Reproductive response of ewes to immunization with Fecundin (ovandrotone)

Ewes of five crossbred genotypes (total of 221 ewes) were immunized with a commercial preparation of androstenedione-7HSA in DEAE dextran adjuvant in a 2-yr trial. In yr 1 ewes were allocated within genotype to a 2 x 2 application of immunization and premating flushing. In yr 2 they were allocated within previous Fecundin treatment into either Fecundin-treated or control groups. First-time immunization with Fecundin increased ovulation rate by .70 ova/ewe in yr 1 and by .85 ova/ewe in yr 2 (P less than .05). Ewes treated in both years produced fewer ova than those treated in the 2nd yr only (P less than .05), but they did not differ in litter size. Although Fecundin reduced conception to first mating, the overall conception rate was not affected. Litter size of treated ewes was increased by .19 and .38 lambs/ewe lambing (P less than .05) in yr 1 and yr 2, respectively. Fecundin treatment in yr 1 produced a carry-over effect in yr 2 by increasing litter size by .26 lamb/ewe (P less than .05) while reducing conception to first mating. The litter size of ewes with two ovulations was reduced by Fecundin treatment in yr 1 (P less than .05) but showed no consistent pattern in yr 2. Overall, ewes with two ovulations produced .7 to .8 more lambs than ewes with one ovulation, and ewes with three ovulations produced .4 more lambs than those with two ovulations. Ewes of different genotypes did not differ in their response to Fecundin.