Department of Animal Science, University of Nebraska-Lincoln, Lincoln, NE 68583, USA.
Department of Animal Science, New Mexico State University, Las Cruces, NM 88003, USA.
Biol Reprod. 2021 Jun 4;104(6):1360-1372. doi: 10.1093/biolre/ioab044.
We hypothesized the manner that heifers achieve puberty may indicate their future reproductive longevity. Heifers with discontinued or delayed cyclicity during puberty attainment may have irregular reproductive cycles, anovulation, and infertility in their first breeding season contributing to a shorter reproductive lifespan. Therefore, plasma progesterone (P4) was measured from weaning to breeding on 611 heifers born 2012-2017 and four pubertal classifications were identified: (1) Early; P4 ≥ 1 ng/ml < March 12 with continued cyclicity, (2) Typical; P4 ≥ 1 ng/ml ≥ March 12 with continued cyclicity, (3) Start-Stop; P4 ≥ 1 ng/ml but discontinued cyclicity, and (4) Non-Cycling; no P4 ≥ 1 ng/ml. Historical herd records indicated that 25% of heifers achieved puberty prior to March 12th in the 10 years prior to the study. Start-Stop and Non-Cycling yearling heifers were lighter indicating reduced growth and reproductive maturity traits compared with Early/Typical heifers. In addition, Non-Cycling/Start-Stop heifers were less responsive to prostaglandin F2 alpha (PGF2α) to initiate estrous behavior and ovulation to be artificially inseminated. Non-Cycling heifers had fewer reproductive tract score-5 and reduced numbers of calves born in the first 21-days-of-calving during their first breeding season. Within the Start-Stop classification, 50% of heifers reinitiated cyclicity with growth traits and reproductive parameters that were similar to heifers in the Early/Typical classification while those that remained non-cyclic were more similar to heifers in the Non-Cycling group. Thus, heifers with discontinued cyclicity or no cyclicity during puberty attainment had delayed reproductive maturity resulting in subfertility and potentially a shorter reproductive lifespan.
我们假设小母牛达到青春期的方式可能表明它们未来的繁殖寿命。在青春期达到时出现周期性中断或延迟的小母牛，其繁殖周期可能不规律、排卵异常且在第一次配种季节不孕，从而导致繁殖寿命缩短。因此，我们从断奶到 2012-2017 年出生的 611 头小母牛的配种期间测量了血浆孕酮（P4），并确定了 4 种青春期分类：（1）早期；P4≥1ng/ml＜3 月 12 日且持续周期性，（2）典型；P4≥1ng/ml≥3 月 12 日且持续周期性，（3）开始-停止；P4≥1ng/ml 但周期性中断，（4）非周期性；没有 P4≥1ng/ml。历史畜群记录表明，在研究前 10 年，25%的小母牛在 3 月 12 日之前达到青春期。开始-停止和非周期性的一岁小母牛体重较轻，表明其生长和繁殖成熟特征与早期/典型小母牛相比有所降低。此外，非周期性/开始-停止的小母牛对前列腺素 F2α（PGF2α）的反应性降低，无法启动发情行为和排卵以进行人工授精。非周期性小母牛在第一次配种季节的头 21 天内，生殖道评分 5 的比例较少，出生的小牛数量减少。在开始-停止分类中，50%的小母牛重新开始周期性，其生长特征和繁殖参数与早期/典型分类中的小母牛相似，而那些持续非周期性的小母牛则与非周期性小母牛更相似。因此，在青春期达到时周期性中断或无周期性的小母牛，其繁殖成熟延迟，导致繁殖力降低，潜在的繁殖寿命缩短。
