3% osmium tetroxide in 50 mM collidine-HCl buffer for 48 h. Adipocytes were removed from fixing buffer and were rinsed with NaCl twice and then placed into 8 M urea for 48 h to liberate fixed adipocytes from connective tissue. Fixed adipocytes were then filtered through a 240-μm filter mesh to remove large debris. This was followed filtration through a 20-μm filter mesh to separate out adipocytes; the remaining fixed adipocytes left on top of the 20-μm filter mesh were used for analysis. Subcutaneous and i.m. adipocytes were counted and sized using a particle sizing and counting analyzer (Multisizer 4 Coulter Counter; Beckman Coulter Inc., Brea, CA). Serum Fatty Acid Analysis Duplicate 1-mL samples of serum collected on d 0, 55, and 100 from 10 randomly chosen steers per treatment were lyophilized (LabConco, Kansas City, MO) and transmethylated according to Park and Goins (1994). The Park and Goins (1994) method uses an alkaline catalyst followed by an acidic catalyst to complete the transmethylation of FFA without rearranging cis/trans double bonds (Duckett et al., 2002). Each sample of FA methyl esters (FAME) was analyzed using an Agilent 6850 gas chromatograph (GC) equipped with an Agilent 7673A automatic sampler (Agilent Technologies, Santa Clara, CA). Separations were completed using a 30-m Famewax capillary column (12497; Restek, Bellefonte, PA) according to Duckett et al. (2009). Samples were run at a split ratio of 5:1. Identification of FA was achieved by comparing retention times of known standards. An internal standard, methyl tricosanoic (C23:0) acid, was incorporated into every sample during methylation to quantify the sample as a percentage of weight of total FA. The CV based on total FAs was 12.2%. Biochemical Assays Serum triglyceride and cholesterol concentrations were determined using previously validated colorimetric assays (Pointe Scientific, Inc., Canton, MI; Long et al., 2014). All samples were run in triplicate. The intra-assay and interassay CV for cholesterol were 3.8 and 2.9%, respectively. The intra-assay and interassay CV for triglycerides were 3.6 and 4.3%, respectively. Serum leptin concentration was determined using a previously validated RIA (Linco Research, St. Charles, MO; Long and Schafer, 2013), and samples were run in duplicate and in a single assay with an intra-assay CV of 2.8%. Statistical Analysis Individual steer was used as the experimental unit for BW variables, ultrasound measures, proximate analysis of steaks and adipocyte parameters, and serum metabolites and hormones. These variables were analyzed using the MIXED model of SAS (SAS Inst. Inc., Cary, NC) with treatment, breed, day (for serum variables) and all resultant interaction in the model, and weaning block as random variables. All feedlot and carcass measures were analyzed with feedlot pen as the experimental unit. These variables were also analyzed using the MIXED model of SAS, with treatment in the model statement. Data are presented as least squares means ± SEM and were considered significantly different when P ≤ 0.05 and a tendency was indicated when P ≤ 0.10. RESULTS Steer BW from birth throughout treatment are provided in Table 3. Steers within both treatments had similar BW at birth and weaning at 150 d of age (P ≥ 0.49). Steer BW remained similar between treatments throughout the rest of the treatment period (P ≥ 0.49). However, at weaning and the start of treatment, there was a breed effect, with AN steers being heavier (P < 0.01 and P = 0.02, respectively) than AN/HP steers. The difference in steer BW due to breed persisted until the middle of treatment (P = 0.04), but there was no difference (P = 0.23) by the end of treatment. Overall BW change during treatment was also similar between treatments (P = 0.86), but AN/HP steers had a greater BW change (P = 0.02) compared to AN steers. Table 3. Body weight (kg) from birth, weaning at 150 ± 5 d of age, and through the end of supplementation of grazing steers individually fed isocaloric supplement containing no rumen bypass fat (control [CON]) or 0.2 kg of an unsaturated rumen undegradable fat source (RUF) 5 d/wk from d 0 to 110 of treatment1   Treatment (Trt)  Breed (Bd)      CON  RUF  Angus  Angus × Hereford  P-value  n  23  24  23  24  Trt  Bd  Trt × Bd  Birth weight  37.6 ± 1.3  36.7 ± 1.2  37.8 ± 1.3  36.5 ± 1.3  0.49  0.34  0.48  Weaning BW (d −14)  213.6 ± 5.8  219.0 ± 5.7  229.5 ± 5.8  203.1 ± 5.7  0.51  0.002  0.68  Start weight (d 0)  217.5 ± 6.1  220.5 ± 5.9  229 ± 6.0  209 ± 6.1  0.72  0.02  0.63  Mid weight (d 55)  231.8 ± 6.2  230.4 ± 5.9  239.4 ± 6.1  222.7 ± 6.1  0.86  0.05  0.53  End weight (d 110)  241.5 ± 7.6  243.9 ± 7.4  248.1 ± 7.7  237.3 ± 7.5  0.78  0.23  0.50  BW change  24.8 ± 3.5  24.2 ± 3.4  