Potential for fecundin to influence the reproductive performance of merino ewes in Western Australia.

Four experiments were conducted at different locations in Western Australia to evaluate the effectiveness of immunizing young (maiden, 1 1/2 year old) and adult Merino ewes with Fecundin to improve their reproductive performances. The ovulation rates of immunized maiden ewes was increased (0.06-0.30) above that of untreated ewes in both experiments 1 and 2. However, there were no significant improvements in the marking percentages for the immunized ewes with the differences between the untreated and immunized ewes ranging from -16.4 to 5.8%. In comparison with untreated ewes immunization 6 and 2 weeks before the start of joining depressed ewe fertility by 26.1% whereas immunization 8 and 4 weeks before the start of joining did not significantly affect fertility. The availability of oat grain ad libitum prior to parturition and during early lactation did not improve the survival of lambs born to immunized ewes. In experiments 3 and 4 immunization of adult Merino ewes increased their ovulation rates (0.41-0.63) above untreated controls and tended to increase the proportion of pregnant ewes which had multiple pregnancies (from -2.3 to 34.2%). The responses at the end of lambing were variable (from -19.8 to 37.5% lambs marked) with high lamb mortalities occurring in some experiments. There was no adverse effect on the reproductive performances following consecutive annual immunizations over 3 years and the absence of treatment for 1 year did not prevent a response in the following year.