206 Attainment and maintenance of pubertal cyclicity may predict high A4 cows with reduced fertility

Abstract

The UNL physiology herd has a population of cows that secrete excess androstenedione (A4) in follicular fluid. These High A4 cows are less fertile, have irregular cycles, are often anovulatory, and have similar characteristics to women with Polycystic Ovary Syndrome (PCOS). Ovarian cortex cultures of High A4 cows secrete more A4 than controls. High A4 cows reached puberty 45 d earlier than control cows. Thus, we hypothesized that heifers reaching puberty earlier were predisposed to become High A4 cows. To test this hypothesis, we collected blood plasma from weaning to breeding (2012–2017) in 611 heifers. A custom SAS program was developed using progesterone >1ng/ml to identify four distinct puberty groups: 1) Early Puberty- 317.0 ± 3.6 days of age (doa) with continued cyclicity (n = 143); 2) Typical Puberty- 378.4 ± 2.1 doa with continued cyclicity (n = 279); 3) Start-Stop Puberty- 265.3 ± 4.1 doa with discontinued cyclicity (n = 91); and 4) Non-Cycling- no P4≥1ng/ml (n = 98). The pattern of Sex Hormone Binding Globulin (SHBG) was increased prior to puberty in Early and Typical and reduced in Start-Stop and Non-Cycling heifers. Early heifers (4.9) had greater prebreeding reproductive tract scores, followed by Typical (4.7), Start-Stop (4.5), and Non-Cycling (4.0) heifers. At breeding, all heifers that showed estrus in response to PGF2a were artificially inseminated. Typical (78.9%), Early (79.5%) and Start-Stop heifers (50.3%) had a greater response compared to Non-Cycling heifers (12.6%). All heifers were exposed to bulls, and overall pregnancy rate was not different. However, a greater percentage of Typical (57.9%), Early (51.0%), and Start-Stop (45.2%) heifers calved in the first 21 d of the calving season compared to Non-Cycling (20.9%). Start-Stop (3.0ng/ml) and Non-Cycling (4.2ng/ml) heifers had increased A4 in ovarian cortex culture media compared to Typical (0.062ng/ml) or Early (0.091ng/ml) puberty heifers. Greater A4 produced by ovarian cortex of Start-Stop and Non-Cycling heifers, irregular cycles and reduced calves in the first 21 d indicates these females may be predisposed to becoming High A4 cows with decreased fertility.

Beef cows with atypical estrous cyclicity at puberty produced calves with deficits in preweaning muscling, metabolic indicators, and myoblast function but not in feedlot performance1

“…Similar adjusted 205-d weaning weights combined with indicators of diminished muscle mass suggest that body composition is affected in calves from cows with irregular or delayed cyclicity. Moreover, the observed differences in actual (i.e., unadjusted) weaning weights were likely due to the later calving dates for cows with atypical pubertal cyclicity, as their poor fertility ( Summers et al, 2014 ; Cupp et al, 2019 ) presumably led them to become pregnant later in the breeding season in this study. Surprisingly, we observed no differences in growth traits among calves during the feeding period even when adjusted for carcass metrics.…”

“…This study was approved by the Institutional Animal Care and Use Committee at the University of Nebraska-Lincoln, which is accredited by Association for Assessment and Accreditation of Laboratory Animal Care International. Steer calves were selected from crossbred Red Angus dams that had been previously classified into groups based on pubertal cyclicity pattern exhibited between weaning and their first breeding season ( Cupp et al, 2019 ). Progesterone concentrations were determined in weekly blood samples over this period, and heifers were considered pubertal when concentrations were greater than 1 ng/mL.…”

“…In cattle, age at puberty and number of estrous cycles prior to first breeding contribute to lifetime reproductive success ( Perry et al, 1991 ). In our university beef herd, we have identified a subset of cows that exhibited irregular pubertal cyclicity patterns between weaning and their first breeding season, which we postulate is associated with high androstenedione in follicular fluid ( Cupp et al, 2019 ). Cows with high androstenedione are subfertile but wean calves that average 17 kg heavier than the herd average ( Summers et al, 2014 ).…”