| Abstract: | The aim of this study was to clarify the relationship between the placental retentiontime (PRT) and the reproductive performance following mating at the foal heat inThoroughbreds. For this purpose, we interviewed 292 farmers over a period of 3 years withquestionnaires evaluating foaling, expulsion of placenta and reproductive performance atthe foal heat in 1,432 mares. The obtained data were later compared with a previous studyof heavy draft mares. The average of the PRT of the 1,432 Thoroughbred mares was 58 ± 88min (mean ± SD). The mean PRT of Thoroughbreds was significantly shorter than that ofthe148 min of heavy draft mares. The incidences of retained placenta (RP) occurring in theThoroughbred mares were 5.2 and 4.0%, for over 3 and 4 hr after foaling, respectively. Theincidence of RP over 4 hr was significantly lower than that of 25% in heavy draft mares.The pregnancy rate at foal heat of the mares in which PRT was less than 3 hr was 37%, andit significantly decreased to 11% for those with PRT of more than 3 hr. In the comparisonof the reproductive performance between Thoroughbred and heavy draft mares, the pregnancyrate of Thoroughbreds dropped drastically to 10% when PRT exceeded 40, and in consequence,the pregnancy rate of Thoroughbreds was significantly lower than the 30% of heavy draftmares, which had a PRT of over 4 hr. In conclusion, the Thoroughbred mares had a lowincidence of RP, however, a PRT exceeding 3 hr severely affected the reproductiveperformance at the foal heat. |
