JOINT ALPHARMA-BEEF SPECIES SYMPOSIUM: Interactions of feed efficiency with beef heifer reproductive development1

Abstract

The influence of nutrition on puberty in beef heifers is complex and under neuroendocrine control. The stores of body fat in mammals are a determinant of the onset and maintenance of puberty. Body fat stores are greater in heifers with greater residual feed intake than in their more efficient herdmates. A 1 unit increase in residual feed intake resulted in a reduction of 7.54 d in age at puberty in Bos taurus beef heifers. However, Bos indicus-influenced heifers, which reach puberty at older ages, were not found to have sexual maturity influenced by selection for residual feed intake. The strong influence of body fat stores on return to estrus after calving does indicate that selection for leaner beef heifers could affect reproductive performance relative to puberty and postpartum rebreeding of first calf heifers. The influence of intermediary metabolism, through signals at the central nervous system, regulates the GnRH pulse generator, thereby influencing pituitary and ovarian function culminating with puberty and return to ovarian cyclicity after calving. Tropically adapted cattle (i.e., Santa Gertrudis and Brahman) selected for low residual feed intake had a lesser response of insulin to a glucose challenge than their less efficient herdmates. These studies indicate the possibility that animals with differing residual feed intake (efficiencies) may have differing intermediary metabolism and, therefore, differing rates of reaching puberty. Selection for low residual feed intake results in selection of leaner heifers that reach puberty at older ages. These leaner heifers calve later in their first and subsequent calving seasons. Selection for residual average daily gain has no negative influence on age at puberty or calving interval. Selection for residual ADG has a negative influence on age at first calving but not calving interval. There may be no acceptable method to improve feed efficiency without harming reproductive efficiency.

Heifer fertility and carry over consequences for life time production in dairy and beef cattle

“…Chronic leptin administration to beef heifers failed, however, to induce puberty at an earlier age (Zieba et al, 2005). The importance of body fat in determining the timing of puberty Larson (2007) concluding that it was not a key component in beef heifers in contrast with Randel and Welsh (2013) who thought that it was. Another metabolic hormone which appears to play an important role is IGF-1.…”

“…Similarly Crowley et al (2011) found a genetic correlation of 0.36 between RADG and age at puberty. In European beef breeds selected for a low RFI the AFC also increased by about 5 to 6 days but there was no difference in later maturing Brahman cattle (Randel and Welsh, 2013).…”

“…Genetic gain over past decades has led to dairy cows with greater milk production capacities (Tsuruta et al, 2005) and beef animals with higher and more efficient growth rates (Randel and Welsh, 2013). This has, however, been accompanied by a negative trend in fertility: poor fertility remains the major reason for culling, thus reducing longevity.…”

“…It is important to remember that heifers are still growing in their first lactation so this needs to be allowed for in ration formulation. Randel and Welsh (2013) reviewed the literature on the relationships between feeding efficiency and reproductive performance in beef heifers. Many beef breeding programmes are selecting for feed efficiency using traits such as residual feed intake (RFI), residual average daily gain (RADG) or feed conversion ratio and it is therefore important to understand how this may impact on the fertility of the replacement heifers.…”

Post-partum Anoestrus in Bali cattle under low-input animal production systems in Eastern Indonesia

“…Several studies have shown that variations in feed intake affected the age at which heifers reach puberty (Reid 1960;Bellows et al 1965;Wiltbank et al 1966;Wiltbank et al 1969;Fajersson et al 1991;Grings et al 1999;Macdonald et al 2005;Mohamed et al 2010;Randel & Welsh 2013). Poor nutrition significantly delays puberty in Bos indicus breeds (Mancio et al 1982;Oyedipe et al 1982) and taurine cattle (Joubert 1954;Sorensen et al 1959;Short & Bellows 1971).…”