19.9 ± 3.5  29.0 ± 3.4  0.86  0.02  0.73    Treatment (Trt)  Breed (Bd)      CON  RUF  Angus  Angus × Hereford  P-value  n  23  24  23  24  Trt  Bd  Trt × Bd  Birth weight  37.6 ± 1.3  36.7 ± 1.2  37.8 ± 1.3  36.5 ± 1.3  0.49  0.34  0.48  Weaning BW (d −14)  213.6 ± 5.8  219.0 ± 5.7  229.5 ± 5.8  203.1 ± 5.7  0.51  0.002  0.68  Start weight (d 0)  217.5 ± 6.1  220.5 ± 5.9  229 ± 6.0  209 ± 6.1  0.72  0.02  0.63  Mid weight (d 55)  231.8 ± 6.2  230.4 ± 5.9  239.4 ± 6.1  222.7 ± 6.1  0.86  0.05  0.53  End weight (d 110)  241.5 ± 7.6  243.9 ± 7.4  248.1 ± 7.7  237.3 ± 7.5  0.78  0.23  0.50  BW change  24.8 ± 3.5  24.2 ± 3.4  19.9 ± 3.5  29.0 ± 3.4  0.86  0.02  0.73  1The treatments from d 0 to 54 were either CON steers fed 1 kg of corn gluten feed (CGF) or RUF steers fed 0.56 kg of CGF plus 0.2 kg of Megalac-R (Church & Dwight Co., Inc., Princeton, NJ) per supplementation event (5 d/wk). At d 55 of treatment, CON steers received 1.5 kg of CGF, and RUF steers received 1.06 kg CGF plus the 0.2 kg of Megalac-R per supplementation event. On d 92 of treatment, CON steers received 2.0 kg of CGF while RUF steers received 1.56 kg CGF plus 0.2 kg Megalac-R per supplementation event. View Large Table 3. Body weight (kg) from birth, weaning at 150 ± 5 d of age, and through the end of supplementation of grazing steers individually fed isocaloric supplement containing no rumen bypass fat (control [CON]) or 0.2 kg of an unsaturated rumen undegradable fat source (RUF) 5 d/wk from d 0 to 110 of treatment1   Treatment (Trt)  Breed (Bd)      CON  RUF  Angus  Angus × Hereford  P-value  n  23  24  23  24  Trt  Bd  Trt × Bd  Birth weight  37.6 ± 1.3  36.7 ± 1.2  37.8 ± 1.3  36.5 ± 1.3  0.49  0.34  0.48  Weaning BW (d −14)  213.6 ± 5.8  219.0 ± 5.7  229.5 ± 5.8  203.1 ± 5.7  0.51  0.002  0.68  Start weight (d 0)  217.5 ± 6.1  220.5 ± 5.9  229 ± 6.0  209 ± 6.1  0.72  0.02  0.63  Mid weight (d 55)  231.8 ± 6.2  230.4 ± 5.9  239.4 ± 6.1  222.7 ± 6.1  0.86  0.05  0.53  End weight (d 110)  241.5 ± 7.6  243.9 ± 7.4  248.1 ± 7.7  237.3 ± 7.5  0.78  0.23  0.50  BW change  24.8 ± 3.5  24.2 ± 3.4  19.9 ± 3.5  29.0 ± 3.4  0.86  0.02  0.73    Treatment (Trt)  Breed (Bd)      CON  RUF  Angus  Angus × Hereford  P-value  n  23  24  23  24  Trt  Bd  Trt × Bd  Birth weight  37.6 ± 1.3  36.7 ± 1.2  37.8 ± 1.3  36.5 ± 1.3  0.49  0.34  0.48  Weaning BW (d −14)  213.6 ± 5.8  219.0 ± 5.7  229.5 ± 5.8  203.1 ± 5.7  0.51  0.002  0.68  Start weight (d 0)  217.5 ± 6.1  220.5 ± 5.9  229 ± 6.0  209 ± 6.1  0.72  0.02  0.63  Mid weight (d 55)  231.8 ± 6.2  230.4 ± 5.9  239.4 ± 6.1  222.7 ± 6.1  0.86  0.05  0.53  End weight (d 110)  241.5 ± 7.6  243.9 ± 7.4  248.1 ± 7.7  237.3 ± 7.5  0.78  0.23  0.50  BW change  24.8 ± 3.5  24.2 ± 3.4  19.9 ± 3.5  29.0 ± 3.4  0.86  0.02  0.73  1The treatments from d 0 to 54 were either CON steers fed 1 kg of corn gluten feed (CGF) or RUF steers fed 0.56 kg of CGF plus 0.2 kg of Megalac-R (Church & Dwight Co., Inc., Princeton, NJ) per supplementation event (5 d/wk). At d 55 of treatment, CON steers received 1.5 kg of CGF, and RUF steers received 1.06 kg CGF plus the 0.2 kg of Megalac-R per supplementation event. On d 92 of treatment, CON steers received 2.0 kg of CGF while RUF steers received 1.56 kg CGF plus 0.2 kg Megalac-R per supplementation event. View Large The ultrasound data from steers at the end of supplementation indicated that RUF steers tended to have a greater (P = 0.08) amount of i.m. fat compared to that of CON steers on d 110 of treatment (4.01 ± 0.25 vs. 3.36 ± 0.25% fat, respectively). However, there was no significant difference (P = 0.83) in muscle depth (1.47 ± 0.04 vs. 1.46 ± 0.04 cm) or backfat thickness (P = 0.67; 0.054 ± 0.010 vs. 0.048 ± 0.009 cm) between CON and RUF steers, respectively, on d 110 of treatment. Serum FA concentrations in both the CON and RUF steers are given in Table 4. During treatment, there was a treatment × day interaction (P < 0.02) for the concentration of palmitic (16:0), stearic (18:0), oleic (18:1 cis-9), linoleic (18:2), and arachidonic (20:4) acids and total FA. These specific FA concentrations slightly increased in CON steers, whereas there was a more prominent increase in RUF steers across the supplementation period. There was a tendency for the RUF steers to have a greater concentration (P < 0.1) of myristic (14:0), pentadecyclic (15:0), and linolenic (18:3) acids and a greater (P = 0.04) concentration of docosapentaenoic acid (DPA) compared to CON steers. Table 4. Serum total and specific fatty acids (mg/ml) of grazing steers individually fed isocaloric supplement containing no bypass fat (control [CON]) or 0.2 kg of an unsaturated rumen undegradable fat source (RUF) 5 d/wk from d 0 to d 110 of treatment (Trt)1   CON  RUF        d 0  d 55  d 110  