Browsing Journal of Range Management, Volume 48, Number 3 (May 1995) by Subjects
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Comparison of fecal analysis and rumen evacuation techniques for sampling diet botanical composition of grazing cattleFecal samples, evacuated rumen samples, and non-evacuated rumen samples were compared at different seasons as techniques for determining diet botanical composition of cattle. The study was conducted at the New Mexico State University College Ranch near Las Cruces. Six rumen-fistulated steers were used spring (28 May-7 June), summer (19 July-8 August). fall 1989 (1-17 October), winter (8-28 January) 1990; 4 rumen-fistulated steers were used during summer (24 July-4 August) 1990. Sampling techniques differed (P < 0.05) for the proportion of some plant species in steer diets at certain seasons. In most cases, these differences were observed only for minor forage species. Similarity (%) between fecal samples, evacuated rumen samples, and non-evacuated rumen samples varied with season and with the particular techniques being compared. Similarity (%) between fecal samples and evacuated rumen samples (74%), and highest in summer (1989) between fecal samples and non-evacuated rumen samples (93%). Differential digestion, sampling procedures, and observer errors may explain these differences. For practical purposes, fecal analysis appears to be one of the best techniques to evaluate diet composition of large herbivores.
Forage intake by beef steers grazing winter wheat with varied herbage allowancesTwo grazing trials were conducted in separate years on a 5.86 ha winter wheat (Triticum aestivum var. Chisholm) pasture divided into 10 experimental paddocks. Paddocks were differentially grazed with beef steers to produce an array of different herbage mass levels, expressed as kg dry matter (DM)/ha. Each experimental paddock was then continuously stocked with 3 beef steers during each 7-day forage intake trial. Daily forage intake, expressed as kg organic matter (OM)/100 kg body weight (BW), was estimated from fecal output (Cr2O3 dilution) of the beef steers and in vitro organic matter disappearance of esophageal masticate collected from each paddock. Estimated daily gain was calculated from forage intake and net energy values calculated from organic matter disappearance data. Forage intake, organic matter disappearance, and estimated daily gain were related to daily herbage allowance, expressed as kg DM 100 kg BW-1 day-1, and herbage mass utilizing a quadratic equation with a plateau function. As herbage allowance increased, organic matter disappearance improved (Y = 62.18 + 1.08 herbage allowance -.022 herbage allowance2; r2 = .64, MSE = 5.06) as did forage intake (Y = 1.3 + .12 herbage allowance -.003 herbage allowance2; r2 = .52, MSE = .07), and estimated daily gain (Y = -.059 + .12 herbage allowance -.003 herbage allowance2; r2 = 59, MSE = .07). Plateaus were achieved at herbage allowance between 20 to 24 kg DM 100 kg BW-1 day-1. Results of this study indicate forage intake and estimated daily gain declined severely as herbage allowance fell below 20 to 24 kg DM 100 kg BW-1 day-1. This data may provide a threshold herbage allowance for initiation of energy supplementation programs for growing cattle on wheat pasture.
Grain supplementation on bluestem range for intensive-early stocked steersA 4-year study was conducted on Kansas Flint Hills bluestem range to monitor animal gain, grass, and forb standing biomass following grazing, plant population dynamics, and in 2 years, subsequent feedlot performance of steers under intensive-early stocking supplemented with increasing levels of sorghum grain. Each year from 1988 through 1991, crossbred beef steers were stocked at 0.24 ha/100 kg of initial steer weight from 5 May to 1; July. Steers in twice-replicated pastures were given no supplementation, 0.91 kg rolled sorghum grain per head daily, or 1.82 kg rolled sorghum grain per head daily, which corresponded to approximately 0, 0.3, and 0.6% of body weight-1. All steers were implanted with estradiol 17 beta in 1988 and zeranol in 1989-91 during initial processing and had unlimited access to a lasalocid/mineral mixture during the entire trial. In 1989 and 1990, representative groups of steers selected from all treatment/pasture combinations were subjected to a feedlot finishing phase and carcass data were obtained. Grass and forb standing crops were estimated each year at livestock removal in mid-July and again in early October. Pretreatment species composition and basal cover were determined in 1988 and compared to those at the end of the study. In mid-July, when cattle were removed, residual standing biomass of grass increased in direct proportion to increasing level of supplement. Standing biomass of grass at the end of the growing season did not differ among pastures with different supplement levels. Forb standing biomass did not differ among pastures with different supplement levels in July or October. Changes in plant populations among treatments during the course of the study were minimal. During the early portion of the grazing period, sorghum grain supplementation did not significantly influence steer gains, but average daily gain during the latter part of the grazing period increased in direct proportion to increasing level of sorghum grain supplement. Daily gain. feed intake, carcass characteristics, and gain:feed ratio were not different among treatments during the feedlot phase. Although conversion efficiencies may be economically marginal, low-level grain supplementation has the potential to increase the daily gain of cattle grazing early-season tallgrass prairie under an intensive-early stocking program.