The effect of nutrition on testicular growth in mature Merino rams involves mechanisms that are independent of changes in GnRH pulse frequency

M.J. Hotzel, S.W. Walkden-Brown, Margaret Blackberry, Graeme Martin

Research output: Contribution to journalArticle

40 Citations (Scopus)

Abstract

In mature Merino rams, changes in diet to below or above the requirements for maintenance of body weight lead to changes in gonadotrophin secretion and testicular growth. However, the effects on testicular growth persist for much longer than those on LH and FSH secretion so that the gonadal and gonadotrophin responses are poorly correlated over time. This suggests that the gonadal effects may be partly independent of changes in the hypothalamic secretion of GnRH, an hypothesis tested in this study. In a short-term experiment (November, late spring, nonbreeding season), we tested whether a high frequency of exogenous GnRH pulses could override the endogenous system and mimic the change in gonadotrophins seen in rams fed a high plane of nutrition. Mature Merino rams (scrotal circumference (mean +/- S.E.M.) 33.6 +/- 0.5 cm, body weight (mean +/- S.E.M.) 59.0 +/- 0.9 kg) were fed 900 g chaff+1.6 kg lupin grain (High diet) or 360 g chaff+60 g lupin grain (Low diet) and infused with 8 pulses of GnRH or saline daily for 5 weeks (n=5/group). Blood was sampled every 20 min for 12 h on days -1 and 14 relative to the start of treatments. Relative to pre-treatment levels, LH pulse frequency and FSH concentrations were decreased on day 14 in saline-infused rams fed the Low diet and increased in saline-infused rams fed the High diet (P
Original languageEnglish
Pages (from-to)75-85
JournalJournal of Endocrinology
Volume147
DOIs
Publication statusPublished - 1995

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