Relationship of Maternal Dietary Energy Intake to Milk Production, Body Composition, and Efficiency of Calf Growth

The purpose of this research is to define cow and calf production responses and overall pair efficiency to a range of feed energy intakes provided to lactating beef cows. Two experiments were conducted in consecutive years using a total of 80 beef cow/calf pairs (40 per year). Each year, 8 cow/calf pairs were assigned to one of 5 intake levels (8.7, 10.8, 12.5, 14.1, 15.2 kg DM •hd •d-1 for 111 d until weaning in yr 1 and 8.6, 9.5, 10.5, 11.4, 12.6 kg DM •hd •d-1 for 125 d until weaning in yr 2). Each pen of 8 cows and their steer calves were managed together as contemporaries and group fed. While the cows were fed the range of feed energy intakes, the calves had ad libitum access to the same diet in a creep area. Calves did not have access to the cows’ feed. Cow and calf BW were recorded every 28 d in yr 1 and every 14 d in yr 2. Cows were assigned a BCS every 28 d. Milk yield and composition were also measured at 28 d intervals. A digestibility trial was conducted each year to determine the relationship of energy intake on DM digestibility and acid detergent fiber (ADF) digestibility in both cows and calves. Dependent variables were regressed on linear and quadratic terms of energy intake. The mixed model included year as random and treatment energy level as a fixed effect, with pen as experimental unit. Cow DM digestibility (P < 0.01) and ADF digestibility (P = 0.03) decreased linearly with increasing cow energy intake. Increasing cow energy intake resulted in increased cow BW (P < 0.01), increased cow BCS (P < 0.01), increased milk yield (P < 0.01), and increased retained energy in cows (quadratic P = 0.05; RE). Calf efficiency (P = 0.03) and pair efficiency (P < 0.01) decreased with increasing cow energy intake.Animal Scienc