The use of approved beta-agonist feed additives improves the efficiency and yield of lean meat production in beef cattle, swine, and turkeys. These compounds act to repartition the use of nutrients consumed by animals toward increased muscle growth and reduced amount of fat gain. They are administered as a feed ingredient because they are orally active. When fed as approved during the last 20 (zilpaterol hydrochloride) to 42 (ractopamine hydrochloride) days before harvest, carcass weight and lean meat yield are significantly increased and meat quality and eating characteristics are changed minimally.

The Cornell Net Carbohydrate and Protein System model was used to formulate a low-protein mixed grass hay and corn diet predicted to create a ruminal N deficiency of 33% in 250-kg Holstein steers. Nitrogen metabolism, digestibility and metabolic status responses were compared between this control diet and a similar diet supplemented with 1.7% urea to compensate for the ruminal N deficiency. A 4 x 4 Latin square design was used to analyze main effects of diet and subcutaneous administration of 500 mug estradiol-17beta (E-2) twice a day. Urea supplementation increased N intake from 60 to 93 g d(-1), improved N balance from 10.1 to 17.7 g d(-1), and improved total tract digestibility of N, neutral detergent fiber (NDF), organic matter (OM), and dry matter (DM) (all P < 0.05), but there was no effect of urea supplementation on total tract digestibility of non-structural carbohydrate (NSC) and N retention (percent of N intake). Plasma urea N increased fourfold (P < 0.05) and plasma insulin increased from 0.32 to 0.50 ng mL(-1) (P = 0.06) when the urea diet was fed. Administration of E-2 did not alter N metabolism or plasma metabolites and insulin at either level of protein intake. It is concluded that supplementing a fiber-rich grass-hay-based diet with urea to achieve ruminal N balance increases digestibility of fiber fractions without altering dietary N utilization. Under these nutritional conditions the use of estrogenic growth promoters remains ineffective independent of ruminal N balance.

Discoveries, understanding, and innovations in meat science during the last century have led to revolutionary changes in meat and poultry production, processing, marketing, and consumption. American Society of Animal Science members have made key contributions in most, if not all, categories of advancement. The first US university meat science program was begun in Minnesota in 1905. Use of mechanical refrigeration in the meatpacking industry, improved transportation and packaging, and home refrigeration provided more flexibility, variety, and consistency in meat and meat products in the early 1900s. Cooperative meat research was begun by 27 universities in 1925, with a focus on the observational characterization of carcass traits and composition, meat quality attributes, and causes of the wide variation in these variables. Scientific study of genetic, nutritional, and environmental influences on the growth, physiology, and postmortem biochemistry of muscle often used muscle-comparative investigations. Rigor mortis, cold shortening and thaw rigor, postmortem muscle metabolism, postmortem tenderization and tenderness variation, and postmortem myoglobin and lipid oxidation were studied vigorously in the 1960s and beyond, defining the biochemical bases for associated outcomes in fresh and processed products. Value-added benefits resulted from implementation of electrical stimulation, boxed beef and modified-atmosphere packaging, restructuring technologies, collagen recovery, and muscle profiling work. Isolation, purification, and definition of the primary structure and biophysical properties of the myofribillar and cytoskeletal proteins in muscle aided the understanding of contraction and postmortem changes. The role of Ca-dependent proteases in meat tenderness and muscle growth is being clarified. The chemistry of meat curing, meat emulsion formation, fermentation, and other processing methods led to new technologies, new meat products, and new benchmarks in product shelf life and quality. Meat safety assurance and our ability to manage the microbiological causes of food-borne illness and spoilage are imminently important now and in the future.

AbstractThe growth of animals can be described as an increase in mass of whole body, tissue(s), organ(s), or cell(s) with time. This type of growth can be characterized by morphometric measurements. Growth also includes developmental aspects of function and metabolism of cells and tissues from conception to maturity. Both types of growth are influenced by genotype, nutritional status, and gender of the animal.

Mechanisms by which ractopamine and other beta-adrenergic agonists stimulate skeletal muscle growth are discussed. Oral administration dose-response studies in surgically altered laboratory animals provide evidence that indirect endocrine-mediated effects are not an essential component of efficacy. Results from age-comparison studies in laboratory animals and livestock species provide evidence that metabolic maturity of skeletal muscle may be a critical factor with regard to efficacy, suggesting that receptor presence and density are important. Temporal studies demonstrate the rapidity of responses associated with protein and lipid metabolism changes, and that progressive decline in rate of anabolic response in skeletal muscle results from chronic administration. Associated results that demonstrate progressive beta-adrenergic receptor density reductions are observed and suggest, likewise, that protein accretion rate and muscle growth rate responses are receptor-mediated. Measurement of in vivo metabolic effects resulting from continuous systemic infusion has been conducted in relatively few experiments. Detailed blood flow and hind limb net flux data are available for a single beta-agonist, cimaterol. Kinetics studies and close arterial infusion of cimaterol in the hind limb of growing cattle demonstrate large transient increases in amino acid extraction from the circulation and similar patterns of net uptake when compared with the contralateral control saline-infused hind limb. Predictions of differential net effects on protein accretion using integration of essential amino acid net flux measurements are corroborated by quantitative documentation of protein mass differences in individual muscles from treated and control hind limbs. Definitive descriptions of specific pathway mechanism(s) of action for increasing protein synthesis have not as yet been reported. Therefore, additional research is required for elucidation of cellular and intracellular components of mechanism(s) of action.

