Intake and digestion of wheat forage by stocker calves and lambs

¹ USDA-ARS Grazinglands Research Laboratory, El Reno, OK 73036
² Department of Animal Science, Oklahoma Agricultural Experiment Station, Stillwater, OK 74078

^* To whom correspondence should be addressed. E-mail: Bill.Phillips{at}ars.usda.gov.

	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 are seen. 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 1 of 2 treatment groups. Group 1 grazed a wheat pasture for 120 d during the winter, while Group 2 was wintered on dormant warm-season grass pastures plus warm-season grass hay and plant-based protein supplements. In the spring (April 2005), all lambs and steers grazed wheat pasture for 14 d and were then housed in metabolism stalls and fed freshly harvested wheat forage to determine forage digestibility and N metabolism. Data were analyzed for lambs and steers separately as a completely randomized design using the individual animal as the experimental unit. 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, respectively; P = 0.01) and steers (1.06 kg vs 1.83 kg, respectively ; P = 0.09) that had grazed wheat pastures all winter. Digestibility of DM, NDF, and ADF fractions and N metabolism of freshly harvested wheat forage by lambs and steers were not different (P > 0.10) between the 2 treatment groups. Less ADG during the first 14 d of wheat pasture grazing is most likely the result of less DMI by non-adapted animals and not due to diet digestibility or N metabolism.

Key Words: adaptation, digestion, intake, stockers, wheat pasture

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