Hypoosmotic swelling test in young Nelore bulls classified as sound and unsound for breeding

This work aimed to study the correlations between the physical characteristics of semen, sperm morphology and the biochemical integrity of the plasmatic membrane of raw sperm in young Nelore bulls (Bos taurus indicus). A total of 420 bulls between 18 and 22 months of age were examined for breeding soundness according to the criteria established by the Brazilian College of Animal Reproduction. After physical and morphological evaluation, semen was tested with a hypoosmotic test. To accomplish this, 10 μl of fresh semen was incubated in 1 ml of hypoosmotic solution (150 mOsm/kg) for 60 min at 37°C. After the breeding soundness evaluation, 83% (350/420) of the bulls were classified as sound for breeding. There were no significant differences between the mean testicular biometry, scrotal circumference and the percentage of spermatozoa reactive to the hypoosmotic test (43.9 ± 21.1% vs. 43.6 ± 19.3%) in bulls classified as sound and unsound for breeding (P > 0.05), although there were significant differences between the averages for all physical and morphological aspects of the sperm between the two groups (P < 0.05). The hypoosmotic test did not correlate with the main characteristics of semen quality (P > 0.05). In this study, the hypoosmotic test was not an efficient predictor of the reproductive potential of young Nelore bulls.