Effects of crude protein level and degradability of limited creep-feeding supplements on performance of beef cow-calf pairs grazing limpograss pastures

- Limited creep-feeding supplementation is efficient to increase calf performance.
- Increasing rumen-undegradable protein supplementation did not increase calf growth.
- Limited creep-feeding supplementation to calves did not increase performance of dams.

Two experiments evaluated the growth performance of cow-calf pairs offered limited creep-feeding supplementation (Exp. 1) and creep-feeding supplements with different crude protein degradability (Exp. 2). In Exps. 1 and 2, Brangus crossbred cow-calf pairs (Bos sp.; 24 and 16 pairs, respectively) were randomly assigned into 1 of 8 limpograss pastures (3 and 2 cow-calf pairs/pasture, respectively). Treatments were randomly assigned to pastures (4 pastures/treatment) and consisted of: (Exp. 1) no creep-feeding supplementation (Control) or daily limit creep-feeding supplementation (Creep; 0.40 kg/d of soybean meal) for 84 d; and (Exp. 2) daily limited creep-feeding supplementation of 0.40 kg/d of soybean meal (SBM; 35% RUP) or 0.40 kg/d of cooker-expeller processed SBM (SP; SoyPLUS, West Central, Ralston, IA; 60% RUP) for 112 d. In both experiments, creep-feed supplements were provided daily at 0800 h in cow-exclusion areas. Body weight of cows and calves were assessed monthly, following 16 h of feed and water withdrawal, whereas cow BCS was determined at the start and end of the study. In both experiments, herbage mass (HM) and hand plucked forage samples for nutritive value analysis were obtained at 14-d intervals from May to August (Exp. 1) and May to September (Exp. 2). Effects of treatment and treatment×time (P≥0.16) were not detected for HM, herbage allowance, in vitro digestible organic matter, and crude protein in both experiments. In Exp. 1, limited creep-feeding supplementation increased calf overall average daily gain (ADG, P=0.0005), but not cow growth (P≥0.19). In Exp. 2, effects of protein degradability were not detected for calf and cow growth performance (P≥0.14). In summary, limit creep-feeding supplementation of 0.40 kg/d of soybean meal for 83 d addressed weather-induced calf nutritional deficiencies and increased calf growth grazing limpograss pastures, without affecting cow growth performance and forage responses. In addition, increasing supplemental RUP consumption from 67 to 115 g/d was not sufficient to impact limpograss herbage mass, nutritional composition, and growth performance of cows and calves.