PS12-18. Divergent Prolactin Receptor Genotype Responses in Growth Performance, Feed Efficiency and Feeding Behavior in Beef Calves.

Abstract

This study evaluated the effects of divergent prolactin receptor (PRLR) genotypes on feed intake, feeding behavior, feed efficiency, and growth performance in beef calves, with the objective of elucidating the physiological and behavioral mechanisms underlying genotype-associated variation in performance. A total of 69 crossbred beef calves were classified as SLICK (heterozygous for one of five mutations conferring the slick phenotype; n = 47), WT (wild-type without a PRLR mutation; n = 14), or NULL (large deletion in PRLR resulting in a functional knockout; n = 8). Calves were allocated to four pens (n = 16 - 18 per pen), with each pen containing representation of all genotypes and separated by sex. Daily feed intake and feeding behavior were continuously recorded using the GrowSafe system and BW was measured weekly over a 71-d experimental period. Data were analyzed using a mixed model, with genotype, sex, and their interaction included as fixed effects, and pen nested within sex included as a random effect. Initial BW and age were included as covariates and removed when not significant (P > 0.05). Dry matter intake (DMI; kg/d) tended (P = 0.09) to be greater in SLICK vs. WT and NULL calves, and a tendency for greater DMI in males vs. females (P = 0.09). DMI expressed as % BW was greater (P < 0.01) in SLICK vs. NULL calves, but did not differ from WT. Growth performance variables, including mid-test BW, final BW, ADG, and metabolic BW, were not affected by genotype (P > 0.56), although males exhibited greater BW than females (P = 0.001). Feed efficiency traits differed among genotypes, with NULL caves exhibiting greater gain-to-feed ratio (G:F; P < 0.01) and lower residual feed intake (RFI; P < 0.01) compared with SLICK, whereas WT did not differ from either group. Among genotypes, G:F differed among groups (P < 0.01), with NULL calves exhibiting greater efficiency than SLICK, whereas WT were intermediate; a genotype x sex interaction was detected (P < 0.01). Feeding behavior metrics revealed distinct genotype-associated patterns. NULL calves exhibited reduced bunk visit frequency (events/day; P < 0.01), whereas SLICK cattle had shorter head-down duration (min/day; P = 0.03). However, SLICK calves compensated with greater eating rate (g/min; P < 0.01). WT tended (P = 0.06) to have greater meal frequency and exhibited longer meal duration (P < 0.01) compared with SLICK and NULL calves. Females had increased bunk visit frequency and longer head-down and meal durations (P < 0.01), whereas males exhibited greater eating rates (P < 0.01). Collectively, these findings indicate that PRLR genotype altered feeding behavior and feed efficiency without affecting growth, suggesting prolactin receptor variation influences energy acquisition and metabolic efficiency, potentially via thermoregulation and nutrient utilization mechanisms