49 USE OF DILUTION OF CRYOPRESERVED SEMEN IN FIXED-TIME ARTIFICIAL INSEMINATION OF MANGALARGA MARCHADOR MARES

Abstract

Equine AI with frozen semen has become more frequent in reproduction centers, but osmotic shock during thawing is still a major problem as it impairs gamete viability and fertility. To overcome this, multi ultrasonographic (US) exams must be performed to ensure AI at the closest time to ovulation possible. The objective was to evaluate, in vivo, the effects of dilution of the cryoprotectant dimethylphormamide on the success of a fixed timed (20 h post-ovulation) AI protocol, in an attempt to reduce osmotic shock and the intense labour usually required during equine AI with frozen semen. Thirty-five Mangalarga Marchador mares were used in this trial. When dominant follicles reached at least 35 mm in diameter, ovulation was induced with 6 mg of equine gonadotrophin extract (EGE) intravenously. Artificial insemination was performed 20 h after ovulation according to 1 of the following protocols: no dilution (n = 14): three 0.5-mL straws were thawed and the semen deposited by a flexible rod at the uterine tip in the ipsilateral horn where the pre-ovulatory follicle was detected; or dilution (n = 21): three 0.5-mL straws were thawed as described and centrifuged after addition of 1.5 mL of BotuSêmen® extender (1:1 dilution). Pregnancy rates were evaluated between treatments, age and presence of intrauterine liquid (IUL) classes and period between ovulation and AI. Data were analysed as a binomial distribution with the GENMOD procedure (SAS, Cary, NC, USA). Pregnancy rate was higher (P < 0.05) for mares inseminated with diluted semen (42.9%) compared to those inseminated with no semen dilution (4.8%). Age and IUL class did not influence pregnancy rates. It can be concluded that reduction of osmotic stress through the dilution of cryopreserved equine semen increased pregnancy rates after AI. Semen dilution, as tested in this trial, yielded good pregnancy rates in a fixed-time AI protocol in mares, simplified mare management greatly and allowed the use of a fixed-time protocol successfully. Supported by CNPQ, CAPES.