Effect of sperm concentration and incubation period of oocyte-spermatozoa on in vitro fertilization in the Gir breed

Abstract

This research evaluated the effect of sperm concentrations and incubation periods among oocyte-spermatozoa on in vitro fertilization with semen of Gir bulls (Bos indicus). In vitro matured oocytes were fertilized with sperm of two bulls, on concentrations of 1, 2 or 4x10⁶ spermatozoa/mL during 12 or 18 hours of incubation, and evaluated the fertilization and polyspermy rate as well as cleavage on 72 hours and blastocyst on eighth day post-fertilization. A second experiment evaluated the effect of concentrations of 1, 2 or 4x10⁶ spermatozoa/mL for 18 hours using sperm of three bulls individually, as well as the effect of 12 and 18 hours of incubation in a concentration of 1 to 2x10⁶ spermatozoa/mL. It was observed an increase (P < 0.05) on polyspermy when the concentration was 4x10⁶ spermatozoa/mL and that the association of this concentration with 18 hours increased (P < 0.05) cleavage rate. The second experiment verified that the increase of incubation period improved (P < 0.05) cleavage rate of one bull, and that when compared among themselves the bulls sperm resulted in different (P < 0.05) cleavage and blastocyst rate in the same concentration or incubation period. The results showed that polyspermy is the main effect of sperm concentration increase and that the efficiency among bulls on in vitro fertilization is dependent on concentration and incubation period.