Aplicações e limites dos testes de Integridade Acrossômica e Reação Acrossômica Induzida por heparina para touros da raça Nelore

The aim of this study was to evaluate the performance and variability of the results of functional tests for assessing acrosome integrity and heparin-induced acrosome reaction (IAR) in young Nellore bulls, as well as to verify their associations with other andrological parameters. Smears were prepared from 16 frozen semen samples of young Nellore bulls and stained with Trypan blue/Giemsa. The overall average post-freezing acrosome integrity was 85 ± 6%, with a reduction to 76 ± 8% after 4 hours of incubation and no large variation between bulls. Marked differences between bulls of the experiment were observed for the heparin IAR tests, with an average of 18 ± 9% (range 44% to 3%). The results suggest that both heparin and heparin + lysophosphatidylcholine were efficient inducers  that should be used together in IAR evaluations. Comparison of the different andrological parameters between bulls with high and low IAR showed a difference (p<0.05) only for pre-freezing motility, with superior results for low IAR bulls (≤ 17%). There were no correlations between the andrological parameters and functional tests of sperm quality (acrosome integrity and IAR). Only pre-freezing sperm motility was negatively correlated with IAR (–0.51, p<0.05). In conclusion, the acrosome integrity and IAR tests are important complementary tests to evaluate the functional quality of sperm since they exhibit high variability between bulls and low association with other andrological parameters. However, the tests should be interpreted within the limits of evaluation of the processes associated with sperm quality and not as a broad indicator of bull fertility or reproductive capacity.