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Applied Animal Science
Volume 38 (1), 2022, Pages 22-32

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

A.K. Kelly1,2, D.A. Kenny2, M. McGee2

College of Health and Agricultural Sciences, University College Dublin, Belfield, Dublin 4, Ireland D04 V1W8;.

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.

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