EVOLUTION AFTER FOUR YEARS OF BREEDING SOUNDNESS EVALUATION (BSE) IN NELLORE ZEBU BULLS AND ASSESSMENT OF THE RELATIONSHIP WITH FERTILITY IN A BREEDING SEASON

Abstract

We studied the evolution and the relationship between the fertility of a cow herd and the breeding soundness evaluation (BSE). During four years, 1092 Nellore zebu bulls were maintained on pasture conditions in Mato Grosso do Sul State – Brazil. After the clinic evaluation, scrotal circumference was measured and semen was collected by electro ejaculation and analyzed for physical and morphological aspects. Scores for CAP were established by sperm progressive motility (MOT), sperm morphology (MORF), and scrotal circumference (PEP). Modifications to original BSE were established by sperm concentration, sperm motility intensity, and testicles morphology. During the breeding season, 157 bulls were chosen from a-c BSE score. Fifteen reproductive groups of bulls were established randomly among three groups of females (Nellore zebu heifers, first-calf cows, mature cows, and first-calf cross-bred cows). After four years of observations, there was a significant increase in BSE varying, respectively, from 59.5 to 79.0 in 1994 to 1997. The BSE scores PEP, MOT and MORF increased in the period from 17.5, 12.7, and 29.3 to 30.1, 14.8, and 34.4, respectively. Correlations were observed among the BSE components with the year and the studied reproductive characteristics. There was a significant increase of bulls in the BSE categories 'a' and 'b' of 9.0% and 46.9% vs. 43.5% and 44.8%, respectively. The data of 1997 breeding season were: 82.0 ± 13.2 points and 83.1 ± 8.4% for BSE and pregnancy rate, respectively. There was a relationship (P <0.001) between BSE and pregnancy rate (r=0.25). The Breeding Soundness Evaluations (BSE) showed a positive correlation with the pregnancy rate in a herd with different categories of females. The use of 'a' and 'b' BSE bull groups is compatible with the high fertility potential of the herd. The ratio bull:cow used underestimates the reproductive potential of the bulls’ fertility. The technique used was important to evaluate the group potential fertility and to modify the reproductive characteristics of bulls herd. 
Keywords: breeding soundness evaluation; cattle; pregnancy rate; sperm morphology.