d 0  d 55  d 110    P-value  n  10  10  10  10  10  10  SE  Trt  d  Trt × d  14:0  5.51  6.00  7.92  7.51  10.29  12.08  1.575  0.08  0.03  0.49  15:0  5.02  7.32  9.35  5.07  12.61  15.75  1.820  0.07  <0.01  0.09  16:0  78.14  95.42  137.03  108.9  233.82  294.81  29.856  0.01  0.0001  <0.01  16:1  10.29  13.18  15.93  12.82  15.26  18.46  3.116  0.54  0.06  0.99  18:0  89.67  120.39  160.34  112.82  274.51  338.24  35.346  0.01  <0.01  <0.01  18:1 t-9  66.63  86.95  126.17  89.39  131.22  154.33  19.838  0.21  <0.01  0.53  18:1 c-9  11.59  14.61  15.24  12.70  28.32  21.39  3.009  0.07  <0.01  <0.01  18:2  86.17  156.28  237.36  137.19  628.88  889.00  86.360  <0.01  <0.01  <0.01  18:3  35.92  44.79  52.55  43.56  69.50  84.48  10.570  0.09  <0.01  0.34  20:4  16.28  21.40  32.12  22.57  46.72  67.93  6.715  0.01  <0.01  0.01  EPA  11.87  13.94  16.68  14.39  18.59  20.39  3.178  0.33  0.13  0.87  DPA  6.12  10.02  16.25  12.72  18.72  21.74  2.839  0.04  <0.01  0.66  Total FA  400.06  550.91  650.58  523.17  1,255.81  1,524.36  88.30  <0.01  <0.01  <0.01    CON  RUF        d 0  d 55  d 110  d 0  d 55  d 110    P-value  n  10  10  10  10  10  10  SE  Trt  d  Trt × d  14:0  5.51  6.00  7.92  7.51  10.29  12.08  1.575  0.08  0.03  0.49  15:0  5.02  7.32  9.35  5.07  12.61  15.75  1.820  0.07  <0.01  0.09  16:0  78.14  95.42  137.03  108.9  233.82  294.81  29.856  0.01  0.0001  <0.01  16:1  10.29  13.18  15.93  12.82  15.26  18.46  3.116  0.54  0.06  0.99  18:0  89.67  120.39  160.34  112.82  274.51  338.24  35.346  0.01  <0.01  <0.01  18:1 t-9  66.63  86.95  126.17  89.39  131.22  154.33  19.838  0.21  <0.01  0.53  18:1 c-9  11.59  14.61  15.24  12.70  28.32  21.39  3.009  0.07  <0.01  <0.01  18:2  86.17  156.28  237.36  137.19  628.88  889.00  86.360  <0.01  <0.01  <0.01  18:3  35.92  44.79  52.55  43.56  69.50  84.48  10.570  0.09  <0.01  0.34  20:4  16.28  21.40  32.12  22.57  46.72  67.93  6.715  0.01  <0.01  0.01  EPA  11.87  13.94  16.68  14.39  18.59  20.39  3.178  0.33  0.13  0.87  DPA  6.12  10.02  16.25  12.72  18.72  21.74  2.839  0.04  <0.01  0.66  Total FA  400.06  550.91  650.58  523.17  1,255.81  1,524.36  88.30  <0.01  <0.01  <0.01  1The treatments from d 0 to 54 were either CON steers fed 1 kg of corn gluten feed (CGF) or RUF steers fed 0.56 kg of CGF plus 0.2 kg of Megalac-R (Church & Dwight Co., Inc., Princeton, NJ) per supplementation event (5 d/wk). At d 55 of treatment, CON steers received 1.5 kg of CGF and RUF steers received 1.06 kg CGF plus the 0.2 kg of Megalac-R per supplementation event. On d 92 of treatment, CON steers received 2.0 kg of CGF while RUF steers received 1.56 kg CGF plus 0.2 kg Megalac-R per supplementation event. View Large Table 4. Serum total and specific fatty acids (mg/ml) of grazing steers individually fed isocaloric supplement containing no bypass fat (control [CON]) or 0.2 kg of an unsaturated rumen undegradable fat source (RUF) 5 d/wk from d 0 to d 110 of treatment (Trt)1   CON  RUF        d 0  d 55  d 110  d 0  d 55  d 110    P-value  n  10  10  10  10  10  10  SE  Trt  d  Trt × d  14:0  5.51  6.00  7.92  7.51  10.29  12.08  1.575  0.08  0.03  0.49  15:0  5.02  7.32  9.35  5.07  12.61  15.75  1.820  0.07  <0.01  0.09  16:0  78.14  95.42  137.03  108.9  233.82  294.81  29.856  0.01  0.0001  <0.01  16:1  10.29  13.18  15.93  12.82  15.26  18.46  3.116  0.54  0.06  0.99  18:0  89.67  120.39  160.34  112.82  274.51  338.24  35.346  0.01  <0.01  <0.01  18:1 t-9  66.63  86.95  126.17  89.39  131.22  154.33  19.838  0.21  <0.01  0.53  18:1 c-9  11.59  14.61  15.24  12.70  28.32  21.39  3.009  0.07  <0.01  <0.01  18:2  86.17  156.28  237.36  137.19  628.88  889.00  86.360  <0.01  <0.01  <0.01  18:3  35.92  44.79  52.55  43.56  69.50  84.48  10.570  0.09  <0.01  0.34  20:4  16.28  21.40  32.12  22.57  46.72  67.93  6.715  0.01  <0.01  0.01  EPA  11.87  13.94  16.68  14.39  18.59  20.39  3.178  0.33  0.13  0.87  DPA  6.12  10.02  16.25  12.72  18.72  21.74  2.839  0.04  <0.01  0.66  Total FA  400.06  550.91  650.58  523.17  1,255.81  1,524.36  88.30  <0.01  <0.01  <0.01    CON  RUF        d 0  d 55  d 110  d 0  d 55  d 110    P-value  n  10  10  10  10  10  10  SE  Trt  d  Trt × d  14:0  5.51  6.00  7.92  7.51  10.29  12.08  1.575  0.08  0.03  0.49  15:0  5.02  7.32  9.35  5.07  12.61  15.75  1.820  0.07  <0.01  0.09  16:0  78.14  95.42  137.03  108.9  233.82  294.81  29.856  0.01  0.0001  <0.01  16:1  10.29  13.18  15.93  12.82  15.26  18.46  3.116  0.54  0.06  0.99  18:0  89.67  120.39  160.34  112.82  274.51  338.24  35.346  0.01  <0.01  <0.01  18:1 t-9  66.63  86.95  126.17  89.39  131.22  154.33  19.838  0.21  <0.01  0.53  18:1 c-9  11.59  14.61  15.24  12.70  28.32  21.39  3.009  0.07  <0.01  <0.01  18:2  86.17  156.28  237.36  