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

Abstract

This paper reviews the current genetic knowledge on issues related with the efficient use of bucks in artificial insemination (AI). Differences between lines have been found to be relevant in semen production and quality traits not necessarily related to their specialisation as maternal or paternal lines. Accurate heritability estimates indicate that genetic selection to increase semen production by improving male libido and/or reducing the number of rejected ejaculates may not be effective. However, total sperm produced per ejaculate appears to be an interesting trait to select for. Semen pH has shown low to medium heritability estimates and a low coefficient of variation, therefore it is not advisable to attempt improvement by direct selection. In general, sperm motility traits have shown low heritabilities, but the rate of motile sperms per ejaculate has been considered convenient to select for. Morphological characteristics of the spermatozoa have been revealed as medium to highly heritable. There is evidence of high genetic correlations between sperm traits before and after freezing-thawing. There are few studies regarding the estimation of heterosis of seminal traits, but results indicate important and favourable direct and maternal heterosis in crosses between maternal lines. However, this has not been confirmed in a cross between 2 paternal lines. Until now, attempts to find parametric or non-parametric functions to predict ejaculate fertility through seminal characteristics routinely recorded in evaluations have been very unsatisfactory. Hence, it may be necessary to find other semen quality markers or assess some of those currently used in a more precise manner, or closer to the AI time, in order to improve the ability to predict ejaculate fertility. Several seminal characteristics phenotypically correlated to male fertility could be considered as potential traits to select for in order to genetically improve this trait. However, only the semen pH has been checked for this purpose, and results show a low genetic correlation of this trait with male fertility. Other traits can be studied in the future, but bearing in mind that the required experiments will need a large number of bucks for an accurate estimation of the genetic correlation of the trait with male fertility. This means that these experiments will be expensive and difficult to set up. The most common criterion for selecting paternal lines, average daily gain, seems not to be genetically correlated to male fertility and seminal traits. Thus, selection for average daily gain has no detrimental consequences on these traits, and a multi-trait selection, including growth rate and seminal traits directly related to an efficient AI semen dose production, is feasible in paternal lines. The male contribution to fertility after natural mating and after AI with semen doses with high concentration is negligible, although it has been found that under more restrictive AI conditions male contributions to fertility and litter size are low, but high...

Relationships between rabbit semen characteristics and fertilising ability after insemination

“…In pigs, Broekhuijse et al (2011) obtained significant (P < 0.05) effects of progressive motility, curvilinear velocity and beat cross frequency on the farrowing rate. Although the presence of gel plugs in the semen is a major criterion for ejaculate rejection in some AI centres (Piles et al, 2013), our results revealed that this characteristic has no effect on either fertility or prolificacy. We did not find any information in the literature on this subject and this result therefore appears to be original.…”

“…In commercial rabbit farms, heterospermic pools that are prepared in rabbit insemination centres are usually used for insemination, whereas breeders practice homospermic inseminations for genetic improvement. In rabbit, it is generally assumed that the male contribution to fertility after AI with high-concentration semen doses is negligible (Piles, 2013), but it could be higher in more restrictive AI conditions. Studies of the relationships between semen characteristics and fertilising ability can be classified into two categories.…”

Can feed supplementation of the refined vegetable oils enhance the seminal quality of rabbit bucks (Oryctolagus cuniculus)?

“…This conclusion was actually based on the analytical findings of the seminal samples collected once a week from rabbit bucks fed on ration treated with soybean and sunflower oils. According to Castellini and Lattaioli (1999), estimating semen quality is important in determining the reproductive efficiency in rabbit bucks, where it has been documented to be correlated with sperm fertilizing ability (Castellini et al, 2000;Brun et al, 2002;Hagen et al, 2002;Castellini, 2007;Piles et al, 2013;Theau-Clément et al, 2016). The present data indicated that semen collected from rabbit bucks supplemented with vegetable oils had higher sperm concentration, total sperm output, percentage of motile sperms, as well as lower percentages of dead and altered acrosomal sperms than the control bucks.…”

Development of new artificial insemination extenders supplemented with GnRH analogues to induce ovulation and proteomic characterization of rabbit semen

“…With AI, the impact of reproductive performance (i.e. male contribution to fertility and prolificacy) of individual males is vital (Piles et al, 2013).…”

“…Many factors influence the production and quality of rabbit semen such as the genetic origin (growth lines have worse seminal qualities and fertility rates than maternal lines) , the season Theau-Clément et al, 2015), the photoperiod (Roca et al, 2005; and the collection frequency . The production of fertile doses is determined by several components: i) male libido and characteristics of the ejaculate which form part of the criterion for ejaculate rejection; ii) volume and sperm concentration of the ejaculate (determining the amount of doses that can be obtained); and iii) the quality of sperm (determining the minimum sperm dosage required to ensure fertilization) (Piles et al, 2013). Subjective estimation of motility and evaluation of sperm morphology are the two laboratory assays most widely used for the rabbit semen evaluation in insemination centers .…”