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Use of active immunization against somatostatin in the manipulation of the ruminant endocrine system
Abstract
Three experiments were conducted to investigate the effects of active immunization against somatostatin (SS) on, 1) the lactational performance of ruminants, 2) growth hormone (GH) secretion and metabolism and 3) the relationship between immunization, plane of nutrition, GH and somatomedin C (SmC) metabolism. In experiment (Exp.)1, 12 lactating Nubian dairy goats (47 kg) were divided between immunized (I) (biweekly injections of SS-human serum globulin conjugate for 16 wk) and control (C) groups, which received globulin alone. Antibody titer, milk yield, constituent secretion and feed efficiency were measured. Immunization against SS did not affect milk or milk constituent yield, feed efficiency, temporal or GRF-challenged GH levels. In Exp. 2, the response of I and C steers which had been previously immunized for 12 wk, as in Exp. 1, to graded intravenous doses of GRF (0, 25, 50 or 100 μg hpGRF-44 NH₂) was measured using eight steers (425 kg), arranged in a 2 X 4 factorial within a completely randomized design. Plasma GH levels were measured at -30, 0, 5, 10, 15 min post-GRF-dose and at 15 min intervals for 6 h. Challenged-GH levels and estimates of total secretion for I and C steers were similar. In Exp. 3, the effects of immunization against SS on GH metabolism and SmC concentrations were tested. Six steers (beginning weight, 225 kg) were immunized against SS, and paired with six C steers of similar weight, were arranged in a 2 X 2 factorial within a completely randomized design. In the two phases of Exp. 3, each animal received a hay- (ryegrass, 8% CP, DM basis) or grain-based diet (14% CP) and estimates of GH metabolism and SmC production were made after primed continuous infusion of 4 mg bovine GH. Animals were fed 1.2 and 1.5% DM of body weight during the respective hay and grain portions of Exp. 3, fasted 18 h before infusion and refed at 2 h after GH infusion. Plasma SmC concentrations were measured up to 22 h after bGH dose. Metabolic clearance rate of GH, for I steers was higher (P <.01) than C steers, but was not affected by diet. Secretion rate was not altered by immunization against SS. Somatomedin C concentrations in I steers remained elevated (P<.05) above controls through the entire 42 wk immunization period. Across both diets, I steers demonstrated elevated overall (P<.05) and peak SmC (P<.01) levels. These data do not indicate that immunization against SS results in any enhancement of lactational performance or GH secretion. Reported improvements in growth rate and feed efficiency achieved through immunization against SS may be mediated through elevated SmC levels.
Description
Typescript (photocopy).Subject
Major nutrition1987 Dissertation K33
Ruminants
Physiology
Somatostatin
Growth factors
Plant growth promoting substances
Collections
Citation
Kenison, Dale Christopher (1987). Use of active immunization against somatostatin in the manipulation of the ruminant endocrine system. Texas A&M University. Texas A&M University. Libraries. Available electronically from https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -32311.
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