Increasing Glucogenic Precursors in Range Supplements Fed T O Young Postpartum Beef Cows Shortens Postpartum Interval

Cattle grazing winter range forage often exhibit yearly variation in response to supplementation. This variation may be predisposed by circulating concentration and subsequent metabolism of glucose, whieh is influenced by the quality and availability of dormant range forage. Therefore, a study conducted at the Corona Range and Livestock Research Center during two dry years, 2000 (driest) and 2001, evaluated the responses of supplements differing in glucogenic precursors fed to young postparcum beef cows. Supplements were fed at 908 g*cow~'*d~l twice weekly for approximately 95 d postparcum and provided 327 g CP, 118 g UIP (LOGLUC); 327 g CP, 158 g UIP (MIDGLUC); or 327 g CP, 164 g UIP + 100 g propionate salt (HIGLUC; NutroCalTM, Kemin Industries, Inc.). Days to postpartum BW nadir were similar (P = 0.56) for both years among supplemented cows (46, 51, and 48 * 3 d for LOGLUC, MIDGLUC, and HIGLUC, respectively). A supplement x year interaction was observed for average daily gains from BW nadir to the end of supplementation (P = 0.05; 0.27, 0.41, and 0.49 i 0.1 l kg.$' in yr 1 and 1.04, 1.07, and 0.90 i 0.07 k g d ' in yr 2 for LOGLUC, MIDGLUC, and HIGLUC, respectively). Adjusted weaning weights for calves were lighter by approximately 16 % in yr 1 compared to yr 2 (P < 0.01; 161 i 1.9 vs. 19.7 + 2.1 kg, for yr 1 and yr 2, respeetively). These results emphasize yearly variations encountered in response to supplementation and suggests that alterations in nutrient partitioning occurs depending on availability of circulating glucose and quality of dormant range forage.