Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2008
Publication Date: 8/26/2008
Citation: Phillips, W.A., Horn, G.W. 2008. Intake and digestion of wheat forage by stocker calves and lambs. Journal of Animal Science. 86(9):2424-2429.
Interpretive Summary: Grazing wheat pastures with sheep and cattle to obtain relatively high rates of body weight gain prior to entering a feedlot for finishing is a major livestock enterprise in the southern Great Plains region. From previous research, we learned that even though wheat pasture is rich in metabolizable nutrients, sheep and cattle gain very little body weight for the first two to three weeks of grazing. This experiment was conducted to determine if sheep and cattle that are adapted to wheat pasture and are rapidly gaining body weight consume feed or utilize what they eat differently than sheep and cattle that are eating wheat forage for the first time. One or both of these factors might explain why body weight gains of grazing livestock are very low during the initial grazing period. From our observations, we concluded that less body weight gain during the first 3 weeks of grazing is most likely the result of less feed intake by the non-adapted animals and not due to differences in feed digestibility. To maintain a reasonable rate of body weight gain, while animals adapt to a new diet of wheat pasture, producers should provide other feeds that sheep and lambs will readily consume to provide needed energy and protein.
Technical Abstract: Because wheat forage contains high concentrations of N, NPN, digestible DM, and water, beef cattle and sheep require an adaptation period before positive BW gains are observed. The objective of the present experiment was to determine the impact of length of exposure of lambs and steers to wheat forage on BW gains, N retention, and forage digestibility. Sixteen steer calves (average BW 210 ± 12 kg) and 20 wether lambs (average BW 31.5 ± 2.0 kg) were randomly assigned to one of two treatment groups. Group 1 grazed a wheat pasture for 120-d during the winter, while group 2 as wintered on dormant warm-season grass pastures plus supplemental hay and protein. In the spring (April 05), all lambs and steers grazed wheat pasture for 14 d and were then housed in metabolism stalls and fed harvested wheat forage for 12 d. Data were analyzed for lambs and steers separately as a completely randomized design using animal as the experimental unit. During the 120-d winter period, lambs and steers assigned to graze winter wheat pasture gained BW more rapidly than lambs (147 g vs 119 g/d; P = 0.05) and steers (0.72 kg vs 0.32 kg/d; P = 0.09) assigned to dormant warm-season pastures. Lambs and steers grazing wheat pasture for the first time in the spring had less ADG during the first 14 d than lambs (80 g vs 270 g; P = 0.01) and steers ( 1.06 kg vs 1.83 kg; P = 0.09) that had grazed wheat pastures all winter. Abruptly shifting sheep or cattle to wheat pasture in the spring will result in less BW gain during the first 14 d as compared to grazers that have been adapted to wheat forage. Less ADG is most likely the result of less DM intake by non-adapted animals and not due to diet digestibility or N metabolism.