224 Unraveling inbreeding depression in Peruvian Paso horses: Implications for functional traits and genetic improvement strategies.

Abstract The Peruvian Paso Horse (PPH) is an equine breed native to Peru, renowned for its distinctive lateral ambling four-stroke gait and smooth, harmonious movement. Since 1947, the National Association of Breeders and Owners of Peruvian Paso Horses (ANCPCPP) has made significant efforts to conserve, selectively breed, and enhance the genetic quality of this breed. The unique smoothness and fluidity of PPH movement result from the interaction of specific biomechanical execution patterns during the gait cycle. However, the potential effects of inbreeding depression on key functional traits, including extension, overreach, term, and acuteness, remain unexplored. Assessing these effects is crucial for refining breeding strategies and ensuring sustainable genetic progress in the breed. This study aimed to estimate the impact of inbreeding depression on extension, overreach, term, and acuteness in PPH. A total of 137 animals (stallions and mares) were included in the analysis. Gait performance was recorded in MP4 video format (1920 × 1080 resolution at 60 frames per second), and each trait was measured three times per stride. The KINOVEA software (version 0.9.5) was used for kinematic analysis. Heritability estimates for each trait were obtained using a multivariate repeated measures animal model, implemented in WOMBAT software. To evaluate the effect of inbreeding on animal performance, a linear regression model was applied, with the evaluated traits as dependent variables and age, sex, breeder, speed, individual inbreeding coefficients, and the rate of inbreeding increase as independent variables. Additionally, a BLUP model was used to estimate breeding values (EBVs) by incorporating the effects of sex, breeder, speed, and age. EBV estimation was conducted using three models: (1) without the inclusion of any inbreeding coefficient, (2) incorporating the individual inbreeding coefficient, and (3) including the rate of inbreeding increase. To determine the association between EBVs with and without inbreeding effects, a Pearson correlation analysis was performed, comparing the top 20 and bottom 20 animals in terms of EBVs, and contrasting these values against EBVs estimated without inbreeding inclusion. The significance of the correlations was assessed using Fisher’s z-statistic, with a reference significance threshold of 99% correlation in all cases. The results, presented in Table 1, indicate a significant effect of inbreeding on acuteness performance, while extension, overreach, and acuteness exhibited significant correlations in EBV estimations. In conclusion, inbreeding depression was observed in several functional traits of the Peruvian Paso Horse, highlighting the necessity of incorporating inbreeding effects into selection programs to optimize genetic improvement and ensure the long-term viability of the breed.