Growth after Hypophyseal Stalk Transection and Hypophysectomy in Beef Calves

Growth hormone (GH) is a metabolic hormone that plays an important role in long-bone growth and muscle accretion in mammals. The anterior pituitary gland at the base of the brain is the primary site of GH production and release into the general circulation. Neurons in the arcuate nucleus of the hypothalamus in the lower part of the brain secrete GH-releasing hormone ([GHRH] or factor [GRF]) and GH-release-inhibiting hormone ([GHRIH] or somatostatin [SRIH]) that acutely modulate GH secretion by the pituitary gland. The pituitary gland is connected to the median eminence of the hypothalamus by a stalk (hypophyseal stalk). Complete surgical removal of the pituitary gland (hypophysectomy) arrests growth and greatly impairs metabolism in laboratory and farm animal species. Daily subcutaneous injection of bovine GH (bGH) in immature hypophysectomized rats significantly increased body growth and epiphyseal plate width of the long-bone (tibia) compared with diluent-treated hypophysectomized controls. Growth rate was less, however, in the bGH-treated animals compared with intact controls. In beef calves, hypophysectomy completely arrested body weight gain and long-bone growth. GH is secreted in an episodic pattern in young growing intact calves. Episodic GH secretion was abolished immediately following hypophyseal stalk transection, and basal GH blood concentration was less than in shamoperated controls. Regardless, growth continued in these stalk-transected calves during a 1,008-day period, but at a lower growth rate than seen in the sham-operated controls. At autopsy, pituitary gland weight was greatly decreased in hypophyseal stalktransected compared with sham-operated calves. Thus, in spite of obliterated episodic GH release and decreased basal secretion of GH, the isolated pituitary gland of hypophyseal stalk transected calves continues to secrete sufficient amounts of GH for significant growth and development throughout a long period.

Long Versus Short Feeding Period for Steer Calves of Three Frame Sizes Fed High Energy Finishing Diets

An experiment was conducted using Angus cross steer calves of three frame sizes (small, medium, and large) to compare performance of two different grow/finish feeding programs. Half of the cattle in each frame size group were fed a high energy ration through the growing period, similar to calves going directly into the feedlot. The other half was fed a low energy ration, similar to a backgrounding diet, for a period prior to the finishing phase. All cattle were fed a high energy ration through the finishing period. The data showed the cattle fed the low energy growing diet experienced some compensatory gains as shown by ultrasound backfat and average daily gains coupled with intakes greater than the increases seen in the high energy treatment. Carcass data and overall performance data showed no ill effects due to the low energy growing ration.