CHANGES IN BODY WEIGHT, FILL AND SHRINK AS A RESULT OF GRAZING WINTER WHEAT PASTURE

Authors: Phillips, William; Coleman, Samuel; Mayeux Jr, Herman

Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2006
Publication Date: 6/12/2006
Citation: Phillips, W.A., Coleman, S.W., Mayeux, H.S. 2006. Changes in body weight, fill and shrink as a result of grazing winter wheat pasture. Professional Animal Scientist. 22:267-272.

Interpretive Summary: The majority of stocker calves used to graze winter wheat pastures in the southern Great Plains are not adapted to the unique dietary chemical composition of winter wheat forage. When first placed on winter wheat pasture, calves may not consume enough forage to make positive weight gain or may oscillate between periods of overeating and fasting. The objective of this experiment was to determine the number of days needed by stocker calves to adapt to a diet of winter wheat forage. Daily changes in bodyweight of calves grazing wheat forage for the first time were more erratic than for steers fed a familiar diet, indicating that calves may not be consuming wheat forage at a constant rate. Calves grazing winter wheat pasture had less gastrointestinal tract fill indicating that nutrient density was regulating intake not gastrointestinal tract capacity. Stocker calves need 14 to 21 days to adjust to wheat forage in the winter and 7 to 14 d in the spring. Development of pre-grazing management practices that could reduce the adaptation period would add millions of dollars to the net return of stocker enterprises.

Technical Abstract: In the southern Great Plains region, the majority of stocker calves used to graze winter wheat pastures are imported and are not adapted to the unique dietary chemical composition of winter wheat forage. The objective of this experiment was to determine changes in bodyweight in stocker calves during the first 28 d of grazing winter wheat forage. In a completely randomized design, bodyweight changes in calves (n= 212) grazing wheat forage for the first time in the spring (n=2) and winter (n=3) were compared to calves fed a familiar diet in dry lot. Calves grazing wheat forage for the first time do not have positive weight gains during the first week of grazing and had 28-d ADG that were lower (P < 0.01) than observed for the control group. It appeared that during the winter grazing period, calves needed 14 to 21 d to adapt to a diet of wheat forage, but during the spring grazing period the adaptation period was much shorter. Calves that grazed winter wheat forage lost less (P < 0.01) bodyweight during a 16-h fast than calves fed hay and a mixed diet (3.7% vs. 5.6%). Once calves had grazed wheat pasture for 28 d, the long term (76 to 105 d) rate of bodyweight gain was greater (P < 0.10) than the ADG of calves grazing wheat pasture for the first time. From these data, we concluded that stocker calves need 14 to 21 d to adjust to the unique chemical composition of wheat forage in the winter and 7 to 14 d in the spring. Development of pre-grazing management practices are needed to reduce the adaptation period and increase stocker performance.