Browsing Journal of Range Management, Volume 48, Number 3 (May 1995) by Subjects
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Chromic oxide contamination of pasture previously used in marker studiesFecal output of range cows was determined during 2 periods of summer (period I) and late summer (period II) grazing using a constant release intraruminal Cr2O3 bolus. Chromic oxide contamination was determined by analyzing forage for Cr2O3 and by obtaining fecal samples from cows prior to bolusing. Control cows were also monitored along with the experimental cows during grazing periods. The overall herd least squares mean for fecal output during period I was lower than the expected value by 48%. Forage during period I contained an average of 55.7 microgram Cr2O3 g-1 of forage or about 45% of the daily dose of the bolus. Forage during period II contained an average of 38.3 microgram Cr2O3 g-1 of forage or about 29% of the daily dose of the bolus. Our results indicate that comparisons of fecal output least squares means by period of the year can be biased by Cr2O3 contamination of forage in pastures which have been previously used for marker studies.
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.