TY - JOUR
AU - Boland, H. T.
AB - ABSTRACT Bermudagrass (Cynodon dactylon [L.] Pers.) is a major feed source for ruminants across the southeastern United States. In 4 consecutive yr, 3 different bermudagrass hybrids, Alicia, Jiggs, and Tifton-85, were evaluated under a low stocking rate as forage and hay sources. The nutritive value, in situ DM digestibility, and performance and grazing behavior of beef steers under similar management were evaluated. Sampling day had an effect (P < 0.05) on all forage variables. Percentages of CP and TDN decreased while concentration of ADF, NDF, lignin, and nonfiber carbohydrates (NFC) increased as grazing season advanced. Alicia had lower nutritive value, showing greater lignin (5.3%) and indigestible fraction (44.9%) compared to Jiggs (4.9 and 35.6%, respectively) and Tifton-85 (4.5 and 40.1%, respectively). Tifton-85 contained the lowest concentration of NFC (11.8%). Steers grazing Jiggs and Tifton-85 had greater ADG (0.51 and 0.55 kg, respectively) and BW gain per hectare (258 and 279 kg, respectively) than those on Alicia (0.36 kg and 184 kg/ha, respectively); results that are probably explained by the lower nutritive value characteristics of the latter. Most grazing behavior variables were affected (P < 0.05) by time of the day (TOD) and grazing period. Two major grazing events were observed at dawn and dusk. Grazing time (32 min) was lowest (P = 0.003) while standing (140 min) and lying (98 min) time were greater (P = 0.001 and 0.04, respectively) from 1100 to 1559 h, probably as an effect of temperature and humidity at that time of the day. During summer, the temperature humidity index (THI) is above 72 (mild heat load) for the entire season and above 79 (severe heat load) during most of the daylight hours from June to August. Heat load likely affected animal performance and grazing behavior; however, some characteristics associated with these bermudagrass hybrids, especially with Alicia, such as its percentages of lignin and indigestible fraction may also partially explain the poor animal performance. In the conditions of the study, environmental variables (temperature and humidity), as well as the type of bermudagrass hybrid, affected animal performance and grazing behavior of recently weaned beef steers. INTRODUCTION Bermudagrass [Cynodon dactylon (L.) Pers.] is an important warm-season, perennial, sod-forming forage grass grown throughout the southeastern United States. Bermudagrass is productive from spring until fall, is well-suited for grazing or hay production, and stands often persist and remain productive for more than 35 yr if properly managed (Hill et al., 2001). Most bermudagrasses are tolerant to different soils, moderate to heavy grazing pressure, variable rainfall distribution, and differing management. Almost all are dual-purpose as standing forage or hay (Hill et al., 2001). Bermudagrass hybrids (cultivars) have different characteristics that impact their nutritive value, productivity, and influence on animal performance. Tifton-85 is an F1 hybrid between a plant introduction from South Africa (PI 290884) and Tifton-68 (Bade, 2000). Tifton-85 is taller and has larger stems, broader leaves, and darker green color than most commercially available bermudagrasses. The great digestibility of Tifton-85 is most likely due to different chemical bond ratios in the plant's fiber fraction (Andrae, 2003). Alicia hybrid was imported from South Africa, spreads primarily by stolons, has fewer rhizomes, but often becomes established more rapidly than other hybrids. Digestibility of Alicia usually is less than most bermudagrasses (Andrae, 2003). Jiggs is a bermudagrass hybrid adapted to various soil types, and even does well on heavy, wet soils. The thin stems of Jiggs also make it a desirable variety for hay production (Bade, 2000). The objective of this study was to evaluate Alicia, Tifton-85, and Jiggs bermudagrass hybrids for hay and beef production, their in situ DM disappearance, and the grazing behavior of beef steers grazing them at a low stocking rate. MATERIALS AND METHODS The present study was conducted during the summer of 4 consecutive yr (2009–2012) at the Louisiana State University Agricultural Center (LSU AgCenter) Iberia Research Station (IRS) located in Jeanerette, LA (29° 57' 54” W latitude; 91° 42' 54” N longitude; altitude 5.5 m). The soil type is classified as Iberia silty clay loam (poorly drained, very fine, smectitic, hyperthermic, Typic Epiaquerts) with risk of flooding, although the experimental area had previously been shaped to improve drainage. All procedures involving animals were approved by the LSU AgCenter Animal Care and Use Committee. Weather Data Monthly information on maximum, minimum, and average temperatures (°C) and rainfall (mm) was obtained from a weather station located at the IRS approximately 230 m from the center of the experimental site. Monthly average weather data for the last 30 yr (1981–2010) were obtained from www.nws.noaa.gov/climate/xmacis.php?wfo = lch (select Jeanerette, LA). Temperature heat index (THI) was determined following Mader et al. (2006) as:  Experimental Pastures and Animals In 4 consecutive yr, 4, 1.33-ha paddocks of each bermudgrass hybrid (Tifton-85, Jiggs, and Alicia) were used. Tifton-85 and Jiggs were planted on an area dominated by old Alicia and Common bermudagrass stands. As part of the renovation of these stands, Tifton-85 and Jiggs were randomly allotted to the area and then re-fenced into their respective 1.33-ha paddocks. In the summer of 2005, Tifton-85 and Jiggs were planted using green sprigs, fertilized with 60 units of N (urea; 46–0-0) and sprayed with Diuron (N-[3,4-dichlophenyl]-N,N-dimethyl urea; 40.7% by weight; Makhteshim Agan of North America, Raleigh, NC) at 2.2 kg/ha of active ingredient immediately after sprigging to control a wide variety of annual and perennial broadleaf and grassy weeds. In the fall of 2006, pastures were grazed for short periods of time using crossbred cows. In the spring of 2007, pastures were fertilized with 60 units of N from urea and sprayed with Roundup (N-[phosphonomethyl] glycine; glyphosate; Monsanto, St. Louis, MO) at 0.44 kg/ha of active ingredient and Diuron at the same rate as before. All pastures were lightly grazed during the summer season and grass was cut once for hay. In 2008, two hay cuttings were produced from each paddock and fertilized twice with 100 units of N from urea. In late April 2009, hay was made from all paddocks and 100 units of N from urea were applied, and forage was allowed to accumulate until the beginning of the experiment. Stands of Alicia used in the present experiment were 30 yr old that had been planted using sprigs, but no information is available at the Iberia Research Station concerning the management of the stand until the year 2000. For 8 yr, it was only used as a hay meadow, with 2 split applications of 100 units of N and 2 cuttings of hay each yr. Plant structure, floristic attributes, and nutritive value data indicate that it still is an Alicia stand (G. Scaglia, unpublished data). All bermudagrass pastures were scouted for armyworms (Spodoptera frugiperda), especially after hay was made and new growth occurred. If there was a need for application (the threshold considered was 30 armyworms/m2), malathion (diethyl 2-[(dimethoxyphosphorothioyl)sulfanyl]butanedioate) at 2.3 L/ha was applied for its control due to no restrictions for grazing. In 2011 and due to a heavy load of