137.19  628.88  889.00  86.360  <0.01  <0.01  <0.01  18:3  35.92  44.79  52.55  43.56  69.50  84.48  10.570  0.09  <0.01  0.34  20:4  16.28  21.40  32.12  22.57  46.72  67.93  6.715  0.01  <0.01  0.01  EPA  11.87  13.94  16.68  14.39  18.59  20.39  3.178  0.33  0.13  0.87  DPA  6.12  10.02  16.25  12.72  18.72  21.74  2.839  0.04  <0.01  0.66  Total FA  400.06  550.91  650.58  523.17  1,255.81  1,524.36  88.30  <0.01  <0.01  <0.01  1The treatments from d 0 to 54 were either CON steers fed 1 kg of corn gluten feed (CGF) or RUF steers fed 0.56 kg of CGF plus 0.2 kg of Megalac-R (Church & Dwight Co., Inc., Princeton, NJ) per supplementation event (5 d/wk). At d 55 of treatment, CON steers received 1.5 kg of CGF and RUF steers received 1.06 kg CGF plus the 0.2 kg of Megalac-R per supplementation event. On d 92 of treatment, CON steers received 2.0 kg of CGF while RUF steers received 1.56 kg CGF plus 0.2 kg Megalac-R per supplementation event. View Large Serum triglyceride concentrations at d 0 were similar (P = 0.17) between treatments, as shown in Fig. 1. The triglyceride concentration of the CON steers remained similar (P = 0.26) from d 0 to 110 of treatment. For RUF steers, there was an increase (P < 0.05) in triglyceride concentration from d 0 to d 55, and this concentration persisted until the end of treatment. Serum cholesterol concentrations were also similar (P = 0.96) between treatments on d 0, as shown in Fig. 2. The cholesterol concentration of the CON steers increased from d 0 to 55 (P = 0.01) and from d 55 to 110 (P < 0.001). The RUF steers had increased (P < 0.001) cholesterol concentrations from d 0 to 55 and from d 55 to 110 of treatment (P = 0.01). Serum cholesterol concentrations were greater (P < 0.05) in RUF steers compared to those in CON steers on d 55 and 110. The concentration of serum leptin (Fig. 3) was similar (P ≥ 0.27) for both CON and RUF steers at d 0 and 55. However, on d 110, there was an increase (P < 0.01) in the leptin concentration for RUF steers compared to CON steers. Figure 1. View largeDownload slide Serum triglyceride concentrations on d 0, 55, and 110 of treatment of grazing steers individually fed isocaloric supplement containing no bypass fat (control [CON]; ■, n = 23) or 0.2 kg of unsaturated rumen undegradable fat source (RUF; ○, n = 24) 5 d/wk from d 0 to 110 (treatment, P = 0.003; day, P < 0.0001; treatment × day, P < 0.0001). Values are means ± SEM. Means without a common letter (a, b) differ (P < 0.01). Figure 1. View largeDownload slide Serum triglyceride concentrations on d 0, 55, and 110 of treatment of grazing steers individually fed isocaloric supplement containing no bypass fat (control [CON]; ■, n = 23) or 0.2 kg of unsaturated rumen undegradable fat source (RUF; ○, n = 24) 5 d/wk from d 0 to 110 (treatment, P = 0.003; day, P < 0.0001; treatment × day, P < 0.0001). Values are means ± SEM. Means without a common letter (a, b) differ (P < 0.01). Figure 2. View largeDownload slide Serum cholesterol concentrations on d 0, 55, and 110 of treatment of grazing steers individually fed isocaloric supplement containing no bypass fat (control [CON]; ■, n = 23) or 0.2 kg of unsaturated rumen undegradable fat source (RUF; ○, n = 24) 5 d/wk from d 0 to 110 (treatment, P < 0.0001; day, P < 0.0001; Treatment × day, P < 0.0001). Values are means ± SEM. Means without a common letter (a, b, c, d, e) differ (P < 0.0001). Figure 2. View largeDownload slide Serum cholesterol concentrations on d 0, 55, and 110 of treatment of grazing steers individually fed isocaloric supplement containing no bypass fat (control [CON]; ■, n = 23) or 0.2 kg of unsaturated rumen undegradable fat source (RUF; ○, n = 24) 5 d/wk from d 0 to 110 (treatment, P < 0.0001; day, P < 0.0001; Treatment × day, P < 0.0001). Values are means ± SEM. Means without a common letter (a, b, c, d, e) differ (P < 0.0001). Figure 3. View largeDownload slide Serum leptin concentrations on d 0, 55, and 110 of treatment of grazing steers individually fed isocaloric supplement containing no bypass fat (control [CON]; ■, n = 23) or 0.2 kg of unsaturated rumen undegradable fat source (RUF; ○, n = 24) 5 d/wk from d 0 to 110 (treatment, P = 0.0238; day, P = 0.0048; treatment × day, P = 0.1628). Values are means ± SEM. Means (a, b) without a common letter differs (P < 0.001). Figure 3. View largeDownload slide Serum leptin concentrations on d 0, 55, and 110 of treatment of grazing steers individually fed isocaloric supplement containing no bypass fat (control [CON]; ■, n = 23) or 0.2 kg of unsaturated rumen undegradable fat source (RUF; ○, n = 24) 5 d/wk from d 0 to 110 (treatment, P = 0.0238; day, P = 0.0048; treatment × day, P = 0.1628). Values are means ± SEM. Means (a, b) without a common letter