Energy metabolism in the digestive tract and liver of cattle: influence of physiological state and nutrition
TL;DR: Most common dietary responses in metabolite uptake by PDV are changes in uptake of ammonia and volatile fatty acids, which emphasize the strong energy: nitrogen interrelationship in the rumen and subsequently the rest of the body.
Abstract: Major functions of portal-drained viscera (PDV) and liver of cattle include absorption of digestion products and modification of the body's supply of intermediary metabolites. The disproportionately high metabolic rate of PDV and liver (7-13% of body tissues) is exemplified by their oxygen uptake (40-50% of whole body). Extensive metabolism of glucose, volatile fatty acids and amino acids by PDV modulates nutrient supply from the diet such that most responses to diet or physiological state are a function of level of diet intake. Similarly, blood flow through PDV is highly correlated with energy intake across a range of body weight, physiological state or diet composition. Most common dietary responses in metabolite uptake by PDV are changes in uptake of ammonia and volatile fatty acids, which emphasize the strong energy: nitrogen interrelationship in the rumen and subsequently the rest of the body. The liver (tissue in series with PDV) removes glucose precursors and ammonia from its blood supply as part of its functions in gluconeogenesis, ammonia detoxification and urea synthesis. The liver also alters amounts and proportions of amino acids supplied by PDV. Accountable percentages of metabolizable energy from net PDV supply include: organic acids, 41-59%; amino acids, 5-13%; and heat energy (from oxygen uptake), 11-22%.
Citations
More filters
TL;DR: In terms of overall ME yield, grain starch is best used when it is fermented in the rumen, however, close coordination of protein and starch supply to the duodenum may improve capture of starch in the form of glucose.
Abstract: Starch is the major energy component of grains. Wheat contains 77% of DM as starch, corn and sorghum contain 72%, and barley and oats contain 57 to 58%. In vitro systems have provided valuable data on kinetic aspects of starch digestion. Molecular biological techniques have provided a clearer picture of the ruminal microbial milieu. Proportions of starch fermented in the rumen can be predicted satisfactorily for a variety of grains and processing methods. Compared with dry rolling, steam processing (flaking or rolling) increases ruminal digestibility of starch (percentage of intake) from 52 to 78% for sorghum, from 75 to 85% for corn, and six percentage units or less for other grains. Recent research provides new insight into pancreatic function and intestinal glucose transport systems. The capacity to digest starch in the intestine ranges from 45 to 85% of starch entering the duodenum, with that capacity apparently limited by the supply of pancreatic amylase. There is evidence that amylase secretion may be enhanced by increasing duodenal entry of protein. Capacity for active transport of glucose across of gut wall does not seem to limit the amount of starch digested that is absorbed as glucose. For ruminants eating medium- to high-concentrate diets, about 30% of their total glucose need comes from glucose absorption, 50% from organic acid absorption (substrates for hepatic gluconeogenesis), and 20% from other sources. When glucose absorption from the gut increases, ruminants generally adjust (decrease) gluconeogenesis to meet their need; that need is directly linked to DE intake. In terms of overall ME yield, grain starch is best used when it is fermented in the rumen. However, close coordination of protein and starch supply to the duodenum may improve capture of starch in the form of glucose.
764 citations
Cites background from "Energy metabolism in the digestive ..."
...The relatively high rate of absorption of ammonia by ruminants (Huntington, 1990) suggests that energy availability, or lack of synchrony between energy and nitrogen supplies, limits the use of available nitrogen by ruminal microorganisms....
[...]
...The liver also removes substantial portions of lactate and amino acids that arrive in portal blood (Huntington, 1990)....
[...]
TL;DR: Higher rates of LBF and steroid metabolism in lactating than in nonlactating cows may indicate chronic effects of higher feed intakes as well.
609 citations
Cites background or result from "Energy metabolism in the digestive ..."
...Teleologically, an increase in LBF in response to increased metabolizable energy intake would serve to aid in transport of digested nutrients from the gut through the liver and on to the rest of the body ( Huntington, 1990 )....
[...]
...Huntington (1990) compared the results from 16 studies in which cattle of various sizes and physiological conditions had hepatic portal blood flow measured....
[...]
