One Hundred Years of Coat Colour Influences on Genetic Diversity in the Process of Development of a Composite Horse Breed

Abstract

Genetic diversity and demographic parameters were computed to evaluate the historic effects of coat colour segregation in the process of configuration of the Hispano-Arabian horse (Há). Pedigree records from 207,100 individuals born between 1884 and 2019 were used. Although coat colour is not a determinant for the admission of Hispano-Arabian individuals as apt for breeding, it may provide a representative visual insight into the gene contribution of Spanish Purebred horses (PRE), given many of the dilution genes described in Há are not present in the Arabian Purebred breed (PRá). The lack of consideration of coat colour inheritance patterns by the entities in charge of individual registration and the dodging behaviour of breeders towards the historic banning policies, may have acted as a buffer for diversity loss (lower than 8%). Inbreeding levels ranged from 1.81% in smokey cream horses to 8.80 for white horses. Contextually, crossbred breeding may increase the likelihood for double dilute combinations to occur as denoted by the increased number of Há horses displaying Pearl coats (53 Há against 3 PRE and 0 PRá). Bans against certain coat colours and patterns may have prevented an appropriate registration of genealogical information from the 4th generation onwards for decades. This may have brought about the elongation of generation intervals. Breeder tastes may have returned to the formerly officially-recognised coat colours (Grey and Bay) and Chestnut/Sorrel. However, coat colour conditioning effects must be evaluated timely for relatively short specific periods, as these may describe cyclic patterns already described in owners' and breeders' tastes over the centuries.

Keywords: Arabian purebred horse; Spanish purebred horse; coat colour; composite breed; genetic diversity.

Figure 1

Evolution of birth number and coat distribution across breeds in the historic population of Arabian and Spanish Purebred and Hispano-Arabian horses from 1900 to 2019.

Figure 2

Coat colour subgroups, sample size historic and current distribution. Coat colours are displayed in increasing order from left to right in the legend, and from bottom to top in graphic form depending on their relative frequency.

Figure 3

Coat colour subgroups sample size distribution across breeds (Spanish and Arabian Purebred and Hispano-Arabian horse breeds). Colours listed in table legend from top to bottom are presented in graphic from left to right.

Figure 4

Historic and current pedigree completeness indices (1st, 2nd, 3rd, 4th and 5th generation) across coat colour subgroups.

Figure 5

Average generational intervals and mean age of the parents at the birth of their offspring (years) across coat colour subgroups.

Figure 6

Distribution of nonrandom mating degree (α), inbreeding rate (F), coancestry (C) and Genetic Conservation Index (GCI) across coat colour subgroups for the Arabian and Spanish Purebred and Hispano-Arabian horses. The graphic should be interpreted as a bird’s-eye view.

Figure 7

Biyearly evolution of average inbreeding (F) from 1900 to 2019 across coat colours subgroups in the Arabian (PRá) and Spanish Purebred (PRE) and Hispano-Arabian (Há) horse breeds.

Figure 8

Cladogram constructed from Nei’s genetic distances among coat colour subgroups.