infestation, there was a need to apply malathion 3 times. Each year, 36 spring-weaned steers (3/8 Gelbvieh, 3/8 Red Angus, and 1/4 Brahman; average BW = 252 ± 9 kg and 9 mo of age) were rotationally stocked on the bermudagrass pastures from June to September for an average of 112 d. Steers were randomly allotted to 6 groups and each group assigned to the different hybrids (6 steers per replicate; 2 replicates per bermudagrass hybrid and two 1.33-ha paddocks in each replicate). Steers were purchased from a commercial ranch and transported to the IRS 3 wk after weaning. The day after arrival, steers were vaccinated with Bovishield Gold FP VL5 (Pfizer Animal Health, New York, NY), clostridium 8-way with Somnus (Bayer Vision; Intervet, Boxmeer, the Netherlands), anthrax spore vaccine (Colorado Serum Co., Denver, CO), Pulmo Guard PHM-1 (Boehringer Ingelheim, Ridgefield, CT) and were dewormed (August only) with Valbazen (Albendazole, Pfizer Animal Health). Thirty days into the experiment all steers were dewormed with Ivomec Plus Injectable (Merial, Duluth, GA). On average, the experiment started (d 0) 13 d (range of 9 to 18 d) after arrival to the IRS. Every year due to stable (Stomoxys calcitrans [L.]) and/or face fly (Musca autumnalis) infestation, two tags (Phyton; Y-Tex Corp., Cody, WY), one in each ear, containing Zetacypermethrin, S-enantiomer (S-cyano[3-phenoxyphenyl]methyl cis/trans 3-[2,2 dichloroethenyl]-2,2 dimethylcyclopropane-carboxylate at 10%) and Piperonyl Butoxide ([butylcarbityl][6-propylpiperonyl] ether and related compounds at 20%), were applied and remained on until the end of the summer (October) when removed and disposed. Grazing Management and Sampling Procedures During the 4 yr of the experiment, all pastures were managed similarly. Hay was made from all pastures in May to pick up extra bermudagrass forage from the previous season as well as volunteer annual ryegrass (Lolium multiflorum, sp.) that grew during winter, and then fertilized with 100 units of N (urea) per ha. Grazing of all pastures started and finished on the same day and were rotationally stocked (stocking rate of 2.3 steers per ha; 6 steers grazing 2.66 ha). Due to the differences in growth rate between hybrids, steers were moved to a new grazing cell at a different times, however, the stocking density for all of the bermudagrass hybrids at the start of the grazing season was similar at 22.2 steers per ha (grazing cells of 0.27 ha) decreasing gradually to 4.5 steers per ha (grazing cells of 1.33 ha) on the last day. Grazing cells were set using strands of polytape in front and behind, and they were extended from the permanent fences on each side of the paddock. Cells were created by moving the back fence to the front so that cattle would not have access to the previously grazed cell when they were moved to a new one. In the first 28 d of the grazing season, the length of the grazing period for all bermudagrass was 4 d and the rest period of 20 d. From d 29 to 56 the same rotation periods were used for Jiggs and Tifton-85, but not for Alicia for which the area of the grazing cells was increased. From d 57 to the end, the grazing cell was gradually increased for all hybrids, although Tifton-85 showed a clear difference in forage mass and green material present. From d 85 to 112, the area of the grazing cells were increased frequently to 1.33 ha (on d 112) for all 3 hybrids. Every time hay was made from one of the 1.33-ha paddocks (within a replicate), 100 units N (as urea) were applied. Grazing management was controlled so that when hay was made there was sufficient forage mass in the other paddock (within replicate) for animals to graze. Three hay cuts were made from each of the bermudagrass hybrids approximately on July, August, and September of each year. Round bales were made with a John Deere 567 baler producing bales with an average weight of 408 kg (weighed in groups of 10 bales at the time of being produced). Number of bales produced per ha and nutritive value of the hay produced are reported. Forage mass was determined at the beginning of the trial (d 0) and every 28 d using a 0.25 m2 quadrat which was randomly placed 10 times within the grazing cell. Before clipping, 10 measurements of forage height (cm) were recorded using a ruler. The average of these measurements (n = 100) represents the pasture height for the paddock at the time of sampling. Forage was clipped using a hand-clipper to a height of 2.54 cm, avoiding soil contamination, placed in paper bags and carried to the laboratory (within an hour), weighed, and placed in a horizontal freezer (-20°C) until drying time. At drying time, bags were placed in a forced-air oven at 55°C for 48 h (AOAC, 2000). After drying, the bag was weighed again for DM determination. Forage mass of each grazing cell was the average of 10 samples. Samples for nutritive value analyses were obtained from those used for forage mass determination. All forage samples were ground to pass a 1-mm screen using a Wiley mill (Laboratory Mill model 4; Arthur H. Thomas Co., Philadelphia, PA). A composite sample was created by taking 5 g of each of the 10 samples, placed in a plastic cup, labeled, and stored until sent for analyses. Forage samples were sent to a commercial laboratory (Dairy One Forage Lab, Ithaca, NY), and analyses on bermudagrass samples were accomplished with NIRS (Foss NIR Systems Model 6500 with Win ISI II v1.5-AOAC 989.03). Cattle were weighed starting at 0800 h on 2 consecutive days, without restriction of feed and water, at the beginning and end of the grazing period, and their weights were averaged for determination of total ADG. Mineral mix that guaranteed 12% Ca, 6% P, 10% NaCl, 2.50% Mg, 0.75% K, 0.0043% Cu, 0.00012 Se, 0.0067% Zn, 200,000 IU of Vitamin A (Lone Star 126; Lone Star Feeds, Corpus Christi, TX), shade (polyurethane; guaranteed 80% interception), and fresh water were available at all times. Water tanks, shades, and mineral feeders were moved to the new grazing cell every time cattle were rotated to it. Grazing Behavior Recordings In yr 1 and 2, grazing behavior was recorded visually, using activity monitors made for cattle. In both cases and each yr, 2 steers were randomly selected from each treatment/replicate (4 steers/treatment) to serve as “testers” to reflect the behavior of their respective group. Visual Observations Visual observations were conducted on 2 steers (testers) per treatment replicate on four 5-d periods (period A, B, C, and D) on d 20, 40, 60, and 100 of each grazing period. Three days after the beginning of the experiment and before starting the observations (period A), cattle were preconditioned to the presence of observers. This was accomplished after an average of 9 d (range from 7 to 13 d depending on the yr) by gradually getting the animals used to the simple presence of an observer who remained still for a few minutes and then walked among them, usually for a period of 2 to 3 h in the morning and then again in the afternoon. While standing or walking, the observer moved gently, avoiding calling the attention of the animals. On average, after 7 d, cattle were not affected by the presence of an individual in their pasture, and by d 10, they were completely used to the observer. In each period, bite rate (number of bites/min) of the tester steers was determined once per hour on each steer as long as there was enough visibility from 0600 to 2100 h, and data were summarized by time of the day (TOD) as indicated