David Pethick

This preliminary study quantified the size and number of adipocytes within Longissimus lumborum intramuscular fat across 5 postnatal stages of growth and 2 post-weaning forage-based feeding systems in Bos taurus genotypes selected to differ in their fat distribution. No differences (P>0.05) in size or number of adipocytes due to feeding system were evident. Adipocyte size was lower (P<0.05) for Hereford than Angus and Wagyu × Angus steers. Overall, number of adipocytes for Hereford was lower than for the other genotypes, although did not differ significantly (P>0.05) within each stage of growth. Stage of growth affected size and number of adipocytes (P<0.05).

Formal carcass classification standards or grading systems enable the trade of carcasses unseen. The vast majority of countries begun with classification systems solely designed to describe the carcass to the purchaser with the definition of quality varying for each destination market. In contrast, other grading schemes [e.g., the US Department of Agriculture (USDA) classification] confer both a yield grade and a quality grade to each carcass. More recently, Australia has developed a unique grading system called Meat Standards Australia (MSA) for individual muscles or cuts in interaction with the cooking method. Currently, there are many national and private carcass grading systems or quality schemes for retail beef related to origin, tradition, or eating quality, each with their own focus and methods of evaluating and describing carcasses and/or beef. This chapter aims to describe the current carcass grading systems and the current quality schemes for retail beef, and will conclude with future and emerging considerations that are likely to influence quality assurance schemes in the future.

Genetic selection for lower fatness is commonly practiced in sheep breeding programs to improve consumer appeal for sheep meal products. This selection strategy may result in changes to glucose production. In particular liver glucose output, which is of particular importance for breeding Merino ewes since then ability to build energy stores in nutritionally marginal environments is paramount for reproductive success. Hepatic glucose output can be measured by administering controlled doses of adrenaline which is a strongly catabolic hormone that among other things stimulates the liver to rapidly increase the output at glucose. This release of glucose is the net result of adrenaline-stimulated mobilisation of stored glycogen combined with glucose synthesis from gluconeogenic precursors. The rate of gluconeogenesis in response to adrenaline may he higher in genetically fat sheep as both the basal and adrenaline-stimulated rates of glucose synthesis are higher in genetically fat rats (Rohner—Jeanrenaud et al., 1986. Sanchez-Gutierrez et al., 2000) Furthermore, obese humans have higher rates of gluconeogenesis and higher concentrations of hepatic glycogen than their lean counterparts, both of which would favour greater glucose release in response to adrenaline (Muller et al., 1997). Thus we hypothesise that glucose output following an adrenaline challenge will be lower in ewes that are genetically leaner.

Beef cattle producers are concerned that selecting for carcass traits such as leanness, or for increased feed efficiency, might be deleterious to maternal efficiency and limit the use of genetic improvement technologies such as Estimated Breeding Values (EBVs). We define maternal efficiency by production parameters such as days to calving, birth weight, growth rate, weaning weight, as well as efficiency measures such as total intake and kg weaned per megajoule of metabolisable energy consumed per cow calf unit – kg weaned/MJ ME intake. Selecting for leanness in cattle is of economic benefit due to the relationship to higher yielding carcasses (Nkrumah et al., 2004). Net Feed Intake (NFI) is a trait used to measure feed efficiency in beef cattle, and is calculated as the actual amount of feed eaten by an individual animal less the expected amount of feed consumed based on the animal’s growth rate and body weight (Koch et al., 1963). Low NFI (high efficiency) is economically desirable due to the potential to reduce feed costs and increase stocking rates. Both traits affect the body condition of dams and this is closely linked to maternal traits in cattle (Morris on et al., 1999; Roche et al., 2000; Meikle et al., 2004). This experiment aims to quantify the impact on the breeder herd of selection for leanness or feed efficiency over three breeding cycles. The impact of level of nutrition was also assessed.

The quantity of glycogen stored in muscle at slaughter is a major determinant of meat quality and profitability. Muscle glycogen levels below ~0.6% can result in high ultimate pH (>5.7) of beef (Ferguson el al. 2001) leading to dark cutting or dark firm dry (DFD) meat. Meat which is DFD has a darker colour, reduced shelf life, bland flavour and variable tenderness (Ferguson el al. 2001). This condition significantly reduces the value of a carcase since an elevated ultimate pH (>5.7) makes it ineligible for grading by Meat Standards Australia and premiums will not be rewarded. Low muscle glycogen pre-slaughter is caused by low glycogen storage as a result of low metabotisable energy intake Knee el al, 2004) and/or stress between mustering and slaughter. Stress stimulates the release of endogenous adrenaline, causing the mobilisation and depletion of muscle glycogen stores. When glycogen stores are low, stressors have the greatest influence on the incidence of DFD meat.

The demand for more profitable, high yielding carcasses by the beef industry has increased selection for animals with more muscle and less fat. Animals that have increased muscle hypertrophy generally have more fast-glycolytic type IIX myofibres (Wegner et al., 2000). The adrenaline responsiveness of muscle with more fast- glycolytic fibres is likely to be greater due to their increased glycolytic and glycogenolytic capacity (Wegner et at. 2000), possibly extenuating the problem of DFD meat in high muscling selection line cattle. Therefore, we hypothesise that selection for muscling will decrease muscle glycogen storage and increase the response of muscle to adrenaline.

Thiazolidinediones (TZD) are synthetic compounds that are currently used clinically as oral antidiabetic drugs. These synthetic PPARy ligands offer a relatively new line of therapy for the treatment of many human conditions including impaired glucose tolerance type 2 diabetes mellitus and hyperinsulinemia (Willson el al, 2000). Studies using an in vita cell culture model of 3T3-L1 adipocyte cells, have suggested the potential of utilising TZD in animal production for the promotion of adipocyte differentiation (Gerhold et al., 2002) and for the possible manipulation of fat mass development (Aleo et al, 2003). Due to their agonistic behaviour towards PPARy, TZD are also known potent inducers of adipocyte differentiation (Mornson, 2000). The action of TZD on adipose tissue is associated with increased glucose and FA uptake, lipogenesis, and glucose oxidation (Hauner, 2002). Studies both in vivo and in vitro, suggest that PPARy activation by TZD ligands possess the ability to increase and improve insulin sensitivity in tissues which are insulin responsive. In the ruminant, the process of lipogenesis occurs almost entirely in the adipose tissue and is under the control of insulin, The present study was conducted to determine the effect of TZD on fat metabolism in sheep.

Gene markers for tenderness have been shown to be related to shear force of meat from cattle (Barendse et al., 2008; Page el al., 2002; White el al., 2005). Four tenderness markers currently available commercially are based on polymorphisms in genes controlling components of the post-mortem tenderisation process, specifically the calpain proteolytic system. The objectives of this study were to quantify the magnitude of effects of tenderness gene markers on growth, feed efficiency, carcass characteristics and beef quality in Brahman cattle, and to quantify interactions within and between tenderness gene markers, gender, hormonal growth promotant, method of carcass hang, and major muscles.