REDUCTION OF REPRODUCTIVE LOSSES

Ova and embryo losses are reduced, and hence fecundity is increased, in a flock of sheep or a group of other domesticated animals by actively immunizing the female animals in the flock or group against a group of steroids which group comprises one steroid from each of the classes of androgens and oestrogens. The immunizations are carried out prior to a mating period lasting at least twice the average oestrus cycle for the species of animal concerned and are such that antibody levels raised in the female animals in the flock against the steroids in the group are sufficiently high to reduce ova and embryo losses and thus increase fecundity while not being so high as to reduce substantially the display of behavioural oestrus by the immunized female animals during the mating period. The immunization is carried out such that the levels of the antibodies against the steroids in the group decline, preferably from 30 to 90 % during the mating period.