Abstract
Intravenous blood samples were collected from newborn, recently-weaned and feedlot groups of four male beef cattle per group prior to slaughter. Following slaughter, pituitaries, thyroids, adrenals and pancreata were excised and weighed. Pituitaries of feedlot steers contained significantly (P<.05) greater amounts of growth hormone (2.83 mg.) than those of the intermediate (1.12 mg.) and newborn (1.70 mg.) animals. Newborn calf pituitaries, however, contained higher (P<.05) concentrations of growth hormone/gm. of gland (3.77 mg.) than those of feedlot (1.73 mg.) and intermediate (0.90 mg.) steers. The ratio of growth hormone to bodyweight was significantly (P<.01) higher in newborn calves. Although group differences were statistically nonsignificant, PBI serum analysis suggested a gradual decline with aging in circulatory thyroxine levels on a mcg.% basis. Feedlot steer thyroids contained significantly (P<.05) greater amounts of total iodine (25.51 mcg.) than those of intermediate (11.61 mcg.) and newborn (8.66 mcg.) calves, and significantly (P<.05) more iodine/gm. of gland (1.73 mcg.) than those of intermediate (1.27 mcg.) calves. For each 1% increase in bodyweight, thyroidal iodine level was 0.21% greater. The ratio of thyroidal iodine to bodyweight, however, was significantly (P<.05) higher in newborn calves. Thyroid follicle diameters were significantly (P<.05) greater in feedlot steers (64.96µ) than in intermediate (49.14µ) and newborn (39.55µ) calves. Bodyweight and weights of the thyroid (0.921), pituitary (0.875), adrenals (0.907) and pancreas (0.983) were highly (P<.01) correlated. Copyright © 1968. American Society of Animal Science. Copyright 1968 by American Society of Animal Science