Journal of Animal Science

Beitz, Donald, C.

doi: 10.1093/ansci/61.Supplement_2.1pmid: N/A

Summary Improvement in the efficiency of production of human food by animals is a principal goal of animal scientists. The purpose of this overview of animal growth is to describe the physiological and metabolic systems that are important to growth of meat-producing animals. Voluntary consumption of feed, digestibility, fermentation losses in the gastrointestinal tract, yields of volatile fatty acids and of microbial cells in the rumina of ruminant animals and specific metabolic actions on absorbed nutrients by the liver are major factors that influence the amount and type of nutrients presented to bone, skeletal muscle and adipose tissue for growth. Gastrointestinal and other hormones and blood flow to growing tissues also regulate types and amounts of nutrients available for growth. The capacity of skeletal muscle and adipose tissue to increase in size is determined by the number of muscle or fat cells available for protein and triglyceride accretion, respectively. When hyperplasia ceases or occurs at negligible rates, then growth occurs by hypertrophy, which is manifested as accretion of protein and triglyceride. Therefore, increases in absorption of nutrients per animals or per unit of feed and increases in deposition of a greater fraction of the absorbed nutrients seem possible and would increase the efficiency of production of human food from feeds by meat-producing animals. This content is only available as a PDF. Author notes 3 " Depts. of Anim. Sci. and Biochem. and Biophys., Iowa State Univ. 1985 by American Society of Animal Science

Florini, James, R.

doi: 10.1093/ansci/61.Supplement_2.21pmid: N/A

Summary The growth-promoting actions of a number of hormones on muscle have been studied by a number of investigators during the past two decades, and some reasonably solid conclusions can now be reached. The somatomedins and insulin are major stimulators of anabolic processes in skeletal muscle; the last remaining uncertainty (absence of evidence that the somatomedins could replace growth hormone in stimulating weight gain in hypophysectomized animals) has recently been removed. The situation with growth hormone is less clear. Evidence from studies on isolated diaphragm muscles is consistent in indicating responsiveness to growth hormone, but most of it was obtained using supraphysiological levels of the hormone, and (in contrast to somatomedin and insulin) it has not been possible to demonstrate direct effects of this hormone on isolated muscle cells. There are some similar problems in the case of insulin—it is not clear to what extent the anabolic actions of insulin can be attributed to its cross-reaction with the somatomedin receptor and/or its effects on energy metabolism, but there is recent convincing evidence that this hormone has direct anabolic effects on muscle cells in culture. The effects of androgens are much more apparent in the whole animal than in isolated muscles or cell culture systems, and they have been more difficult to characterize. The thyroid hormones are clearly required for normal growth and development in the intact animal, but there is not much information on their actions on isolated muscle or cultured cells. Surprisingly, Cortisol exhibits some growth-promoting effects, but these may be attributable to maintenance of the cells in a “healthy” state rather than to a direct stimulation of anabolic processes. In no case is there any detailed biochemical information on the mechanisms by which any of these growth-promoting actions occur, although it is reasonable to infer that the presence of a cytoplasmic receptor for testosterone in muscle indicates a typical steroid-induced activation of RNA synthesis and a resultant increase in protein synthesis. Thus, although a good deal of progress has been made in cataloging the hormones most likely to have direct effects on the growth of muscle, much remains to be done in determining just how those hormones act. This content is only available as a PDF. 1985 by American Society of Animal Science

Young, Vernon, R.

doi: 10.1093/ansci/61.Supplement_2.39pmid: N/A

Introduction An understanding of the processes involved, and their regulation, in the postnatal increase in muscle mass, with its associated accumulation of protein, is fundamental to securing effective approaches for improving production from meat-animal species. In this paper a number of areas of direct importance in relation to muscle protein accretion will be discussed, with the hope that this will provide an additional basis for identifying where research efforts might be directed in order to obtain knowledge that will be of value in the practical context of meat production. There have been a number of recent reviews published that have dealt with this subject (e.g., Millward and Waterlow, 1978; Burleigh, 1980; Lindsay and Buttery, 1980; Swick, 1982) and, therefore, a selected and brief account of some specific issues will follow. We will begin with a summary statement of the early stages in the development of skeletal muscle and the changes in muscle nucleic acid and protein that occur during the period of postnatal growth. This will be followed by an overview of the organization of the translational aspects of protein synthesis. The continuous turnover of proteins implies that the accumulation of proteins in the muscle cell can be regulated through changes in rates of both synthesis and degradation. However, this latter aspect of the overall process of turnover will receive limited mention in view of the more detailed discussion given to this particular topic elsewhere in this symposium. The effects of various stimuli, particularly nutritional factors and physical exercise, will This content is only available as a PDF. Author notes 2 Present address: Massachusetts Institute of Technology, Cambridge, MA 02139. 3 Laboratory of Human Nutrition, Dept. of Nutr. and Food Sci. 1985 by American Society of Animal Science

