Genetic and environmental analysis of dystocia and stillbirths in draft horses

Abstract

Genetic parameters and environmental factors were estimated for foaling ease (FE) and stillbirths (SBs) in four breeds of draft horses based on 11 229, 38 877, 35 764 and 13 274 FE and SB scores recorded between 1998 and 2010 for Ardennais (A), Breton (B), Comtois (C) and Percheron (P), respectively. Incidences for the three FE categories were: easy or without help 91.0% (A) to 95.4% (B), difficult 3.4% (B) to 7.1% (A) and intervention of a veterinarian 1.1% (B) to 1.9% (A). The frequency of SB ranged between 5.4% (B) and 9.4% (A). A multiple-trait threshold animal model was used that included the effects of sex of foal, region, month, year of foaling, combined maternal age and parity, direct genetic, maternal genetic and permanent environments. Estimates were obtained using Markov Chain Monte Carlo Gibbs sampling. The most unfavourable effect was first parity, which decreased the probability of easy foaling to 78.6% for A and 88.3% for B. Interaction with age showed that the risk for first foaling for mares aged 3 years was higher than at 4 or 5 to 9 years. This was also observed for SB with an increased probability of SB at first foaling of 17.9% (A) or 9.6% (B). The most unfavourable month was found to be the most frequent month for foaling (April) and not the most demanding months weather-wise (winter). For FE, direct heritabilities were A 0.27 (0.06), B 0.14 (0.03), C 0.18 (0.03) and P 0.18 (0.04), and maternal heritabilities were A 0.25 (0.06), B 0.19 (0.04), C 0.12 (0.03) and P 0.21 (0.06). Genetic correlations between direct and maternal genetic effects were A −0.29 (0.14), B −0.39 (0.12), C −0.09 (0.14) and P −0.54 (0.17). For SB, direct heritabilities were A 0.52 (0.09), B 0.42 (0.04), C 0.28 (0.04) and P 0.39 (0.05), and maternal heritabilities were A 0.25 (0.05), B 0.10 (0.02), C 0.07 (0.02) and P 0.14 (0.02). Genetic correlations between direct and maternal genetic effects were A −0.85 (0.06), B −0.63 (0.06), C −0.64 (0.11) and P −0.69 (0.06). Direct genetic correlations between FE and SB traits were A 0.60 (0.10), B 0.58 (0.10), C 0.36 (0.10) and P 0.29 (0.15). Maternal genetic correlations between FE and SB traits were A 0.67 (0.10), B 0.47 (0.13), C 0.28 (0.15) and P 0.39 (0.15). These estimates are posterior means of the Gibbs samples and are within the upper limits of comparable results reported in cattle.

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.…”

“…Ultrasound scanning has been known to miss embryos that are small because of delayed fertilisation occurring several days after the spermatozoa have entered the mare’s reproductive tract . To mitigate this, some researchers adopt daily ultrasound examinations for increased accuracy, observing the mare’s ovulatory follicle (≥ 3.5 cm), and then calculating GL from the day prior to ovulation …”

“…Retrospective studies using different stud book sources may need to adjust data to enable meta‐analysis. In France, the policy of the Haras Nationaux , the national studbook, requires ultrasound confirmation 14 and 20 days post‐insemination, plus a positive result at 43–45 days post‐fertilisation . Despite this, study data still required correction, for some breeders had declared the first day of mating rather than the last.…”

“…19 To mitigate this, some researchers adopt daily ultrasound examinations for increased accuracy, 29 observing the mare's ovulatory follicle (≥ 3.5 cm), and then calculating GL from the day prior to ovulation. 13,18,21 Retrospective studies using different stud book sources may need to adjust data to enable meta-analysis. In France, the policy of the Haras Nationaux, the national studbook, requires ultrasound confirmation 14 and 20 days post-insemination, plus a positive result at 43-45 days post-fertilisation.…”

“…In France, the policy of the Haras Nationaux, the national studbook, requires ultrasound confirmation 14 and 20 days post-insemination, plus a positive result at 43-45 days post-fertilisation. 15,21 Despite this, study data still required correction, for some breeders had declared the first day of mating rather than the last. In an effort to reconcile recent data with older registry data, other studies have used service dates rather than ovulation dates, acknowledging that the actual GL could be up to 1 week shorter.…”