below. The order in which each steer (within period) was observed was predetermined and was the same every time. To avoid affecting grazing behavior, a single observer, positioned approximately 35 m from the steer, registered the number of bites using binoculars and a chronometer. If the animal was not grazing, the activity (standing, walking, or lying) and whether or not the animal was ruminating was also recorded. Use of Activity Monitors In yr 1 and 2, grazing behavior recordings were conducted through the entire grazing season on 4 steers/bermudagrass hybrid, each wearing an animal activity monitor. This monitor (IceTag, version 2.004; IceRobotics, Midlothian, Scotland) was attached to a Velcro strap on the left rear leg just above the metatarsophalangeal joint. These units measured animal activity 8 times/s with an internal accelerometer. Percentage of time spent standing, active, lying, and number of steps taken by the steer was recorded. Data were downloaded from on-board memory to a personal computer and analyzed by IceTagAnalyser software (version 2.009; IceRobotics). Raw activity monitor data were transformed using the procedure of Aharoni et al. (2009) to partition out the amount of time spent standing still, grazing, and walking without grazing. In brief, the data were first summarized into 5-min intervals. If less than 10 steps were taken during that interval, the animal was considered to be standing still, if between 10 and 80 steps were taken, the animal was considered to be grazing, and if more than 80 steps were taken, the animal was considered to be walking without grazing. Information obtained from each animal activity monitor was summarized by day (24 h) and averaged every 28 d within year. The same information was also summarized by TOD: 0600 to 1059 h, 1100 to 1559 h, 1600 to 2059 h, 2100 to 2359 h, 2400 to 0259 h, and 0300 to 0559 h. In Situ DM Disappearance In yr 3 during the month of August, rates of in situ DM disappearance of the 3 bermudagrass hybrids were determined using 4 ruminally cannulated crossbred (Bos taurus × Bos indicus) beef heifers (initial BW = 313 ± 17 kg; average 18 mo of age). Forage samples taken monthly (d 0, 28, 56, 84, and 112) during the grazing season in yr 1 and 2 by clipping at 2.54 cm and avoiding soil contamination were used. Forage samples were placed in a forced-air oven at 55°C for 48 h and ground through a 2-mm screen in a Wiley mill (Arthur H. Thomas, Philadelphia, PA). Dacron bags (10 × 20 cm and pore size of 50 μm; ANKOM Technology, Macedon, NY) were used in duplicate in each incubation time and filled with 5-g samples of dried forage; this resulted in a sample size to bag surface area ratio (Vanzant et al., 1998) of 12.5 mg/cm2. Forage samples were incubated in duplicate in the rumen for 0, 2, 4, 8, 12, 24, 36, 48, 72, and 96 h. Heifers grazed on Jiggs bermudagrass pastures for 15 d before and during the 4 d of the experimental period. Water and mineral mix (same as the one provided to the steers) were available at all times. Bags from each incubation time were placed in individual polyester mesh bags attached to a string and incubated (together with a control empty bag for each incubation time) in the rumen. All bags (except 0 h) were incubated at time zero, taken out of the rumen at the specified time, and placed on ice for transport and subsequently frozen at -20°C for storage. One week after the conclusion of the experiment, all bags were removed from the freezer, thawed, and placed in a washing machine (General Electric large capacity 6-cycle washer) with cold water, on delicate setting for a 1-min rinse and 2-min spin for 10 consecutive cycles. Zero-h bags were included in the washing procedure. Bags were then placed in a forced-draft oven at 50°C for 48 h and weighed for DM disappearance. Statistical Analyses The experiment was a completely randomized design with 2 replicates. Data were analyzed with PROC Mixed of SAS (version 9.1.3; SAS Inst. Inc., Cary, NC) using the compound symmetry covariance structure. Treatment (bermudagrass hybrids) and period were the fixed effects and yr the random effect. Forage mass and height, hay production, and nutritive value of standing forage and hay were analyzed for treatment, sampling date, and their interaction. For ADG, the effects of treatment, period, and their interaction were determined. Sampling date (for forage variables) and period (for ADG) were the repeated measures. Productivity (beef produced/ha) was analyzed for treatment effect. In all cases, paddock was the experimental unit. Degradation data for DM were fitted to the nonlinear regression model described by Ørskov et al. (1980): P = A + B (1 – e–Ct) using the NLIN procedure of SAS. The model allows calculating digestion constants, where P = proportion (%) of DM degraded at time t, A = the readily digested fraction, B = the slowly digested fraction, C = the rate of digestion for the slowly digested fraction, t = time of incubation, and % indigestible as 100 – (A+B). Data obtained were analyzed for treatment, sampling date, and their interaction using the same procedure as described for forage characteristics. Grazing behavior data were analyzed with PROC Mixed of SAS. Data from behavior recordings (time spent standing, active, lying, and number of steps) were summarized daily (24 h) and analyzed for treatment, period (30 d), and their interaction. Year was considered the random effect, steer within treatment by year was the experimental unit, and day as repeated measure. Data were also analyzed for TOD, treatment, period, and their interaction. Year was considered the random effect, steer within treatment by year was the experimental unit, and TOD within day was the repeated measure. Bite rate (number of bites/min) data were analyzed using PROC Mixed of SAS. Effect of treatment (fixed effect), period, and their interaction were analyzed. Year was considered random, period was the fixed effect, and steer within treatment by year was the experimental unit. Least squares means are reported for all variables with means separated by Tukey's adjustment. In all cases, level of significance was considered as α ≤ 0.05, and trends were defined as P > 0.05 but ≤ 0.10. PROC REG of SAS was used to explain relationships between grazing behavior variables. RESULTS AND DISCUSSION Weather Data Weather data are presented in Table 1 and Fig. 1 and 2 from June to September of each year (grazing period). During the grazing period of the 4 yr that the experiment was conducted, the maximum and minimum temperatures were higher (Table 1) and the rainfall was lower (Fig. 1) than the historic data collected. Even though the average total rainfall for the grazing season on every year was less than historic values, there were months with higher precipitation than the historic rainfall (Fig. 2), for example, July 2009, 2010, and 2011 experienced more rain than the historic registry. Even though no devastating hurricanes occur during these yr, several tropical storms were responsible for high precipitations for different yr and at different times during the grazing season. Table 1. Average monthly temperatures (°C) for the grazing period across years and historical data (1981–2010)   Year      2009  2010  2011  2012  Historic  Month  Max  Min  Max  Min  Max  Min  Max  Min  Max  Min  June  34.1  21.8  33.2  24.4  34.7  23.5  33.7  22.3  31.3  21.9  July  33.6  23.9  33.3  24.5  33.2  24.3  32.8  23.6  32.2  22.8  August  33.3  23.0  34.0  24.7  