Journal of Animal Science

doi: 10.2527/1991.69suppl_21xpmid: N/A

Article PDF first page preview Close This content is only available as a PDF. Copyright, 1991, The American Society of Animal Science

Etherton, T., D.;Smith, S., B.

doi: 10.2527/1991.69suppl_22xpmid: N/A

Abstract This review discusses the efficacy and biological mechanisms by which somatotropin (ST) and β-adrenergic agonists improve growth performance. These metabolism modifiers increase growth rate, improve productive efficiency (feed efficiency), and increase carcass leanness. The ST-dependent reduction in adipose tissue accretion is the result of remarkable decreases in glucose transport, lipogenesis, and the ability of insulin to stimulate these processes in the adipocyte. Lipolysis is not affected by pST. The effects of ST are chronic in nature rather than acute, as was previously believed. This temporal profile may reflect a ST-dependent decrease in the transcription of important regulatory genes such as the glucose transporter(s) and key lipogenic enzymes. The effects of ST on cell proliferation are mediated by insulin-like growth factor I (IGF-I). A number of IGF binding proteins (IGFBP) are found in serum and are produced locally in a wide variety of tissues. The IGFBP have been shown to modulate the biological effects of IGF-I. The effects observed (either stimulatory or inhibitory) depend on the IGFBP used and the tissue studied. The significance of IGFBP-dependent modulation of IGF-I action remains to be established. β-adrenergic agonists (clenbuterol, cimaterol, and ractopamine) also alter growth rate and carcass composition of growing meat animals. β-adrenergic agonists seem to decrease carcass fat content by decreasing lipogenesis and stimulating lipolysis. The increase in muscle growth observed in animals treated with β-adrenergic agonists is associated with an enhancement of satellite cell proliferation, stimulation of myofibrillar protein synthesis, and depression of myofibrillar protein degradation. This content is only available as a PDF. Author notes 1 Dept. of Anim. Sci., Texas A&M Univ. Copyright, 1991, The American Society of Animal Science

McClelland, John, W.

doi: 10.2527/1991.69suppl_227xpmid: N/A

Abstract Repartitioning technology may offer the livestock industry a significant opportunity to reduce the costs of production of meat animals. However, mere are significant questions about the economic impacts of this new technology. These questions suggest a careful review of issues that are likely to affect the development and adoption of repartitioning technologies. This paper reviews and develops these issues and discusses the economic impacts of scenarios in which technology does not change. The results show that there could be significant costs in the form of higher prices and reduced income if technology remains unchanged in the agricultural sector. This content is only available as a PDF. Author notes 1 The views expressed are the author's and do not necessarily represent policies or views of the USDA. Copyright, 1991, The American Society of Animal Science

Condon, R., J.;Muir, L., A.;Leach,, L.

doi: 10.2527/1991.69suppl_238xpmid: N/A

Abstract The Federal Food, Drug and Cosmetic Act (FFDCA) requires that prior to interstate shipment of a new animal drug there must be an approved application for that new animal drug. Section 512(j) of the FFDCA provides an exemption for an unapproved new animal drug when it is used by qualified experts solely for investigation of the drug's safety and effectiveness. This exemption forms the basis of the Investigational New Animal Drug regulations enforced by FDA's Center for Veterinary Medicine (CVM). Prior to shipment of an unapproved new animal drug intended for clinical investigational use, the sponsor must notify CVM and provide details about who, where, what, how much, and why the shipment is to be made. If the sponsor wants to use edible products from these treated animals, authorization must be obtained from CVM prior to marketing of those products. The sponsor is prohibited from unduly prolonging the distribution of the unapproved drug for investigational use and must not commercially distribute or test-market the unapproved drug. Neither the sponsor, nor anyone acting on behalf of the sponsor, may represent that the unapproved drug is safe or effective for the purposes being investigated. This content is only available as a PDF. Author notes 1 HFV-126, Center for Vet. Med., Food and Drag Administration, 5600 Fishers Lane, Rockville, MD 20857. 3 A. L. Laboratories, One Executive Drive, P.O. Box 1399, Fort Lee, NJ 07024. 4 Animal Health Institute, P.O. Box 1417-D50, Alexandria, VA 22313. Copyright, 1991, The American Society of Animal Science

Seebeck, R., M.

