Plasma FSH, LH and immunoreactive inhibin concentrations in FecB(B)/FecB(B) and FecB+/FecB+ Booroola ewes and rams from birth to 12 months of age

Abstract

Endocrine and developmental changes were examined in Booroola FecB(B)/FecB(B) (BE, n = 16) and FecB+/FecB+ (++, n = 20) ewe lambs, and BB (n = 17) and ++ (n = 19) ram lambs from 2 to 53 weeks of age. Blood samples were taken weekly for the measurement of plasma concentrations of FSH, LH, immunoreactive inhibin, progesterone (ewe lambs) and testosterone (ram lambs). Behavioral oestrus in the ewe lambs and testicular volume and the breakdown of foreskin adhesions in ram lambs were recorded. Blood samples were taken from another flock of BE (n = 134) and ++ (n = 109) ram lambs at 20 weeks of age for the analysis of immunoreactive inhibin. In ewe and ram lambs, there appeared to be genotype differences for FSH, LH and immunoreactive inhibin at specific times during the neonatal period. In BB and ++ ewe lambs, respectively, mean FSH concentrations were 4.3 and 2.0 ng ml-1 (SED 0.54) between 4 and 6 weeks, 2.6 and 3.4 ng ml-1 (SED 0.33) between 12 and 28 weeks, and 1.8 and 1.9 ng ml-1 (SED 0.18) between 34 and 53 weeks of age. Mean plasma LH concentrations were lower in BB than in ++ ewe lambs from 26 to 53 weeks of age (P < 0.05) but not earlier. Mean concentrations of immunoreactive inhibin were also lower in BB than in ++ ewe lambs between 2 and 11 weeks (16.0 and 27.4 iu ml-1, respectively; P < 0.01), but thereafter no differences were apparent. In BE ram lambs, FSH concentrations were high for 3 - 4 weeks longer than in the ++ animals during the first 10 weeks of life. Likewise there were periods between 11 and 20 weeks of age when the plasma LH concentrations were higher in BB than in ++ ram (P < 0.05) lambs. Subsequently, between 19 and 33 weeks of age, the immunoreactive inhibin concentrations were consistently higher (P < 0.05) in BB than in ++ rams and this difference between the genotypes was confirmed in the larger study of 243 ram lambs at 20 weeks of: age (BB> ++; P < 0.0005). The endocrine differences, in males and females, could not be attributed to either litter size, livemass or sire. However, limited numbers of sires (two BE and two ++) were used in the present study, so potential sire effects cannot be ruled out. In ewe lambs, the time of onset of puberty did not differ between genotypes. In ram lambs, the onset of puberty was not determined but testicular development, assessed by changes in testosterone concentrations, did not differ between genotypes. Differences in penile development and changes in testicular volume between the genotypes were observed but these were confounded by differences in livemass or sire. The evidence suggests that there are FecB(B)-related differences in pituitary and gonadal hormones in neonatal ewes and rams. It is hypothesized that these differences between genotypes are part of a sequence of developmental differences that begin in fetal life.