Sire x stud interaction for body measurement traits in Spanish Purebred horses.

The research investigates how the interaction of stallion and stud (the environment in which the horse is bred) affects certain physical traits in Spanish Purebred horses. These traits include body measurements such as height, length, and circumference of certain body parts. The study found that including this interaction in genetic models for horse breeding brings about more realistic results and may therefore be advisable in horse breeding policies.

Research Objective and Context

• The study aimed to assess the implications of including sire x stud (ss) interaction – the performance of the same or closely related stallions across different breeding environments – in genetic parameter estimation models for traits expected to be selected in breeding. This was carried out using eight body measurements of Spanish Purebred (Andalusian) horses. The need for this research is emphasized by the fact that there have been no prior studies analyzing the influence of ss interaction on the estimation of genetic parameters in horses.

Research Methods and Data

• A large sample of body measurements from 11,894 horses was analyzed. The traits measured were height at withers, height at chest, leg length, body length, width of chest, heart girth circumference, knee perimeter, and cannon bone circumference.
• Genetic parameters and estimated breeding values (EBV) were calculated using animal models by Restricted Maximum Likelihood Estimation (REML), with and without the inclusion of ss interaction.

Research Findings

• The inclusion of the ss interaction in the model gave reduced estimates of trait heritability.
• When the ss interaction was included in the model, the genetic correlations estimated were generally greater than those obtained using the simpler model.
• The variation explained by the ss interaction as a proportion of the total phenotypic variance ranged from 0.02 (for height at withers) to 0.11 (for width of chest).
• The correlations in body measurement traits associated with the ss interaction were positive, significant, and ranged from moderate to low.
• The range of EBV estimated using the model including the ss interaction decreased compared to those estimated using the simpler model, and the rank order of the EBV was affected.
• The models incorporating the ss interaction were found to fit the data significantly better than the simpler model.

Research Implications

• The results of the study suggest that the ss interaction significantly affects the estimation of genetic parameters relating to horse body measurements. This interaction could be due to selective breeding or management practices that create greater similarity between offspring from the same sire within a stud.
• Therefore, it is advisable to include the ss interaction in genetic models used in horse breeding schemes as they could provide a more realistic estimation.
• This research contributes significantly to the field of animal breeding research and suggests improvements for breeding policies in terms of considering environmental interactions in genetic parameter estimations.