36.1  24.6  32.9  23.9  32.4  22.4  September  31.1  22.0  32.7  21.7  31.2  19.1  32.2  21.3  30.4  19.9    Year      2009  2010  2011  2012  Historic  Month  Max  Min  Max  Min  Max  Min  Max  Min  Max  Min  June  34.1  21.8  33.2  24.4  34.7  23.5  33.7  22.3  31.3  21.9  July  33.6  23.9  33.3  24.5  33.2  24.3  32.8  23.6  32.2  22.8  August  33.3  23.0  34.0  24.7  36.1  24.6  32.9  23.9  32.4  22.4  September  31.1  22.0  32.7  21.7  31.2  19.1  32.2  21.3  30.4  19.9  View Large Table 1. Average monthly temperatures (°C) for the grazing period across years and historical data (1981–2010)   Year      2009  2010  2011  2012  Historic  Month  Max  Min  Max  Min  Max  Min  Max  Min  Max  Min  June  34.1  21.8  33.2  24.4  34.7  23.5  33.7  22.3  31.3  21.9  July  33.6  23.9  33.3  24.5  33.2  24.3  32.8  23.6  32.2  22.8  August  33.3  23.0  34.0  24.7  36.1  24.6  32.9  23.9  32.4  22.4  September  31.1  22.0  32.7  21.7  31.2  19.1  32.2  21.3  30.4  19.9    Year      2009  2010  2011  2012  Historic  Month  Max  Min  Max  Min  Max  Min  Max  Min  Max  Min  June  34.1  21.8  33.2  24.4  34.7  23.5  33.7  22.3  31.3  21.9  July  33.6  23.9  33.3  24.5  33.2  24.3  32.8  23.6  32.2  22.8  August  33.3  23.0  34.0  24.7  36.1  24.6  32.9  23.9  32.4  22.4  September  31.1  22.0  32.7  21.7  31.2  19.1  32.2  21.3  30.4  19.9  View Large Figure 1. View largeDownload slide Rainfall (mm) during the grazing season and historic data for the same period (June–September). Figure 1. View largeDownload slide Rainfall (mm) during the grazing season and historic data for the same period (June–September). Figure 2. View largeDownload slide Monthly rainfall (mm) during the grazing season for each year and historic data for the same period (June–September). Figure 2. View largeDownload slide Monthly rainfall (mm) during the grazing season for each year and historic data for the same period (June–September). Forage Properties, Grazing Management, and Animal Performance Forage Characteristics and Nutritive Value Forage mass, height, and bulk density were affected (P < 0.05) by sampling day, while treatment only affected (P = 0.03) forage height, with no interactions detected (P ≥ 0.06) for these variables (Table 2). Relative to the animal requirements, the amount (mass and height) of forage on offer exceeded their needs (Paterson et al., 1994), and there was no DMI limitation across the grazing period (Table 2). Forage mass and height were not limiting at any point in time during the experimental period and throughout the years. It has been demonstrated under different conditions that Tifton-85 produces more DM than any other variety (Hill et al., 2001). Forage height was over 30 cm at all sampling dates (Table 2), which may explain the lack of difference in forage mass between the different cultivars (hybrids). Fagundes et al. (1999) reported similar rates of DM accumulation for Tifton-85, Florikirk, and Coastcross-1 pastures when sward heights exceed 20 cm. Tifton-85 is taller, with wider leaves and larger stems, than most hybrids (Hill et al., 2001), but in the conditions of the present experiment, Tifton-85 had similar height to Jiggs (36.3 and 38.4 cm, respectively) and both were taller (P = 0.03) than Alicia (33.2 cm). Bulk density values are smaller than those reported by Fisher et al. (1991) working with Coastal bermudagrass (273 kg DM/ha/cm) on continuously stocked pastures grazed to similar herbage mass with respect to other treatments evaluated and sampled to 4 cm of height. Carnevalli et al. (1999) reported bulk density of Tifton-85 bermudagrass ranging from 370 to 610 kg/ha/cm. One of the possible reasons for this difference is due to plant architecture because taller swards of bermudagrass tend to have a reduced bulk density (Beaty et al., 1966). In the present study, the shorter sward height was 30.7 cm on d 56, and the smaller forage mass was 2,887 kg DM/ha, values that were notably greater than those reported by Fisher et al. (1991) of 7 cm and 1,900 kg DM/ha. Another reason might be the low stocking rate at which the swards were grazed in the present experiment. Lower grazing height under continuous stocking was associated with greater total and leaf bulk density (Carnevalli et al., 1999). Table 2. Effect of sampling day on forage characteristics and nutritive value of bermudagrass hybrids (TRT)   Sampling day    P- value1  Item2  0  28  56  84  112  SEM  TRT  DAY  TRT × DAY  FM, kg DM/ha  2,887  4,363  4,494  4,137  4,004  428  0.50  0.0001  0.55  FH, cm  36.4  44.4  30.7  34.7  33.8  2.9  0.03  0.0005  0.06  BD, kg DM/ha/cm  84.3  105.1  170.5  128.7  113.8  18.2  0.36  0.0001  0.46  CP, % DM  13.4a  11.9a  9.2b  10.0b  8.9b  0.74  0.17  0.0001  0.66  ADF, % DM  38.7c  41.8b  42.9ab  42.6b  44.1a  0.65  0.26  0.0001  0.06  NDF, % DM  68.1  70.6  70.7  70.3  71.5  0.67  0.001  0.001  0.22  TDN, %  59.9  56.5  57.3  57.3  55.7  1.13  0.007  0.0001  0.004  Lignin, % DM  3.9c  4.9b  5.2ab  5.0b  5.6a  0.26  0.006  0.0001  0.14  NFC, % DM  11.7b  11.5b  15.9a  14.9a  16.3a  0.99  0.0001  0.0001  0.06  WSC, % DM  5.4  5.2  5.7  6.1  5.4  0.29  0.006  0.21  0.32    Sampling day    P- value1  Item2  0  28  56  84  112  SEM  TRT  DAY  TRT × DAY  FM, kg DM/ha  2,887  4,363  4,494  4,137  4,004  428  0.50  0.0001  0.55  FH, cm  36.4  44.4  30.7  34.7  33.8  2.9  0.03  0.0005  0.06  BD, kg DM/ha/cm  84.3  105.1  170.5  128.7  113.8  18.2  0.36  0.0001  0.46  CP, % DM  13.4a  11.9a  9.2b  10.0b  8.9b  0.74  0.17  0.0001  0.66  ADF, % DM  38.7c  41.8b  42.9ab  42.6b  44.1a  0.65  0.26  0.0001  0.06  NDF, % DM  68.1  70.6  70.7  70.3  71.5  0.67  0.001  0.001  0.22  TDN, %  59.9  56.5  57.3  57.3  55.7  1.13  0.007  0.0001  0.004  Lignin, % DM  3.9c  4.9b  5.2ab  5.0b  5.6a  0.26  0.006  0.0001  0.14  NFC, % DM  11.7b  11.5b  15.9a  14.9a  16.3a  0.99  0.0001  0.0001  0.06  WSC, % DM  5.4  5.2  5.7  6.1  5.4  0.29  0.006  0.21  0.32  a–cWithin a row, means without a common superscript differ (P < 0.05). 1TRT = Treatment (bermudagrass hybrid) effect; DAY = Sampling day effect. 2FM = Forage mass, FH = Forage height, BD = Bulk density, NFC = Non-Fiber Carbohydrate (starch, simple sugars, and soluble fiber), WSC = Water soluble carbohydrates (glucose, fructose, sucrose, and fructans). View Large Table 2. Effect of sampling day on forage characteristics and nutritive value of bermudagrass hybrids (TRT)   Sampling day    P- value1  Item2  0  28  56  84  112  SEM  TRT  DAY  TRT × DAY  FM, kg DM/ha  2,887  4,363  4,494  4,137  4,004  428  0.50  0.0001  0.55  FH, cm  36.4  44.4  30.7  34.7  33.8  2.9  0.03  0.0005  0.06  BD, kg DM/ha/cm  84.3  105.1  170.5  128.7  113.8  18.2  0.36  0.0001  0.46  CP, % DM  13.4a  11.9a  9.2b  10.0b  8.9b  0.74  0.17  0.0001  0.66  ADF, % DM  38.7c  41.8b  42.9ab  42.6b  44.1a  0.65  0.26  0.0001  0.06  NDF, % DM  68.1  70.6  70.7  70.3  71.5  0.67  0.001  0.001  0.22  TDN, %  59.9  56.5  57.3  57.3  55.7  1.13  0.007  0.0001  0.004  Lignin, % DM  3.9c  4.9b  5.2ab  5.0b  5.6a  0.26  0.006  0.0001  0.14  NFC, % DM  11.7b  11.5b  15.9a  14.9a  16.3a  0.99  0.0001  0.0001  0.06  WSC, % DM  5.4  5.2  5.7  6.1  5.4  0.29  0.006  0.21  0.32    Sampling day    P- value1  Item2  0  28  56  84  112  SEM  TRT  DAY  TRT × DAY  FM, kg DM/ha  2,887  4,363  4,494  4,137  4,004  428  0.50  0.0001  0.55  FH, cm  36.4  44.4  30.7  34.7  33.8  2.9  0.03  0.0005  0.06  BD, kg DM/ha/cm  84.3  105.1  170.5  128.7  113.8  18.2  0.36  0.0001  0.46  CP, % DM  13.4a  11.9a  9.2b  10.0b  8.9b  0.74  0.17  0.0001  0.66  ADF, % DM  38.7c  41.8b  42.9ab  42.6b  44.1a  0.65  0.26  0.0001  0.06  NDF, % DM  68.1  70.6  70.7  70.3  71.5  0.67  0.001  0.001  0.22  TDN, %  59.9  56.5  57.3  57.3  55.7  1.13  0.007  0.0001  0.004  Lignin, % DM  3.9c  4.9b  5.2ab  5.0b  5.6a  0.26  0.006  0.0001  0.14  NFC, % DM  11.7b  11.5b  15.9a  14.9a  16.3a  0.99  0.0001  0.0001  0.06  WSC, % DM  5.4  5.2  5.7  6.1  5.4  0.29  0.006  0.21  0.32  a–cWithin a row, means without a common superscript differ (P < 0.05). 