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Hormonal Regulation of Growth
Pages 184-241

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From page 184...
... In addition, exogenous growth hormone administration reportedly improves growth performance and carcass characteristics of livestock (Machlin, 1972; Wagner and Veenhuizen, 19784. 184 Now a new mechanism has been found through which the growth performance and carcass characteristics of all poultry and livestock species are dramatically improved (Baker et al., 1984; Beermann et al., 1986; Dalrymple et al., 1984; Moser et al., 1986; Muir et al., 1985; Ricks et al., 1984~.
From page 185...
... EFFECTS OF BETA-AGONISTS ON GROWTH PERFORMANCE AND CARCASS CHARACTERISTICS Numerous growth trials have been conducted with different beta-agonists at varying dose levels in poultry, swine, sheep, and, to a lesser extent, cattle (Baker et al., 1984; Beermann et al., 1986; Dalrymple et al., 1984; Moser et al., 1986; Muir et al., 1985; Ricks et al., 1984~. The results of these trials are summarized in Tables 1 and 2.
From page 186...
... In terms of carcass composition, sheep respond] with a 10 percent increase in total carcass protein and a 15 to 30 percent increase in the loineye area.
From page 187...
... These data suggest that beta-agonists, unlike growth hormone, apparently are not able to stimulate milk production, even though both beta-agonists and growth hormone appear to function through a repartitioning of nutrients. EFFECTS OF BETA-AGONISTS ON LIPID METABOLISM Free fatty acid (FFA)
From page 188...
... . Lipogenesis was estimated by measuring the incorporation of i4C-acetate into fatty acids from TGs.
From page 189...
... EFFECTS OF BETA-AGONISTS ON SKELETAL MUSCLE PROTEIN METABOLISM Skeletal muscle celDs have beta-receptors, ant! beta-agonists increase skeletal muscle protein in animals.
From page 190...
... , but the rates consumption was increased only at the two APPENDIX of protein synthesis had decreased 20 percent relative to the controls. These observations suggest that clenbutero} increases skeletal muscle protein in the rat by reducing the rate of muscle protein degradation.
From page 191...
... In addition, blood samples were obtained and assayed for plasma growth hormone, insulin, somatomedin-C (SM-C) , and glucose.
From page 192...
... 1984. Effects of ovine growth hormone and other anterior pituitary hormones on lipolyis of rat and ovine adipose tissue in vitro.
From page 193...
... 1978. Growth performance, carcass deposition and plasma hormone levels in wether lambs when treated with growth hormone and thyroprotein.
From page 194...
... The central question is, what research options are available now and in the foreseeable future that may provide effective ways to manipulate meat animal growth performance? This paper focuses on the concept that an elevation of blood concentrations of growth hormone (GH, or somatotropin)
From page 195...
... 1986. Stimulation of pig growth performance by longterm treatment with pituitary porcine growth hormone (pGH)
From page 196...
... In cultured porcine and bovine adipose tissue, GH antagonizes insulin action (Etherton and Evock, 1986; Walton et al., 1986~. In viva, treatment of pigs with GH decreases the rate of APPENDIX synthesis of fatty acids and markedly blunts the sensitivity and responsiveness of adipocytes to insulin and free IGF-I (Walton et al., 1987a)
From page 197...
... . PROSPECTS FOR INCREASING GROWTH PERFORMANCE Growth hormone clearly increases meat animal growth performance, but before a 197 GH-based product is developed for application in animal agriculture, two questions must be answered.
From page 198...
... 1986b. Stimulation of pig growth performance by porcine growth hormone and growth hormone-releasing factor.
From page 199...
... 1987a. Exogenous pituitary and recombinant porcine growth hormones induce insulin and insulin-like growth factor I resistance in pig adipose tissue.
From page 200...
... (1982) isolated several growth hormone releasing factor (GRF)
From page 201...
... animals showed Effect of Deactivation of Somatostatin on Growth Hormone _~N Immunologic Deactivation /\ | Growth l | Hormone | Muscle Tissue Growth FIGURE 2 Imbalance created by deactivation of somatostatin.
From page 202...
... 1985. Effect of passive immunization against Somatostatin on plasma growth hormone and performance of growing rats.
From page 203...
... 1980. Temporal concentrations of growth hormone, thyrotropin, insulin and glucagon in sheep immunized against somatostatin.
From page 204...
... 1.19 1.40a Average daily gain response (%) 17.6 Feed efficiency (feed/gain)
From page 205...
... 338 350a Gain (kg) 103 llSa Average daily gain (kg)
From page 206...
... 1985. Effect of passive immunization against somatostatin on plasma growth hormone and performance of growing rats.
From page 207...
... 1985. Patterns of growth hormone-releasing factor and somatostatin secretion into the hypophysial-portal circulation of the rat.
From page 208...
... development of organ systems, as well as processes such as milk secretion that are of economic importance. Recombinant derived bovine growth hormone (bSTH)
From page 209...
... The anterior pituitary produces hormones essential for lactogenesis. Prolactin causes localized initiation of milk secretion when injected into the rabbit mammary gland (Forsyth, 1983; Schmidt, 1971; Tucker, 1974)
From page 210...
... Thyroprotein feeding increases milk production for 2 to 4 months and also results in a transitory increase in butter fat percentage. It appears that feeding thyroprotein causes an increased need
From page 211...
... The motor innervation of the mammary gland per se plays no part in normal milk ejection. Myoepithelial cells have been isolated and grown in primary cell culture (Gorewit and McOsker, 1983)
From page 212...
... In part, milk secretion rate depends on the pressure that accumulates within the mammary gland. When milk accumulates within the mammary gland for a long enough period of time, pressure is built up to a sufficient level to inhibit .senretion and milk is resorbed by the blood Schmidt, 1971~.
