Regulation of protein, lipid, and bone accretion in steers treated with zeranol or transgenic mice expressing mutant bovine growth hormone genes

Two experiments were conducted to determine the effects of zeranol or bovine growth hormone (bGH) on protein, lipid, and bone. In the first, steers were treated with 0, 24, 36, 48, 60, 72, 84, or 96 mg of zeranol which increased (;Transgenic mice expressing different mutations of the bGH gene were used to assess the effect of bGH on empty body composition, tibia characteristics, and the relationships among empty body components and bone characteristics. The smaller, G-1 mice consumed more food as a percentage of empty body weight, yet had less protein and similar quantities of fat as controls. The M11-1 mice were similar to controls until about 60 d of age. The M4-1 mice were larger than controls, and gained protein through 68 d of age, indicating they were not mature.;Tibia characteristics of the G-1 mice indicated longitudinal growth and bone mineralization were not as depressed as protein deposition or overall growth. Both stress and modulus of elasticity measures for M4-1 mice indicated their bones were not as mineralized as controls. This suggests the increased growth in M4-1 mice resulted in repartitioning of minerals (confirmed by the relationship between empty body ash and tibia mechanical characteristics), or the bGH analog had an effect on bone growth patterns which differed from its effects on other tissues.;The rapid rates of gain in zeranol implanted steers and the M4-1 mice resulted in sufficiently increased mineral demands to meet essential soft tissue growth functions that bone mineralization was compromised. Because protein deposition was depressed to a greater degree than bone growth or mineralization in G-1 mice, even though feed intake was greater as a percentage of empty body weight, this bGH analog appears to affect specific tissue types differently. GH regulation of specific tissues is prioritized and related to GH structure.