D. R. Hagen

Hemicastration of neonatal boars: hormonal responses and testicular messenger RNA for insulin-like growth factor-I

Abstract The objectives of these studies were to define more completely the hormonal responses of neonatal boars to hemicastration, especially that for inhibin, and to examine the possible involvement of insulin-like growth factor (IGF)-I in steroidogenic compensation by the remaining testis. 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 castrated. Individual testicular weights of HC boars at day 31 were 86% higher than those for IC boars. Boars in the HC group had higher concentrations of follicle stimulating hormone in plasma and lower concentrations of inhibin than did IC boars, while there was no effect of treatment on concentrations of luteinizing hormone, growth hormone or testosterone. In Experiment 2, boars were HC or left as IC at day 7 and fully castrated at day 9. Blood samples were taken on each day for quantification of testosterone concentrations, and RNA was extracted from day 9-testes for Northern analysis with a probe for IGF-I. There was no 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 conclusion, responses in hormonal secretion following hemicastration of neonatal boars are similar to those in other domestic animals. The compensatory 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 differences exist in the regulation of testicular IGF-I production.