Grazing management affects nutrient intake by steers grazing tallgrass prairie

Abstract

Indicators of nutrient intake were compared for beef steers grazing tallgrass prairie managed with continuous grazing or 8-paddock short-duration grazing. Two replicates of each grazing system were evaluated during the 2 year study. Stocking rates for the grazing systems were similar in both years. Within each treatment replicate, 3 steers fitted with ruminal and duodenal cannulae grazed for the entire grazing season (late April through late September) with larger groups of intact steers. Rest periods for the 8-paddock cells were lengthened as the season progressed and forage accumulation rate slowed. Trials occurred in early June and early August in year 1 and early July and early September in year 2. Flow of organic matter and nitrogen at the duodenum, fecal nitrogen concentration, and fecal output were used as indicators of nutritional status. Chromic oxide was used as a flow marker. Flow of organic matter, total nitrogen, and microbial nitrogen at the duodenum in addition to fecal output were lower (P < 0.04) with short-duration grazing and indicate that forage intake and digestible organic matter intake were depressed in steers on the short-duration grazing treatment. Forage digestible organic matter intake, estimated from microbial protein flow, was 19.3% lower (P < 0.03) on short-duration grazing. Fecal nitrogen concentration was higher (P < 0.03) for steers under continuous grazing. Diet crude protein estimated from fecal nitrogen was 24.4 g kg-1 organic matter higher for continuous grazing. These results suggest that both diet nutrient composition and intake were depressed in steers in the short-duration grazing treatment. These observations partially explain the lower weight gains and higher end-of-season residual standing vegetation noted with short-duration grazing in concurrent grazing trials on these rangelands.