26 SPERM MOTILITY DECREASING AND SEMEN FERTILITY IN THE BULL EVALUATED BY BIOSPECKLE

Abstract

Sperm motility decreasing in a semen sample over time is an indirect approach to assess spermatozoa viability and should be related to the ejaculate fertility. The biospeckle (BSL) is an interacting phenomenon between laser light and biological specimens that allows measurement of sperm kinetic activity by means of an index called the inertial moment (IM). The aim of this work was to evaluate sperm motility diminishing in frozen bovine semen with BSL and analyze semen fertility in relation to the motility decreasing behavior patterns showed by different semen samples. Fertility was assessed by beef heifer conception rates after AI. Semen of 6 mature IA donor bulls (Bos taurus indicus) was previously divided in 2 groups (group I: motility ≥50%; group II: motility <50%), each group comprised 3 animals. Semen was thawed at 37°C for 30 sin a water bath. One aliquot of 10 μL was placed in a warmed slide, covered with a slip, and evaluated by light microscopy and BSL just after thawing. Then, samples were kept at room temperature to induce a decrease in sperm motility. Each sample was illuminated 6 times by laser light at intervals of 2 min (n = 36) and IM values were obtained. The semen samples were used in an AI program of beef heifers (n = 166) under the same nutrition and management conditions. All inseminations were done by the same technician, and donor bulls were used consecutively throughout the breeding season. Pregnancy diagnosis was done by ultrasound images (Falco 100, 6 MHz, Pie Medical, Crawley, UK) 28 days after insemination. The SISVAR software was used in variance analysis and comparison of means by the Tukey test. Group I showed greater (P < 0.05) IM mean value (153.5 ± 27.48) compared with group II (107.94 ± 30.61), which means that this group had higher sperm motility during the time of evaluation. In addition, conception rates (0.63 ± 0.49) for group I were also higher (P < 0.05) compared with group II. Apparently semen fertility is related to the sperm kinetics measured by the IM. Mean IM values (134.0 ± 22.65 and 96 ± 22.34, groups I and II, respectively) obtained in the last illumination for each group did not differ (P > 0.05), but a tendency to differ was observed when a greater number of illuminations was done. Our data suggest that the BSL was capable of identifying spermatozoa surviving between high and low motility groups, and the sperm motility decreasing measured by the IM might be an objective approach to evaluate semen fertilization potential.

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