A variety of issues concerning the sustainability of beef production systems, including alternative land use decisions and liquidation in cow inventory, have magnified the need to enhance system efficiency. One approach to increasing production efficiency is through the intensification of cow-calf systems. In intensified systems cows will be housed in a controlled environment (i.e. drylot) for at least a portion of their reproductive cycle, subsequently offering the opportunity to develop nutritional manipulation strategies to optimize cow efficiency. An experiment was conducted to analyze the effects of dietary energy density and intake on maintenance energy requirements in beef cows. In a 2 x 2 factorial treatment arrangement, thirty-two crossbred cows were fed either a high- (H, 2.54 Mcal ME/kg) or a low-energy (L, 1.96 Mcal ME/kg) diet at one of two levels of intake (80; 80% NRC NE requirements, 120; 120% NRC NE requirements). Several methods using empirical equations were used to estimate body energy on d 0 and 56 as a proxy for RE. HE was calculated as the difference between ME and RE. Body weight gain tended to be greater (P = 0.08) in H than L, but was not different (P = 0.12) between 120 than 80. Retained energy tended to be greater (P <= 0.10) in H than L and greater (P <= 0.08) in 120 than 80. Heat energy per EBW^0.75 was greater (P < 0.01) in L than H and greater (P < 0.01) in 120 than 80, with no interaction (P = 0.29). Birth weight and adjusted 205-d weaning weight of the calves from treated cows were not affected by diet (P > 0.22) or level of intake (P > 0.56). Feed requirement for maintenance was calculated to be 92.54 and 168.06 kcal ME/EBW^0.75 for H and L, respectively. Fasting heat production was estimated to be 54.60 and 74.78 kcal/EBW^0.75 for H and L, respectively. Overall, increasing dietary energy density resulted in a decrease in maintenance requirements of approximately 28% and intake restriction decreased HE by approximately 28%, with no interaction, suggesting additive effects. Limit feeding high-energy diets to beef cows has the potential to increase the efficiency of production and land use in U.S. cow-calf systems.
- Sawyer, Jason Associate Professor and Associate Department Head