GROWTH-PATTERNS AND BODY-COMPOSITION OF TRANSGENIC MICE EXPRESSING MUTATED BOVINE SOMATOTROPIN GENES

The objectives of this study mere to determine growth rates, feed inta kes, feed efficiencies, and chemical composition of mice from three tr ansgenic lines in 10-d periods from meaning to near maturity. Lines M4 , M11, and G119K express bovine somatotropin (bST) mutations E117L, L1 21P-E126G, and G119K and display phenotypes of large, near normal, and small body size, respectively. M4 mice were 28% larger at 28 d and 84 % larger at 68 d than non-transgenic control (NTC) mice. M11 mice were the same size at 28 d as NTC but were 25% larger at 68 d. G119K mice were 34% and 25% smaller than NTC at 28 and 68 d, respectively. Growth rates of G119K mice and NTC were similar, whereas growth rates of M11 and M4 mice were increased (P < .05). Feed intakes of M4 and M11 mice were greater than those of NTC mice (P < .05), whereas feed intakes o f G119K mice were lower than those of NTC mice (P < .05). Feed efficie ncy (gain/feed) was improved in M4 and M11 mice (P < .05) and not alte red in G119K mice compared to that of NTC mice (P > .05). Chemical com position was also altered by expression of bST analogs in transgenic m ice. G119K and M4 mice had increased body fat percentages and decrease d body protein percentages in comparison to M11 and NTC mice (P < .05) . These lines of transgenic mice provide models of accelerated growth with concurrent increases in both protein and fat mass (M4), accelerat ed growth with increased protein mass (M11), and decreased growth with decreased protein mass (G119K) to further investigate effects of bST on lipid and protein metabolism.