Factors Concerning Early Embryonic Death in Thoroughbred Mares in South Korea

Abstract

ABSTRACT. A total of 384 Thoroughbred mares were investigated to determine and evaluate the features of early embryonic death at nine equine farms on Jeju Island, South Korea, from 2001 to 2003. Overall, 771 matings for 384 mares resulted in 376 pregnancies 15 days after ovulation. Subsequently, 12.2% (46/376) of these early conceptuses were lost within 45 days after ovulation. Furthermore, about three quarters of the 46 embryonic deaths occurred between 16 and 25 days after ovulation. The incidence of embryonic death was highest in the barren (17.2%), more than 15 years old (15.4%), and more than 10 parities (18.2%) groups compared with the other groups (9.1-16.9%). Mares mated in March, April, and during the first estrus postpartum had higher embryonic death rates, (19.6%, 17.2%, and 24.6%, respectively). Mares with abnormal fluid and cysts in the uterus (18.0%) or multiple embryonic vesicles (23.1%) had higher embryonic death rates than those with normal uterine conditions (9.8%) or single embryonic vesicles (10.5%). The condition of mares, such as breeding condition and the environment of the embryo or fetus, are the major factors in relation to occurrence of early embryonic death. KEY WORDS: breeding condition, embryonic death, Thoroughbred, uterine environment.J. Vet. Med. Sci. 69(8): 787-792, 2007 Horses are long-day breeders and have lower reproductive efficiency compared with sheep and cows [32]. The fertility of mares depends on their individual fertility status. Some mares show total fertility rates of 90% if they are highly fertile, while ordinary mares have total fertility rates ranging from 81% to 92%, which are still higher than those of other animals [2,3]. Sullivan et al. [31] reported a fouryear cumulative pregnancy rate of 74% for Thoroughbred breeding, which was lower than the 85% rate for Quarter horses. Bruck et al. [4] stated that 85% of Thoroughbred mares achieve pregnancy and 69.3% of them give birth to live foals. Rose and Hodgson [25] reported that Thoroughbred mares worldwide have a foaling rate ranging from 60% to 70% on average. Davies Morel [7] suggested that the foaling rates of Thoroughbred mares range from 50% to 80%. Thus, Thoroughbred mares have proven low reproductive efficiency despite their high pregnancy rates. Furthermore, high embryonic mortality is cited as the main reason for low reproduction [7,32].Reproductive dysfunction in mares is closely linked to low fertility caused by improper care and maintenance, artificial control of breeding season, and hormonal and genital disorders [5,7]. In addition, the morphology and diameter of the fetus are important factors for pregnancy and embryonic death rate of mares [5,7]. Embryonic death in mares is primarily associated with genetic and environmental factors [3,21,29,32]. Vaginal infections and other uterine abnormalities have a particularly significant impact on premature loss of the fetus by failing to meet the metabolic needs of pregnancy [3,21,29,32]. At the same time, irregular and unbalanced nutrition and psycholog...

Analysis of several factors of variation of gestation loss in breeding mares

“…However, it was lower than those observed for Thoroughbreds in India, 19% (Sharma et al, 2010) or 12% in South Korea (Yang and Cho, 2007).…”

“…Fertility is therefore first affected by the age of the mare; the rate of fetal loss is affected later. This age effect of the breeding mare on the rate of gestation loss was observed in an identical manner by all authors (Allen et al, 2007;Yang and Cho, 2007;Vanderwall, 2008;Sharma et al 2010). During the genital life of a mare, her stock of oocytes loses their capacity to be fertilized more rapidly than the ageing of their oviducts and uterus.…”

“…Here we may suppose that the hormonal state of the mare induced by the day/night rhythm influences both the fertilizing conditions and maintaining of gestation. The same effect was observed in South Korea by Yang and Cho (2007). However, in India where the day/night variations are less important, this season effect was not observed; the rate of loss was identical all throughout the year (Sharma et al, 2010).…”

Factors Influencing the Frequency of Pregnancy Loss among Thoroughbred Mares in Hidaka, Japan

“…Thus, pregnancy loss is an important factor that reduces reproductive efficiency [1,4]. Reported embryonic loss rates range from 3.0% to 12.2% [3][4][5][6][7] and vary according to country and region (Kentucky, United States: 8.9% [1]; Newmarket, England: 7.4% [3]; South Korea: 12.2% [7]). The abortion rate ranges from 8.9% to 12.9% [1,3].…”

Uterine blood flow and perfusion in mares with uterine cysts: effect of the size of the cystic area and age

“…The reported incidence in horses ranges from 13 to 55% (Wilson 1985, Adams et al 1987, Bracher et al 1992, Tannus & Thun 1995. Uterine cysts appear to have clinical importance (Adams et al 1987, Tannus & Thun 1995, reviewed by Stanton et al 2004, Yang & Cho 2007.…”