If heifers “use up” their ovarian reserves early in life, they may have shorter productive herd lives, compared to same-age herdmates with lower follicle counts. That’s the hypothesis evaluated by a team of researchers led by James Ireland, Professor of Animal Science and Physiology at Michigan State University.
“It is well-established that women with polycystic ovarian syndrome have a relatively high antral follicle count (AFC), and are subfertile compared with their counterparts without the disorder,” said Ireland. “We wanted to evaluate whether heifers with high AFC are subfertile, and, therefore, removed from the herd at a greater rate than their age-matched herdmates with lower counts.” Their findings were published in the June 2017 issue of the Journal of Dairy Science.
In the study, Holstein heifers 11 to 15 months old were subjected to a single ultrasound measurement of the number of follicles at 96 hours after the second of two doses of prostaglandin F2α. They were classified into high- (≥25 follicles), mid- (16–24), or low-range (≤15) follicle number group (FNG). A total of 408 heifers in the study subsequently achieved lactation. They were monitored daily for reproductive performance and health parameters until their fifth to sixth lactations. The results showed:
· Heifers in the high-range FNG had a 180-day shorter productive herd life; reduced survival rate; and greater probability of being culled after birth of the first calf compared with heifers in the low-range FNG.
· Animals in the high-range FNG also had greater days open and services per conception, and lower pregnancy rates during the first, second, or third lactations, compared with their herdmates in the low-range FNG.
The researchers concluded that dairy heifers with 25 or more follicles 3 mm or larger in diameter have suboptimal fertility and a shorter productive herd life, compared to herdmates with fewer follicles.
Ireland said this information, coupled with the recent finding that follicle numbers are a moderately heritable genetic trait in dairy cows, could mean that follicle assessment may someday become a factor in dairy heifer culling decisions.