Abstract This work aimed to associate sexual behavior with serum testosterone and the height of sensitive epithelium of vomeronasal organ (VNO) of Nellore bulls raised extensively and subjected to the VNO blocking during pre-puberty. Thirty-four bulls were divided into three groups. G1 (control group; n = 11): animals were kept intact; G2 (n = 10): animals had their incisive ducts bilaterally cauterized; G3 (n = 13): animals were bilaterally orchy-epiectomized. Five libido tests and blood sampling were performed in three months intervals from pre-puberty until sexual maturity. VNO were collected for histological evaluations by sacrificing the bulls weighting 480 kg. The experiment was conducted in a complete randomized design. No differences in libido among groups were observed in the first three tests. Attempt to mount, complete mount and the libido score increased at the fourth libido test only for the G1. Scenting and licking increased while the Flehmen reflex (FR) decreased at the fifth libido test for G2 and G3. Positive association between the FR and VNO sensitive epithelium height in G2 was observed. The olfactory stimuli entrance in the VNO is influenced by the Flehmen reflex, and that such organ plays a key role in the libido of Nellore bulls.

Resumo Objetivou-se avaliar o comportamento sexual e suas correlações com as concentrações séricas de testosterona e a altura do epitélio sensitivo do órgão vomeronasal (OVN) em machos Nelore (Bos taurus indicus), criados extensivamente e submetidos ao bloqueio do OVN na pré-puberdade. Foram utilizados 34 animais: G1-animais controle, denominados inteiros (n=11), G2-animais com os ductos incisivos bilateralmente cauterizados, denominados bloqueados (n=10) e G3-animais bilateralmente orquiepidectomizados, denominados castrados (n=13). Os animais foram avaliados a cada três meses até a maturidade sexual, sendo realizados cinco testes de libido e coletas de sangue. Foram abatidos os animais com 480 kg, onde foram obtidos os OVN, para avaliação histológica. O delineamento experimental foi inteiramente casualizado. Não houve diferenças (P>0,05) entre grupos nos primeiros três testes de libido. No quarto teste, houve aumento da tentativa de monta, monta completa e escore da libido apenas nos grupos dos inteiros (P<0,05). No quinto teste, houve aumento em cheirar e lamber e redução no reflexo de flehmen (RF) nos bloqueados e castrados (P<0,05). Observou-se alta associação entre o RF e altura do epitélio sensitivo do OVN nos bloqueados (r=0,75; P=0,05). Concluiu-se que a entrada dos estímulos olfatórios ao OVN é influenciada pelo RF e que este órgão exerce importante função no comportamento sexual em machos Nelore.

In order to determine the profile of leptin and insulin values in seminal plasma and their correlations with sperm patterns during the peripuberty, a total of 16 crossbred Gyr dairy bulls were monitored from 60 days before to 60 days after puberty, separated into two groups, early and regular, according to the onset of puberty. Hormone values were determined by radioimmunoassay after gel filtration in fast performance liquid chromatography and semen patterns, according to the Brazilian College of Animal Reproduction. Insulin concentrations in seminal plasma did not differ between groups, nor between the ages, with the pooling of the data showing average of 35.15±16.93, 36.60±26.21, 26.82±09.81, and 43.56±31.71 32.24±16.71 U/mL for the pubertal period of -60, -30, 0, +30 and +60 days, respectively. These values were not correlated with sperm parameters, but differed in the group of animals with the highest percentage of major defects (31.08±18.58 U/mL) compared with those with lower percentage of these sperm defects (40.01±25.37 U/mL). Leptin was not correlated with sperm parameters and did not differ between groups or stage of sexual development, with concentrations of 23.10±10.43, 24.35±9.42, 22.41±9.90, 23.76±9.69 and 24.99±11.42 ng/mL for the periods of puberty aforementioned, respectively, after being grouped. These results demonstrated the binding of insulin to the structural quality of the sperm cell, and this hormone is indicated in andrologycal evaluation of future breeding soundness.