by Donald Stotts
Parsons, Kansas —
If a horse farm experiences low conception or foaling rates, it is likely that some step in breeding management is the cause rather than the breeding efficiency of the mare.
“To promote good conception and foaling rates, the horse breeder first must identify the farm's efficiency status and compare it to a realistic optimum,” said Dave Freeman, Oklahoma State University Cooperative Extension equine specialist. “There are three basic steps breeding managers should examine to accomplish this.”
The first step is to look at pregnancy rates. Pregnancy rate is the number of mares diagnosed pregnant divided by the number of mares bred and then multiplied by 100. Pregnancy rates can be affected by reproductive status of mares, the age of mares and the time of breeding in relation to the estrous season.
“For example, early season pregnancy rates may be lower because of transitional estrus irregularities in some mares,” Freeman said. “In addition, the number of mares handled and bred on a farm can affect pregnancy rate if stallion semen production, time or labor constraints result in poor management.”
Regardless, on an average population of mares, pregnancy rates should be at least 80 percent with goals of 90 percent or more.
Another useful breeding efficiency tool is to look at cycles per conception. The obvious goal of the breeding manager is to approach one cycle per conception for the breeding season. In other words, have each mare settled on one heat cycle.
“Goals between 1.3 cycles and 1.7 cycles per conception would yield an average of 1.5 cycles per conception,” Freeman said. “This would indicate that half the mares were settled on one heat cycle while the remaining mares were settled on the subsequent estrus. As a practical management tool, that's fairly efficient.”
The third step is to study the foaling rate, the number of mares foaling divided by the number of mares bred multiplied by 100. The difference between foaling rate and pregnancy rate is pregnancy loss.
“Remember, the ultimate goal is to get a live foal on the ground,” Freeman said. “Pregnancy losses greater than 10 percent indicate a problem requiring immediate attention.”
Pregnancy loss may be affected by early embryonic loss or misdiagnosis of pregnancy. Late gestation losses may be caused by rhinopneumonitis or ingestion of endophyte-infected fescue.
While pregnancy rate, cycles per conception and foaling rate do not identify the cause of poor reproductive performance, they do assist in identifying performance of the different steps of the breeding program.
“If any of the three indices are not satisfactory, then the breeding manager should review all management practices during or following the breeding season,” Freeman said. “After review and consultation, new procedures can be implemented.”
In turn, the effectiveness of new procedures can be measured by comparing them with rates from past breeding seasons.