Effects of CB154 on serum hormone level and lactogenesis in dairy cows.

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Abstract
During 2 wk prepartum, 100 mg of 2-Br-.alpha.-ergocryptine (CB 154), a potent prolactin inhibitor, was s.c. administered to dairy cows 8-10 times. Simultaneous injections of an antiserum to bovine prolactin around parturition were also given to a CB 154-administered cow. The serum prolactin (PRL) level decreased to less than 2 ng/ml immediately after the commencement of CB 154 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 2 wk after calving. No reduction of serum growth hormone and triiodothyronine levels was detected. Lactogenesis was more or less suppressed by CB 154 administration. The mean milk production in 3 cows during a week postpartum was 58.5% of that of the previous lactation. It took 30-50 days to attain the milk yield of the previous lactation. In the cow administered with CB 154 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, Ig[immunoglobulin]G and .beta.-lactoglobulin in colostrum and milk from the cows treated with CB 154 were significantly higher than those from the control cows. On the contrary, the concentration of .alpha.-lactalbumin in colostrum from the cows given CB 154 was 40% of that the control cows (P < 0.001). The concentrations of lactose and .alpha.-lactalbumin on the 6th day postpartum were also significantly lower than those of the control cows. The suppression of PRL secretion around parturition after CB 154 treatment apparently induces the reduction of syntheses of .alpha.-lactalbumin, lactose and the depression of milk production during lactogenesis.