In dairy cows the serum cortisol (FK) and dehydroepiandrosterone (DHEA) levels reached a maximum immediately after parturition and then returned to normal before long. The serum DHEA level 24 hours after parturition was significantly lower (P<0.01) than that before parturition. The serum corticosterone (BK) level was hardly influenced by parturition. The serum estrone (E1) and estradiol-17 β(E2) levels were the highest immediately after parturition and decreased rapidly with the lapse of time after parturition. The serum progesterone (P) level decreased gradually as the parturition drew near. Especially, it decreased rapidly on the day and the following day of parturition. The serum FK and DHEA level increased in fetuses with the advance in intrauterine age and reached a maximum immediately after parturition. They began to decrease markedly in calves 12 hours after birth. The serum BK level, as well as the serum FK level, began to increase in fetuses at 8 months of age and attained a maximum immediately after parturition to be reduced rapidly thereafter.
The MIC of tyamulin (TN), an antibiotic of the diterpene group, was studied in comparison with tylosin, spiramycin, tetracycline, and chlortetracycline. It was 0.01-0.1μg/ml to Ureaplasma, showing that TN had a higher antibacterial ability than the other four drugs. It was 0.1-2.5μg/ml to Mycoplasma dispar, being almost the Same as that of any other drug. The MIC of TN was 0.01-0.05μg/ml to Mycoplasma hyopneumoniae of porcine origin, indicating that TN had a slightly higher antibacterial ability than tylosin. It was 0.01-0.025μg/ml to Mycoplasma gallisepticum of avian origin, exhibiting that the antibacterial ability of TN was almost the same as that of tylosin or spiramycin and distinctly higher than that of chlortetracycline.