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/

Endocrine and developmental changes were examined in Booroola FecB(B)/ FecB(B) (BB, n = 16) and FecB(+)/FecB(+) (++, n = 20) ewe lambs, and B B (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 test osterone (ram lambs). Behavioural oestrus in the ewe lambs and testicu lar volume and the breakdown of foreskin adhesions in ram lambs were r ecorded. Blood samples were taken from another flock of BB (n = 134) a nd ++ (n = 109) ram lambs at 20 weeks of age for the analysis of immun oreactive 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 an d 6 weeks, 2.6 and 3.4 ng ml(-1) (SED 0.33) between 12 and 28 weeks, a nd 1.8 and 1.9 ng ml(-1) (SED 0.18) between 34 and 53 weeks of age. Me an 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 < 0.0 1), but thereafter no differences were apparent. In BB ram lambs, FSH concentrations were high for 3-4 weeks longer than in the ++ animals d uring the first 10 weeks of life. Likewise there were periods between 11 and 20 weeks of age when the plasma LH concentrations were higher i n BB than in ++ ram (P < 0.05) lambs. Subsequently, between 19 and 33 weeks of age, the immunoreactive inhibin concentrations were consisten tly higher (P < 0.05) in BB than in ++ rams and this difference betwee n 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 m ales and females, could not be attributed to either litter size, livem ass or sire. However, limited numbers of sires (two BB and two ++) wer e 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 betwee n genotypes. In ram lambs, the onset of puberty was not determined but testicular development, assessed by changes in testosterone concentra tions, did not differ between genotypes. Differences in penile develop ment and changes in testicular volume between the genotypes were obser ved but these were confounded by differences in livemass or sire. The evidence suggests that there are FecB(B)-related differences in pituit ary and gonadal hormones in neonatal ewes and rams. It is hypothesized that these differences between genotypes are part of a sequence of de velopmental differences that begin in fetal life.