Responses of Prolactin and Hair Growth to Selection for Age at Puberty in Angus Cattle

The study conducted on 629 Angus heifer progeny over 7 years aimed to examine the impact of genetic selection for age at puberty (AP) on serum prolactin (PRL) levels and hair growth. The heifers were split into two groups, one selected for early puberty (AGE-) and the other for late puberty (AGE+), with a 62-day difference in AP. Results showed that PRL concentration was 11% lower in the AGE- group post-puberty, suggesting that selection for AP influences PRL levels, possibly indicating a change in day length sensitivity. However, hair growth was not significantly different between the two groups. Heritability estimates for AP, PRL, cortisol concentration, hair weight, and hair length were 0.26, 0.23, 0.22, 0.21, and 0.09, respectively, with a genetic correlation of -0.29 between AP and PRL, indicating a moderate inverse relationship. The study concluded that while selection for AP alters PRL concentration, it does not significantly impact hair growth, and further research is needed to explore these relationships in autumn-born cattle.