Rumiant supplementation of gluconeogenic substrates via drinking water

Abstract

Dark cutting or high pH meat is found in all meat species, inducing significant losses to the meat industry. Dark cutting meat is a direct consequence of low muscle glycogen at slaughter, which affects the normal acidification of meat during rigor development, hence, the ultimate pH remains high. The ultimate pH of the meat has a great influence on certain meat quality parameters, such as color, water holding capacity, and tenderness. An animal exposed to stress previous to slaughter may significantly depletes its glycogen reserves. This situation leads to a high ultimate pH if the animal is slaughtered before it has sufficient time to replenish their muscle glycogen stores. Due to stress during pre-slaughter handling is an inevitable process, a strategy to mitigate its effect may be increase muscle glycogen levels prior to slaughter. Supplementation of ruminants prior to slaughter with glycerol or fructose as a source of gluconeogenic substrates may improve muscle glycogen concentrations at slaughter and meat quality. However, dietary carbohydrates are extensively fermented in the rumen and less than 10% of the glucose requirement is absorbed from the digestive tract, thus gluconeogenesis must provide around 90% of the total glucose needs in ruminants. It has been shown 60-80% of drinking water bypasses the rumen. Therefore, gluconeogenic substrates supplemented via drinking water may escape microbial fermentation in the rumen and be absorbed in the small intestine to be available for utilization by the tissues. In experiment 1, described in chapter two, Angus-cross steers (n=36) received 4.3% crude glycerin or high fructose corn syrup via drinking water in addition to a high concentrate diet. The objective of this study was to supply substrates for gluconeogenesis and de novo fatty acid synthesis via drinking water to increase marbling and glycogen concentration in the muscle. Overall, crude glycerin or high fructose corn syrup supplementation via drinking water did not alter carcass or meat quality variables but did alter the size and distribution of intramuscular adipocytes. These results indicate that a longer supplementation time or a higher substrate level may be needed in order to obtain differences in meat quality. In experiment 2, described in chapter three, Southdown wether lambs (n=18) were used to investigate the effect of glycerol or fructose at 12% via drinking during 28-d grazing period and 2-d fasting previous to slaughter on animal performance, postmortem glycolysis and pH decline, proximate and fatty acid composition of tissues, and changes in gene expression of enzymes involved in lipid and glucose metabolism in liver. Overall, glycerol supplementation increased ADG during the grazing period, reduced BW shrink during fasting, and increased HCW. Glycerol supplementation favored muscle glycogen at early postmortem times and glycogen content in the liver, decreased lipid mobilization during fastening and upregulated mRNA expression of lipogenic and glucose transport genes in liver.