differs (P < 0.001). During the finishing phase, CON steers consumed 10.7 ± 0.2 kg of DM per head/d, and the RUF steers consumed 10.6 ± 0.2 kg of DM per head/d (P = 0.43). The ADG was similar (P = 0.90) between treatments (2.18 ± 0.04 vs. 2.14 ± 0.04 kg/d for CON vs. RUF, respectively). The G:F and overall BW gain were also similar (P = 0.45 and P = 0.90, respectively) between treatments (4.94 ± 0.11 kg/kg and 380 ± 9 kg vs. 4.92 ± 0.11 kg/kg and 379 ± 9 kg for CON vs. RUF, respectively). The carcass composition of steers is shown in Table 5. There was no difference in HCW between CON and RUF carcasses (P = 0.90). There was no difference in yield grade, LM area, backfat thickness, or KPH (P ≥ 0.41). There was a difference (P = 0.01) in marbling score, where the RUF carcasses have a greater marbling score compared to the CON carcasses. This difference was confirmed by the ether extract of the strip loin steaks that indicated that steaks from the RUF steers had greater amounts of ether extract (P = 0.01; Table 5) compared to steaks from CON steers. The percent moisture of steaks from steers of either treatment was similar (P = 0.54). Table 5. The effects of treatment (Trt) on carcass composition of steers individually fed isocaloric supplement containing no bypass fat (control [CON]) or 0.2 kg of an unsaturated rumen undegradable fat source (RUF) 5 d/wk for 110 d, beginning at 5 mo of age and harvested at 385 ± 10 d of age1   Treatment (Trt)  P-value    CON  RUF  Trt  n  4  4    HCW, kg  375.70 ± 15.30  378.48 ± 15.30  0.902  Yield grade  3.80 ± 0.18  4.03 ± 0.18  0.414  LM area, cm2  83.45 ± 2.01  80.93 ± 2.01  0.409  Backfat, cm  1.63 ± 0.14  1.65 ± 0.14  0.900  KPH, %  3.35 ± 0.04  3.38 ± 0.04  0.670  Marbling score2  48.23 ± 0.82  52.48 ± 0.82  0.010  Ether extract3, %  6.81 ± 0.16  7.63 ± 0.16  0.011  Moisture3, %  69.76 ± 0.42  69.37 ± 0.42  0.539    Treatment (Trt)  P-value    CON  RUF  Trt  n  4  4    HCW, kg  375.70 ± 15.30  378.48 ± 15.30  0.902  Yield grade  3.80 ± 0.18  4.03 ± 0.18  0.414  LM area, cm2  83.45 ± 2.01  80.93 ± 2.01  0.409  Backfat, cm  1.63 ± 0.14  1.65 ± 0.14  0.900  KPH, %  3.35 ± 0.04  3.38 ± 0.04  0.670  Marbling score2  48.23 ± 0.82  52.48 ± 0.82  0.010  Ether extract3, %  6.81 ± 0.16  7.63 ± 0.16  0.011  Moisture3, %  69.76 ± 0.42  69.37 ± 0.42  0.539  1The treatments from d 0 to 54 were either CON steers fed 1 kg of corn gluten feed (CGF) or RUF steers fed 0.56 kg of CGF plus 0.2 kg of Megalac-R (Church & Dwight Co., Inc., Princeton, NJ) per supplementation event (5 d/wk). At d 55 of treatment, CON steers received 1.5 kg of CGF and RUF steers received 1.06 kg CGF plus the 0.2 kg of Megalac-R per supplementation event. On d 92 of treatment, CON steers received 2.0 kg of CGF while RUF steers received 1.56 kg CGF plus 0.2 kg Megalac-R per supplementation event. 2Marbling score: 40 = small 00; 50 = modest 00. 3Determined from striploin steak. View Large Table 5. The effects of treatment (Trt) on carcass composition of steers individually fed isocaloric supplement containing no bypass fat (control [CON]) or 0.2 kg of an unsaturated rumen undegradable fat source (RUF) 5 d/wk for 110 d, beginning at 5 mo of age and harvested at 385 ± 10 d of age1   Treatment (Trt)  P-value    CON  RUF  Trt  n  4  4    HCW, kg  375.70 ± 15.30  378.48 ± 15.30  0.902  Yield grade  3.80 ± 0.18  4.03 ± 0.18  0.414  LM area, cm2  83.45 ± 2.01  80.93 ± 2.01  0.409  Backfat, cm  1.63 ± 0.14  1.65 ± 0.14  0.900  KPH, %  3.35 ± 0.04  3.38 ± 0.04  0.670  Marbling score2  48.23 ± 0.82  52.48 ± 0.82  0.010  Ether extract3, %  6.81 ± 0.16  7.63 ± 0.16  0.011  Moisture3, %  69.76 ± 0.42  69.37 ± 0.42  0.539    Treatment (Trt)  P-value    CON  RUF  Trt  n  4  4    HCW, kg  375.70 ± 15.30  378.48 ± 15.30  0.902  Yield grade  3.80 ± 0.18  4.03 ± 0.18  0.414  LM area, cm2  83.45 ± 2.01  80.93 ± 2.01  0.409  Backfat, cm  1.63 ± 0.14  1.65 ± 0.14  0.900  KPH, %  3.35 ± 0.04  3.38 ± 0.04  0.670  Marbling score2  48.23 ± 0.82  52.48 ± 0.82  0.010  Ether extract3, %  6.81 ± 0.16  7.63 ± 0.16  0.011  Moisture3, %  69.76 ± 0.42  69.37 ± 0.42  0.539  1The treatments from d 0 to 54 were either CON steers fed 1 kg of corn gluten feed (CGF) or RUF steers fed 0.56 kg of CGF plus 0.2 kg of Megalac-R (Church & Dwight Co., Inc., Princeton, NJ) per supplementation event (5 d/wk). At d 55 of treatment, CON steers received 1.5 kg of CGF and RUF steers received 1.06 kg CGF plus the 0.2 kg of Megalac-R per supplementation event. On d 92 of treatment, CON steers received 2.0 kg of CGF while RUF steers received 1.56 kg CGF plus 0.2 kg Megalac-R per supplementation event. 2Marbling score: 40 = small 00; 50 = modest 00. 