1TRT = Treatment (bermudagrass hybrid) effect; DAY = Sampling day effect. 2FM = Forage mass, FH = Forage height, BD = Bulk density, NFC = Non-Fiber Carbohydrate (starch, simple sugars, and soluble fiber), WSC = Water soluble carbohydrates (glucose, fructose, sucrose, and fructans). View Large All variables except water soluble carbohydrates (WSC) were affected (P < 0.05) by sampling day (Table 2). Early in the grazing season (d 0 and 28), the nutritive value of bermudagrass was greater than at mid- and late season, gradually declining to d 112, with the exception of the concentration of nonfiber carbohydrates (NFC) that increased throughout the grazing season. Forage yield and nutritional qualities of pasture are influenced by numerous factors representing ecological conditions and management activities. Those factors include frequency of cutting, species composition, plant maturity, climatic conditions, soil fertility status, and harvest season (Van Soest, 1982). The 2 most influential factors that affect forage nutritive value and forage utilization are forage species and forage maturity. According to Van Soest (1982), as a pasture matures, fiber and lignin contents are high while protein content is low. Regardless of this decline, TDN of the bermudagrass pastures was within normal range; however, CP concentration was lower and NDF and ADF concentration greater than other published information for these or other hybrids (Mandebvu et al., 1999a; Hill et al., 2001; Burns and Fisher, 2008). Treatment effect was detected (P < 0.05) for DM percentages of NDF, TDN, lignin, NFC, and WSC. It is widely accepted that NDF in Tifton-85 is greater than for any other hybrids (Hill et al., 2001) and that its digestibility is much greater despite the NDF concentration. Mandebvu et al. (1999a,b) demonstrated that the lower concentration of ester- and ether-linked ferulic acid in Tifton-85 compared to other hybrids explained its greater digestibility. The lower digestibility of Alicia (Eichhorn et al., 1983) can be explained also by the greater concentration of these linkages, recognizing as well that Alicia contained greater concentration of lignin, although % lignin has not been highly correlated with bermudagrass digestibility (Hill et al., 2001). In the present study, %NDF for Tifton-85 (71.5%) was significantly greater (P < 0.001; SEM = 0.5) than Alicia (70.2%), while Jiggs presented the smallest value (69.1%). The opposite was observed for lignin concentration (P < 0.001; SEM = 0.2), as it was greater for Alicia (5.3%), intermediate for Jiggs (4.9%), and smallest for Tifton-85 (4.5%). Simple sugars, starch, fructans, soluble fiber, and organic acids comprise NFC, while WSC includes glucose, fructose, sucrose, and fructans (Hall, 2007). The effect of sampling day on NFC can be explained by the increase in starch concentration that occurs with advanced plant maturity, starting at 1.3% on d 0 and increasing to 3.8% on d 112 (SEM = 0.4). Similar results were observed by Kagan et al. (2011). Depending on the hybrid under consideration, concentration of NFC and/or WSC may differ. Mandebvu et al. (1999b) reported that Coastal bermudagrass had smaller concentrations of total neutral sugars, arabinose, glucose, and xylose than Tifton-85. The authors are not aware of any published data comparing these variables on the 3 hybrids under the same grazing environment. Under the conditions of the present experiment, Tifton-85 presented the lowest concentration of NFC (11.8%), Alicia was intermediate (14.1%), and Jiggs had the greatest concentration (15.7%). These data are also explained by the difference in starch concentration among hybrids (1.72, 3.69, and 3.85% for Tifton-85, Alicia, and Jiggs, respectively). The WSC concentrations in Alicia and Jiggs (5.6 and 6.1, respectively) were not different from each other (P = 0.11), but both were greater than that for Tifton-85 (4.9%). In Situ DM Disappearance Table 3 showed the in situ DM disappearance coefficients for each hybrid as well as for each sampling date. The readily digested fraction (A) was similar (P > 0.05) between Alicia (14.8%) and Tifton-85 (12.1%), while A was greater (P = 0.02) for Jiggs (18.1%). The slowly digested fraction (B) was similar between Tifton-85 and Jiggs but greater than Alicia, while C was not different between hybrids. The results for A and B led to an indigestible fraction that was greater for Alicia (associate with greater percentages of lignin; Table 2), intermediate for Tifton-85, and smaller for Jiggs. Similar results for Tifton-85 were obtained by Mandebvu et al. (1999b) when compared to Coastal bermudagrass. The increase in A on d 84 coincided with relative improvements in forage nutritive value of the forage when compared to d 56 and 112. This is associated with time of N fertilization, which occurred on average between d 52 and 63 of the grazing season across years. The indigestible fraction, as expected, increased as plant maturity increased. Table 3. In situ DM disappearance of three bermudagrass hybrids at different sampling dates   Bermudagrass    Sampling day    Fraction1  Alicia  Jiggs  Tifton-85  SEM  0  28  56  84  112  SEM  A  14.8b  18.1a  12.1b  2.2  16.1ab  19.0a  11.3b  17.5a  12.3b  3.7  B  40.3b  46.3a  47.8a  1.9  42.1  48.9  43.7  45.0  43.6  3.9  C  2.6  2.7  2.8  0.2  2.5  3.0  2.7  2.6  2.9  0.5  Indigestible  44.9a  35.6c  40.1b  2.0  41.8ab  40.1ab  45.0a  37.5b  44.1ab  4.0    Bermudagrass    Sampling day    Fraction1  Alicia  Jiggs  Tifton-85  SEM  0  28  56  84  112  SEM  A  14.8b  18.1a  12.1b  2.2  16.1ab  19.0a  11.3b  17.5a  12.3b  3.7  B  40.3b  46.3a  47.8a  1.9  42.1  48.9  43.7  45.0  43.6  3.9  C  2.6  2.7  2.8  0.2  2.5  3.0  2.7  2.6  2.9  0.5  Indigestible  44.9a  35.6c  40.1b  2.0  41.8ab  40.1ab  45.0a  37.5b  44.1ab  4.0  a–cWithin a row, means without a common superscript differ (P < 0.05). 1A = readily digested fraction, B = slowly digested fraction, C = rate of digestion for the slowly digested fraction, and Indigestible = % indigestible calculated as 100– (A+B). View Large Table 3. In situ DM disappearance of three bermudagrass hybrids at different sampling dates   Bermudagrass    Sampling day    Fraction1  Alicia  Jiggs  Tifton-85  SEM  0  28  56  84  112  SEM  A  14.8b  18.1a  12.1b  2.2  16.1ab  19.0a  11.3b  17.5a  12.3b  3.7  B  40.3b  46.3a  47.8a  1.9  42.1  48.9  43.7  45.0  43.6  3.9  C  2.6  2.7  2.8  0.2  2.5  3.0  2.7  2.6  2.9  0.5  Indigestible  44.9a  35.6c  40.1b  2.0  41.8ab  40.1ab  45.0a  37.5b  44.1ab  4.0    Bermudagrass    Sampling day    Fraction1  Alicia  Jiggs  Tifton-85  SEM  0  28  56  84  112  SEM  A  14.8b  18.1a  12.1b  2.2  16.1ab  19.0a  11.3b  17.5a  12.3b  3.7  B  40.3b  46.3a  47.8a  1.9  42.1  48.9  43.7  45.0  43.6  3.9  C  2.6  2.7  2.8  0.2  2.5  3.0  2.7  2.6  2.9  0.5  Indigestible  44.9a  35.6c  40.1b  2.0  41.8ab  40.1ab  45.0a  37.5b  44.1ab  4.0  a–cWithin a row, means without a common superscript differ (P < 0.05). 