Johnson, Patricia, R.;Francendese, Albert, A.

doi: 10.1093/ansci/61.Supplement_2.57pmid: N/A

Summary This paper reviews the status of the concept that adipose tissue mass is actively regulated and that the morphology of the tissue influences such regulation. The role of vascularization and innervation of the tissue in respect to growth control is discussed briefly. Theories concerning the origin of the precursor adipocyte are presented along with new morphological data related to this question. New techniques of in vitro cell culture and their contributions to our understanding of the processes involved in adipocyte proliferation and differentiation are presented. This content is only available as a PDF. Author notes 2 Current address: Life Sciences Division-LS-3, Los Alamos National Lab., Los Alamos, NM 87544. 3 Current address: Life Sciences Division-LS-3, Los Alamos National Lab., Los Alamos, NM 87544. 4 Dept. of Biology. 1985 by American Society of Animal Science

, Van Sickle, David C.

doi: 10.1093/ansci/61.Supplement_2.76pmid: N/A

Summary This article is divided into the following segments: Bone Growth—Some generalities about its definition as well as types of bone growth and their relationship to other organ systems. Structural and Functional Aspects of Bone Growth—Discussion of postnatal endochondral and intramembranous osteogenesis as well as differentiation of the concepts of bone modeling and remodeling. Control of Bone Growth-Discussion of systemic (e.g., genetic) and local factors (e.g., hormones, EGF, etc.) affecting osteogenesis as well as their effect on the bone remodeling sequence (ARF). In the final segment–Future Areas of Osteogenic Research-Future nutritional requirements, genetic engineering, as well as emerging cellular and tissue mechanisms are highlighted. Published research from 1862 to present is integrated into this author's understanding about bone growth as well as how it may be focused in the future. This content is only available as a PDF. Author notes 2 Dept. of Anat., School of Vet. Med. 1985 by American Society of Animal Science

Dickerson, Gordon, E.

doi: 10.1093/ansci/61.Supplement_2.104pmid: N/A

Summary Potential genetic changes in components of animal growth were evaluated for expected effects on feed and nonfeed costs per unit of live weight or lean meat output from integrated life-cycle production systems. Faster growth, alone, would reduce costs either of liveweight or lean meat most for nonfeed inputs when animals are marketed by age or maturity rather than at fixed weight, but would reduce both feed and non-feed costs of lean output moderately under fixed weight marketing. Faster growth reduces costs more if only market animals are affected and(or) in species with high rates of reproduction. Increased growth rate reduces costs least for feed inputs under constant-age marketing, and when there is no premium for leaness under constant weight marketing, for maternal breed roles in crossbreeding, and(or) in species with low reproductive rates. Less fat deposition also would reduce both feed and nonfeed costs of lean meat for all breed roles in crossbreeding but may even increase feed and total costs of live weight marketed, especially in species with low reproductive rates and in maternal crossing stocks. Faster rate of maturing for live weight is confounded with higher ratio of fat to lean deposition, and faster maturing rate for lean growth is less feasible and would require earlier sexual maturity to reduce meat costs in purebreeding systems when reproductive rate is low. Lowered metabolic rate independent of body composition and other functional traits would reduce meat costs significantly, but biological feasibility seems uncertain. More critical evidence is needed concerning genetic variation in above-maintenance feed costs of protein and fat deposition. This content is only available as a PDF. Author notes 2 Roman L. Hruska U.S. Meat Animal Research Center, ARS, USDA, 225 Marvel Baker Hall, Clay Center, NE 68933. 1985 by American Society of Animal Science

Taylor, C., S.