From page 213...
... Mammary gland blood flow rate is highly correlates] to milk production.
From page 214...
... . Plasma proteins may provide a small portion of the essential amino acids of milk protein synthesized in the mammary gland.
From page 215...
... The malonyl-CoA pathway appears to be the predominant route of fatty acid synthe 215 sis. Two pathways for esterification of fatty acids may be present in the mammary gland: the phosphaticlic acid pathway, which is the most common, an(l formation of 1,2-(liglycericle from acylation of 2-monn~lvo~riri (Dils, 19831.
From page 216...
... the effect of growth hormone on milk production and feet! utilization in dairy cows.
From page 217...
... Cows treated with natural anterior pituitary growth hormone responded with substantial increases in milk production.
From page 218...
... function and clevelopment. GENETICALLY SUPERIOR COWS AND bSTH-TREATED COWS There are many similarities between genetically superior cows and cows treated with growth hormone (Pee} and Bauman, 1987~.
From page 219...
... immecliately to the animal's future ability to produce milk. Several workers have shown that serum concentrations of growth hormone are associated with milk production (Barnes et al., 1985; Flux et al., 1984; Hart et al., 1978~.
From page 220...
... Thus, milk secretion requires the interplay of hormonal, nutritional, and neurohormonal processes in adclition to evacuation of the milk by suckling or milking. A very unique aspect of the mammary gland is that a gradual drop in the level of milk production occurs after the peak level of secretion.
From page 221...
... 1973. Effect of growth hormone on milk production and feed utilization in dairy cows.
From page 222...
... 1983. Effect of exogenous growth hormone in early and late lactation on lactational performance in dairy cows.
From page 223...
... ^~o~ ~oLocy Chubs, E
From page 224...
... The short-chain acids are synthesized within the mammary gland from acetate and beta-hydroxybutyrate; long-chain acids are almost exclusively derived from blood plasma fatty acids of dietary origin; and intermediate-chain acids arise from both sources. In broad terms, about 50 percent of the fatty acids in milk are synthesized in the mammary gland and the other 50 percent are derived directly from blood.
From page 225...
... Some of these changes are influenced by environment, diet, and rates of fatty acid synthesis in the mammary gland. Seasonal variations in milk fat percentages are well recognized, with summer months
From page 226...
... Growth hormone affected both synthesis of fatty acids in the mammary gland and uptake of preformed fatty acids from the blood, depending on dose level and energy balance of the cow. Sutton (1980)
From page 227...
... Declines in milk fat percentage with high-grain feeding are accompanied by a change in milk fatty acid composition from saturated fatty acids to more unsaturated acids, especially those containing 16 carbons or less (Banks et al., 1983; Sutton, 1980~. The type of forage and its effect on milk fat percentage are influenced by forage particle size, maturity, and fiber content of the forage.
From page 228...
... Infusions of protein or amino acids (Schwab et al., 1976) have had variable or no effect on milk fat percentage.
From page 229...
... Only a brief summary of changes in milk fat percentage and composition is reported here. The changes in milk fat percentage and composition observed with the use of fat in diets of dairy cows are a reflection of the change in output of different fatty acids from the mammary gland; short- and mediumchain fatty acids (C4 to Ci4)
From page 230...
... In general, the addition of unprotected fat to dairy diets results in variable effects on milk yield and milk fat composition. The addition offats, oils, or long-chain fatty acids depresses the synthesis of C4 to Cal fatty acids in the mammary gland.
From page 231...
... The synthesis of milk protein requires that both essential and nonessential amino acids be supplied to the mammary gland (Clark et al., 1978; Mepham, 1982~. Uptake 231 of free amino acids from the blood by the mammary gland can occur via several transport systems (Baumrucker, 1985~.
From page 232...
... that it would take about 11 generations for milk protein percentages to equal milk fat percentages if protein yield with no change in fat percentage were used as the selection criterion. EnvironmentlManagement ness, 1985; Ng-Kwai-Hang et al., 1982; Rogers ant]
From page 233...
... of bovine growth hormone. Nutrition Dietary crude protein affects milk yield and consequently milk protein yield more than milk protein percentage (Emery, 1978; Kaufman, 1980; Thomas, 1980, 1983~.
From page 234...
... reported that milk protein percentage increases 0.015 percent for each Meal of additional net energy fed from 9 to 40 Mcal/ciay and that the increaser! protein percentage was usually accompanied by an increased milk yield.
From page 235...
... The milk protein beta-lactalbumin must be present for glucose and UDP-galactose to combine. Thus, beta-lactalbumin appears to be a prime regulator of lactose synthesis (Kuhn, 1983; Larson, 1985~.
From page 236...
... Trace elements may increase slightly in mastitic milk (TalIamy and Randolph, 19704. Administration of exogenous growth hormone has relatively little effect on the percentages of minerals in milk, but yields of minerals increased with increasing milk procluction (Epparc]
From page 237...
... Unsaturated fatty acids are hydrogenated extensively in the rumen. Milk protein percentage and composition can be manipulates]
From page 238...
... Milk fat percentage and composition can be changed through feeding, whereas milk protein percentage is best changed through genetics. Any changes will be slow in coming and minor compared to those achieved through processing and manufacturing.
From page 239...
... 1985. Effect of dose of bovine growth hormone on milk composition: Alpha-lactalbumin, fatty acids, and mineral elements.
From page 240...
... 1985. The effects of long-term administration of bovine growth hormone on the lactational performance of identical-twin dairy cows.
From page 241...
... 1978. Breeding for increased milk protein.


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