1A = readily digested fraction, B = slowly digested fraction, C = rate of digestion for the slowly digested fraction, and Indigestible = % indigestible calculated as 100– (A+B). View Large Grazing Management All bermudagrass hybrids were managed at the same stocking rate of 2.3 steers/ha. This stocking rate is lower than those that are typically used for grazing bermudagrass swards. Actual stocking rates of bermudagrass pastures are dependent on an array of factors related to the forage, including cultivar, soil fertility status, fertilization, and climatic conditions. Postgrazing ownership and economic objectives should dictate the stocking rate of choice. In the present experiment, the purpose of selecting a low stocking rate was to allow steers the maximum ADG possible and at the same time to have the flexibility of producing hay. Table 4 presents the average stocking density by 28-d period for each bermudagrass hybrid. Pastures were stocked at 22.2 steers/ha (6 steers in a grazing cell which was of 0.27 ha) at the beginning of each grazing season. Even though forage growth was not measured, there was a clear difference between hybrids. The criteria to decide when to increase the area of the grazing cell were a combination of factors such as forage mass and height, amount of green material present (visually determined by an experienced observer), and ADG of the steers. Table 4. Average stocking density (steers per hectare) by grazing period for each bermudagrass hybrid   Grazing days  Bermudagrass  0–28  29–56  57–84  85–112  Alicia  22.2  17.1  8.6  6.2  Jiggs  22.2  22.2  16.5  8.6  Tifton-85  22.2  22.2  20.1  9.2    Grazing days  Bermudagrass  0–28  29–56  57–84  85–112  Alicia  22.2  17.1  8.6  6.2  Jiggs  22.2  22.2  16.5  8.6  Tifton-85  22.2  22.2  20.1  9.2  View Large Table 4. Average stocking density (steers per hectare) by grazing period for each bermudagrass hybrid   Grazing days  Bermudagrass  0–28  29–56  57–84  85–112  Alicia  22.2  17.1  8.6  6.2  Jiggs  22.2  22.2  16.5  8.6  Tifton-85  22.2  22.2  20.1  9.2    Grazing days  Bermudagrass  0–28  29–56  57–84  85–112  Alicia  22.2  17.1  8.6  6.2  Jiggs  22.2  22.2  16.5  8.6  Tifton-85  22.2  22.2  20.1  9.2  View Large Hay Production Hay was produced on grazing cells after first or second grazing cycles, which improved nutritive value and mass of the bermudagrass stands. Table 5 shows the average number of round bales of hay produced per ha and the nutritive value of the hay produced. Alicia produced less bales (P = 0.03) than Jiggs; however, it was similar to Tifton-85. There was no effect of grazing period (P = 0.07) on number of bales per ha produced. Treatment and grazing period affected (P < 0.05) certain nutritive value characteristics (Table 5). Hay produced from Tifton-85 had lower CP, NFC, WSC, and greater NDF concentrations than Alicia and Jiggs, although there was no difference on TDN (P = 0.12). Alicia produced hay with greater lignin concentration. These results are similar to those found for standing forage (Table 2). Grazing period had an effect (P < 0.05) on the nutritive value of the hay produced. Crude protein concentration was greater and % lignin was lower (P < 0.05) on hay produced on d 57–84, while WSC and NFC concentrations were greater (P < 0.05) on hay produced between d 85 and 112. These results also followed a similar trend as standing forage. The greater CP likely resulted from the N fertilizer that was applied at an average across yr of 38 d (period ranged from 31 to 49 d) to the day hay was made. Table 5. Effect of bermudagrass hybrid and grazing period on number of round bales produced per ha and their nutritive value   Bermudagrass    Grazing periods    Item1  Alicia  Jiggs  Tifton-85  SEM  0–28  29–56  57–84  85–112  SEM  Bales/ha  14.1b  15.9a  14.9ab  0.8  0  14.7  16.1  12.8  1.8  CP, %DM  12.5a  12.1a  11.0b  0.4  —  12.6ab  14.8a  8.3b  2.9  ADF, %DM  41.0  39.7  41.5  0.5  —  42.0  39.1  41.0  1.3  NDF, %DM  69.2b  69.3b  73.6a  1.8  —  71.9  68.9  71.0  1.6  TDN, %  54.2  54.5  54.5  0.3  —  52  56.3  54.8  2.1  Lignin, %DM  6.0a  5.6b  5.5b  0.2  —  6.2a  4.9b  5.9ab  0.6  NFC, %DM  14.2a  13.5a  11.1b  0.6  —  10.5b  11.7ab  16.6a  2.7  WSC, %DM  7.5ab  7.8a  6.6b  0.5  —  6.2b  6.6b  9.1a  1.3    Bermudagrass    Grazing periods    Item1  Alicia  Jiggs  Tifton-85  SEM  0–28  29–56  57–84  85–112  SEM  Bales/ha  14.1b  15.9a  14.9ab  0.8  0  14.7  16.1  12.8  1.8  CP, %DM  12.5a  12.1a  11.0b  0.4  —  12.6ab  14.8a  8.3b  2.9  ADF, %DM  41.0  39.7  41.5  0.5  —  42.0  39.1  41.0  1.3  NDF, %DM  69.2b  69.3b  73.6a  1.8  —  71.9  68.9  71.0  1.6  TDN, %  54.2  54.5  54.5  0.3  —  52  56.3  54.8  2.1  Lignin, %DM  6.0a  5.6b  5.5b  0.2  —  6.2a  4.9b  5.9ab  0.6  NFC, %DM  14.2a  13.5a  11.1b  0.6  —  10.5b  11.7ab  16.6a  2.7  WSC, %DM  7.5ab  7.8a  6.6b  0.5  —  6.2b  6.6b  9.1a  1.3  a,bWithin a row, means without a common superscript differ (P < 0.05). 1NFC = Non-Fiber Carbohydrate (starch, simple sugars, and soluble fiber), WSC = Water soluble carbohydrates (glucose, fructose, sucrose, and fructans). View Large Table 5. Effect of bermudagrass hybrid and grazing period on number of round bales produced per ha and their nutritive value   Bermudagrass    Grazing periods    Item1  Alicia  Jiggs  Tifton-85  SEM  0–28  29–56  57–84  85–112  SEM  Bales/ha  14.1b  15.9a  14.9ab  0.8  0  14.7  16.1  12.8  1.8  CP, %DM  12.5a  12.1a  11.0b  0.4  —  12.6ab  14.8a  8.3b  2.9  ADF, %DM  41.0  39.7  41.5  0.5  —  42.0  39.1  41.0  1.3  NDF, %DM  69.2b  69.3b  73.6a  1.8  —  71.9  68.9  71.0  1.6  TDN, %  54.2  54.5  54.5  0.3  —  52  56.3  54.8  2.1  Lignin, %DM  6.0a  5.6b  5.5b  0.2  —  6.2a  4.9b  5.9ab  0.6  NFC, %DM  14.2a  13.5a  11.1b  0.6  —  10.5b  11.7ab  16.6a  2.7  WSC, %DM  7.5ab  7.8a  6.6b  0.5  —  6.2b  6.6b  9.1a  1.3    Bermudagrass    Grazing periods    Item1  Alicia  Jiggs  Tifton-85  SEM  0–28  29–56  57–84  85–112  SEM  Bales/ha  14.1b  15.9a  14.9ab  0.8  0  14.7  16.1  12.8  1.8  CP, %DM  12.5a  12.1a  11.0b  0.4  —  12.6ab  14.8a  8.3b  2.9  ADF, %DM  41.0  39.7  41.5  0.5  —  42.0  39.1  41.0  1.3  NDF, %DM  69.2b  69.3b  73.6a  1.8  —  71.9  68.9  71.0  1.6  TDN, %  54.2  54.5  54.5  0.3  —  52  56.3  54.8  2.1  Lignin, %DM  6.0a  5.6b  5.5b  0.2  —  6.2a  4.9b  5.9ab  0.6  NFC, %DM  14.2a  13.5a  11.1b  0.6  —  10.5b  11.7ab  16.6a  2.7  WSC, %DM  7.5ab  7.8a  6.6b  0.5  —  6.2b  6.6b  9.1a  1.3  a,bWithin a row, means without a common superscript differ (P < 0.05). 