Relationship between the Placental Retention Time and the Reproductive Performance at the Foal Heat in Thoroughbred and a Comparison with Heavy Draft.
The aim of this study was to clarify the relationship between the placental retention time (PRT) and the reproductive performance following mating at the foal heat in Thoroughbreds. For this purpose, we interviewed 292 farmers over a period of 3 years with questionnaires evaluating foaling, expulsion of placenta and reproductive performance at the foal heat in 1,432 mares. The obtained data were later compared with a previous study of heavy draft mares. The average of the PRT of the 1,432 Thoroughbred mares was 58 ± 88 min (mean ± SD). The mean PRT of Thoroughbreds was significantly shorter than that of the148 min of heavy draft mares. The incidences of retained placenta (RP) occurring in the Thoroughbred mares were 5.2 and 4.0%, for over 3 and 4 hr after foaling, respectively. The incidence 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%, and it significantly decreased to 11% for those with PRT of more than 3 hr. In the comparison of the reproductive performance between Thoroughbred and heavy draft mares, the pregnancy rate 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 draft mares, which had a PRT of over 4 hr. In conclusion, the Thoroughbred mares had a low incidence of RP, however, a PRT exceeding 3 hr severely affected the reproductive performance at the foal heat.
Obihiro University of Agriculture and Veterinary Medicine, Nishi 2-sen, Inada-cho, Obihiro, Hokkaido 080-8555, Japan.
Mitsuo
M
Ishii
Obihiro University of Agriculture and Veterinary Medicine, Nishi 2-sen, Inada-cho, Obihiro, Hokkaido 080-8555, Japan.
Takahiro
T
Aoki
Obihiro University of Agriculture and Veterinary Medicine, Nishi 2-sen, Inada-cho, Obihiro, Hokkaido 080-8555, Japan.
Kazuhiro
K
Yamakawa
Obihiro University of Agriculture and Veterinary Medicine, Nishi 2-sen, Inada-cho, Obihiro, Hokkaido 080-8555, Japan.
Fumie
F
Magata
NOSAI-Hidaka-Tobu, 2-5-4 Sakaimachi-Higashi, Urakawa-cho, Urakawa-gun, Hokkaido 057-0033, Japan.
Chikara
C
Gojo
Hidaka Horse Breeders' Associtaion, 2-1-1 Tsukiji, Urakawa-cho, Urakawa-gun, Hokkaido 057-0024, Japan.
Katsumi
K
Ito
Obihiro University of Agriculture and Veterinary Medicine, Nishi 2-sen, Inada-cho, Obihiro, Hokkaido 080-8555, Japan.
Mitsunori
M
Kayano
Equine Science Division, Hidaka Training and Research Center Japan Racing Association, 535-13 Nishicha, Urakawa-cho, Urakawa-gun, Hokkaido 057-0171, Japan.
Yasuo
Y
Nambo
Thoroughbred; foaling; heavy draft; placental retention time; reproductive performance