فایل ورد کامل امکان پذیری انتخاب برای سهم مرد در زنده ماندن جنین به عنوان راهی برای بهبود عملکرد تولید مثل نر و کیفیت مایع منی در خرگوش ها

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تعداد صفحات این فایل: ۱۲ صفحه

بخشی از مقاله انگلیسیعنوان انگلیسی:Feasibility of selection for male contribution to embryo survival as a way of improving male reproductive performance and semen quality in rabbits~~en~~

Abstract

The objective of this research was assess the male contribution to the number of implanted embryos (IE) and embryo survival (ES) estimated as the rate of variance due to male genetic and permanent environmental effects regarding total variance. In prolific species, the number of embryos and ES at early stages of gestation could be considered as fertility measurements because it indicates the number and rate of fertilized ova which are able to initiate the embryo development. Analyzed traits were ovulation rate (OR) estimated as the number of corpora lutea in both ovaries, IE estimated as the number of implantation sites, and ES calculated as IE/OR. A total of 1477 records from 900 females were used to analyze OR, whereas 1081 records from 855 females and 201 males were used to analyze IE and ES. The number of animals in the pedigree was 1107. The model included the systematic effects of year-season, parity order, lactation, and the random effects of additive genetics and permanent environmental effects due to the female (for OR) or both sexes (for IE and ES). Gibbs sampling was used to estimate posterior distributions of model parameters. The heritabilities of the male contribution to IE and ES were low (0.05 [0.01, 0.10] and 0.07 [0.02, 0.12]) but these estimates are probably biased downward since laparoscopy was only performed on those does that were pregnant at d 12 of gestation, instead of on all mated does. The genetic correlations between all analyzed traits and also between male and female genetic components of IE and ES were inaccurate, and it was not possible to draw any conclusion about them. The proportion of variation due to the male nonadditive genetic plus permanent environmental effects for IE and ES was almost negligible (0.027 [0.001, 0.058] and 0.031 [0.002, 0.068] for IE and ES, respectively), being the repeatability for male contribution on IE and ES around 8 and 10%, respectively

۱ Introduction

In recent years, the use of artificial insemination (AI) in rabbit commercial farms has become a common practice. Bucks from paternal lines used for AI not only must have good characteristics of growth and feed efficiency, but also high fertility, seminal production, and quality. Accordingly, traits related to AI efficiency, including both ejaculate and semen characteristics and male contribution to fertility and prolificacy, have acquired importance.

Increasing the production of fertile doses through improving some of its components (i.e., traits involved in semen production and quality) requires establishing the set of seminal characteristics to be measured and the optimal levels of those traits. In addition, measurement of these laboratorial markers is usually expensive and laborious, which make them inappropriate as selection criteria. As fertility and prolificacy are consequence of both male and female effects plus the interaction between them, a better alternative could be improving male contribution to fertility and prolificacy, since both traits depend strongly on semen quality (Foote, 2003). Few studies have focused on the feasibility of this kind of selection to improve AI efficiency. First studies performed in rabbit species showed that male contributions to fertility (Piles et al., 2005), or to prolificacy (Piles et al., 2006) were almost null after natural mating. Similar results were found when AI was performed with fresh semen (Tusell et al., 2011). The low male contribution (i.e., male genetic and permanent environmental effects) to prolificacy measured at birth is due mainly to the fact that litter size depends on female contribution and gestational environmental effects. However, failures of fertilization or embryogenesis due to male effect are important before implantation (Saacke et al., 2000), whereas they are masked at later stages of gestation when male is not involved in any biological process. Consequently, male effects on fertility and prolificacy are expected to be better observed at early stages of gestation.

We postulate that male reproductive performance and semen quality could be improved by selecting for male contribution to embryo survival (ES), which is defined in rabbit as survival from ovulation to implantation at d 7 of gestation (Mocé et al., 2010). The aim of this research was to assess male contribution to the number of implanted embryos (IE) and ES to confirm or reject this hypothesis.

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