Reproductive Performance of Tunisian Arabian Stallions: A Study on the Variance and Estimation of Heritability

SIMPLE SUMMARY: Stallion fertility is a vast subject, with a wide array of factors that can impact reproductive performance in either positive or negative ways. To better valorize horses’ genetic resources and understand the factors affecting variations in stallion fertility per cycle and end-of-season fertility, we have performed a statistical analysis study on some breeding factors: year of breeding, stud farm, age of the stallion, number of covered mares per stallion, reproduction methods, and age of the mare using 94 purebred Arabian stallions in four different regions of Tunisia. The pertinent results are: Sidi Thabet’s stud farm contained the highest number of purebred Arabian stallions. The majority of stallions were between 15 and 21 years old and had covered 1 to 20 mares; 95.19% of the stallions were used in natural mating. Depending on the year and stud, there was a variation in the fertility per cycle and end-of-season fertility of the stallions. The use of artificial insemination with fresh semen showed a high average value for fertility per cycle and end-of-season fertility. The used statistical model showed that the breeding year, the stud, the age of the stallion, the number of covered mares by stallions, and the method of reproduction significantly affected both fertility per cycle and end-of-season fertility (with p = 0.001). Moderate to high heritability estimations for fertility per cycle (h(s)(2) = 0.08) and end-of-season fertility (h(es)(2) = 0.36) were obtained. Identification of the stallion fertility variations based on different breeding factors is useful to improve the stallion’s reproductive efficiency, to help the breeders to make the most relevant choices before the beginning of the breeding season, and to have better profitability and the sustainable use of their animals. ABSTRACT: A consistently high level of stallion fertility plays an economically important role in modern horse breeding. To better understand the factors affecting variation in stallion fertility, we have performed a statistical analysis study on some breeding factors: year of breeding, stud farm, age of the stallion, number of covered mares per stallion, reproduction methods, and age of the mare. This work was conducted on 94 purebred Arabian stallions in four different regions of Tunisia. The results showed an increase in the number of stallions during the study period, ranging from 11.33% in 2011 to 13.29% in 2018. Sidi Thabet’s stud farm contained the highest number of purebred Arabian stallions. The majority of stallions were between 15 and 21 years old and had covered 1 to 20 mares; 95.19% of stallions were used in natural mating (Nat); 50.36% had low fertility, 17.69% had medium fertility, and 32.3% had excellent fertility according to fertility standards. Depending on the year and stud, there was a variation in fertility per cycle (FERPCE) and end-of-season fertility (FERPSE) of the stallions. The highest average FERPCE and FERPSE values were obtained using artificial insemination with fresh semen (AIF). Analysis of FERPCE and FERPSE showed that the model used in our study explained 40.21% of total variability observations for FERPCE and 42.1% for FERPSE. The used statistical model showed that the breeding year, the stud, the age of the stallion, the number of covered mares by stallions and the method of reproduction significantly affected both FERPCE and FERPSE (with p = 0.001). Low to moderate heritability estimations for FERPCE (h(s)(2) = 0.08) and FERPSE (h(es)(2) = 0.36) were obtained.