3Determined from striploin steak. View Large The average adipocyte diameter of i.m. adipose tissue was 56.2 ± 0.7 μm for CON steers and 51.9 ± 0.8 μm for RUF steers (P = 0.001). The size distribution of adipocytes in i.m. and s.c. adipose depots is given in Fig. 4. There was a tendency (P = 0.06) for the i.m. depot to have a greater percentage of adipocytes in the 20- to 30-μm diameter range for the RUF steer compared to the CON steers. The increase in average adipocyte diameter for CON steers is accounted for by the increase (P < 0.01) in the percentage of adipocytes in the 150- to 180-μm range and by a tendency (P = 0.07) for an increased percentage of adipocytes in the 120- to 150-μm range. There were no differences (P = 0.36) between the 2 treatments for s.c. adipocyte diameter size or distribution (Fig. 4b). Figure 4. View largeDownload slide Size distribution of i.m. adipocytes (a) and s.c. adipocytes (b) as a percentage of total adipocytes, measured in steaks from steers individually fed isocaloric supplement containing no bypass fat (control [CON]; open bar, n = 21) or 0.2 kg of unsaturated rumen undegradable fat source (RUF; shaded bar, n = 20) at harvest. Intramuscular adipose tissue treatment P < 0.001 and s.c. adipose tissue treatment P = 0.362. Values are means ± SEM. *, Means differ P < 0.05; #, means differ P < 0.10. Figure 4. View largeDownload slide Size distribution of i.m. adipocytes (a) and s.c. adipocytes (b) as a percentage of total adipocytes, measured in steaks from steers individually fed isocaloric supplement containing no bypass fat (control [CON]; open bar, n = 21) or 0.2 kg of unsaturated rumen undegradable fat source (RUF; shaded bar, n = 20) at harvest. Intramuscular adipose tissue treatment P < 0.001 and s.c. adipose tissue treatment P = 0.362. Values are means ± SEM. *, Means differ P < 0.05; #, means differ P < 0.10. DISCUSSION There is limited information on the effects of supplemental rumen bypass fat on the carcass quality of early-weaned steers. The data from this experiment shows that the supplemental treatments appear to be isocaloric as fed, evident by no difference in BW between the 2 treatment groups. This is similar to many other studies that supplemented isocaloric fat-containing diets (Lammoglia et al., 1999; Whitney et al., 2000; Garcia et al., 2003); however, the diets in those studies were also isonitrogenous. For our RUF supplements, the lack of being isonitrogenous did not appear to affect animal performance in terms of BW gain during the supplementation period. The isocaloric supplement containing rumen undegradable essential, unsaturated FA increased the i.m. fat content of RUF steers and subsequently the marbling scores while the backfat thickness remained similar between treatments. Furthermore, the i.m. adipocyte diameters and size distribution were altered by supplementation, while the s.c. adipocyte diameters and size distribution remained unaltered. The FA supplementation also influenced specific blood hormone concentrations similar to the results of the unsaturated FA supplementation from Long et al. (2014). Serum FA concentrations and total lipid content were also affected by supplementation. Supplementation of the rumen undegradable unsaturated FA source that contained a high percentage of linoleic acid (18:2; 26.8% of DM) subsequently increased the serum concentration of linoleic acid in RUF steers. Hawkins et al. (1995) and Ryan et al. (1995) showed that supplementing cattle with dietary lipids increased concentrations of serum lipids. Additionally, the supplemental FA were associated with Ca salts, which are known to decrease the rate of biohydrogenation within the rumen and thereby provide the animal with a greater amount of PUFA for postruminal absorption (Jenkins and Palmquist, 1984; Wu et. al., 1991). Adipogenesis is the differentiation of preadipocytes into mature adipocytes. Adipocytes can grow by both hyperplasia (increase in cell number) and hypertrophy (increase in cell volume; Hood and Allen, 1973; Cianzio et al., 1985). Intramuscular adipocytes of the RUF steers tended to have an increase in the percent of adipocytes in the smaller diameter range (20 to 30 μm). The linoleic acid in the RUF supplement may have influenced adipocyte hyperplasia and differentiation. Linoleic acid is a precursor for a downstream activation of cell-surface receptor/ligand systems that initiate the expression of CCAAT enhancer binding protein-β (C/EBP-β) and C/EBP-δ (Gaillard et al., 1989; Negrel et al., 1989; Vassaux et al., 1992). An increase in the expression of C/EBP-β and C/EBP-δ causes an increase in PPARγ (Wu et al., 1995) both directly and through the activation of C/EBP-α (Cao et al., 1991; Yeh et al., 1995; Farmer, 2006; Rosen and MacDouglad, 2006; Lefterova and Lazar, 2009). Peroxisome proliferator-activated