Morphological indicators of puberty in 3/4 and 5/8 Girolando heifers

Age at puberty is a key determinant of reproductive efficiency in dairy systems and may vary according to genetic composition and body development. The aim of this study was to evaluate morphometric predictors of puberty onset and to compare puberty timing between 3/4 and 5/8 Girolando heifers. A total of 60 heifers (3/4, n = 18; 5/8, n = 42), aged 6.9 to 13.5 months, were raised under semi-intensive system. Every 21 days, morphometric traits were recorded, and ovarian ultrasonography was performed to detect the presence of corpus luteum (CL). Linear regression was used to describe age-related changes in morphometric traits, logistic regression to estimate the probability of ovulation, and survival analysis (Cox regression) to evaluate time to puberty. Morphometric traits increased significantly with age in both genetic groups. Rump length, ilium width, rump area, and estimated body weight were associated with a 50% probability of ovulation at 45.30 cm, 40.87 cm, 1506.91 cm², and 339.06 kg, respectively. Mean age at puberty was 452.8 ± 20.18 days for 3/4 and 481.14 ± 28.99 days for 5/8 heifers (p > 0.4). Survival analysis indicated that the probability of not reaching puberty began to decline at approximately 55 weeks of age. Rump area was the morphometric trait most strongly associated with earlier ovulation. In conclusion, pelvic morphometric traits, particularly rump area adjusted to 365 days of age, are relevant indicators of reproductive maturation in Girolando heifers and may support management decisions aimed at improving reproductive efficiency.