Morphological and physiological measures as predictors of age at puberty and conception in beef heifer genotypes

Abstract

Objective: This study examined the utility of postweaning morphological and physiological measures as predictors of age of puberty and conception in beef heifers. Materials and Methods: Data were used from 309 spring-born heifer progeny [initial age 231 d (SD = 16); BW 256 kg (SD = 52)] of beef and dairy dams sired by early-maturing (EM) or late-maturing (LM) breeds and bred (12 wk) to calve at 24 mo of age within a grass-based production system. Body weight, composition and linear measurements, blood metabolites, pubertal age, and pregnancy were determined. Results and Discussion: Mean ages at puberty and conception were 429 d (range = 275–496 d) and 458 d (range = 398–534 d), respectively. Pubertal age was strongly correlated with age at first AI (r = 0.68) and conception (r = 0.48). Body weight deposition from 8 to 13 mo of age was negatively associated with age at puberty (r = −0.33), first AI (r = −0.17), and conception (r = −0.12). Pubertal age was negatively associated with BW at 10 and 13 mo (r = −0.15 to −0.19), ultrasonic measures of fatness from 10 to 15 mo of age (r = −0.15 to −0.30), IGF-1 concentrations from 8 to 13 mo (r = −0.22 to −0.31), and insulin (r = −0.22 to −0.24) and leptin (r = −0.18 to −0.21) concentrations at 10 and 13 mo. Prediction equations developed using multiple regression explained 25% of the variation in pubertal age for EM heifers [IGF-1 concentrations at 8 mo (15%), leptin (4%) and glucose (3%) concentrations at 10 mo, and BW at 13 mo (3%)] and 30% for LM heifers [IGF-1 (18%) and glucose (5%) concentrations at 8 mo and insulin concentrations (4%) and lumbar fat thickness (3%) at 13 mo]. Implications and Applications: In relatively well-grown replacement beef heifers, BW was a weak predictor of pubertal status. Physiological measures, particularly IGF-1 concentrations at 8 mo of age, were superior.