OVARIAN RESPONSE TO HCG INJECTIONS DURING THE PREPUBERTAL PERIOD IN 3BREEDS OF SHEEP WITH DIFFERENT OVULATION RATES AND LITTER SIZES

A positive correlation was reported between ovulation (OR) rate in res ponse to hCG in prepubertal ewe lambs and adult ewes. The finding sugg ested that the response to hCG may be used to select prepubertal ewe l ambs for prolificacy. We studied plasma FSH concentrations and ovarian response to hCG injection during the prepubertal period in breeds wit h high (Chios), medium (Florina) and low (Karagouniki) OR and litter s izes (LS). The results showed that Chios ewe lambs presented a higher profile of plasma FSH during the 3rd to 7th wk of age when compared to the breeds with medium (Florina) and low (Karagouniki) OR and LS. The ovarian response to hCG showed that the Chios ewe lambs responded ear lier, by exhibiting ovulation at 6 wks and more effectively, by demons trating a higher OR than the other two breeds. There was no correlatio n among plasma FSH concentrations during prepubertal age (3rd to 7th w k), ovulation rate after hCG injection, or litter size at first and se cond lambing for all breeds. Therefore we concluded that the plasma FS H concentrations and/or the ovarian response to hCG injection during t he prepubertal period is not a suitable criterion for early selection for litter size in the adult ewe of these breeds. (C) 1997 by Elsevier Science Inc.