BEEF SPECIES SYMPOSIUM: Beef production without mature cows.

Nutrients in animal feed get partitioned to growth, lactation, pregnancy, fat accretion, and/or maintenance. For mature beef cows, >80% of nutrients consumed annually go to unproductive maintenance. Integrated over the entire U.S. beef cattle production system, nearly one-half of the nutrients consumed go to maintenance of cow herds. This accounts for much of the inefficiency of beef production and can be minimized by the single-calf heifer system, in which heifers are fattened and slaughtered after having their first calf. We propose a modification, use of sexed semen, so that most heifers replace themselves with a heifer calf. This greatly decreases the size of the inherently inefficient cow herd required for beef production and greatly increases efficiency of beef production in terms of nutrients consumed and waste produced, such as methane, by increasing the ratio of nutrients used for growth to those used for maintenance. Additional management is required including AI, early weaning, and the attention required when calving 2-yr-old heifers. Low conception rates with sexed semen and less efficient growth of females than males also must be considered. However, these issues seem greatly outweighed by the benefits of increased efficiency from decreasing cow herd size while eliminating the need for breeding back lactating first-calf heifers, the need for castration, and health problems inherent in older cows such as mastitis and lameness. Moreover, the decreased generation interval can greatly accelerate genetic progress.