Relationships between Growth Traits, Carcass Traits and Muscle Nucleic Acid Concentrations in the Bovine

Abstract

Two experiments were conducted to characterize and relate semitendinosus muscle nucleic acid concentrations to physiological maturity as expressed by carcass composition. In experiment 1, 16 Hereford-Angus and reciprocal crosses (H×A−A×H), 16 Maine-Anjou (MA), and 14 Gelbvieh (Gelb) sired crossbred steers were chosen to represent cattle with differing maturity rates. They were individually fed the same ration and slaughtered when their efficiency of ration energy utilization (after accounting for maintenance requirements) exceeded 8.0 Meal net energy per kg gain 2 consecutive weeks. Although the MA and Gelb gained faster (P<.01) and both showed a higher percentage of carcass lean (P = .06) than H×A−A×H cattle, muscle RNA or DNA concentrations did not differ. In experiment 2, small framed (H×A−A×H) and large framed (Charolais, Gelbvieh, Maine-Anjou and Brown Swiss) crossbred steers were fed two levels of dietary protein (13.4% continuously and 13.4% changing to 8.7%) and two levels of dietary energy (2.94 and 2.59 Meal ME/kg dry matter). The cattle were slaughtered on a constant lot live weight basis. The H×A−A×H were slaughtered at either 453 or 488 kg and the larger framed cattle at either 610 or 662 kg. These weights were chosen to approximate the same carcass composition for both types of cattle. Breed type did not affect average daily gain (ADG), predicted carcass chemical composition or muscle nucleic acid concentrations; however, the combinations of dietary energy and protein density affected both ADG and muscle DNA concentration. Steers fed the high energy-high protein (HEHP) diet gained faster (P< .05) than those fed high energy-low protein (HELP) and low energy-high protein (LEHP) diets, and the cattle on low energy-low protein (LELP) gained slowest (P<.05). Muscle samples from HELP fed cattle had higher (P<.05) DNA concentrations than samples from the HEHP and LELP cattle. Also, DNA concentrations were higher (P<.05) for LEHP cattle than for the LELP cattle. In general, RNA and DNA concentrations contributed little to the understanding of nutritional or breed-type influences on growth or composition.