Ovarian response to hCG injections during the prepubertal period in three breeds of sheep with different ovulation rates and litter sizes

Abstract

A positive correlation was reported between ovulation (OR) rate in response to hCG in prepubertal ewe lambs and adult ewes. The finding suggested that the response to hCG may be used to select prepubertal ewe lambs for prolificacy. We studied plasma FSH concentrations and ovarian response to hCG injection during the prepubertal period in breeds with high (Chios), medium (Florina) and low (Karagouniki) OR and litter sizes (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 earlier, by exhibiting ovulation at 6 wks and more effectively, by demonstrating a higher OR than the other two breeds. There was no correlation among plasma FSH concentrations during prepubertal age (3rd to 7th wk), ovulation rate after hCG injection, or litter size at first and second lambing for all breeds. Therefore we concluded that the plasma FSH concentrations and/or the ovarian response to hCG injection during the prepubertal period is not a suitable criterion for early selection for litter size in the adult ewe of these breeds.