Abstract
During two weeks prepartum, one hundred mg of 2-Br-α-ergocryptine (CB154), a potent prolactin inhibitor, was subcutaneously administered to dairy cows 8 to 10 times. Simultaneous injections of an antiserum to bovine prolactin around parturition were also given to a CB154-administered cow. The serum prolactin (PRL) level decreased to less than 2ng/ml immediately after the commencement of CB154 injection, and the low level continued until calving. PRL surge near parturition which usually emerged in normal calving, completely disappeared. The low serum PRL level continued till at least two weeks after calving. No reduction of serum growth hormone and triiodothyronine levels was detected. Lactogenesis was more or less suppressed by CB154 administration. The mean milk production in three cows during a week postpartum was 58.5% of that of the previous lactation. It took 30 to 50 days to attain the milk yield of the previous lactation. In the cow administered with CB154 and an antiserum to bovine PRL simultaneously, the milk production reduced to 43.7% of that of the previous lactation. The milk production was not achieved to that of the previous lactation even on the 50th day after calving. The concentrations of total milk protein, IgG, and β-lactoglobulin in colostrum and milk from the cows treated with CB154 were significantly higher than those from the control cows. On the contrary, the concentration of a-lactalbumin in colostrum from the cows given CB154 was 40% of that the control cows (p<0.001). The concentrations of lactose and a-lactalbumin on the 6th day postpartum were also significantly lower than those of the control cows. These results indicate that the suppression of PRL secretion around parturition after CB154 treatment induces the reduction of syntheses of a-lactalbumin, lactose and the depression of milk production during lactogenesis.
