Interaction of genotype × artificial insemination conditions for male effect on fertility and prolificacy1

Abstract

Failures in fertilization or embryogenesis have been shown to be partly the result of poor semen quality. When AI is practiced, fertilization rate depends on the number and quality of spermatozoa in the insemination dose around the time of application. Individual variation in the male effect on fertility (success or failure to conceive; Fert) and prolificacy (total number of kids born per litter; TB) could also depend on these factors, and it could be better observed under limited conditions of AI, such as decreased sperm concentration, small or null preselection of ejaculates for any semen quality trait, or a long storage period of the AI doses. The aim of this research was to determine if an interaction existed between male genotype and the AI conditions for male effects on Fert and TB after AI was performed under different conditions. Fertility and TB were assumed to be different traits and were analyzed in 2 sets of independent analyses. In the first step, the different conditions were determined uniquely by the sperm dosage. Artificial insemination was performed at 10 and 40 × 10(6) spermatozoa/mL. In the second step, the different conditions were determined by all the factors involved in the AI process as a whole (conditions and duration of the storage period of the dose, genetic type of the female, and environmental conditions on the farm). Data from AI from the former experiment were analyzed with data from AI performed under different conditions. Threshold and linear 2-trait models were assumed for Fert and TB, respectively. The sperm dosage had a clear effect on Fert and TB, which favored the greater dosage (+0.13% and +1.25 kids born, respectively). Prolificacy was more sensitive to sperm reduction than was fertility. Male heritabilities for Fert were 0.09 for both sperm dosages, and were 0.08 and 0.06 for male TB with a smaller and larger sperm dosage, respectively. No genotype × sperm dosage interaction was found. Therefore, the same response to selection to improve male Fert and TB could be achieved at any sperm concentration. However, an interaction between male genotype and the AI conditions as a whole seemed to exist, indicating that the AI conditions for selection for Fert and TB could be modified to maximize genetic progress. Consequently, the optimization of a breeding program for male Fert and TB under a given set of semen utilization conditions is achievable.