Genetic and Environmental Factors Influencing Gestation Length in Lusitano Horses.
Authors: Rodrigues Joana A, Gonçalves Ana Rita, Antunes Luís, Bettencourt Elisa V, Gama Luis T
Journal: Journal of equine veterinary science
Summary
# Gestation Length in Lusitano Horses: Genetic and Environmental Influences Over 35 years of breeding records from the Alter Real stud, researchers analysed 1,027 gestations in Lusitano horses to establish the relative contributions of genetics and management to gestation length (GL), which averaged 338.1 days with a standard deviation of 9.26 days. Using mixed-model analysis of variance and animal model methodology, the team examined multiple factors: foal sex, inbreeding coefficients, mare age, conception month, year, and individual stallion effects. Maternal age emerged as a significant linear predictor, with GL increasing approximately 0.155 days per year, whilst conception timing proved influential—gestations initiated between January and April ran longest, declining by approximately 5 days for May conceptions and 10 days for June-July matings; importantly, individual stallions demonstrated consistent effects on GL, with most producing offspring gestations within a ±5-day range. The heritability estimates revealed maternal genetic effects (0.39) substantially outweighed direct fetal genetic effects (0.19), and mare repeatability of 0.427 indicated that individual mares maintain consistent gestation patterns across their reproductive lifetime. For practitioners, these findings suggest that whilst genetic selection based on maternal lines is viable, management of conception timing and awareness of mare age effects on gestation duration should inform breeding programmes and parturition planning.
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Practical Takeaways
- •Mares have predictable individual gestation lengths across their reproductive lifetime; record your mare's typical gestations to improve foaling date predictions
- •Plan breeding programs to conceive in January-April to achieve gestations closer to 338 days; conceptions in summer months will result in noticeably shorter gestations (5-10 days less)
- •Older mares will consistently have slightly longer gestations than younger mares; adjust foaling date expectations accordingly for aged breeding stock
Key Findings
- •Mean gestation length in Lusitano horses is 338.1 ± 9.26 days with gestation length increasing linearly by 0.155 days per year of mare age
- •Conception month significantly affects gestation length, with 5-10 day reductions observed when breeding occurred in May through July compared to January-April
- •Maternal genetic effects account for heritability of 0.39 while direct genetic effects account for 0.19, with repeatability of 0.427 indicating individual mares are consistent in their gestation length across lifetime
- •Stallion effects and year of breeding significantly influence gestation length, but foal sex and inbreeding have no significant effect