The objectives of this study were to evaluate the effects of two levels of concentrate and lipids in the diets on the testosterone serum concentration of Zebu bulls, as well as the daily-nightly recurrent behavior of the referred hormone. Sixteen Zebu bulls were allotted to four treatments during 90 days of experimental period: T1 (high concentrate and high lipid), T2 (high concentrate and low lipid), T3 (low concentrate and high lipid), and T4 (low concentrate and low lipid). The diets were formulated to be isoproteics and the forage to concentrate ratio was 45:55% (T1 and T2) and 80:20 % (T3 and T4). Blood samples were collected from 15 to 15 days at fixed intervals of four hours, during 24 hours, to determine the testosterone serum concentration. The intake of dry matter, ether extract, and crude protein was greater for the animals fed diets with high level of concentrate and smaller for the animals fed diets with low concentrate levels. The neutral detergent fiber (NDF) and ether extract intake were greater in the animals fed diets with low level of concentrate and high level of lipid, respectively. Serum testosterone concentration were not affected by the different concentrate and lipid levels in the diets and ranged from .1 to 9.0 ng/mL, with average of 1.24 ng/mL. There was a difference in the serum testosterone concentration in relation to the observed collection time, being the collection times of 4:30 p.m. and 00:30 a.m. presenting the highest serum testosterone concentration in relation to the 4:30 and 12:30 h, and it did not differ from the others collection times, however, it was not characterized as a surge.
concentrate; lipid; testosterone; Zebu bulls
