Fecundin: An immunological approach to enhance fertility in sheep

Abstract

Recently developed technology involves the use of hormone-binding antibodies to regulate endocrine and thus reproductive functions. This approach is based upon neutralisation of the biological actions of an endogenous hormone, by antigen-antibody complex formation in vivo, with the antibody acting to bind the hormone in competition with target cell receptors. Active immunisation of sheep against androstenedione increases ovulation rate, although several studies indicate reduced mating activity and conception rate in immunised ewes. Normal fertilisation rates for sheep are close to 90%, but lambing rates are usually lower. Several causative factors have been indicated for the economically important embryo mortality levels, and it is accepted that embryonic wastage increases with increasing ovulation rate. A large-scale trial was carried out on Merino ewes immunised against Fecundin to study fertilisation and early embryonic mortality. One of the main facts to emerge was that mating management is crucial in expression of oestrus, ovulation rate and level of embryonic mortality. When rams were introduced to ewes within 14 days of booster injection, there was a reduction in the proportion of ewes marked, with an apparent shortening of the cycle, and an increase in ovulation rate. In addition, embryo recovery rates were reduced in Fecundin-treated ewes. Similar problems with recovery rates were recorded in oestradiol immune ewes. The effects of Fecundin as an aid in superovulatory treatment were tested in mature cyclic ewes during the month of October. Immunisation increased the mean number of ovulations (12.5 ± 1.1 vs. 10.8 ± 1.0) and fertilised ova (4.0 ± 0.7 vs. 2.9 ± 0.7). There may be differences in the magnitude of the androstenedione antibody response to Fecundin within breeds. There is clearly a need for more research on the use of Fecundin as an aid to superovulation in the ewe; small numbers of ewes have been treated in all experiments.