PITUITARY AND PLASMA-LEVELS OF GROWTH-HORMONE IN BOOROOLA SHEEP THAT ARE EITHER HOMOZYGOUS CARRIERS OR NONCARRIERS OF THE FECB(B) FECUNDITYGENE

The aim of this study was to examine the effect of the FecB(B) fecundi ty gene on plasma concentrations and pituitary content of growth hormo ne (GH) in sheep. No differences were found between homozygous carrier s (BB) and non carriers (++) of the FecB(B) gene with regard to pituit ary GH contents in both ovariectomized and intact ewes. However, ovari ectomized ewes had higher levels of pituitary GH than intact ewes (P < 0.01). There were no differences between FecB(B) genotypes with respe ct to plasma concentrations of GH in 6-year-old ovariectomized ewes bl ed every 10 min for 12 h or in ram lambs bled weekly during their firs t year of life. GH levels in the rams decreased until week 27, increas ed to a peak at week 31 then decreased before increasing again at week 43. Mean plasma GH concentrations in the ewe lambs bled weekly for a year decreased until week 19 then remained at approximately this level for the remainder of the year. Mean GH plasma concentrations in the r am lambs were higher than in the ewe lambs (P < 0.001). Ewe lambs that were homozygous for the FecB(B) had lower body weights (P < 0.05) and had higher levels of GH (P < 0.01) than non carrier ewe lambs during their first year. Before the average age of first behavioural oestrus (36 weeks) GH levels in the ewe lambs were negatively correlated with body weights (r = -0.69, P < 0.001, n = 22). When body weight was incl uded as a covariate in analysis of variance the genotype difference in ewe lamb plasma GH concentrations was no longer significant. In summa ry, pituitaries from ovariectomized ewes had higher levels of GH than those from intact ewes. There were no FecB(B) gene specific difference s in pituitary levels of GH, the profile of plasma GH in 6-year-old ov ariectomized ewes or in ram lambs during their first year of life. BB ewe lambs had higher levels of GH than ++ ewe lambs during their first year; however, this difference was probably due to the BB ewes having lower body weights than the ++ ewes because body weight was negativel y correlated with mean GH levels.