1NFC = Non-Fiber Carbohydrate (starch, simple sugars, and soluble fiber), WSC = Water soluble carbohydrates (glucose, fructose, sucrose, and fructans). View Large Animal Performance The partial (for each 28-d period) and cumulative ADG of steers grazing the different bermudagrass hybrids are presented in Table 6. Differences between treatments were observed (P = 0.04) for cumulative ADG on d 84, which were maintained up to d 112. During the last 28 d of the grazing season, Alicia bermudagrass nutritive value was low with a high percent of dead material (data not shown), even though the forage mass on d 85 was 3,806 kg DM/ha. Authors did not find any published data comparing the performance of weaned steers on these 3 bermudagrass hybrids; however, other similar data generated in the Gulf Coast states that serve as a comparison are presented. In a 3-yr study, DeRouen and Ward (2005) reported ADG of stockers grazing common bermudagrass (grazing season from mid-May to late August) at an average stocking rate of 7.5 heads per hectare that oscillated from 0.55 to 0.63 kg. Banta (2012) reported work conducted in Overton, TX, on Tifton-85 in which 332 kg steers at 7.5, 10, or 12.5 heads per hectare gained approximately 0.7 kg for grazing periods between 83 and 92 d. Based on these published data, ADG of the steers in the present experiment was similar to that reported by Oliver (1972, 1978) for spring-weaned calves, but much lower when compared to data reported by DeRouen and Ward (2005) and Parish et al. (2013). Table 6. Partial (for each 28 d period) and cumulative ADG (kg) of beef steers grazing different bermudagrass hybrids and production per hectare (kg/ha) for the entire grazing period   Bermudagrass    Alicia  Jiggs  Tifton-85  SEM  Day 28      Partial ADG, kg  0.49  0.63  0.57  0.09      Cumulative ADG, kg  0.49  0.63  0.57  0.09  Day 56      Partial ADG, kg  0.38  0.53  0.64  0.16      Cumulative ADG, kg  0.44  0.58  0.61  0.10  Day 84      Partial ADG, kg  0.46  0.59  0.68  0.14      Cumulative ADG, kg  0.44b  0.58a  0.63a  0.05  Day 112      Partial ADG, kg  0.12b  0.31a  0.32a  0.06      Cumulative ADG, kg  0.36b  0.51a  0.55a  0.04  Beef produced, kg/ha  183.8b  258.7a  279.2a  19.9    Bermudagrass    Alicia  Jiggs  Tifton-85  SEM  Day 28      Partial ADG, kg  0.49  0.63  0.57  0.09      Cumulative ADG, kg  0.49  0.63  0.57  0.09  Day 56      Partial ADG, kg  0.38  0.53  0.64  0.16      Cumulative ADG, kg  0.44  0.58  0.61  0.10  Day 84      Partial ADG, kg  0.46  0.59  0.68  0.14      Cumulative ADG, kg  0.44b  0.58a  0.63a  0.05  Day 112      Partial ADG, kg  0.12b  0.31a  0.32a  0.06      Cumulative ADG, kg  0.36b  0.51a  0.55a  0.04  Beef produced, kg/ha  183.8b  258.7a  279.2a  19.9  a,bWithin a row, means without a common superscript differ (P < 0.05). View Large Table 6. Partial (for each 28 d period) and cumulative ADG (kg) of beef steers grazing different bermudagrass hybrids and production per hectare (kg/ha) for the entire grazing period   Bermudagrass    Alicia  Jiggs  Tifton-85  SEM  Day 28      Partial ADG, kg  0.49  0.63  0.57  0.09      Cumulative ADG, kg  0.49  0.63  0.57  0.09  Day 56      Partial ADG, kg  0.38  0.53  0.64  0.16      Cumulative ADG, kg  0.44  0.58  0.61  0.10  Day 84      Partial ADG, kg  0.46  0.59  0.68  0.14      Cumulative ADG, kg  0.44b  0.58a  0.63a  0.05  Day 112      Partial ADG, kg  0.12b  0.31a  0.32a  0.06      Cumulative ADG, kg  0.36b  0.51a  0.55a  0.04  Beef produced, kg/ha  183.8b  258.7a  279.2a  19.9    Bermudagrass    Alicia  Jiggs  Tifton-85  SEM  Day 28      Partial ADG, kg  0.49  0.63  0.57  0.09      Cumulative ADG, kg  0.49  0.63  0.57  0.09  Day 56      Partial ADG, kg  0.38  0.53  0.64  0.16      Cumulative ADG, kg  0.44  0.58  0.61  0.10  Day 84      Partial ADG, kg  0.46  0.59  0.68  0.14      Cumulative ADG, kg  0.44b  0.58a  0.63a  0.05  Day 112      Partial ADG, kg  0.12b  0.31a  0.32a  0.06      Cumulative ADG, kg  0.36b  0.51a  0.55a  0.04  Beef produced, kg/ha  183.8b  258.7a  279.2a  19.9  a,bWithin a row, means without a common superscript differ (P < 0.05). View Large Grazing Behavior The effect of TOD on grazing behavior of the steers is presented in Table 7. Time of the day affected (P < 0.05) all variables except the time spent walking (P = 0.06). Grazing time is usually divided into several well-defined periods of activity during the day and night, and depending on swards and environmental conditions, the number of periods may differ, although there are 2 clearly defined: at early hours in the morning and late afternoon into evening (Hodgson et al., 1994). In the present experiment, forage mass was never a limiting factor, although it can be argued that bermudagrass may not have the nutritive value (Tables 2 and 3) to meet the nutrient requirements for spring-weaned calves (NRC, 2000). Steers grazed longer during the period between 1600 and 2100 h (Table 6), followed by the one between 0600 and 1100 h, with some time dedicated to grazing on the other periods. This intensity of grazing in the late afternoon and evening is consistent with most of the reports of longer evening than morning grazing periods (Kropp et al., 1973; Hinch et al., 1982; Erlinger et al., 1990; Champion et al., 1994). There was an effect of bermudagrass hybrid (P < 0.05) on grazing time. In a 24-h period, steers grazing Alicia spent less time (P = 0.04) grazing (413 min) when compared to Jiggs and Tifton-85 (492 and 477 min, respectively). This effect is probably associated with the lower nutritive value of Alicia (Tables 2 and 3) when compared to the other 2 bermudagrass hybrids, which in turn affected animal performance (Table 5). In a review of literature, Kilgour (2012) indicated that during the hours of daylight, the average time that cattle spent grazing ranged from 4.5 to 9.3 h, whereas over the whole 24-h period, the time spent grazing ranged from 6.8 to 13.0 h. In all of the studies where grazing during daylight and darkness were differentiated, the amount of grazing during the daylight was greater than that during the dark, although the magnitude of the difference was highly variable. On average, in the present experiment, steers grazed for 7.7 h for the 24-h period mostly during daylight (Table 7). Through a wide array of experiments during the hours of daylight, duration of walking ranged from 0.2 h to 1.4 h, while over the whole 24 h it ranged from 0.2 to 2.9 h (Kilgour, 2012). Even though there was not an impact on walking time (1.4 h for 24 h), there was an effect on number of steps taken (P = 0.001) at different periods during the day, which is greatly associated (r = 0.71) with the time animals spent grazing. Standing time was affected by period of the day, with the greatest number of minutes in this activity being recorded between 1100 and 1600 h. The classic response of cattle to thermal load is to remain in the standing position (Cook et al., 2007), so it was not surprising to obtain these findings. Number of grazing bouts was also influenced by TOD with a greater number of grazing bouts in the evening hours, which coincides with greater grazing and walking time. Forbes et al. (1998) reported 7 to 10 grazing bouts in 24 h for Angus, Brahman, Angus x Brahman, and Tuli x Brahman heifers in east Texas grazing Coastal bermudagrass. In the present experiment, the number of grazing bouts is lowerm, although it was only determined during daylight hours. It can be assumed that the number would go up since there were approximately 1.5 h of grazing time between 2100 and 0600 h. Table 7. Effect of time of the day (TOD) on grazing behavior parameters of beef steers grazing bermudagrass hybrids (TRT)   Time of the day, TOD1    P-values2  Item  1  2  3  4  5  6  SEM  TRT  TOD  TRT × TOD  Grazing, min  124b  32c  210a  39c  26c  32c  18  0.04  0.003  0.67  Standing, min  88b  140a  40c  40c  31c  61bc  22  0.07  0.001  0.08  Walking, min  12  8  14  17  6  27  13  0.13  0.06  0.18  Number of steps  490b  92cd  746a  161c  79d  120cd  39  0.81  0.001  0.42  Lying, min  61b  98a  28c  82ab  107a  57bc  25  0.01  0.04  0.36  Number bouts3  2  1  3  ND  ND  ND  0.2  0.05  0.004  0.09    Time of the day, TOD1    P-values2  Item  1  2  3  4  5  6  SEM  TRT  TOD  TRT × TOD  Grazing, min  124b  32c  210a  39c  26c  32c  18  0.04  0.003  0.67  Standing, min  88b  140a  40c  40c  31c  61bc  22  0.07  0.001  0.08  Walking, min  12  8  14  17  6  27  13  0.13  0.06  0.18  Number of steps  490b  92cd  746a  161c  79d  120cd  39  0.81  0.001  0.42  Lying, min  61b  98a  28c  82ab  107a  57bc  25  0.01  0.04  0.36  Number bouts3  2  1  3  ND  ND  ND  0.2  0.05  0.004  0.09  a–dWithin a row, means without a common superscript differ (P < 0.05). 