Understanding the relationship of condition and cleanliness of cows to microbiological counts on their carcasses should be useful in designing animal and carcass handling/processing protocols to identify potential sources of Salmonella and Escherichia coli O157:H7 and to reduce microbial contamination. Eighty cull cows from twelve lots were weighed and categorized for breed; then, four live animal characteristics were evaluated including body condition, filth on the animal, ambulatory (lameness) condition and feces condition. The cows were harvested during a 4-day period and the carcasses were weighed, graded and sampled for microbiological analyses. Aerobic plate counts (APC), total coliform counts (TCC) and E. coli counts (ECC) were determined on samples taken at three plant locations (pre-evisceration, post final wash, and post 24 hr chill) from two carcass sites (brisket and round). In addition, samples of fresh feces, hide-surface sponged samples and carcass tissue samples were analyzed for Salmonella and E. coli O157:H7. Live weight, carcass weight, and carcass grade had a significant (P<0.05) effect on APC; lot number and slaughtering date had a significant effect on APC, TCC, and ECC; and ambulatory (lameness) score had a significant effect on APC and TCC. In 77 fresh fecal samples and 80 hide-surface sponged samples, incidence of E. coli O157:H7 was 0% and 0%, respectively, while incidence of Salmonella was 0% and 13.8%, respectively. Of the 427 carcass samples, 0% tested positive for E. coli O157:H7 and 1.2% tested positive for Salmonella. These results suggest that most live animal and carcass characteristics were not related to the microbial contamination of carcasses, and that activities associated with slaughtering/dressing were the source of most of the differences in microbiological contamination on carcasses.

The consequences of a 42 d exposure to elevated growth hormone (GH) on adipose tissue were assessed using the regulatable ovine metallothionein- ovine GH (oMt1a-oGH) transgene in male and female GH transgenic (TG) mice. Activation of transgene expression at 21 d of age followed by inactivation of transgene expression at 63 d of age (TG-on/off) increased individual white adipose tissue (WAT) depots and total body lipid stores in both males and females. WAT, expressed as a percentage of fasted body weight, did not differ in wildtype (WT) and continuously activated TG males and females up to 105 d of age, but was increased approximately 270% following inactivation of the transgene. Inguinal depot adipocytes were more numerous in both male and female TG +/- relative to WT or TG animals. The ensuring obesity was not accompanied by a decrease in thermogenic capacity of brown adipose tissue, as indexed by uncoupling protein quantity. GH transgene expression was accompanied by elevated insulin levels that were restored to WT levels upon cessation of transgene expression (p > 0.1). Early, transient exposure to elevated GH increased total body lipid by nearly threefold independent of gender; the increased lipid content was sustained and reflected WAT hypertrophy and hyperplasia. The oMt1a-oGH mouse provides a novel model of induced obesity in response to inactivation of a GH-transgene by the withdrawal of the transgene stimulus.

The chronology of changes in body weights, food intakes and plasma concentrations of selected metabolic hormones and metabolites were determined in sheep during the induction (dynamic) and static phases of diet-induced obesity. Lean adult Dorset ewes weighing 47 kg were fed a pelleted hay-grain diet at maintenance (lean; n = 7) or were fed the same diet ad libitum to a maximum intake of 3 kg·sheep-1·d-1 (obese; n = 8) for 78 wk. Body weight of obese sheep doubled (97 vs. 47 kg) by wk 42 of ad libitum intake. Average daily intakes of dry matter (12.8 g/kg) and digestible energy (165 kJ/kg) were comparable in maintenance-fed lean sheep and ad libitum-fed obese sheep consuming maintenance after wk 50, which began the static phase of obesity. Fasting plasma concentrations of insulin in the obese sheep increased steadily from 50 ± 6 pmol/L at wk 0 to a sustained plateau of 249 ± 21 pmol/L after wk 30. Plasma levels of glucose, immunoreactive glucagon and thyroid hormones were consistently greater (P < 0.05) in obese sheep than in lean sheep after wk 2, 3 and 25, respectively, of the experiment. Concentration of lipid (49 vs. 25%) in the carcass stripped of internal fat was greater (P < 0.01) in obese sheep than in lean sheep, but concentration of protein (10.4 vs. 15.3%) was less in the heavier carcass (58 vs. 24 kg) of the obese sheep. We conclude that hyperinsulinemia and abnormal fuel metabolism are early events during dynamic obesity and these defects persist throughout the static phase of obesity. Maintenance energy requirements relative to unit body weight (W1.0) seem similar in lean and dietary obese sheep.