Age biggest factor in fertility of thoroughbred mares – study

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Mare age is the biggest factor affecting fertility in thoroughbred mares, a study has shown.

Researchers based in Ireland set out to examine and evaluate a range of factors that could influence the fertility of thoroughbred mares.

They concluded that they can be effectively managed to achieve good reproductive performance at commercial studs.

Elizabeth Lane and her colleagues collected and analysed data from 3743 oestrous cycles among 2385 mares on a large thoroughbred farm in Ireland.

Fourteen stallions, which ranged in aged from 4 to 15, and with an average age of just over 8, were used over the mares in a total of 4141 matings. The 2385 mares had an average age of 9.4, and ranged from 3–24 years.

The researchers found that, of the breeding stock, 12% were maiden mares, 64% had a foal at foot, and 24% were barren, slipped or rested mares.

The average pregnancy rate per cycle was 67.8% over the two seasons during which the study took place. It was 68.6% in 2008 and 66.9% in 2009.

Mare factors evaluated for their potential influence on fertility included age, reproductive status, month of foaling, labour problems, month of cover, foal heat, cycle number, treatments and walk-in status.

The stallion factors considered included stallion identity, age, shuttle status, the time elapsed between covers and high stallion usage on the per cycle pregnancy rate and pregnancy loss.

Old age and cover within 20 days after giving birth were associated with lowered pregnancy rates, the study team reported online in the journal, Reproduction in Domestic Animals.

High mare age and barren, slipped or rested reproductive status increased the likelihood of pregnancy loss.

Uterine inflammation or infection, if appropriately treated, did not affect fertility, they found.

“Only high usage of stallions (used more than 21 times in previous week) was associated with lowered pregnancy rates,” they said.

“However, shuttle stallions were more likely to have increased pregnancy survival, perhaps reflecting a bias in stallion selection.”

They concluded: “Mare age exerted the greatest influence on fertility; nonetheless, thoroughbreds can be effectively managed to achieve high reproductive performance in a commercial setting.”

Ireland is the third-largest producer of thoroughbreds globally, responsible for about 10 percent of the world’s thoroughbred foals each year.

The researchers were variously affiliated with University College Dublin; Lyons Research Farm, which is part of the university; Forenaghts Stud in County Kildare, Ireland; and Newmarket Equine Hospital in Suffolk, England.

Lane, E., Bijnen, M., Osborne, M., More, S., Henderson, I., Duffy, P. and Crowe, M. (2016), Key Factors Affecting Reproductive Success of Thoroughbred Mares and Stallions on a Commercial Stud Farm. Reproduction in Domestic Animals. doi: 10.1111/rda.12655

The abstract can be read here

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