Impact of mutations in PRLR for hair weight, circulating prolactin concentrations, feed intake, and growth of beef cattle in a hot and humid climate.

BACKGROUND: In cattle, mutations in the prolactin receptor gene (PRLR) causing loss of tyrosine residues important for JAK-STAT signaling result in a short hair coat and increased ability to regulate body temperature during heat stress. Such mutations, referred to as slick mutations, occur naturally and have been introduced into cattle by gene editing. AIM: Consequences of inheritance of various mutations in PRLR for growth in beef cattle raised in a hot, humid climate (Florida) were evaluated. METHODS: Beef cows (predominantly Angus) were inseminated with semen from a single Angus sire mosaic for slick mutations in PRLR. Calves were born from November to January, raised with their dams until weaning on July 14 at 169 to 245 days of age, and then placed in a 56-day feed efficiency trial (August 25-October 21) in which individual feed intakes and body weights were recorded. RESULTS: There were a variety of genotypes for PRLR. The number of calves at weaning included 64 that were heterozygous for one of five mutations causing a slick phenotype (SLICK), 6 wild-type calves without a mutation affecting the prolactin receptor (WT), and 7 calves heterozygous for a large deletion in the PRLR gene resulting in a functional knockout (NULL). Hair weights were greatest for NULL and, after 3 months of age, least for slick. While body weight was not affected by PRLR genotype through weaning, average daily gain, dry matter intake, and body weight at the end of the trial adjusted for starting weight were significantly greatest for SLICK, intermediate for WT, and least for NULL. Residual feed intake was significantly greater (i.e., lower efficiency) for SLICK than WT or NULL. Vaginal temperatures during the feed efficiency trial were higher for NULL than SLICK heifers. CONCLUSIONS: Genotype for PRLR has important effects on ability for post-weaning growth. These effects are most likely related to differences in hair growth and ability to regulate body temperature during hot weather.