Implications of disparate uterine and ovarian development observed among heifers evaluated during the peripubertal period.

The incidence and implications of disparate ovarian and uterine development during the peripubertal period were evaluated in two experiments. In Experiment 1, two consecutive pre-breeding evaluations were performed on 469 heifers. In Experiment 2, data from 22,174 heifers were retrospectively analyzed. For heifers in both experiments, ovarian and uterine maturity were independently assessed via transrectal evaluation, and a two-digit reproductive tract score (RTS: first digit = ovarian; second digit = uterine) was assigned. Measures of the physical maturity of heifers were recorded at the time of pre-breeding evaluation. Heifers were subjected to 14-day progestin-based protocols for synchronization of estrus, and artificial insemination (AI) was performed. Pregnancy diagnosis was performed via transrectal ultrasonography. Incidence of disparate ovarian and uterine score was 33.7 % (158/469) in Experiment 1 % and 16.3 % (3622/22,174) in Experiment 2. Observations of disparate ovarian and uterine maturity were correlated with physical maturity. Heifers with RTS < 3-3 demonstrated poor reproductive performance, as lesser proportions of these animals conceived to the first AI service in Experiment 2 (P < 0.01) or throughout the breeding season in Experiment 1 (P = 0.03). Conception did not differ between heifers assigned congruent or disparate scores of greater than RTS = 3-3. Disparities in ovarian and uterine development are likely observed as the result of rapid, yet asynchronous growth of reproductive tissues during the peripubertal period and are not indicative of inherently reduced potential for fertility. Independent assessment of ovarian and uterine maturity may increase precision in characterizing physiologic maturity of mixed groups of prepubertal, peripubertal, and pubertal heifers.