TL;DR: Techniques of modern biochemistry promise to further understanding of the mechanisms of metabolic adaptation during the peripartal period, and to quantify the effects of nutrition and environment during pre- and postpartum periods on hepatic glucose and lipid metabolism.
593 citations
Cites background from "Energy metabolism in the digestive ..."
...Hepatic blood flow is known to increase as digestible energy intake increases (Huntington, 1990)....
[...]
TL;DR: Estimates of ENL are important for determining true ileal N and amino acid digestibilities and for identifying means to improve the efficiency of N and energy utilization in growing pigs.
Abstract: During the past two decades endogenous gut N losses (ENL) at the distal ileum in the growing pig have received considerable attention in swine nutrition research. Estimates of ENL are important for...
259 citations
Cites background from "Energy metabolism in the digestive ..."
...Although the gut represents a proportionally small part of the whole animal body, it is reported to account for a significant amount of the total body energy expenditure (Gill et al. 1989; Yen et al. 1989; Huntington 1990)....
[...]
TL;DR: The main limit to use of dietary starch to support live weight gain is digestion and absorption from the small intestine, and increased oxidation of glucose at greater starch intakes may alter energetic efficiency by sparing other oxidizable substrates, like amino acids.
Abstract: Growing cattle in the United States consume up to 6 kg of starch daily, mainly from corn or sorghum grain. Total tract apparent digestibility of starch usually ranges from 90 to 100% of starch intake. Ruminal starch digestion ranges from 75 to 80% of starch intake and is not greatly affected by intake over a range of 1 to 5 kg of starch/d. Starch apparently digested in the small intestine decreases from 80 to 34% as starch entering the small intestine increases from 0.2 to 2 kg/d. Starch apparently digested in the large intestine ranges from 44 to 46% of starch entering the large intestine. Approximately 70% of starch digested in the small intestine appears as glucose in the bloodstream. Within the range of starch intakes that do not cause rumen upsets, increasing starch (and energy) intake increases the amount of starch digested in the rumen, increases the supply of starch to the small intestine, increases starch digested in small intestine (albeit at reduced efficiency), and increases starch digested in the large intestine, such that total tract digestibility remains relatively constant. With increased starch intake, most of the starch is still digested in the rumen, but increasing amounts of starch escape ruminal and intestinal digestion, and disappear distal to the ileocecal junction. Again, within the range of starch intakes that do not cause rumen upsets, as starch intake increases, hepatic gluconeogenesis increases, glucose entry increases, and glucose irreversible loss increases, with a significant portion lost as CO2. The ability to increase use of dietary starch to support greater weight gains or improved marbling could come from increasing starch digestion in a healthy rumen or in the small intestine, but we conclude that the main limit to use of dietary starch to support live weight gain is digestion and absorption from the small intestine. Increased oxidation of glucose at greater starch intakes may alter energetic efficiency by sparing other oxidizable substrates, like amino acids.
221 citations
References
More filters
TL;DR: A model for N pathways in sheep is proposed and, for this diet, many of the pool sizes and turn-over rates have been either deduced or estimated directly.
Abstract: 1. To obtain a quantitative model for nitrogen pathways in sheep, a study of ammonia and urea metabolism was made by using isotope dilution techniques with [15N]ammonium sulphate and [15N]urea and [14C]urea.2. Single injection and continuous infusion techniques of isotope dilution were used for measuring ammonia and urea entry rates.3. Sheep were given 33 g of chaffed lucerne hay every hour; the mean dietary N intake was 23.4 g/d.4. It was estimated that 59% of the dietary N was digested in the reticulo-rumen; 29% of the digested N was utilized as amino acids by the micro-organisms, and 71% was degraded to ammonia.5. Of the 14.2 g N/d entering the ruminal ammonia pool, 9.9 g N/d left and did not return to the pool, the difference of 4.3 g N/d represented recycling, largely within the rumen itself (through the pathways: ruminal ammonia → microbial protein → amino acids → ammonia).6. Urea was synthesized in the body at a rate of 18.4 g N/d from 2.0 g N/d of ammonia absorbed through the rumen wall and 16.4 g N/d apparently arising from deamination of amino acids and ammonia absorbed from the lower digestive tract.7. In the 24 h after intraruminal injection of [15N]ammonium salt, 40–50% of the N entering the plasma urea pool arose from ruminal ammonia; 26% of the 15N injected was excreted in urinary N.8. Although 5.1g N/d as urea was degraded apparently in the digestive tract, only 1.2g N/d appeared in ruminal ammonia; it is suggested that the remainder may have been degraded in the lower digestive tract.9. A large proportion of the urea N entering the digestive tract is apparently degraded and absorbed and the ammonia incorporated in the pools of nitrogenous compounds that turn over only slowly. This may be a mechanism for the continuous supply to the liver of ammonia for these syntheses.10. There was incorporation of 15N into bacterial fractions isolated from rumen contents after intraruminal and intravenous administration of [15N]ammonium salts and [15N]urea respectively.11. A model for N pathways in sheep is proposed and, for this diet, many of the pool sizes and turn-over rates have been either deduced or estimated directly.
