Induction of abortion in cattle with prostaglandin F2alpha and oestradiol valerate

Twenty, 2 to 5 months pregnant heifers were injected with 25 mg. and 12.5 mg. Prostaglandin F2alpha on two consecutive days or with a single dose of 20 mg. of a long acting oestrogen (oestradiol valerate). Abortion occurred at an average interval of 3,6 days in the 10 PG F2alpha treated animals and after 10,8 days in 8 out of 10 oestradiol valerate treated heifers. The foetuses of the PG F2alpha treated heifers were in a fresh state while the oestradiol foetuses were already degenerating at the time of abortion. A rather severe vaginal discharge after abortion was more often observed in oestradiol valerate induced abortion. Development of the mammary glands and prolonged oestrus periods also was more pronounced in these animals. In both treatments the concentration of progestins in peripheral blood dropped to less than 1 ng/ml at the time of abortion. The decline was very rapid after administration of PG F2alpha and rather slow after oestradiol valerate. Based on its rapid luteolytic effect and rapid elimination after administration which prevents interferring with the endocrine system for a prolonged time, PG F2alpha is preferred as an abortifacient during the first 4 to 5 months of pregnancy in cattle.