Genetic and permanent environmental variability of twinning in Thoroughbred horses estimated via three threshold models

Abstract

Twinning is a serious problem in Thoroughbred horses, as most of the multiple pregnancies are miscarried and live foals present lower performance values. The aim of this study was to estimate the heritability and repeatability of twinning in Thoroughbred horses. A total of 12648 pregnancies of 2033 Thoroughbred mares born between 1929 and 1994 in 11 studs were included. The analysis was performed by the use of AI-REML algorithm under three threshold animal models. The first model included effects of stud, mare's birth period and interaction between them as fixed. The second model included the interaction between the stud and mare's birth period as random, whereas in the third model stud effects were also treated as random. The models were compared based on the deviances. Phenotypic and genetic trends were evaluated as well. The twinning rate was 3.5%. The study involved 443 twins and two triplets. Heritability estimates varied from 0.24 (model III) to 0.29 (model I), whereas repeatability estimates ranged from 0.33 (model I) to 0.34 (model III). The fluctuations of average annual genetic effects may result from segregation of the major gene in the population.

Bayesian analysis of genetic backgrounds of twinning rate in Thoroughbred horses

“…These estimates ranged from 0.003 to 0.09 (Van Vleck and Gregory, 1996;Gregory et al, 1997). As expected, the higher heritability estimates of twinning rates were received by the use of threshold animal model both in horses (Wolc et al, 2006) and in cattle (Van Tassel et al, 1998).…”

Effects of inbreeding and other genetic components on equine fertility

“…The heritabilities of traits related to equine fertility, such as sperm production (van Eldik et al, 2006) or twinning (Wolc et al, 2006) have been studied using the REML, but they are not really comparable with the heritability of a more general trait such as the foaling rate.…”

“…Threshold models have been used in similar studies on bovine fertility (Kadarmideen et al, 2000;Guerra et al, 2006) and in a twinning study for horses (Wolc et al, 2006), but linear models are used as well (Jamrozik et al, 2005). For a dichotomous variable that is based on an underlying normally distributed trait such as the foaling rate, a threshold model would be theoretically correct.…”

Whole‐genome sequence analysis reveals candidate genomic footprints and genes associated with reproductive traits in Thoroughbred horse

“…By contrast to most livestock species, twinning is an unfavourable trait in horse breeding programmes, and is also a serious problem in Thoroughbred mares (Wolc, Bresinska, & Szwaczkowski, 2006). A pregnant mare can lose her foal for a variety of reasons, but twin pregnancy is the most common noninfectious cause of abortion in mares (Weber et al, 2018).…”