STEP-UP PROTEIN SUPPLEMENTATION FOR BEEF-COWS GRAZING DORMANT, TALLGRASS PRAIRIE

Protein supplementation contributes significantly to expenses of maint aining pregnant beef cows (Bos taurus) on winter range. Two experiment s evaluated winter supplementation schemes for grazing beef cows. Dehy drated alfalfa (Medicago sativa L.) pellets (DEHY) or soybean [Glycine max (L.) Merr.] meal/sorghum [Sorghum bicolor (L.) Moench.] grain (SS ) supplements were fed during the third trimester of gestation. In Exp . 1, treatments were: (i) 5.3 lb/head/d DEHY, (ii) 3.7 lb/head/d SS; ( iii) 3.8 lb/head/d DEHY, and (iv) DEHY averaging 3.7 lb/head/d across the supplementation period but fed in increasing amounts with advancin g gestation (step-fed). In Exp. 2, the two supplements were each used with two feeding methods: level- or step-feeding (as in Exp. 1). Amoun ts fed averaged 5.8, 5.7, 4.3, and 4.2 lb/head/d for level-fed DEHY, s tep-fed DEHY, level-fed SS, and step-fed SS. In Exp. 1, weight loss to within 48 h postpartum was less for 5.3 DEHY (-123 lb) than for 3.7 S S (-157 lb), 3.8 DEHY (-171 lb), or step-fed DEHY (-181 lb), and cumul ative body condition (BC) change was less for 5.3 DEHY (-0.38) and 3.7 SS (-0.43) than for 3.8 DEHY (-0.76) or step-fed DEHY (-0.86). In Exp . 2, weight loss to within 48 h postpartum was less for DEHY groups th an for SS groups and was unaffected by feeding method (-104, -109, -16 1, and -155 lb for level-fed DEHY, step-fed DEHY, level-fed SS, and st ep-fed SS). A supplement type x method interaction occurred for BC cha nge (-0.20, -0.26, -0.49, and -0.19 for level-fed DEHY, step-fed DEHY, level-fed SS, and step-fed SS). Treatments did not affect subsequent reproductive performance in either experiment. Although caution is adv ised in extrapolating these results to cows in poor condition, step-fe eding does not appear to offer significant benefits over level-feeding for cows calving in moderate body condition.