HEMICASTRATION OF NEONATAL BOARS - HORMONAL RESPONSES AND TESTICULAR MESSENGER-RNA FOR INSULIN-LIKE GROWTH-FACTOR-I

The objectives of these studies were to define more completely the hor monal responses of neonatal boars to hemicastration, especially that f or inhibin, and to examine the possible involvement of insulin-like gr owth factor (IGF)-I in steroidogenic compensation by the remaining tes tis. In Experiment 1, boars were either hemicastrated (HC) or left as intact controls (IC) at 7 days of age. Blood samples were obtained on day 7 and every 4 days thereafter until day 31 when boars were fully c astrated. Individual testicular weights of HC boars at day 31 were 86% higher than those for IC boars. Boars in the HC group had higher conc entrations of follicle stimulating hormone in plasma and lower concent rations of inhibin than did IC boars, while there was no effect of tre atment on concentrations of luteinizing hormone, growth hormone or tes tosterone. In Experiment 2, boars were HC or left as IC at day 7 and f ully castrated at day 9. Blood samples were taken on each day for quan tification of testosterone concentrations, and RNA was extracted from day 9-testes for Northern analysis with a probe for IGF-I. There was n o difference between treatments for concentrations of testosterone on either day, or for IGF-I mRNA on day 9. However, boars from one litter had greater expression of IGF-I mRNA than did other boars.In conclusi on, responses in hormonal secretion following hemicastration of neonat al boars are similar to those in other domestic animals. The compensat ory secretion of testosterone in HC boars is apparently not regulated by IGF-I at 2 days following treatment. Further study would determine if IGF-I is involved earlier in the response, or if genetic difference s exist in the regulation of testicular IGF-I production.