Nutrition-gene interaction (post-genomics): Changes in gene expression through nutritional manipulations

Full text: Consumers in the developed world have demanded quality and consistency from animal products marketed to them, and as a result implementation of quality assurance systems has been a major industry priority. These systems are based on the principle that quality, as defined by the consumer, can be influenced at critical control points in the production chain. Consumer demands for sustainable production practices have also led to adoption of strategies sometimes counter to eating quality objectives. For example, Bos indicus animals are used in extensive grazing systems of northern Australia because of their drought and parasite tolerance, but have inferior eating quality. Given the environmental rigours of this northern production system, cattle producers are attempting to optimise decisions regarding all variables that influence their enterprises. These include breed and genotype, slaughter age, lifetime nutrition, health management strategy, growth promotion strategy, weather predictions, stocking rate, and eating quality criteria. In this paper, we will review what is known about development of the intrinsic factors (those extant at the time of slaughter) of bovine skeletal muscle as they relate to the subsequent eating quality attributes of meat. These attributes include toughness, colour, fat content, and nutritive value, but exclude food safety. We will focus on current understanding of nutritional regulation of the candidate genes known to underlie each of these attributes, and where appropriate draw on understanding developed in other mammalian species. We will discuss two experimental studies that are likely to contribute to our understanding of functional gene networks that are responsive to nutritional restriction. The first investigated the effects of severe nutritional restriction and compensatory growth in Bos indicus cross cattle during the post-weaning period. The study was motivated by our previous finding that nutritional effects on meat toughness were long-lived and of sufficient magnitude to be of commercial and scientific interest. The second study involved pre-weaning nutritional restriction of cattle of specific genotpye: heterozygotes for the double muscling (mh) mutation; and Wagyu cross cattle. The aim of the study was to determine whether the expression of double muscling or marbling can be affected by restricted prenatal and preweaning nutrition. The cattle used in these studies were selected on the basis of sire breeding values for the marbling, or double muscling traits. Where appropriate, individual animals were genotyped for key meat quality genetic polymorphisms (e.g. the TG5 marker for marbling). Postweaning nutritional treatments were designed to at least halt weight gain in the animals, and at most lead to a loss of 15% of body weight over 100 days. Pre-weaning nutritional treatments involved restricting nutrition of the pregnant cows from ∼ 100 days of pregnancy, and continued restriction of both cow and calf until the calves were weaned. Tissue samples were collected by repeat biopsy and at slaughter. Muscle and fat phenotyping is currently underway and involves: muscle fibre typing; muscle fascicular structural characterisation; carcass yield; and eating quality objective measures. Gene expression profiling is being performed on a subset of the animals using a bovine muscle and fat cDNA microarray. Bioinformatic tools have been developed to not only identify the genes that are either up- or down-regulated in the respective nutritional treatments, but also to identify co-regulated genes. In the longer term, animal productionists need accurate models for breed and nutritional effects on the intrinsic properties of muscle, so that they can predict the effects of nutritional regimens on eating quality of meat. Polymorphic responses of individual genes are important contributors to the whole response, but need to be viewed in perspective with the larger scale homeostatic and homeorhetic responses of the animal. Given the wealth of information that has come from the Cattle Industry Cooperative Research Centre, we now have a framework on which to build a mechanistic understanding of at least the genetic effects on meat eating quality. We acknowledge with thanks, the work of a large team of researchers within the Cooperative Research Centre who have contributed to the experimental studies we will review. (author)