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US Department of Agriculture, Clay Center, NE 68933 and and US Department of Nebraska, Lincoln 68583
Abstract
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-17ß (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<.01) fashion with age of boar. However, T concentrations at 250 d of age had declined (P<.01) to values similar to concentrations of boars at 130 d of age. Serum C concentrations (d –2) were lower (P<.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<.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.
1 Published as Paper Number 82-1728, Journal Series, Nebraska Agr. Exp. Sta. Research was supported in part by USDA Cooperative State Research Service grant 701-15-42.
2 The authors express appreciation to Mark Anderson, Robert Byrkit, Jenell Dague, Jean Gray and Toni Tolles for their invaluable technical expertise, Mike MacNeil for helping with the statistical analysis and Linda Parnell for expert secretarial assistance.
3 Mention of a trade name, proprietary product or specific equipment does not constitute a guarantee and(or) endorsement by the USDA and does not imply its approval to the exclusion of other similar products that also may be suitable.
4 Dept. of Anim. Sci., Univ. of Nebraska.
5 Research conducted while a Univ. of Nebraska predoctoral student located at Roman L. Hruska U.S. Meat Animal Research Center, Present address: Dept. of Anim. Sci., Lilly Hall, Purdue Univ., West Lafayette, IN 47907.
6 Roman L. Hruska U.S. Meat Animal Research Center, USDA, ARS.
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