doi: 10.1093/ansci/61.Supplement_2.118pmid: N/A

Summary On the premise that each genotype has its own inbuilt genetic size factor operating throughout growth, two formal genetic size-scaling rules have been proposed. A major outcome of the scaling rule for time variables is the concept of metabolic age. The corresponding concept for cumulated growth variables is degree of maturity. Genetic comparisons made at the same metabolic age or at the same degree of maturity are independent of adult size. By averaging over genotypes at each metabolic age or degree at maturity, mean size-scaled growth curves are obtained which provide a unified description of mammalian growth. Mean mammalian growth curves are presented for body weight, growth rate, body composition, heat production, maintenance requirements, food intake, and food efficiency. For any trait, deviations from these mean values or curves can then be studied; variation independent of genetic variation in adult size can be evaluated, and deviant species or strains identified. Unscaled expected values can also be calculated for any genotype of given adult weight whenever mean size-scaled values are available. Results based on genetic size-scaling are reviewed for genetic differences between species, between breeds or strains within a species, between sexes, and between sires within a breed. This content is only available as a PDF. Author notes 2 Computer graphs by A. J. Moore. 1985 by American Society of Animal Science

Faras, Anthony, J.;Muscoplat, Charles, C.

doi: 10.1093/ansci/61.Supplement_2.144pmid: N/A

Summary Two major developments in the new biology, namely recombinant DNA and hybridoma technology, have been employed to address problems in animal health and production. In this article we review three means by which these technologies have been employed to improve animal production: 1) prevent losses from infectious disease by facilitating the development of efficacious vaccines and monoclonal antibodies; 2) increase growth and milk production by providing unlimited quantities of genetically engineered animal growth promotants; and 3) increase the nutritional quality of animal feed. This paper will first review the basic features of these new bio-technological developments and then discuss the kinds of reagents that have been developed by these technologies and how they will benefit animal health and production in the future. “Life is the evolution of molecular machines… The beauty of something is not the atoms that go into it, but the way they are arranged.” This content is only available as a PDF. Author notes 2 Dept. of Microbiol., Univ. of Minnesota Medical School. 3 Molecular Genetics, Inc., 10320 Bren Road East. 1985 by American Society of Animal Science

Muir, Larry, A.

doi: 10.1093/ansci/61.Supplement_2.154pmid: N/A

Summary This paper is a review of the non-nutritive, exogenous substances which improve animal growth and feed conversion. These agents are categorized according to the methods through which they improve livestock performance. Categories defined and discussed include antimicrobial production improvers, rumen additives, anabolic growth promotants and “other” production improvers. The exogenous substances covered include primarily drugs with an approved New Animal Drug Application (NADA) with the U.S. Food and Drug Administration. Two exceptions are thiopeptin, an antibiotic, and trenbolone acetate, a synthetic androgen. These compounds are discussed because they work through modes of action where approved drugs are not available. Agents for the control of parasitic diseases will not be covered. The modes of action through which these substances act are examined in detail. Some recent studies involving the effects of exogenous hormones on the growth, feed conversion and carcass composition of normal, growing lambs are presented. The hormones discussed include growth hormone, prolactin and thyrotrophin-releasing hormone. Also, a study on the effects of exogenous GH on milk production is included. Finally, the future of production improvers for livestock is discussed. This content is only available as a PDF. Author notes 2 Dept. of Anim, Nutr, and Physiol. 1985 by American Society of Animal Science

Zimbelman, R., G.

doi: 10.1093/ansci/61.Supplement_2.181pmid: N/A

Abstract The comments will be an overview of the merits of the symposium, some personal philosophy, some hopes for the future, and a perspective on some current items which are very relative to the area of animal growth. This will not be a summary of the technical aspects of the presentations covered during the symposium for several reasons. First of all, it's the end of two very full days and I'm sure that many of the presentations were so challenging that you would rather become more philosophical at this point. Secondly, there was so much information provided here that I would not know where to start to summarize it all. Thirdly, some of my colleagues have questioned my judgment in taking on a summarization assignment in any case and they would certainly find my judgment faulty if I even pretended to accept such an assignment. Fourth, Gene Allen, when he asked me to do the summarization, said he didn't except a summary of all of the scientific aspects of what has been covered in the last two days. I believe the fact that this was a multidisciplinary and comparative symposium adds to its value. It is good that the committee chose speakers from outside the American Society of Animal Science when they have expertise and are the best person to provide us an overview. Wouldn't it be nice, however, if the best speakers in the world on each topic of interest were animal scientists. Obviously, comparative aspects of different species are This content is only available as a PDF. 1985 by American Society of Animal Science