Abstract
Angus X Holstein heifers (N = 40) were used to investigate the effects of nutritional manipulation of growth and exogenous bovine somatotropin (rbST) on feedlot performance, visceral organ mass, skeletal development, carcass composition and mammary gland development. Heifers (182 ︢8 d of age and 159 ︢12 kg BW) were provided s.c. injections of exciplent (EX) or rbST (500 mg) every 14 d and continuous (CG) or intermittent growth (IG) pattern treatments in a 2 X 2 factorial arrangement of treatments. CG heifers were individually limit-fed a 580-. concentrate diet to gain .8 kg/d throughout the experiment. IG heifers underwent two successive growth cycles with each cycle consisting of a 3 mo growth restriction phase (.25 kg/d) and a realimentation phase. All heifers were slaughtered at a final BW of 390 kg. The parenchymal tissue (PT) of the left mammary gland was dissected from surrounding extraparenchymal tissue (EPT) while PT and EPT of the right mammary gland were estimated using computer tomography. There was a rbST X growth pattern (GP) interaction (P < .01) for overall ADG. In CG heifers, ADG was higher (P < .001) in rbST heifers than EX heifers, but in IG heifers, ADG was similar in rbST and EX heifers. Percentage fat of the 9-10-11 rib section was reduced (P < .001) from 26-. in EX heifers to 16.40-. in rbST heifers. Percentage fat of the 9-10-11 rib was also reduced (P < .01) in IG heifers (23.4 vs 18.80-.). Weight of dissectable PT was greater (P < .01) in rbST heifers (441.2 g) than in EX heifers (287.4 g). The proportion of dissectable PT was significantly increased by rbST (36.9 vs 21.5t) and IG (33.7 vs 24.6%) heifers. The proportion of PT as measured by CT was also greater (P < .01) in rbST heifers (26.9 vs 13.00-.). Both IG and rbST were effective at reducing 9-10-11 rib fat and fat infiltration of the mammary gland. The magnitude of change, however, was greater for rbST treated heifers. Computer tomography was an effective technique for quantifying PT content of mammary gland.
Glaser, Darrell Edward (1993). Effects of bovine growth hormone and nutritional manipulation on carcass and mammary gland development in beef heifers. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1993 -THESIS -G548.