Sexual behavior, ponderal development and testicular and levels of testosterone in young bulls of the Nelore breed / Comportamento sexual, desenvolvimento ponderal e testicular e níveis de testosterona em tourinhos da raça Nelore

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The goal of the present study was to characterize the sexual behavior in young animals, verify its relationship with the libido in more advanced ages; and verify the relationship between the libido and the serum concentration of testosterone, testicular measurements and pondered development. 13 Nelore calves clinically normal, raised extensively, being followed from 3 to 10 months were used. The observations of the sexual behavior (libido testing) were done during the day (6 a.m. to 6 p.m.) coming to a total of twelve hours of evaluation. The pondered characteristics, the testicular measurements and the blood samples for the determination of the testosterone concentration were obtained monthly. There was a difference in body weight from three to six months of age (p <0.05), however, no difference was noticed between four and five months of age (p >0.05). During the post-weaning period there was no difference in body weight for the age groups of eight to tem months of age (p >0.05), and at the age of seven months, the average body weight showed an intermediate value, which did not differ form the one obtained on the eighth and ninth months (p >0.05). The smallest daily weight gain was observed from seven to nine months of age (p <0.05), with no difference happening between the recorded averages for this two stages of age (p >0.05), the highest values however were observed from 3 to 6 months of age (p <0.05), there was also no difference among these two (p >0.05). The average scrotal perimeter by age varied from 15.82 to 18.31cm measured on the third and tenth month of age respectively, with these numbers being considered adequate for animals before puberty and the scrotal perimeter presenting linear behavior according to the age (R2 = 0.47, p <0.01). A high relationship between age and body weight was observed (r = 0,89) and also of body weight and scrotal perimeter (r = 0.67), and a medium relationship was observed between age and the scrotal perimeter (r = 0.57). There were great oscillations in the frequency of animals that presented some physiological signs of behavior. At three months of age most calves (61.5%) presented the companion of females in the heat. At four and five months of age, there was a big decrease, with only two or three animals demonstrating this kind of behavior, and from the sixth until the tenth month of age none of the animals showed this kind of behavior. At nine months of age three animals demonstrated the physiological sign of companion of a female in heat. In the same way, there was a great decrease, due to the age, in the behavior characterized by smelling and licking the female in heats body. The physiological signs of the vulva smelling and licking and Flehmen reflex increased with the age, since at ten months old all animals seemed positive to this characteristic. As for the pre copulatory signs a great reduction was observed in the attempt of mount behavior and an increase was observed in the behavior of the attempt of mount as the animals got older, being that at tem months old 100% of the animals presented this physiological sign. The libido scores attributed to the animals from three to ten months old presented cubic behavior when related to the age (R2 = 0.27; p <0.0001), considering that in the last test the frequency of good and very good libido was of bigger. There was no difference in the testosterone concentration among the different age groups (p >0.05), with values below 1 ng/mL, and did not present correlation to the age, to the testicular measurements, libido and daily body weight gains (p >0.05). It was concluded that Nelore males can show sexual interest at early age, however the ways of showing it can vary and they do not depend on testosterone concentration, scrotal perimeter or body weight.

ASSUNTO(S)

reprodução testosterona biometria testículos testis bovino testosterone reproduction beef cattle reproducao animal biometry

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