Energy Requirements and Production Efficiency of Lactating Beef Cows in a Drylot System

Population growth and alternative use of agricultural lands continues at an alarming rate, posing many challenges to food growers worldwide� particularly for meat-animal producers. Limited grazing land availability, adverse weather conditions, excess feedyard capacity, and volatility in the market are among the factors that have stimulated interest in the expansion of semi-confinement and confinement systems (controlled environments) for beef cattle production. The purpose of this research is to define cow and calf responses to a range of feed intakes and resulting energy provided to the cows. A total of 40 lactating beef cows were fed 135, 159, 176, 200, and 223 kcal NEm�(kg BW0.75)-1�d-1 for 111 d until weaning. This range of feed energy was accomplished by increasing the amount of feed provided using the same diet across all treatments. The diet consisted primarily of Sweet Bran� (wet corn gluten feed), prairie hay, cracked corn, and mineral supplement. Steer calves were offered the same diet as ad libitum creep feed along with milk and did not have access to cow feed. Body weight, body condition, milk yield and composition, and body composition were measured on cows; BW, creep intake, and body composition was also taken for steer calves. Eight cows were fed each of the energy intake levels in separate pens. Dependent variables were regressed on the linear and quadratic terms of energy intake. Increasing cow energy intake beyond maternal tissue maintenance is inefficient, as cows gained BW (P < .05) and condition (P < .01) and calves became fleshy (P < .05). Milk production increased (P < .01) as intake increased, which was not well-utilized by the calf. Additionally, cows maintained maternal tissue maintenance during lactation at an intake of 157 kcal NEm�(kg BW0.75)-1�d-1 and maintenance energy requirement was calculated at 84.7 kcal NEm�(kg BW0.75)-1�d-1, based on feed energy values. Utilizing digestibility data, a lactating beef cow required 108 kcal NEm�(kg BW0.75)-1�d-1.Animal Scienc