Effects of depilatory doses of epidermal growth factor on subsequent fertility, pregnancy rate and lambing performance in Merino ewes

Abstract

In the present study on Merino ewes, murine epidermal growth factor (mEGF) and genetically engineered methionine epidermal growth factor (met-EGF), given at depilatory dose rates (120 8g mEGF/kg body weight (n = 82) and 250 8g met-EGF/kg body weight (n = 100) respectively), were assessed for effects on fertility, pregnancy rate and lambing performance. Following EGF injection, the ewes were fitted with a net retention system to hold the fleece on the animals for 5 weeks, at the end of which time the wool was harvested from the EGF-treated ewes by hand and was shorn conventionally from non EGF-treated controls (n = 100). All ewes were then joined to raddled-harnessed entire rams (2%) for 6 weeks. The dates of raddle markings recorded during the teaser period and during joining to entire rams revealed that the majority (97%) of control ewes were in oestrus at expected times during the joining period, whilst significantly (P < 0.001) fewer ewes in the mEGF (75%) and the met-EGF (65%) treated groups exhibited oestrus at the expected time. The majority of the ewes that were delayed in onset of oestrus were at the mid to late luteal stages of the oestrous cycle at the time of EGF treatment. There was no material difference between the three groups in the number of ewes returning to service during the joining period, or in the number of empty ewes. The three groups were also similar in the proportions of ewes bearing single or twin lambs, in the overall lambing percentage (controls 108010, mEGF 109%, et-EGF 107%) and survival of lambs to weaning. No abnormalities were found in any of the lambs. It appears that an interval of 5 weeks between dosing and joining is sufficient time for EGF-treated ewes to resume normal cyclicity and fertility.