Recent advances in research on bovine muscle and meat sensory quality. II. Influence of rearing factors on muscle characteristics.

摘要

Genetic and rearing factors, including natural feeding of cattle on pasture, may change muscle characteristics, and hence meat sensory quality traits of beef. This review reports how muscle characteristics important for meat quality (which were described in the first paper) are regulated by some rearing factors after birth and after weaning until slaughter of the animals. After birth, the regulation of gene expression and energy metabolism by nutrients has been evidenced in ruminants as in monogastrics. For instance, overfeeding of veal calves induces dysregulation of glucose metabolism, which may be considered as a waste of energy. Furthermore, changes in energy-yielding substrates which occur at weaning induce a regulation of key proteins or enzymes involved in nutrient uptake (namely glucose transporter and lipoprotein lipase gene expression). Plasticity of muscle characteristics, and hence variability in beef quality, have also been demonstrated in growing cattle to depend on rearing factors such as animal age, sex and genetic type, compensatory growth and grass-feeding on pasture. For instance, beef from young bulls is not tasty enough due to low intramuscular fat content compared to heifers, steers or cows. From birth to puberty, the proportion of fast glycolytic muscle fibres increases at the expense of oxidative muscle fibres. On the opposite, feed restriction induces a reduction in the proportion of fast glycolytic muscle fibres, thereby increasing oxidative muscle metabolism. It is associated with a reduction in plasma levels of circulating thyroid hormones. Grass feeding on pasture also increases oxidative muscle metabolism compared to indoor maize-silage feeding. This is probably due to higher plasma levels of circulating lipids with grass feeding and maybe to the physical activity of cattle in the fields. These examples underline the relationships between the hormonal and nutritional status of the animals. Muscle hypertrophy of genetic origin is generally associated with a lower intramuscular collagen content and a higher proportion of fast glycolytic fibres, thereby reducing muscle oxidative metabolism and also intramuscular fat contents. These modifications are favourable for tenderness but detrimental to flavour. All these observations indicate that beef producers can modulate muscle characteristics (and hence beef sensory quality) by modifying the growth path, nutritional factors and/or genetic factors of the animals. The challenge is now to develop a modelling approach to better predict muscle composition (and hence beef quality) from a combination of all this biological information in a practical way informative for the consumers and useful to the beef industry..