Differences between Belclare and Suffolk ewes in fertilization rate, embryo quality and accessory sperm number after cervical or laparoscopic artificial insemination

Department of Animal Science, Centre for Integrative Biology, Conway Institute for Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland.
Theriogenology (Impact Factor: 1.8). 04/2005; 63(7):1995-2005. DOI: 10.1016/j.theriogenology.2004.09.005
Source: PubMed


Ewe breed has been shown to have a major effect on pregnancy rates following cervical AI using frozen-thawed semen. The main objective of this study was to examine the differences between purebred Belclare and Suffolk ewes (multiparous) in fertilization rate, number of accessory sperm and stage of embryo development on day 6 after cervical or laparoscopic AI with frozen-thawed semen. In experiment 1, Belclare and Suffolk ewes were synchronized for 12 days and were either cervically inseminated (year 1: n=28 and 31; year 2: n=16 and 15, respectively) or laparoscopically inseminated (year 2: n=13 and 14). In experiment 2, superovulated Belclare (n=4) and Suffolk (n=13) ewes were laparoscopically inseminated. All ewes were slaughtered 6 days after AI; oocytes/embryos were recovered, morphologically graded and stained to assess the number of cells and accessory spermatozoa. Data from both experiments were combined for statistical analysis. The proportion of ewes with fertilized oocytes was significantly higher following laparoscopic AI compared with cervical AI (54% versus 19%). More Belclare than Suffolk ewes yielded fertilized oocyte(s) after cervical AI (34% versus 10%, P<0.02) but there was no difference after laparoscopic AI (62% versus 60%). From the ewes that yielded at least one fertilized oocyte the proportion of Belclare ewes with embryos at the morula/blastocyst stage was significantly greater than for Suffolk ewes (94% versus 59%, P<0.02). A higher proportion of Belclare than Suffolk ewes had evidence of sperm reaching the site of fertilization following cervical AI (39% versus 15%, P<0.02) but there was no difference after laparoscopic AI (62% versus 64%, P>0.8). Amongst the ewes with evidence of sperm at the site of fertilization, laparoscopic AI resulted in a higher number of sperm per oocyte/embryo or per ewe than cervical AI (P<0.01). These results suggested that the difference in pregnancy rate between Suffolk and Belclare ewes following cervical AI was due to: (i) sperm traversing the cervix and uterus in a higher proportion of Belclare than Suffolk ewes, leading to a higher incidence of fertilization and (ii) the lower developmental competence of fertilized oocytes from Suffolk ewes.

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Available from: Dimitrios Rizos
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    • "Artifi cial insemination is essential for the implementation of a sheep genetic improvement program to maximize progeny per ram and conduct evaluations of rams without compromising biosecurity (Hanrahan, 2003; Fair et al., 2005). The number of progeny is determined by total sperm output of the ram, number of sperm used per insemination, number of ewes lambing per insemination, and litter size. "
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    • "The morphology of the cervix is very variable, and differences between animals, during the cycle (Kershaw et al. 2005) and between breeds (Kaabi et al. 2006) have been reported. The differences in fertility reported between breeds of sheep after insemination with frozen–thawed semen might be related to differences in sperm transit in the genital tract of the ewe (Fair et al. 2005). The physiological study of sperm transit and quality in the female genital tract has to date been limited by the lack of techniques to observe the behavior of spermatozoa in the genital tract of the living female at a cellular level. "
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    • "Laparoscopy insemination with frozen-thawed semen gave better fertility results than transcervical or cervical IA (Anel et al. 2005; Fair et al. 2005). This method needs special and costly equipment and well qualified technicians (Paulenz et al. 2004; Fair et al. 2005). In UK, routine laparoscopic insemination of sheep with frozen-thawed semen is regulated (Baner 1995) for animal welfare reasons and not allowed in Norway and Sweden (Paulenz et al. 2004), where the prevailing AI technique is based on cervical insemination and is most conducted on a do it yourself basis (Paulenz et al. 2002). "
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