receptor-γ and C/EBP-α work synergistically and reciprocally to activate adipogenesis (Mandrip and Lane, 1997). The greater percentage of lipid in the striploin steaks and the marbling score of the RUF suggest that the RUF supplement affected i.m. adipocytes by increased hyperplastic growth of i.m. adipocytes of the RUF steers. This could also be interpreted as a depot specific effect, as the i.m. depot experienced a difference in mean diameter and size distribution, and the s.c. depot did not. Although there were no differences in BW at 110 d due to treatment, RUF steers exhibited increased i.m. fat content at the end of treatment, which was determined by ultrasonography. It has been stated that it is wise to apply nutritional treatment to young animals due to the high possibility that there are a greater number of multipotent stem cells and preadipocytes at a young age (Harper and Pethick 2004; Du et al., 2010). Also, a study using rats showed that with an increase in age there was a decrease in expression in a major regulator of adipogenesis, C/EBP-α (Karagiannides et al., 2001). If cattle also experience that decrease in the expression of C/EBP-α, it could serve as another contributing factor in trying to influence adipogenesis earlier in life. By offering the FA supplementation early in the steers' lives, a greater number of undifferentiated stem cells could potentially be driven toward adipogenic confirmation. Also, Wegner et al. (1998) challenged the traditional idea that i.m. fat is a late developing fat depot (Cianzio et al., 1985) by suggesting that the adiposity of muscle develops much earlier in the animals life than is evidenced by marbling. The RUF steers also had greater serum concentrations of total FA on d 110, which is supported by the findings of Long et al. (2014) that showed the same results in heifers that were supplemented rumen bypass unsaturated FA. This increase in total FA is indicative of the greater amount of FA available in their diet and the greater amount of unsaturated FA that reached the small intestine due to decreased biohydrogenation (Zinn et al., 2000). The serum concentration of 18:2 increased in the CON steers over the supplementation period, but there was an increase in concentration of a much greater magnitude for the RUF steers. Also, 18:3 had a tendency to increase in RUF steers. Our findings are supported by previous studies that reported PUFA supplementation increased plasma concentration of linoleic (18:2) and linolenic (18:3) acids in cattle (Lessard et al., 2003, 2004; Farran et al., 2008). Arachidonic acid (20:4) also had a treatment × day effect similar to linoleic, whereas DPA (22:5) had a treatment effect similar to linolenic acid. This could be attributed to linoleic acid being a precursor for arachidonic acid and linolenic acid being a precursor for DPA. Therefore, the increase in linoleic and linolenic acid serum concentrations could have led to the conversion into other omega-6 and omega-3 FA, respectively. Also, C15:0, C16:0, C18:0, and C18:1 c-9 serum FA concentrations had a treatment × day effect where the RUF steers had a greater concentration, which further supports that the RUF diet offered a greater amount of FA. Serum triglyceride concentrations in the RUF steers were greater than those of the CON steers, possibly due to a greater amount of FA being offered in the RUF diet. Therefore, there was an increase in the availability of FFA to be stored as triglycerides within adipocytes. This increase in triglycerides, due to supplementation of rumen bypass unsaturated FA, is supported by Long et al. (2014). The increase in the amount of FA provided in the diet could have also led to RUF steers having a greater increase in cholesterol concentrations. A similar study that also supplemented rumen bypass fat to beef heifers suggested that the diet is the most likely explanation for the increase in cholesterol, either directly due to the diet or through an increase in the substrate, acetyl CoA, (Long et al., 2007) since all 27 carbon atoms of de novo cholesterol are derived from acetyl CoA (Berg et al., 2002). Leptin, a protein hormone produced in adipocytes that travels via the blood, is involved with feed intake regulation and energy homeostasis. Therefore, the increase in leptin concentration could be attributed to the increase in RUF intake. A greater concentration of FA bypassed the rumen to the small intestines, and thereby a greater amount of energy reached the small intestines. Chilliard et al. (1998) stated that several studies that used multispecies RIA have indicated that blood leptin is regulated by the level of energy intake and body condition. Chilliard et al. (2005) reported that the BCS, or adiposity, is the