Fecundity of domestic livestock

摘要

A method for increasing the fecundity of a flock of female sheep or goats comprising immunizing the animals in the flock against a steroidal androgen, such as 4-androstene-3, 17-dione or testosterone, or a steroidal oestrogen, such as oestrone, as by administering an immunogenic steroid/protein conjugate to the animals, to produce a mean steroid-binding antibody titre in the flock in the range of 1 in 500 to 1 in 3000 at the start of a mating period lasting at least twice the length of the average oestrous cycle for animals in the flock, and to maintain that titre so that it does not fall outside the range 1 in 200 to 1 in 2000 at the conclusion of the mating period, the overall decline in the titre being no more than 75% during the mating period. The antibody response to suitable immunogens is controlled by the time elapsing between primary and secondary immunizations and by the molar ratio of the steroid derivative to the protein when immunization is brought about by administration of an immunogenic steroid/protein conjugate.