1Time of the day, TOD: 1 = 0600–1059, 2 = 1100–1559, 3 = 1600–2059, 4 = 2100–2359, 5 = 2400–0259, 6 = 0300–0559 2TRT = Treatment (bermudagrass hybrid) effect. 3ND = Not determined. View Large Table 7. Effect of time of the day (TOD) on grazing behavior parameters of beef steers grazing bermudagrass hybrids (TRT)   Time of the day, TOD1    P-values2  Item  1  2  3  4  5  6  SEM  TRT  TOD  TRT × TOD  Grazing, min  124b  32c  210a  39c  26c  32c  18  0.04  0.003  0.67  Standing, min  88b  140a  40c  40c  31c  61bc  22  0.07  0.001  0.08  Walking, min  12  8  14  17  6  27  13  0.13  0.06  0.18  Number of steps  490b  92cd  746a  161c  79d  120cd  39  0.81  0.001  0.42  Lying, min  61b  98a  28c  82ab  107a  57bc  25  0.01  0.04  0.36  Number bouts3  2  1  3  ND  ND  ND  0.2  0.05  0.004  0.09    Time of the day, TOD1    P-values2  Item  1  2  3  4  5  6  SEM  TRT  TOD  TRT × TOD  Grazing, min  124b  32c  210a  39c  26c  32c  18  0.04  0.003  0.67  Standing, min  88b  140a  40c  40c  31c  61bc  22  0.07  0.001  0.08  Walking, min  12  8  14  17  6  27  13  0.13  0.06  0.18  Number of steps  490b  92cd  746a  161c  79d  120cd  39  0.81  0.001  0.42  Lying, min  61b  98a  28c  82ab  107a  57bc  25  0.01  0.04  0.36  Number bouts3  2  1  3  ND  ND  ND  0.2  0.05  0.004  0.09  a–dWithin a row, means without a common superscript differ (P < 0.05). 1Time of the day, TOD: 1 = 0600–1059, 2 = 1100–1559, 3 = 1600–2059, 4 = 2100–2359, 5 = 2400–0259, 6 = 0300–0559 2TRT = Treatment (bermudagrass hybrid) effect. 3ND = Not determined. View Large Table 8 summarized the effect of period on grazing behavior variables. Grazing and walking time were greater (P < 0.05) between d 0 and 28 and from d 85 to 112 of the grazing period while standing time (577 min) was greater (P = 0.002) from d 57 to 84. Lying time was lowest (P = 0.002) from d 57 to 84 (307 min), which was statistically similar (P = 0.09) to d 85 to 112 (399 min). This type of behavior coincided with the time of the year of higher temperatures (Table 1), which when associated with the “normal” high humidity in south Louisiana may have been the major explanation for these responses. It has long being recognized that temperature and humidity affect the physiology of animals and thus influence their activities, including grazing (Ehrenreich and Bjugstad, 1966). Figure 3 shows the THI for the 4 mo of the grazing season (average of the 4 yr) by TOD. Bos taurus cattle have been shown to exhibit mild heat load when the THI exceeds 72 (Armstrong, 1994) and exhibit severe heat load when the THI is around 79 (Hahn and Mader, 1997). Steers in the present experiment were 75% Bos Taurus and 25% Bos indicus. Sprinkle et al. (2000) working with Angus, Brahman x Angus, and Tuli x Angus lactating and nonlactating cows showed that in the early summer, the Tuli x Angus cows spent more time in the shade than did the Brahman x Angus and less during late summer. Only 19% of the hourly time periods in the early summer had a THI less than 72; however, there were 59% of the hourly time periods that had a THI between 72 and 79 and 22% of the hourly periods with a THI exceeding 79. These results indicated that Brahman crosses had a better adaptation to elevated temperatures than Tuli crosses (Sprinkle et al., 2000). It can be clearly observed in Fig. 3 that between 0600 and 0000 h, the THI is above that considered to provoke mild heat stress on cattle for all 4 mo of grazing season. Even more dramatic is the THI for June, July, and August between 0600 and 2100 h. For all 3 mo, the THI was above the THI that would cause a severe heat load. In the present study, all variables on grazing behavior presented in Tables 6 and 7 can be explained by this factor: less time grazing, walking, and lying and more time standing (to dissipate heat) during the period of peak THI as well as during the first 3 mo of the grazing period. It is clear that the combined adverse effects of excessive heat and humidity and the low nutritive value of bermudagrass hybrids produced an adverse environment resulted in an environment that resulted in poor performance of young beef calves. Table 8. Effect of grazing period on behavior parameters of beef steers grazing bermudagrass hybrids   Grazing period, d    P-value1  Item  0–28  29–56  57–84  85–112  SEM  TRT  PER  TRT × PER  Grazing, min  618a  441b  407b  587a  175  0.31  0.03  0.08  Standing, min  369b  399b  577a  409b  71  0.06  0.01  0.21  Walking, min  118a  61b  52b  97a  13  0.07  0.03  0.09  Number of steps  1920  1491  1227  1783  252  0.04  0.05  0.11  Lying, min  446a  416a  307b  399ab  59  0.03  0.002  0.06  Bite rate, bites/min2  40.2a  42.1a  38.7ab  35.3b  2.0  0.002  0.03  0.14    Grazing period, d    P-value1  Item  0–28  29–56  57–84  85–112  SEM  TRT  PER  TRT × PER  Grazing, min  618a  441b  407b  587a  175  0.31  0.03  0.08  Standing, min  369b  399b  577a  409b  71  0.06  0.01  0.21  Walking, min  118a  61b  52b  97a  13  0.07  0.03  0.09  Number of steps  1920  1491  1227  1783  252  0.04  0.05  0.11  Lying, min  446a  416a  307b  399ab  59  0.03  0.002  0.06  Bite rate, bites/min2  40.2a  42.1a  38.7ab  35.3b  2.0  0.002  0.03  0.14  a,bWithin a row, means without a common superscript differ (P < 0.05). 1TRT = Treatment effect (bermudagrass hybrid); PER = Grazing period effect. 2Bite rate was determined on 5 consecutive days on d 20, 40, 60, and 100 of each yr. View Large Table 8. Effect of grazing period on behavior parameters of beef steers grazing bermudagrass hybrids   Grazing period, d    P-value1  Item  0–28  29–56  57–84  85–112  SEM  TRT  PER  TRT × PER  Grazing, min  618a  441b  407b  587a  175  0.31  0.03  0.08  Standing, min  369b  399b  577a  409b  71  0.06  0.01  0.21  Walking, min  118a  61b  52b  97a  13  0.07  0.03  0.09  Number of steps  1920  1491  1227  1783  252  0.04  0.05  0.11  Lying, min  446a  416a  307b  399ab  59  0.03  0.002  0.06  Bite rate, bites/min2  40.2a  42.1a  38.7ab  35.3b  2.0  0.002  0.03  0.14    Grazing period, d    P-value1  Item  0–28  29–56  57–84  85–112  SEM  TRT  PER  TRT × PER  Grazing, min  618a  441b  407b  587a  175  0.31  0.03  0.08  Standing, min  369b  399b  577a  409b  71  0.06  0.01  0.21  Walking, min  118a  61b  52b  97a  13  0.07  0.03  0.09  Number of steps  1920  1491  1227  1783  252  0.04  0.05  0.11  Lying, min  446a  416a  307b  399ab  59  0.03  0.002  0.06  Bite rate, bites/min2  40.2a  42.1a  38.7ab  35.3b  2.0  0.002  0.03  0.14  a,bWithin a row, means without a common superscript differ (P < 0.05). 1TRT = Treatment effect (bermudagrass hybrid); PER = Grazing period effect. 2Bite rate was determined on 5 consecutive days on d 20, 40, 60, and 100 of each yr. 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Funds provided in part by Southern SARE (LS09-221) and NIFA/AFRI (2011-67023-30098). American Society of Animal Science
TI - The effect of bermudagrass hybrid on forage characteristics, animal performance, and grazing behavior of beef steers ,
JF - Journal of Animal Science
DO - 10.2527/jas.2013-6959
DA - 2014-03-01
UR - https://www.deepdyve.com/lp/oxford-university-press/the-effect-of-bermudagrass-hybrid-on-forage-characteristics-animal-M7i2rzWkZN
SP - 1228
EP - 1238
VL - 92
IS - 3
DP - DeepDyve
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