Abstract: This study was designed to evaluate the relationship between testicular biometry and semen quality and determine the sexual maturity age of selected yearling Nellore bulls extensively raised in the Brazilian tropical savannah. Three hundred sixty-one bulls participating in a performance test were divided in age classes (17, 18, 19 and 20 months) and submitted to Breeding Soundness Evaluation (BSE). Measurements of Scrotal Circumference (SC), testicular length and testicular weight were used to study the testicular biometry including the calculation of Testicular Weight and Volume (TW, TV) by means of previously described formulas. Progressive sperm motility (MOT), sperm vigor, mass movement and sperm morphology (major, minor and total defects) were evaluated and results used to classify the bulls as apt (n = 202) or not apt (n = 159). SC ranged between 29.1 and 30.5 cm with differences for age classes (p<0.05). TW and TV increased with age from 198.4-327.2 g and 187.7-309.3 cm3, respectively with differences. MOT differed in all age classes (p<0.05). Proportion of major and minor sperm defects did not differ but there was a significance for tail defects between the age classes. There was a positive and moderate correlation between body weight and SC; a negative and moderate correlation with total sperm defects. The BSE was an effective tool to evaluate the bulls and the results permitted to conclude that selection of Nellore bulls raised under extensively conditions in the Brazilian tropical savannah can be indicated from 17 months of age.
M.A.O. Viu, C.U. Magnabosco, B.D. Oliveira Filho, D.T. Lopes, R.N.G. Porto, H.T. Ferraz and M.L. Gambarini, 2015. Testicular Biometry, Semen Quality and Sexual Maturity of Nellore Young Bulls Raised in the Brazilian Tropical Savannah. Journal of Animal and Veterinary Advances, 14: 144-150.