Submitted to: Journal of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 9/7/2013
Publication Date: N/A
Interpretive Summary: Abstract only
Technical Abstract: Feed constitutes the greatest proportion of costs in cow-calf production. Therefore, genetic merit for feed efficiency has received interest from producers, but has generally been assessed in growing animals. The objectives of this study were to determine the main factors that contribute to variance in feed intake and determine whether proportion Brahman genetics interacts with those factors. Ninety cows, varying in proportion Brahman influence (0, 1/4 and 1/2), were fed in groups of 30 over 3 seasons (2 spring- and 1 fall-calving) in pens designed to determine individual feed intake. Within about 3 wk postpartum, cows and their calves were evaluated throughout lactation. Cow and calf weights and milk production and composition were determined at monthly intervals. Sorghum silage was the primary dietary component for cows, being supplemented with a grain and cottonseed mix to mimic forage from rangeland. Calves were offered whole oats in separate creep feeders. Diet samples were taken at weekly intervals and analyzed for CP and IVDMD while refusals were taken as needed. The diets averaged 8.2, 7.6, and 8.8% CP and 55.7, 50.3, and 48.9% IVDMD for each of the seasons, respectively. Digestible dry matter intake of cows was the variable of interest and analyzed using GLM of SAS. The model included class effects of season and proportion of Brahman geneticis. Continuous variables average daily milk energy produced, calf ADG, cow weight, and season-long weight change, and interactions of season and proportion of Brahman genetics with the continuous variables. Season (P < 0.01), milk energy (P = 0.07), calf ADG (P < 0.01), and the interaction of B with calf ADG (P < 0.08) and cow weight (P = 0.06) influenced digestible dry matter intake (R2 = 0.9). Each additional kg of calf ADG required 1.13 kg DDM, but cows with either 0 or 1/2 Brahman required less than those with 1/4 Brahman influence. A kg of milk energy required 1.32 kg additional DDM. Cows generally lost weight over the lactation period on these diets, but the level of loss did not influence variation in intake. Dry matter intake of these cows was greater than that predicted by the NRC equation.