Pubertal development of the boar: testosterone, estradiol-17 beta, cortisol and LH concentrations before and after castration at various ages.

Forty-eight Landrace x Duroc boars were assigned at weaning to eight castration ages (40, 70, 100, 130, 160, 190, 220 and 250 d). Catheterization of the external jugular vein was performed 5 d before scheduled castration. Blood samples were collected every .5 h between 0800 and 1200 h, 2 d before (-2) and on d +1, +2, +3, +4, +8 and +16 after castration. Testosterone (T) was determined in serum samples collected every .5 h on d -2. Serum concentrations of estradiol-17 beta (E2), cortisol (C) and luteinizing hormone (LH) were quantified by radioimmunoassays in pooled (within boar) samples collected on d -2. In addition, LH was determined in pooled (within boar) samples collected on d +1, +2, +3, +4, +8 and +16 after castration. Mean concentrations of T and E2 (d -2) increased in a near linear (P less than .01) fashion with age of boar. However, T concentrations at 250 d of age had declined (P less than .01) to values similar to concentrations of boars at 130 d of age. Serum C concentrations (d -2) were lower (P less than .01) at 100, 130 and 160 d of age compared with an average C concentration of 19 ng/ml for all other age groups. Mean concentrations of LH (d -2) did not differ among any of the ages. Luteinizing hormone concentrations were elevated (P less than .01) within 1 to 2 d following castration at 40, 70, 100, 130 and 160 d of age. Serum T concentrations of individual boars varied greatly at all ages as determined by half-hourly sampling over a 4-h period. The results indicate that in the boar: (1) T concentrations increase as pubertal development progresses and decline as maturity nears; (2) E2 concentrations increase steadily through pubertal development; (3) C concentrations are depressed at 100, 130 and 160 d of age relative to concentrations before and after that period; (4) LH concentrations are constant during pubertal development, and (5) a decrease in the sensitivity of the negative feedback mechanism controlling LH occurs after 160 d of age.