Mathematics Can Assist Evaluation Of Horse Breeding Activity

By Donald Stotts

STILLWATER - Mathematics is often associated more with feats of engineering or abstract thought than with raising horses, but mathematics can play a vital role in meeting breeding objectives. The goal of breeding farm activities is to produce live foals, said Dave Freeman, Oklahoma Cooperative Extension Service equine specialist. "Review of past breeding and foal histories allows for more accurate assessment of procedures that aid in obtaining a live foal," Freeman said. "Annual breeding season records can be summarized to aid in the evaluation of breeding procedures used on the farm."

Several ratios can be calculated from breeding records to determine how well the goal of producing live foals was reached. Freeman said the most routinely conducted evaluation is pregnancy rate. Pregnancy rate is the number of mares pregnant on a specific day divided by the number of mares bred.

"Pregnancy rate can be determined on the basis of one ovulatory period or on the total breeding season," Freeman said. For example, an early pregnancy check of 20 mares reveals that 17 have embryos and three remain unbred. The pregnancy rate is 17 divided by 20 times 100, a figure of 85 percent. Number of cycles per pregnancy further defines breeding efficiency. The smaller the average number of cycles per pregnancy, the greater the efficiency, Freeman said.

Given the operation in example one, a review of records indicates that 10 mares were settled on one heat cycle, five mares were settled on two heat cycles and two mares were settled on three cycles. The number of cycles per pregnancy would be [(10x1)+(5x2)+(2x3)] divided by 17, the number of mares that got pregnant. Thus, the average number of cycles per pregnancy would be 1.5 cycles. Freeman said foaling rate is another useful tool. It indicates the percent of matings that produced a live foal. Foaling rate is determined by dividing the number of foals by the number of mares mated then multiplying by 100. If 15 of 20 mares bred produced live foals, the foaling rate would be 75 percent (15/20 x 100).

"The foaling rate provides the overall ratio of efficiency, but more specific ratios such as pregnancy loss rate, embryo loss rate, fetal loss rate and stillbirth fetal loss rate are needed to identify important differences at specific times of gestation," Freeman said. Pregnancy loss rate is the number of mares not foaling divided by the number pregnant on the first pregnancy check, usually around day 20.

Embryo loss rate is the number not pregnant at the end of the embryo stage (day 40) divided by the number pregnant on a specific day, such as the day of the first pregnancy check. Fetal loss rate is the number not foaling divided by the number pregnant on a specific day. "Records provide the basis for making decisions on breeding individual mares, allow evaluation of operational success in producing foals and provide evidence of the need for changes in breeding management activities," Freeman said.

Freeman said records need to be designed to provide accurate information that is understandable and readily accessible; records should allow cross referencing from one record to another, and should minimize time spent recording without jeopardizing accuracy and detail. "It's generally best for one person to be responsible for record keeping throughout the breeding season because this method tends to promote clarity and consistency," he said.

Freeman said horse owners breeding small numbers of mares may find written information to be adequate for record keeping, but managers of larger operations should make use of one of many record keeping computer programs available commercially.