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Browsing by Author "Waggoner, David Kent"

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    Colostrum feeding and its effects on serum cortisol, thyroxine, immunoglobin G and cytosolic glucocorticoid receptors in skeletal muscle in the bovine neonate
    Waggoner, David Kent (Virginia Tech, 1987)
    The effect of feeding colostrum or milk to newborn calves on serum cortisol, thyroxine and immunoglobulin G was investigated. Twenty-four calves (12 males and 12 females) were obtained immediately postpartum and randomly assigned to one of two rations after being blocked by breed and sex. Both rations were force-fed at birth, 12, 24 and 36 h postpartum. Blood sampling was performed at 0 time, 1, 2, 3, 4, 6 and 12 h postfeeding with this regime followed for a 48 h period (4 feedings). The average serum cortisol concentration was highest at birth, 221.9 and 245.6 ng/ml for colostrum and milk-fed calves, respectively. Cortisol levels between treatments were different (P<.05) at 2, 3, 12, 14, 18, 24, 37 and 48 h postpartum. The sex of the calf did not affect the mean cortisol concentrations. No treatment difference was observed for serum thyroxine. A sex difference was observed with the female calves exhibiting higher average thyroxine concentrations over the entire trial. A reduction in thyroxine concentration occurred with time (P<.001) as mean concentrations peaked at 4 h postpartum (22.1 μg/dl) and declined to 10.6 μg/dl by 48 h postpartum. Both treatment groups were born with similar serum immunoglobulin G levels (~0.7 mg/ml). However, at approximately 4 h postpartum, the colostrum-fed calves acquired an increase (P<.001) in serum immunoglobulin G, peaking at 24 h postpartum (26.83 mg/ml) and remaining much higher throughout the entire trial. There was a treatment difference (P<.001) between the two groups following the 4 h sample. Muscle samples (20-30g) were surgically removed from the right semitendinosus at 36 h postpartum from 14 neonatal beef calves (male and female), homogenized, and centrifuged at 105,000 x g at 4 C for 60 min. The supernatant (cytosol) was harvested and receptor quantitation, binding kinetics and ligand specificity assays were performed via [1,2,4,³H] dexamethasone. There were no binding differences between the colostrum and milk-fed calves' muscle samples. The average protein content of the muscle cytosol fraction was 50.82 mg/ml. The binding component displayed a high apparent equilibrium dissociation constant for the binding of [³H] dexamethasone (K d = 2.34x10 ⁻⁸ ). The apparent maximum number of binding sites determined from Scatchard plots was approximately 37.61 fmol/mg of protein in the case of the dexamethasone receptor. Maximum binding appeared to reached between 16 and 24 h (48.5 and 48.2 %, respectively). Competition assays indicated all of the ligands tested had an affinity for the glucocorticoid receptor. The percent of specific binding for each was: dexamethasone (66+/-14), corticosterone (52+/-10), cortisol (58+/-13), estradiol-17, beta (37+/-7), progesterone (29+/-9), testosterone (10+/-3), and triamcinolone (41+/-11).