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.

Breeding programmes to improve male reproductive performance and efficiency of insemination dose production in paternal lines: feasibility and limitations

“…The first studies showed that fertility and prolificacy after natural mating had an almost null male contribution (Piles et al, 2005;Piles et al, 2006). Results from following studies confirmed a similar effect when AI is performed at high sperm dosage (Tusell et al, 2010). Tusell et al (2010) indicated that these conditions of AI are not optimal for detecting individual variation among males, probably because the number and quality of sperm at mating time of most of the males exceeds the threshold needed to reach fertility (Amann and Hammerstedt, 2002).…”

“…Results from following studies confirmed a similar effect when AI is performed at high sperm dosage (Tusell et al, 2010). Tusell et al (2010) indicated that these conditions of AI are not optimal for detecting individual variation among males, probably because the number and quality of sperm at mating time of most of the males exceeds the threshold needed to reach fertility (Amann and Hammerstedt, 2002). Thus, although differences among males that are independent on sperm dosage are maintained, differences among males that can, at least in part, be overcome by increasing the amount of sperm are not detected (Saacke et al, 2000).…”

“…The genetic correlation between the female and male contributions to fertility has been found to be moderate to high and positive in a maternal line and a paternal line of rabbits (Piles et al, 2005;Tusell et al, 2010;David et al, 2011;Piles and Tusell, 2012), which indicates that selection for the contribution to fertility of one of the sexes, if successful, could have a favourable correlated response in the contribution to the same trait of the other sex. This correlated response could be responsible, at least in part, for the observed differences in semen quality traits among bucks from maternal and paternal lines (Vicente et al, 2000).…”

“…conditions and duration of dose storage, female physiological status and environmental conditions on the farm, could also lead to an interaction with the male genotype. By using the character state model (Falconer, 1952), Tusell et al (2010) demonstrated that male contributions to fertility and litter size after AI were low, but higher in magnitude than those obtained after natural mating. They found that there could be an interaction between the male genotype and AI conditions, and postulate that it would be possible to find the conditions that give the maximum genetic progress to optimise the breeding programme for male fertility and prolificacy under given conditions of semen utilisation.…”

Relationships between rabbit semen characteristics and fertilising ability after insemination

“…Moreover, spectrophotometry cannot be used because of the highly variable number of semen particles that interact with sperms for light absorption. Considering the number of motile sperms per dose, it appears that, contrary to fertility, the optimal number of motile sperms for prolificacy falls into the intermediate class (16.7 to 26.7 10 6 spz/ml), which seems to be in agreement with Tussel et al (2010). This could possibly imply that a high number of sperms could have a detrimental effect on prolificacy.…”