doi: 10.2527/1991.69suppl_243xpmid: N/A

Abstract Experimental conditions and designs suitable for studying the effects of technologies that aim to alter the proportions of lean and fat in meat animals are described. Probably the most important feature of these designs is that they take into account the fact that developmental changes in body composition that occur during growth influence the composition of most classes of livestock within their market weight range. Other desirable characteristics for making the experiments efficient and unbiased are also discussed. Estimates of the animal replication required to achieve the objective of the experiment are made by calculating the power of the experiment, and methodology and its application are described for the different types of experiments relevant to the assessment of these technologies. How animals are to be allocated to a particular experiment is also discussed. Methods of statistical analysis to be used are to match the biology and the experimental design, and some particular characteristics relating to statistical analysis are discussed. This content is only available as a PDF. Copyright, 1991, The American Society of Animal Science

Boyd, R., D.;Bauman, D., E.;Fox, D., G.;Scanes, C., G.

doi: 10.2527/1991.69suppl_256xpmid: N/A

Abstract Somatotropin (ST) and β-adrenergic agonists (β-agonists) have afforded scientists a significant opportunity to alter nutrient metabolism and, thereby, the partition of absorbed nutrients for lean tissue growth. The potential is well illustrated with growing swine treated with porcine ST during the 50 to 100 kg phase of growth. Relative changes and levels achieved for both protein and lipid deposition are unprecedented. Data presented herein also demonstrate that the biological response to bovine ST in growing cattle may have previously been constrained by inadequate provision of indispensable amino acids. The effects of both ST and β-agonists on protein (amino acids) and energy utilization are primarily postabsorptive. Somatotropin improved the partition of absorbed amino acids to protein deposition in growing pigs, cattle, and sheep fed conventional diets by as much as 20 to 40%. Accordingly, the opportunity exists to minimize a significant inefficiency in nutrient expenditure. Whether an increase in protein intake is required to accommodate the ST-stimulated increase depends on the partial efficiency of absorbed amino acid use for protein deposition. The dynamic natures of these and other components were considered using simple and complex models to estimate how selected indispensable amino acid and nitrogen needs would be altered for growing swine and cattle. The impact of β-agonists on the partial efficiency of amino acid use for protein deposition remains unclear because the data are not sufficiently quantitative. Of special interest, and in contrast to ST, is the differential muscle growth that characterizes the response to p-agonists. This suggests that protein input for muscle growth may be less because of conserved visceral growth and that the pattern of dietary amino acids needed to accommodate the tissue requirement for protein deposition in pigs treated with β-agonists may differ from that in pigs fed conventional diets or treated with ST. Neither metabolism modifier improves me efficiency of energy use. In fact, a subtle decrease may exist because the protein component of energy gain is inherently inefficient compared with lipid. This would increase maintenance energy expenditure. Thus, any opportunity for improvement in energetic efficiency may exist only to the extent that the daily maintenance requirement is diluted via more rapid growth. This content is only available as a PDF. Author notes 1 " The authors gratefully acknowledge K. Roneker for preparing the figures for this manuscript. 3 " Anim. Sci. Dept. Copyright, 1991, The American Society of Animal Science

Day, Billy, N.;Britt, Jack, H.

doi: 10.2527/1991.69suppl_276xpmid: N/A

Abstract Metabolic modifiers have the potential to alter reproductive performance in pigs and cattle because 1) fertility is related to body fatness, 2) reproductive organs are targets for metabolic modifiers and metabolic hormones and 3) germ cells and their associated somatic cells produce and are targets for growth factors whose production may be altered by metabolic modifiers. Research with pigs and cattle has focused mainly on how treatment during growing and finishing phases affects subsequent reproductive performance. Some studies have been conducted during the peripuberal period, and others have assessed the effects of metabolic modifiers during early pregnancy. In general, metabolic modifiers alter lean:fat ratios in favor of lean and in some cases enhance rates of growth. In pigs, treatment of growing animals with doses expected to be used commercially does not affect subsequent reproductive performance. In some studies, gilts treated with higher doses of pituitary-derived growth hormone (GH) exhibited altered ovarian function, as manifested by increased concentrations of insulin-like growth factor-I in follicular fluid and by decreased secretion of progesterone by granulosa cells in culture. In contrast, gilts treated with lower doses of porcine somatotropin (pST) during the finishing phase, during the peripuberal period, and during early pregnancy reproduced normally. In ruminants, enhanced growth from treatment with bovine somatotropin (bST) or growth hormone-releasing factor (GRF) leads to a larger skeletal size and a larger pelvic opening, a potential benefit at parturition. Enhanced mammary development may also be a consequence of treatment with bST. Reproduction in heifers is not affected by treatment with doses of metabolic modifiers expected to be used commercially. Overall, the benefits from using metabolic modifiers should greatly outweigh any reproductive risks associated with their application in pigs and cattle. This content is only available as a PDF. Author notes 1 Dept. of Anim. Sci. Univ. of Missouri. 2 Dept. of Anim. Sci., North Carolina State Univ., to whom reprint requests should be sent. Copyright, 1991, The American Society of Animal Science

