PROTEIN SUPPLEMENTATION OF STOCKER CATTLE IN THE NORTHERN GREAT-PLAINS

A comparison of the response of varying classes of growing beef cattle to protein supplementation was conducted on Northern Great Plains ran geland during the summer and early fall. Response was evaluated in 2 e xperiments, conducted in 1988 and 1989, by measuring organic matter in take and body weight gain in 13-month-old (spring-born steers) and 7-m onth-old steers (fall-born steers), which received either a 26% crude protein supplement or no supplement. Weight gain was also monitored in 7-month old heifers (fall-born heifers). In experiment 1, spring-born steers were fed 1.28 kg and fall-born steers and heifers 1.64 kg of p rotein supplement every other day. During experiment 2, spring-born st eers were fed supplement at a rate of 1 kg and fall-born steers and he ifers at 1.8 kg every other day. Intake of forage organic matter for s teers was not affected (P > 0.10) by supplementation in either experim ent. In experiment 1, total organic matter intake tended to be increas ed by protein supplementation in June but not in August (date x supple mentation level interaction, P = 0.08). Forage organic matter digestib ility was greater (P < 0.01) in June than in August during experiment 1 and in August than September in experiment 2. In experiment 1, this difference was greater for fall-born steers than spring-born steers. I n experiment 1, supplementation increased (P < 0.01) average daily gai n of cattle from 0.63 to 0.78 kg/day. In experiment 2, daily gain of c attle was increased (P < 0.01) from 0.62 to 0.82 kg/day with protein s upplementation. Also, in experiment 2, cattle receiving supplement wer e 18 kg heavier (P < 0.05) at the end of the grazing season than unsup plemented controls. Protein supplementation increased weight gains of growing cattle in the late summer in the Northern Great Plains. The ad vantage was most consistent for fall-born steers with higher relative protein requirements.