Pattern of gonadotropin secretion and ultrasonographic evaluation of developmental changes in the testis of early and late maturing bull calves

Effect of vaccination against gonadotropin-releasing factor (GnRF) with Bopriva® in the prepubertal bull calf

“…In the experiments mentioned above blood was collected at short intervals of 10-12 min during several hours and the basal, amplitude and mean concentrations of LH determined. This approach allows detecting increases in LH pulse frequency which is mainly responsible for the prepubertal gonadotropin rise (Evans et al, 1993) reported in previous studies (Aravindakshan et al, 2000;Bagu et al, 2006;Chandolia et al, 1997;Evans et al, 1993). A possible cause for the different findings may be breed influence, as our experiment was performed with Holstein calves whereas Hereford (Chandolia et al, 1997;Evans et al, 1993) or crossbreeds of Hereford and Charolais (Aravindakshan et al, 2000;Bagu et al, 2006) were used in the previous studies.…”

“…This approach allows detecting increases in LH pulse frequency which is mainly responsible for the prepubertal gonadotropin rise (Evans et al, 1993) reported in previous studies (Aravindakshan et al, 2000;Bagu et al, 2006;Chandolia et al, 1997;Evans et al, 1993). A possible cause for the different findings may be breed influence, as our experiment was performed with Holstein calves whereas Hereford (Chandolia et al, 1997;Evans et al, 1993) or crossbreeds of Hereford and Charolais (Aravindakshan et al, 2000;Bagu et al, 2006) were used in the previous studies. Moreover, it has been known that diet and weight gain may also influence LH secretion and the attainment of puberty (Barth et al, 2008;Brito et al, 2007aBrito et al, , 2007b.…”

“…In bull calves, blood concentrations of gonadotropins increase long before the animal reaches puberty. It has been shown that LH starts to rise from 6 weeks of age reaching peak values between 12 to 16 weeks and subsequently drops to basal concentrations at week 25 of life remaining low until attainment of puberty (Amann and Walker, 1983;Aravindakshan et al, 2000;Bagu et al, 2006;Evans et al, 1996;Lacroix and Pelletier, 1979;McCarthy et al, 1979;Rawlings and Evans, 1995;Rawlings et al, 1978Rawlings et al, , 2008Rodriguez and Wise, 1989). The early rise in gonadotropin secretion seems to be essential for normal testicular development and reproductive maturation in bull calves Rawlings et al, 2008).…”

Effect of feed restriction during calfhood on serum concentrations of metabolic hormones, gonadotropins, testosterone, and on sexual development in bulls

“…This observation supported the hypothesis that the pattern of LH secretion during the early gonadotropin rise during calfhood is the main determinant of age of puberty in bulls. In that regard, late-maturing bulls had lower LH secretion than early maturing bulls during the early gonadotropin rise (Evans et al 1995, Aravindakshan et al 2000. Moreover, bulls receiving a low-nutrition diet had reduced LH pulse frequency during the early gonadotropin rise and were older at puberty than those receiving medium or high nutrition (Brito et al 2007a).…”

“…Luteinizing hormone (LH) secretion during the period of the early gonadotropin rise seems to be the main determinant of age at puberty in bulls. Whereas increased LH pulse frequency and mean concentration during the early rise were associated with a reduced age at puberty (Evans et al 1995, Aravindakshan et al 2000, inhibiting LH secretion during the early gonadotropin rise delayed puberty in bulls (Chandolia et al 1997b). In bulls, nutrition during calfhood had direct effects on the GnRH pulse generator in the hypothalamus; low nutrition decreased LH secretion, whereas high nutrition increased secretion (Brito et al 2007a(Brito et al , 2007b.…”