Environmental Sources of Variation in the Gestation Length of the Horse

Genetic study of gestation length in andalusian and arabian mares

“…Regarding the AB breed, we obtained a gestation period of 340.3 days, longer than that of 336.4 days found by Howell and Rollins (1951) and of 337.4 days found by Mauch (1937), but shorter than the values obtained by other authors who studied this breed in the Iberian Peninsula, such as Pozo-Lora (1954) in Spain (343 days) and Mario and Vidal (1986) in Portugal (348.3 days).…”

“…The main environmental factors influencing gestation period are related to age of the mother, nutrition, sex of the foal, year and month of conception, season of conception and photoperiod (Staffe, 1935;Mauch, 1937;Howell and Rollins, 1951;Pozo-Lora, 1954;Flade and Frederich, 1963;Hevia et al, 1994;Panchal et al, 1995;Davies-Morel et al, 2002;Vassilev et al, 2002). Nevertheless, other factors have been studied, such as the colour of coat (Dring et al, 1981;Blesa et al, 1999) or the influence of moon phase (Blesa et al, 1999), even though the results were not significant.…”

“…As for the estimation method, one should refer to the works of Howell and Rollins (1951) on the AB breed with a heritability value of 0.36 (using a paternal half-sibs model), of Rodero and Pozo-Lora (1960) for SPB with 0.97 (with a maternal half-sibs model) and, finally, of Hintz et al (1979b) on the AB breed with values of 0.25 (paternal half-sibs model), 0.97 (maternal half-sibs model) and 0.60 (full sibs model). These classical methods offer no advantage over the BLUP method and usually overestimate heritability due to the inclusion of other genetic effects (dominance and epistatic effects), especially the maternal and full sibs models (Falconer and Mackay, 1996).…”

Production of monozygotic (identical) horse twins by embryo micromanipulation

“…Gestation length in the mare ranges from 315 to 360 days and is influenced by maternal size (Walton & Hammond, 1938), fetal genotype and the stage of the breeding season when conception occurs (Asdell, 1946;Howell & Rollins, 1951). Development in utero can also be affected by degenerative wear and tear changes of the endometrium such as cystic fibrosis and glandular atrophy (Kenney, 1978).…”

Gestational length in Carthusian broodmares: effects of breeding season, foal gender, age of mare, year of parturition, parity and sire

“…In addition, mares with body conditions of four or less have overall pregnancy rate reductions as large as 20% less than mares in better body condition. Moreover, early pregnancy losses are significantly greater in mares with body scores of four or less (Howell andRollins 1951, Heneke et al 1984).…”