22 IN VITRO FERTILITY ESTIMATES USING SPERM KINETICS VARIABLES AND CONCEPTION RATES IN BEEF HEIFERS

Abstract

Sperm motility is a physical parameter evaluated in semen samples of the bull and is thought to be related to the fertility in the male. Despite being a characteristic of simple and fast evaluation, motility estimates involve subjective components when analyzed by light microscopy (LM) that might restrain their evaluation in some conditions. Moreover, in some species, poor correlations were observed between spermatozoa motility and semen fertility. The incidence of coherent light in a semen sample generates a phenomenon called biospeckle (BSL) that is capable of measuring the kinetics activity of the spermatozoa. In this work the relationship among sperm kinetics variables evaluated by LM and BSL and conception rates in beef heifers was investigated, with the purpose to predict frozen semen fertility when laser light is used. Sixty semen samples of 6 mature AI donor bulls (Bos taurus indicus) herein named A, B, C, D, E, and F were thawed at 37°C for 30 s in a water bath and evaluated by LM and BSL. In LM evaluation, an index (IND) was proposed to group together, in a single mean estimate, the spermatozoa motility (M: % scale) and velocity (V: 1 to 5 scale) according to the equation IND = [V × 20 + M]/2. In the BSL evaluation, each sample was illuminated (n = 10 per bull) by a laser beam (He-Ne, 632 nm and 10 MW) for 40 s and a mean inertial moment (IM) was obtained for each donor bull. These semen samples were used in an AI program of beef heifers (n = 166) clinically examined for reproductive health, body condition, and weight. Pregnancy diagnosis was done by ultrasound images (Falco 100, 6 MHz, Pie Medical, Crawley, UK) 28 days after insemination. Fertility estimates were done by the generalized linear model using logistic regression (stepwise methodology), generating an equation to predict the conception rate of the semen, the variables of which were IM and IND. Results of the predicted conception rates (pCR) using IM and IND and the observed conception rates (oCR) were A (0.5490; 0.57), B (0.6483; 0.68), C (0.7108; 0.71), D (0.4552; 0.28), E (0.4797; 0.54), F (0.3825; 0.47), respectively. Positive correlations (P < 0.05) were observed between pCR and oCR (r = 0.79) showing a similar behavior between in vitro and in vivo estimates. Results of this work showed that there is a high correlation between spermatozoa kinetics and semen fertility in the bull and that BSL motility analysis could be used as an approach to evaluate the fertility of semen samples.

Financial support: FAPEMIG grant EDT 94/07, CNPq.