key component in leptin regulation, both tissue and blood, while having a powerful interaction with other factors. However, Ciccioli et al. (2003) showed that blood leptin concentration was greatly affected by a nutritional treatment during a period where BCS remained similar. Additional factors that are believed to influence leptin levels include meal time (Ingvartsen and Boisclair, 2001; Delavaud et al., 2002), nutrients (Blache et al., 2000; Delavaud et al., 2000), other hormones (Leury et al., 2003; Block et al., 2003), and environment (Kokkonen et al., 2002; Garcia et al., 2003; Reist et al., 2003). Therefore, the increase in leptin levels at d 110 could be attributed to a nutrient effect of the rumen undegradable unsaturated FA since the diet was the only altered effect in our steers. Long et al. (2007) had similar findings and also showed that the increase in leptin was correlated with supplementation of FA, although they used saturated FA. Long et al. (2014) showed that even the composition of the supplemental FA could be a contributing factor to increased leptin levels. Furthermore, it has been shown in rodents that FA, specifically linoleic acid, could also influence leptin levels (Takahashi et al., 1999; Rodríguez et al., 2003). It should also be noted that there is a tendency for differences in i.m. fat content at the same time as differences in serum leptin. Carcass measurements were not affected by treatment with the exception of the marbling score, which was to be greater in RUF steers. This increased marbling took steers from a USDA low Choice grade to an average Choice, thereby, increasing both the quality and value of the carcasses (USDA, 1997). A similar effect of increased marbling scores and a tendency for increased percent Choice was reported when 7-mo-old steers were fed essential FA during a 28-d preconditioning period (Cooke et al., 2011). Intramuscular adipocyte distribution was also influenced by the unsaturated FA supplementation. Although adipocytes within the i.m. depot grow biphasically, first by hyperplasia followed by hypertrophy and so on (Allen, 1976), the increase in the percentage of i.m. adipocytes with a diameter of 20 to 30 μm could be indicative of an earlier increased hyperplastic growth of the i.m. fat cells. Harper and Pethick (2004) stated that cattle have a certain number of fat cells on entering the feedlot and that the high-energy diets provided during the finishing phase simply fill those adipocytes with lipids. Therefore, the RUF steers could have entered the feedlot phase with a greater number of i.m. adipocytes, due to increased hyperplastic growth earlier in life, than that of the CON steers. Then, while in the feedlot, those adipocytes accumulated lipids in the form of triglycerides. This is supported by the fact that RUF steers had a greater percentage of total lipids in the LM. Conversely, there was no difference in the s.c. adipose tissue thickness, cell size, or distribution between treatments. The lack of difference in s.c. adipocytes could be attributed to early development of the s.c. fat depot and subsequent completion of hyperplastic growth by 8 mo of age (Hood and Allen, 1973). Therefore, the hyperplastic growth of the s.c. adipose depots could potentially have stopped before the end of treatment and only conducted hypertrophic growth while in the feedlot where all steers received the same diets. Furthermore, KPH, the only other fat depot examined, was similar between treatments, which agrees with the visceral fat depots developing even earlier than s.c. (Vernon, 1981). Therefore, it may be possible that the supplementation of unsaturated FA had a depot-specific effect on the i.m. depot. The results from this study indicate that supplementation of ruminal unsaturated bypass FA can positively influence i.m. adipose tissue deposition in early-weaned steers. By weaning steers early, we had the opportunity to provide the steers with the unsaturated FA source at a point where there were potentially a greater amount of undifferentiated multipotent stem cells and/or preadipocytes (Du et al., 2010). Therefore, the unsaturated FA that bypass the rumen, and thereby biohydrogenation, can be utilized more efficiently and influence undifferentiated stem cells and preadipocytes to commit to becoming adipocytes. 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TI - The effect of supplementing rumen undegradable unsaturated fatty acids on marbling in early-weaned steers
JF - Journal of Animal Science
DO - 10.2527/jas.2015-9809
DA - 2016-02-01
UR - https://www.deepdyve.com/lp/oxford-university-press/the-effect-of-supplementing-rumen-undegradable-unsaturated-fatty-acids-pD0I4TkwKE
SP - 833
EP - 844
VL - 94
IS - 2
DP - DeepDyve
ER -