A large number of blood samples was taken from the jugular vein of 18 cows or heifers during parturition, especially during stage II. In 9 animals an increase in serum growth hormone was observed and the peak occurred within the period which began when the forelegs of the calf became visible in the vulva, and ended a few minutes after expulsion of the calf. In typical cases, the growth hormone peak was preceded by a progressive increase, and followed by a gradual decrease in the hormone level. The total duration of the phenomenon amounted to a few hours. During the days before and after parturition, no change in growth hormone concentration could be noted. The serum free fatty acid values were high during parturition.
Animals Cattle