Birth season and dam parity affect the anogenital ratio in dairy heifers

摘要: In dairy cattle, the anogenital distance (AGD) is considered as a marker of reproductive performance and is defined as the length from the centre of the anus to the dorsal commissure of the vulva (AGDv) or the clitoral base (AGDc). Studies have shown that AGD is not associated with postnatal body growth, suggesting a role of the prenatal environment. We explored the influence of prenatal factors on AGD in 427 Holstein Friesian heifers of an age of 14±1.1 months. Maternal and reproductive data of the heifers were collected. Linear mixed models, with herd as random factor, were built to explore the effect of birth season and dam parity on AGDs. AGDc nor AGDv was influenced by birth season. Yet, the anogenital ratio (AGR defined as AGDv/AGDc) tended to be greater in heifers born during summer compared with winter-born heifers (LSMean±SE respectively 60.0±1.0 and 57.5±0.6%, p= 0.05). Summer-born heifers were 457±8.6 days old at conception, compared with 444±7.6 days for winter-born heifers (p= 0.12). Dam parity had no effect on offspring AGDc, but AGDv tended to be 1.5 mm shorter in daughters from multiparous than from primiparous dams (p= 0.07). Hence, daughters of multiparous dams had a smaller AGR than heifers born out of primiparous dams (58.1±0.6 and 59.9±0.6% respectively, p= 0.002). Daughters of multiparous dams had better fertility results: they were 11 days younger at conception (441±7.7 vs. 452±7.9 days, p= 0.03) and tended to need lesser inseminations to conceive (1.37±0.06 vs. 1.53±0.07, p= 0.06). The results suggest that birth season and dam parity affect the AGR and fertility results in dairy heifers …