Genetic and environmental analysis of dystocia and stillbirths in draft horses.

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.

The role of DNA microarrays in the evaluation of fetal death.

Fetal death occurs in 15% of clinically recognized pregnancies. Cytogenetic abnormalities are present in 50% of spontaneous abortions (fetal deaths < 20 weeks) whereas the rate is 6% to 13% for stillbirths (fetal deaths ≥ 20 weeks). Microarray has been demonstrated to increase the diagnosis of genetic abnormalities by providing coverage of the entire genome at a higher density, detecting as small as 50 to 100 kb deletions or duplications, known as copy number changes. Microarray is particularly suited for evaluation of fetal death because DNA can still be analyzed in macerated fetuses and nonviable tissue, two situations where culturing and karyotyping is known to have low yield. Microarray has already proven successful in providing additional genetic information beyond karyotype in spontaneous abortion. The few studies on the use of microarray in stillbirth evaluation have been promising, demonstrating an increase in the diagnosis of clinically relevant genetic abnormalities when compared with karyotype. As the cost and technology improve, microarray may ultimately become the first line screen for genetic abnormalities in stillbirth. The accurate diagnosis of a genetic abnormality as the cause for fetal death may provide closure for families, prevent unnecessary treatments, and enable clinicians to more accurately counsel and manage subsequent pregnancies.