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Peri-operative amino acid administration and the metabolic response to surgery
- Eva Selldén
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- Journal:
- Proceedings of the Nutrition Society / Volume 61 / Issue 3 / August 2002
- Published online by Cambridge University Press:
- 28 July 2008, pp. 337-343
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General anaesthesia causes hypothermia due to decreased metabolic rate and impaired thermoregulation. Many warming devices are in use to prevent heat loss, but little attention has been paid to stimulating the body's own heat generation. All nutrients raise energy expenditure, and the highest thermic effect is ascribed to amino acids and proteins, 30–40% in the awake state. Amino acids infused during general anaesthesia exert a thermic effect that is enhanced compared with that in the awake state. At awakening from anaesthesia, post-operative hypothermia may be prevented without shivering. The tissues involved and the mechanisms by which nutrients stimulate heat production are still not completely understood. However, these findings support the existence of an inhibitory action normally exerted by central thermosensors, in order to maintain oxidative metabolism within certain limits, to prevent hyperthermia. During anaesthesia central thermosensors are silenced and, hence, amino acid thermogenesis is exaggerated. The amino acid-induced heat generation during anaesthesia predominantly occurs in extra-splanchnic tissues, most probably in skeletal muscle. It may reflect an increased protein turnover, as both protein breakdown and synthesis are energy-consuming processes known to generate heat. Possibly, amino acid infusion provides substrates, otherwise mobilized from the body's own tissues, needed for wound healing and immunological function. However, other cellular mechanisms may also contribute to this non-shivering thermogenesis.
Post-ruminal or intravenous infusions of carbohydrates or amino acids to dairy cows 2. Late lactation
- I. Schei, A. Danfær, L. T. Mydland, H. Volden
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The objectives of this study were to compare the effects of post-ruminal and intravenous infusions of wheat starch or glucose (CHO) or a mixture of amino acids (AA) on milk protein yield, nitrogen (N) utilisation, plasma metabolites and mammary extraction rate of dairy cows in late lactation. Eight cow, ruminally fistulated, was assigned to two 4 × 4 Latin squares during 14-day periods, where the last 7 days were for infusions. Infusions were: (1) starch in the abomasum (SP), (2) glucose in the blood (GB), (3) AA in the abomasum (AP), and (4) AA in the blood (AB). The experiment started 165 ± 4 days (mean ± s.e.) post partum (milk yield 22.5 ± 1.1 kg) Daily amounts of nutrients infused were 257, 283, 233, and 260 g for SP, GB, AP and AB, respectively. The cows were fed a basal diet consisting of a concentrate mixture and grass silage (55:45 on a dry-matter (DM) basis), where total dry-matter intake (DMI) was 13.3 kg/day. Milk production was affected by site of infusion within substrate, whereas infusion substrates within infusion site (CHO or AA) were of minor importance. Responses to intravenous infusions (GB or AB) were similar to those in early lactation, but more pronounced. Compared with SP infusion, GB infusion increased ( P < 0.05) milk yield, energy-corrected milk (ECM), protein and lactose yield by 1.4 and 0.9 kg, 38 and 59 g, respectively. The AB infusion had 1.4 and 1.3 kg, 51, 52 and 50 g higher ( P < 0.05) milk yield, ECM, protein, fat and lactose yields than the AP infusion, respectively. N balance data indicated higher losses of metabolic faecal nitrogen (MFN) by abomasal than by intravenous infusions, but the catabolism of AA was lower than in early lactation indicated by no difference ( P < 0.05) in urinary N excretion between treatments. Intravenous AA infusion increased plasma glucose and insulin above that of intravenous glucose infusion. The treatment effects on plasma insulin concentrations were higher in late than in early lactation, suggesting a higher sensitivity in late lactation even at similar negative energy balance. Compared with the SP infusion, GB infusion showed lower ( P < 0.05) concentrations of essential AA (EAA) and branched-chain AA (BCAA) resulting in a higher AA utilisation because of a higher milk protein production. AP infusion increased ( P < 0.05) plasma non-essential AA concentration compared with AB infusion, but infusion site of AA had no effect ( P>0.05) on plasma EAA or BCAA. It is concluded that it is the nutrient supply and not the lactation stage per se that is important for the response in milk production. Nevertheless, stage of lactation affects the N metabolism and the response in plasma hormone concentrations even when cows are in negative energy balance in both lactation stages.
Post-ruminal or intravenous infusions of carbohydrates or amino acids to dairy cows 1. Early lactation
- I. Schei, A. Danfær, I. A. Boman, H. Volden
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The objectives of this study were to compare the effects of post-ruminal and intravenous infusions of wheat starch or glucose (CHO) or a mixture of amino acids (AA) on milk protein yield, nitrogen utilisation, plasma metabolites and mammary extraction rate of dairy cows in early lactation. Eight cow, ruminally fistulated, was assigned to two 4 × 4 Latin squares during 14-day periods, where the last 7 days were for infusions. Infusions were: (1) starch in the abomasum (SP), (2) glucose in the blood (GB), (3) AA in the abomasum (AP), and (4) AA in the blood (AB). The experiment started 54 ± 4 days (mean ± s.e.) post partum (milk yield 33.4 ± 1.7 kg). Daily amounts of nutrients infused were 378, 365, 341, and 333 g for SP, GB, AP and AB, respectively. The cows were fed a basal diet consisting of a concentrate mixture and grass silage (55:45 on dry-matter (DM) basis), and DM intake was 17.2 kg/day. Milk production was affected by site of infusion within substrate, whereas infusion substrates within infusion site (CHO or AA) were of minor importance. Compared with SP infusion, GB infusion increased ( P < 0.05) milk protein yield and concentration by 55 g and 1 g/kg. The AB infusion tended to ( P < 0.10) increase milk yield and ECM and increased ( P < 0.05) protein yield and concentration by 1.8 and 2.2 kg, 83 g and 1.1 g/kg compared with AP infusion, respectively. Nitrogen balance data indicated higher losses of metabolic faecal nitrogen (MFN) by abomasal than by intravenous infusions, and an increased ( P < 0.05) catabolism for AP and AB infusions compared with SP and GB infusions. GB infusion did not increase ( P>0.10) plasma glucose or insulin concentrations above that of SP infusion. Compared with the SP infusion, the GB infusion had minor effect on plasma AA. AP infusion increased ( P < 0.05) plasma non-essential AA (NEAA) concentration compared with AB infusion, whereas infusion site of AA had no effect ( P>0.05) on essential AA (EAA) or branched-chain AA (BCAA). Although a higher milk protein synthesis was observed for AB infusion, the mammary extraction rate was not higher ( P>0.05) than for AP infusion. Across infusion site, AP and AB infusions increased plasma concentration of EAA and BCAA, but compared with GB infusion, the mammary extraction rates tended ( P < 0.10) to be lower. It is concluded that abomasal nutrient infusion increases loss of MFN and that the gastrointestinal metabolism influences the nutrients available for milk synthesis. Our conclusion is that when glucose was infused, AA limited a further milk protein synthesis, but when AA was infused, glucose or energy substrate might have been the limiting factor. Our results verify that glucogenic substrates are limiting when cows are in negative energy balance.