Uso de diluição seriada de sêmen criopreservado na inseminação artificial em tempo fixo de éguas mangalarga marchador

Abstract

Equine artificial insemination with frozen semen has become more frequent and research is being undertaken to improve its results. The objective was to evaluate in vivo the effects of a serial dilution of the cryprotector "dimethylphormamide" on the success of the 20 hour (post ovulation) fixed time- artificial insemination protocol in Mangalarga Marchador mares. Diluted (n=14) and non diluted (n=21) frozen thawed-semen were tested. Pregnancy rates were evaluated between the treatments, the age classes, period between ovulation and insemination and presence or not of intra-uterine liquid, as evaluated by ultra-sonography. Data were analyzed as a binomial distribution after logit transformed according to the GENMOD (SAS, Cary-NC, EUA) procedure. Pregnancy rate was higher (P<0.05) for mares inseminated with diluted semen (42.9%) compared to those inseminated according to the conventional methodology (4.8%), with no semen dilution. Mares which ovulated until 16 hours after the AI showed higher pregnancy (33.3%) than mares ovulating afterwards (5.9%). Age did not influence pregnancy rates. It can be concluded that the reduction of the osmotic stress through the serial dilution of cryopreserved equine semen increases pregnancy rates. Moreover, a time interval between AI and ovulation equal to or bellow 16 hours was a determinant factor to improve pregnancy. Artificial insemination with lower spermatozoa and cryoprotector concentrations are less harmful to the reproductive tract of mares.