The Modulation of the Bioactivity of Bovine Luteinizing Hormone by Somatotropin and Nutritional Manipulation
Abstract
Twenty Angus X Holstein heifers were randomly assigned to one of four treatment groups (n=5) in a 2 X 2 factorial arrangement to evaluate the effects of recombinant bovine somatotropin (bST) and(or) nutritional manipulation on bioactive LH. The four treatment groups were arranged as follows: (I) continuous growth (CG) + excipient (EX), (II) CG + ST, (III) discontinuous growth (IG) + EX and (IV) IG + ST. CG heifers were fed a 68% concentrate diet formulated to provide for a growth rate of .8 kg/d throughout treatment. Two successive periods of intermittent growth were imposed on IG heifers by alternately feeding a 68% concentrate diet formulated for growth at .25 kg/d (restricted growth) for 3 months and then realimentation on a 90% concentrate diet fed ad libitum (compensatory growth) for 2 months. EX groups received excipient injections, while ST groups received injections (sc) of 500 mg bST every 14-d. Blood samples were collected at 20-min intervals for 6 h at ages 9, 11 and 14 mo (sample periods 1, 2 and 3, respectively). Bioactive LH was quantified by a validated in vitro rat Leydig cell testosterone assay. There was a sample period x treatment interaction (P<.05) for mean bioactive LH concentration. Mean bioactive LH concentration across sample period was greater (P<.05) for CG + EX heifers (.20 ng/ml) than for IG + ST heifers (.07 ng/ml). There was an effect of sample period (P<.05) on number of LH pulses and mean amplitude of LH pulses. Treatment affected (P<.05) mean amplitude of LH pulses but not number of LH pulses. Mean amplitude was greater for group CO + EX than for group 10 + ST (.36 and .09 ng/ml, respectively). These results suggest that nutritional manipulation designed to achieve intermittent growth patterns in combination with somatotropin administration reduces mean concentration and pulse amplitude of bioactive LH in heifers.
Description
Program year: 1990/1991Digitized from print original stored in HDR
Subject
bovine somatotropinintermittent growth
nutritional manipulation
mean concentration
pulse amplitude
Bioactive LH
Citation
McIntush, Eric Wynne (1991). The Modulation of the Bioactivity of Bovine Luteinizing Hormone by Somatotropin and Nutritional Manipulation. University Undergraduate Fellow. Available electronically from https : / /hdl .handle .net /1969 .1 /CAPSTONE -DelgadorodriguezM _1998.