Variation in Feed Efficiency of Growing Heifers and Implications for Intensified Cow-Calf Production

Global demand for food has been projected to increase 70% by 2050 in order to support a growing population that is becoming more urbanized and affluent. As disposable incomes increase in developing countries, people will elect to include more animal-protein foods in their diet. This rising demand for animal protein will require a concomitant increase in the supply of cereal grains as well as protein and forage feedstuffs to support livestock production systems. Unfortunately, the increase in demand for livestock feed has coincided with a reallocation of cropland resources to support the production of biofuels from cereal grains, which has created higher and more volatile costs of feed inputs in recent years (Figure 1). As ruminant animals are capable of utilizing low-quality feedstuffs not directly usable by humans or non-ruminant animals, beef producers are poised to play a key role in meeting future global demands for animal-based protein foods. However, the biological efficiency of converting feed to meat is much lower in ruminant animals compared to pork and poultry, due primarily to inherent disadvantages in reproductive rates that greatly increase the cost of maintaining the cow herd. In fact, the cow herd consumes 82% of total feed inputs in calf-fed production systems, and 64% of total feed inputs in yearling-fed systems (Basarab et al., 2012). Thus, since 70 to 75% of total energy requirements for beef production are used for maintenance, more then half of total feed energy inputs needed to produce beef is associated with the energetic costs of supporting maintenance energy requirements of cows. Numerous studies have reported breed differences in cow maintenance energy requirements, and there is evidence to demonstrate that substantial genetic variation in maintenance requirements exist within breeds (Taylor et al., 1986; Hotovy et al., 1991). However, the opportunity to select for lower maintenance requirements is limited by our inability to easily measure this trait. Moreover, numerous studies have demonstrated that positive genetic relationships exist between maintenance requirements and genetic merit for productive traits like milk production and growth (Taylor et al., 1986; Frisch and Vercoe, 1981). Thus, the necessity to focus our efforts on selection for efficiency of feed utilization in postweaning animals, with the expectation that appropriate selection for feed efficiency in growing cattle will generate progeny that are efficient in all sectors of the industry. While feed efficiency traits have been fairly well characterized in growing cattle, there is a critical need to better understand the associations between genetic merit for feed efficiency in postweaning animals and life-cycle efficiency of the cow herd.