Andrea S. Cupp
Date of this Version
Nafziger, S. (2019). Attainment and maintenance of pubertal cyclicity may predict High A4 cows with reduced fertility. (Master of Science), University of Nebraska, Lincoln, NE.
Puberty attainment was investigated in heifers. Blood samples were collected from weaning until breeding during 6 years from heifers born in 2012-2017. Plasma progesterone concentrations ≥ 1 ng/ml were used to indicate cyclicity, and heifers were categorized into one of four puberty groups using SAS: 1) Early heifers reached puberty before March 12 and cycled continuously during the sampling period, 2) Typical heifers reached puberty on or after March 12 and cycled continuously, 3) Start-Stop heifers had at least one occurrence of progesterone ≥ 1 ng/ml but discontinued cycling during the sampling period, and 4) Non-Cycling heifers had no occurrence of progesterone ≥ 1 ng/ml during the sampling period.
Early and Typical Heifers had increased average daily gain during the preweaning period, resulting in higher adjusted yearling weights heifers compared to Start-Stop and Non-Cycling heifers. At pre-breeding ultrasound, Early heifers had the highest percentage reproductive tract score 5, followed by Typical, Start-Stop, and Non-Cycling heifers. At breeding, a greater percentage of Typical and Early heifers displayed estrus in response to prostaglandin and were artificially inseminated, followed by Start-Stop heifers and Non-Cycling heifers. All heifers were exposed to bulls, and overall pregnancy rate did not differ between puberty groups. Fewer Non-Cycling heifers calved in the first 21 days of the calving season. Approximately 10 heifers from each puberty group were intensively studied in years 2014-2017 during the peripubertal period. Non-Cycling heifers had reduced progesterone concentrations and increased mean FSH, and Start-Stop and Non-Cycling heifers appeared to have reduced SHBG compared to Typical and Early heifers. At the conclusion of the intensive study, heifers were stimulated with FSH and ovariectomized. Interestingly, Non-Cycling ovarian cortex secreted more androstenedione in culture media compared to Typical and Early cortex. Ovarian cortex from cows previously classified as Start-Stop or Non-Cycling also secreted increased androstenedione in culture media compared to cortex from Typical cows. Since ovarian cortex from High A4 cows secretes increased androstenedione in culture media, these findings together with endocrine and fertility parameters indicate that Start-Stop and Non-Cycling heifers have similar High A4 cow traits which may result in their reduced fertility.
Advisor: Andrea S. Cupp