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Plasma samples from intact, adrenalectomized, adrenalectomized and castrated and castrated bulls were assayed for LH, testosterone, androstenedione and oestradiol-17β from birth to 26 weeks of age. The adrenalectomized bulls, unlike the intact bulls, failed to show a rise in androstenedione at 14·5 weeks of age or a rise in testosterone at 20 weeks of age. Testosterone levels in the castrated animals remained below 0·4 ng/ml whereas androstenedione reached levels similar to those in intact bulls by 26 weeks of age. In all animals the concentration of oestradiol-17β in plasma remained below 25 pg/ml, although intact bulls had the highest levels. Levels of LH rose after castration but not after adrenalectomy. These data show that in bull calves absence of the adrenal glands during prepuberty delays the rise in pubertal testosterone by at least 10 weeks.
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Ministry of Agriculture and Fisheries, Research Division, Ruakura Agricultural Research Centre, Hamilton, New Zealand
(Received 17 April 1978)
An increase in the plasma concentration of luteinizing hormone (LH) occurs in response to castration in bull calves aged 1–4 months; this response is of similar magnitude to that seen in cattle castrated as adults (Odell, Hescox & Kiddy, 1970). In bull calves castrated at birth, however, there is no increase in the plasma concentration of LH until after 28 days of age (Bass, Peterson, Payne & Jarnet, 1977). In other species a range of responses to castration has been reported. Gonadectomy of male guinea-pigs 0–35 days after birth produces an increase in the plasma concentration of LH similar to that observed in guineapigs castrated as adults (Donovan, ter Haar, Lockhart, MacKinnon, Mattock & Peddie, 1975). In contrast, the castration of young male macaques does not cause an immediate increase in the
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ABSTRACT
The effect of immunizing against somatostatin (SRIF), with SRIF conjugated to bovine thyroglobulin, was examined in cross-bred sheep fed either cut pasture or lucerne pellets. Plasma concentrations of GH were unaffected by SRIF immunization, but were lower in pellet-fed sheep. Plasma concentrations of insulin-like growth factor I (IGF-I) increased after immunization in sheep on both diets. Pasture-fed sheep had lower plasma concentrations of IGF-I than those on pellets. Sheep showed a small increase in growth rate in response to immunization. Immunization had no effect on carcass composition and did not affect plasma concentrations of IGF-II, free fatty acids or glucose. The results show that even though SRIF immunization increases plasma concentrations of IGF-I, it does not necessarily result in a large increase in growth rate.
J. Endocr. (1987) 112, 27–31
