GRAZING PATTERNS, DIET QUALITY, AND PERFORMANCE OF COW- CALF PAIRS GRAZING SHORT GRASS PRAIRIE USING CONTINUOUS OR HIGH STOCKING DENSITY GRAZING STRATEGIES

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2021-02-12
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Abstract

Two experiments were performed at the WTAMU Nance Ranch (Canyon, TX) to compare different grazing strategies. The first measured differences in intensity of defoliation among species when cattle were allotted the same mean daily herbage allowance but with different stocking densities and grazing period lengths on reclaimed farmland dominated by old world bluestem (Bothriocloa ischaemum L.). Eighty-seven cows were randomly assigned to four treatment herds from January 12 – February 13, 2018. Fifty-nine mature cows (567 kg ± 10.8 kg, std. dev.) were stocked to achieve a target mean daily herbage allowance of 68 kg standing biomass . hd-1 . day-1 for the grazing period allotted among four replicates of the continuous grazing treatment. Another 28 cows received the same daily herbage allowance, but moved daily in small paddocks among four replicates, consecutively. Paddock size was determined each day by standing biomass in the area to be used to achieve an herbage allowance of 68 kg standing biomass . hd-1 . day-1. Botanical composition of standing herbage was measured before and after completion of the study in order to measure herbage disappearance by species. At the end of the grazing season, a nearest-plant step point transect was used to measure severity of defoliation by species between treatments. Total standing herbage at the beginning and end of the grazing season was not different (p>0.05) between treatments. Neither herbage removal nor proportional weight remaining were different (p>0.05) between treatments for any species measured. The before and after index (BAI) was used to estimate the relative change in standing biomass (BAIweight) or composition (BAIcomp) by weight for individual species in the plant community. Neither BAIweight nor BAIcomp were different between treatments for any species measured. Proportional utilization index (PUI) was developed to evaluate differences in utilization among species comprising different proportions of the plant community among replicates. The only difference in PUI from the expected (even defoliation severity between species and treatment) was observed in minor species. The objectives of the second study were to: 1) measure differences in diet quality using fecal near-infrared reflectance spectroscopy and performance of cow-calf pairs; and 2) quantify and compare vegetation defoliation and regrowth patterns on native rangeland in the Texas Panhandle when cattle were managed using continuous or rotational grazing employing weekly moves at the same stocking rate and intensity. Eighty lactating cow-calf pairs were weighed and assigned to two treatment groups among six native shortgrass-dominated rangeland pastures dominated by blue grama (Chondrosum gracilis Willd.), and gummy lovegrass (Eragrostis curtipedicellata Buckley). Botanical composition was measured before the study began to measure standing biomass by species, and after completion of the study in order to measure biomass disappearance by species. Grazing distribution was measured using point transects out to 386 meters from the water tank. Fecal near-infrared reflectance spectroscopy (F.NIR) was used to compare differences in diet quality between HSD and CG treatments. Weights of cows and calves and average daily gain were recorded and compared between treatments. Cattle in the CG treatment maintained higher (p<0.05) mean dietary DOM and CP levels, but there were no significant differences in any measure of individual performance between treatments. Major species (blue grama and gummy lovegrass) exhibited no significant differences in TDN and CP levels between treatments. Total defoliation intensity at the end of the grazing season was different (p<0.05) between treatments in periods 1, 5, 6, and 7. Standing biomass of gummy lovegrass was lower (p<0.05) at the end of the grazing season in HSD than CG. Standing biomass and composition of cool season annual grasses were lower (p<0.05) at the end of the grazing season in CG than HSD.

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Keywords
grazing strategies, high density grazing, continuous grazing, herbage allowance, stocking rate, stocking intensity, defoliation patterns, proportional utilization index, before and after index
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