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

Abstract

The files for ultrasound diagnosis of gestating mares belonging to the French equine herd recorded for 3 consecutive years were joined with the files for foal birth of these same mares, allowing the statistical analysis of factors of pregnancy loss. For 28 872 positive diagnoses of gestation, 2898 losses were recorded, that is, a global rate of gestation interruption of 9.12%. The etiology of these interruptions is mainly extrinsic: the year and month of insemination, as well as region for climatic reasons. The intrinsic causes that are implicated are breed of the father (heavy breeds except the hypermetric ones lose fewer pregnancies than warmblooded breeds), age of the mother (losses are lower in mares of 7 to 10 years of age) and status (mares with foals have fewer pregnancy losses than mares not having foaled the previous year), as well as fetuses with consanguinity (when this increases, the pregnancy losses increase as well). However, the additive genetic effect is extremely low; it corresponds to heritability below 5% and few effects of the environment, common to the offspring of the same mare, were identified. This therefore gives little hope of being able to select against the 'gestation loss' trait.Keywords: horse, gestation loss, factor of variation, logistic regression ImplicationsFor 28 872 positive diagnoses of gestation, 2898 losses were recorded, that is, a global rate of gestation interruption of 9.12%. The etiology of these interruptions is mainly extrinsic: the year and month of insemination, as well as region. The intrinsic causes that are implicated are breed of the father (heavy breeds except the hypermetric ones lose fewer pregnancies than warm-blooded breeds), age of the mother (losses are mower in mares of 7 to 10 years of age) and status (mares with foals have fewer pregnancy losses than mares not having foaled the previous year), as well as fetuses with consanguinity (when this increases, the pregnancy losses increase as well). However, the additive effect is extremely low; it corresponds to a heritability below 5% and few effects of environment, common to breeding mares, were identified. This therefore gives little hope of being able to select against the 'gestation loss' trait.

Genetic and environmental analysis of dystocia and stillbirths in draft horses

“…Squires et al (2013) also reported significantly lower dystocia (8.5%) for maiden mares compared with multiparous mares (14.2% for foaling mares and 12.7% for barren mares), again in thoroughbreds. Our results were comparable to those reported by Langlois et al (2012) when they analysed gestation losses (i.e. between diagnosis of gestation and birth).…”

“…No differences in the incidence of dystocia depending on the month of parturition were reported by Squires et al. (2013) and an increase of gestation losses was observed by Langlois et al (2012) for mares that were bred during month of last mating. In dairy cattle, on the contrary, winter months are the less favourable (Steinbock et al , 2003; Eaglen and Bijma, 2009).…”

“…For FE, they are the same as those described by Langlois et al (2012) for foetal losses. However, for SB they differ from those reported previously in C and P breeds (in this study we observed that SB was higher in C than P, whereas in the previous report higher gestation losses were observed in P and Boulonnais than in C).…”

“…Their results suggested that foetal growth was controlled by the mare, hence concealing many genetic differences in the foal. Since then, the components of dystocia and stillbirths (SBs; gestation length, position and posture of the foetus, size of mare and foal, placenta characteristics and duration of labour) have been studied to elucidate the underlying mechanisms and to prevent their occurrence (Ginther and Williams, 1996; Allen et al , 2002; Allen et al , 2007; Langlois et al , 2012; McCue and Ferris, 2012; Squires et al , 2013). These studies were for the most part conducted on warmblood horses (thoroughbred, quarter horses) where both the foal and the mare are worth enough to call for adequate care at foaling.…”

Equine gestational length and location: is there more that the research could be telling us?

“…Researchers are addressing equine heredity with cohorts of a previously unseen scale. In France, where all breed registry data includes ultrasound confirmation of pregnancy under the Haras Nationaux (national studbook) regulations, researchers retrospectively studied over 350,000 gestations, with the aim of refining knowledge of the sire and dam’s genetic contribution to gestation length and fetal health . Such studies enable GL data to be collected on an equally major scale.…”