Genetic parameters of rabbit semen traits and male fertilising ability

This study aimed to estimate genetic parameters for rabbit semen production, semen characteristics and fertilising ability following artificial insemination. It involved five successive batches of 30-36 bucks each, 22 weeks of semen collection, and 11 weeks of semen recording per batch. Semen analyses were based on 2312 ejaculates. A total of 2019 inseminations were performed on 674 females with semen from 236 ejaculates from 128 bucks. Heritability estimates of semen traits ranged from 0.05 to 0.18. At approximately 0.05-0.06 for pH, volume and mass motility, they were higher for concentration (0.10) and the total number of sperms per ejaculate (0.12), and even higher for motility traits based on computer-assisted semen analysis. The percentage of motile sperms had the highest heritability (0.18) and appeared to be a good candidate criterion to select for both sperm number and motility. The heritability estimates were close to zero for all three criteria of fertilising ability: fertility (F), prolificacy (live births, LB) and their product (LB per insemination). A permanent environmental effect of the male seemed to be higher for LB (0.04) than for F (0.01). The rabbit does accounted for approximately 10% of the variance of the three criteria. With respect to the female, the male contribution was negligible for fertility and in a ratio of 4-10 for the number of live births. In our experimental conditions, prolificacy would thus be more highly influenced by the buck than fertility.

Mass sperm motility is associated with fertility in sheep

The study was to focus on the relationship between wave motion (mass sperm motility, measured by a mass sperm motility score, manually assessed by artificial insemination (AI) center operators) and fertility in male sheep. A dataset of 711,562 artificial inseminations performed in seven breeds by five French AI centers during the 2001-2005 time period was used for the analysis. Factors influencing the outcome of the insemination, which is a binary response observed at lambing of either success (1) or failure (0), were studied using a joint model within each breed and AI center (eight separate analyses). The joint model is a multivariate model where all information related to the female, the male and the insemination process were included to improve the estimation of the factor effects. Results were consistent for all analyses. The male factors affecting AI results were the age of the ram and the mass motility. After correction for the other factors of variation, the lambing rate increased quasi linearly from three to more than ten points with the mass sperm motility score depending on the breed and the AI center. The consistency of the relationship for all breeds indicated that mass sperm motility is predictive of the fertility resulting when sperm are used from a specific ejaculate. Nonetheless, predictability could be improved if an objective measurement of mass sperm motility were available as a substitute for the subjective scoring currently in use in AI centers.

Using the product threshold model for estimating separately the effect of temperature on male and female fertility

Animals under environmental thermal stress conditions have reduced fertility due to impairment of some mechanisms involved in their reproductive performance that are different in males and females. As a consequence, the most sensitive periods of time and the magnitude of effect of temperature on fertility can differ between sexes. The objective of this study was to estimate separately the effect of temperature in different periods around the insemination time on male and on female fertility by using the product threshold model. This model assumes that an observed reproduction outcome is the result of the product of 2 unobserved variables corresponding to the unobserved fertilities of the 2 individuals involved in the mating. A total of 7,625 AI records from rabbits belonging to a line selected for growth rate and indoor daily temperature records were used. The average maximum daily temperature and the proportion of days in which the maximum temperature was greater than 25°C were used as temperature descriptors. These descriptors were calculated for several periods around the day of AI. In the case of males, 4 periods of time covered different stages of the spermatogenesis, the transit through the epididymus of the sperm, and the day of AI. For females, 5 periods of time covered the phases of preovulatory follicular maturation including day of AI and ovulation, fertilization and peri-implantational stage of the embryos, embryonic and early fetal periods of gestation, and finally, late gestation until birth. The effect of the different temperature descriptors was estimated in the corresponding male and female liabilities in a set of threshold product models. The temperature of the day of AI seems to be the most relevant temperature descriptor affecting male fertility because greater temperature records on the day of AI caused a decrease in male fertility (-6% in male fertility rate with respect to thermoneutrality). Departures from the thermal zone in temperature descriptors covering several periods before AI until early gestation had a negative effect on female fertility, with the pre- and peri-implantational period of the embryos being especially sensitive (from -5 to -6% in female fertility rate with respect to thermoneutrality). The latest period of gestation was unaffected by the temperature. Overall, magnitude and persistency of the temperatures reached in the conditions of this study do not seem to be great enough to have a large effect on male and female rabbit fertility.