The effect of time evaluation of bull libido on sexual behavior and the bull breeding activity for different bull:cow proportions were studied. Correlations between libido and scrotal circumference and sperm quality were estimated. Twenty selected bulls based on andrologic evaluation and on libido test were randomly allotted to four treatments in the following bull:cow proportions: T1= 1:25; T2= 1:50; T3= 1:75; and T4= 1:100. The increase in the time of the libido test from 10 to 15min reduced the percentage of bulls classified as questionable and good libido, and increased the percentage of bulls with very good and excellent libido. Ten minutes of libido test negatively affected sexual activity of the bulls. Out of 1250 cows from all treatments, 738 (59.0%) were marked, according to the following numbers: by one bull, 624 cows (84.5%), by two bulls, 112 cows (15.2%) and by three bulls, 2 cows (0.3%), suggesting that in a natural multibull breeding 45-day-season-system most of the cows are mated by only one bull. The estimated correlations between libido and sperm quality and scrotal circumference were low.
zebu; bull; fertility; libido; sexual behavior
