[Activity of serum gonadotropins in pregnant zebras and mares]

Blood was collected from 28 zebra mare (Equus burchellia antiquorum) immediately after being shot in the Kruger National Park. The serum was separated within two hours after collection and then stored at -15 degrees C for later assay. Of these, thirteen selected samples were tested for gonadotrophic activity. The stage of pregnancy was determined from a foetal growth curve. Blood samples from pregnant horse mares were collected by venipuncture. Nine mares were sampled. Seven blood samples at different stages of pregnancy were collected from one mare, four from another and only one sample each from the other seven mares. The stage of pregnancy was calculated from the date of last service. The levels of gonadotrophic activity of the serum samples were estimated through its effect on the weight of mouse ovaries. Five groups of five virgin female white mice were injected subcutaneously with zero, 0,025 ml, 0,075 ml and 0,1 ml of serum per mouse on two successive days and killed by ether inhalation 48 hours after the last injection. The mean weight per overy was determined for each level of every sample injected and a dose: response curve drawn from which the percentage increase in ovarian weight caused by the 2 X 0,05 ml dosage level of each serum sample was estimated. The curves obtained by plotting gonadotrophic activity at various stages of pregnancy for horse and zebra mares are generally similar but differ in certain details. PMS obtained from horses has a greater activity and appears to be secreted over a shorter period of time i.e. it disappeared by the 160th to 180th day of pregnancy. In zebra mares, on the other hand, a relatively lower activity was found during the peak period (65th to 80th days) but it was maintained loger and was still detectable at 229 days but absent at 365 days after conception.