Klasing, Kirk, C.;Wagner, William, C.;Kelley, Keith, W.

doi: 10.2527/1991.69suppl_288xpmid: N/A

Abstract Metabolic modifiers often have more than one function (pleiotropy), and different metabolic modifiers may cause the same biological effect (redundancy). The properties of pleiotropy and redundancy require that a number of approaches be used to determine the effect of metabolic modifiers on the health of food-producing animals. These include an evaluation of immunocompetence, response to stress, metabolic diseases, interaction with the environment, behavioral and social changes, and structural integrity. All these approaches are discussed for the evaluation of metabolic modifiers, with particular emphasis on somatotropin. This content is only available as a PDF. Author notes 1 Dept. of Avian Sci., Univ. of California. 2 Dept. of Vet. Biosci., Univ. of Illinois. 3 Dept. of Anim. Sci., Univ. of Illinois. Copyright, 1991, The American Society of Animal Science

McLaren, D., G.;Buchanan, D., S.

doi: 10.2527/1991.69suppl_2100xpmid: N/A

Abstract Commercial use of compounds such as somatotropin and β-adrenergic agonists that divert food energy toward production of lean vs fat meat might occur in the 1990s. Emerging biotechnologies to alter the fat:lean ratio of livestock will have a profound effect on genetic improvement programs. This paper considers the implications of commercial use of so-called repartitioning agents for such programs. Consequences of such use for any meat animal species include establishment of optimal testing procedures (e.g., treated vs untreated seedstock); effects of repartitioning agents on phenotypic, genetic, and economic parameters required to compute genetic evaluations; and consideration of ideal market weight, mature size, appetite, soundness, meat quality, and response to repartitioning agents when defining selection objectives. Experimental results in pigs suggest that significant improvements in growth and carcass characteristics would be expected from treatment with repartitioning agents over the range of genotypes currently used in the U.S., although some interactions between genotype, treatment, and slaughter weight are likely. Repartitioning agents might make use of prolific Chinese swine and Booroola Merino sheep practical in U.S. production systems. Differential uptake of repartitioning technologies might increase carcass variability, encouraging “lean-value”-based payment schemes as markets become more specialized and consumers seek “healthier,” more convenient meals. Meat packers may favor lean (i.e., treated), heavy slaughter animals. Data needed to evaluate effects of repartitioning agents on genetic parameters are unlikely to become available until such compounds are used extensively in commercial production. It will be necessary to adjust genetic improvement programs to meet the needs of commercial livestock producers if significant uptake of repartitioning technologies occurs. Ultimately, creation of transgenic animals might supersede existing technologies and pose fresh challenges to animal breeders. This content is only available as a PDF. Author notes 2 " Dept. of Anim. Sci., Univ. of Illinois. Present address: Pig Improvement Co., Inc., P.O. Box 348, Franklin, KY 42135-0348. 3 " Dept. of Anim. Sci., Oklahoma State Univ. Copyright, 1991, The American Society of Animal Science

McKeith, F., K.;Merkel, R., A.

doi: 10.2527/1991.69suppl_2116xpmid: N/A

Abstract Consumers are altering their diets to reduce their consumption of fat. Meat products contain variable amounts of fat; however, to maintain consumer demand for meat and meat products, the meat industry must respond to the changes in consumer attitudes. The meat industry may be divided into fresh and processed (cured meats and sausage products) components. To enhance the composition of fresh meat products, we must reduce the overall fatness of the animal. This may be accomplished using traditional approaches (nutrition, genetics, or management), or the use of repartitioning agents may be an effective means of accomplishing this goal. Reducing total carcass fat will reduce the fat available for processing and will result in the need to alter processing technology for some sausage and processed meat products. Changing the processing procedures and(or) the ingredients used in processed meat products will allow acceptable reduced-fat processed meat products to be developed. This content is only available as a PDF. Author notes 1 Dept. of Anim. Sci., 205 Meat Sciences Lab., 1503 S. Maryland Dr., Urbana, IL 61801. (217) 333-1684. 2 Dept. of Food Sci. and Human Nutr., Michigan State Univ. Copyright, 1991, The American Society of Animal Science