310 citations
"Energy metabolism in the digestive ..." refers background in this paper
...Earlier work with 15N similarly showed transfer of urea N was predominantly to the lower gut of sheep fed forage (Nolan and Leng, 1972)....
[...]
...Earlier work with 15 N similarly showed transfer of urea N was predominantly to the lower gut of sheep fed forage (Nolan and Leng, 1972)....
[...]
233 citations
"Energy metabolism in the digestive ..." refers background in this paper
...About 90 % of butyrate produced in the rumen is oxidized by PDV (Bergman and Wolff, 1971) and (3-hydroxybutyrate is...
[...]
...About 90 % of butyrate produced in the rumen is oxidized by PDV (Bergman and Wolff, 1971) and (3-hydroxybutyrate is a major product of that metabolism....
[...]
...Several studies with sheep and cattle (Bergman and Wolff, 1971; Pethick et al, 1981; Huntington et al, 1983; Seal et al, 1989) show that = 33 % of the acetate and 50-80 % of the propionate produced in the rumen are metabolized by PDV....
[...]
TL;DR: The daily rates of synthesis of protein by the whole body and by the individual tissues were determined in two Hereford × Friesian heifers and a dry Friesians cow.
Abstract: The daily rates of synthesis of protein by the whole body and by the individual tissues were determined in two Hereford × Friesian heifers (236 kg and 263 kg live weight), and a dry Friesian cow (628 kg live weight). The rate of whole-body protein synthesis (g protein/d) was estimated from the total flux through the blood of [ 3 H]leucine and [ 3 H]tyrosine following infusion at a constant rate for 8 h. The fractional rates of protein synthesis ( k s ) in the tissues (g synthesized/d per g tissue protein) were obtained after slaughter of the animals at the end of the infusion period. The fractional rate of protein synthesis was calculated assuming that the specific radioactivity of free tyrosine in either the blood (to give k s, b ) or the tissue homogenate (to give k s, h ) defined closely the specific radioactivity of the amino acid precursor for protein synthesis. Total protein synthesis ( A s, b or A s, h ; g/d) in an individual tissue was calculated as the product of k s, b ) (or k s, h ) × protein content. Based on the total leucine flux, i.e. without correction for oxidation, 1.6 kg protein were synthesized daily in the heifers; for the cow this value was 2.0 kg/d. The sum of the daily total synthesis in the major tissues (muscle+bone+brain, gastrointestinal tract (GIT), liver, hide) gave values of 1.4–1.9 kg/d based on A s, b , and 2.2–3.0 kg/d based on A s, h . The percentage contributions of the individual tissues to the total protein synthesis were similar in all three animals, for example based on A s, h muscle was 12–16; carcass (muscle+bone+brain) 32–33; GIT 38–46; liver 7–8; skin 14–21%. The contribution of muscle to total synthesis estimated from the leucine flux was 19–22%; this value is in agreement with those calculated on the same basis for other species. The energy cost of protein synthesis was estimated to account for a maximum of 30% of heat production.
229 citations
"Energy metabolism in the digestive ..." refers background in this paper
...In general, use of amino acids by PDV is related to the high rate of protein synthesis in PDV (Lobley et al, 1980)....
[...]
TL;DR: Progress has been considerable in understanding some aspects of ruminant gluconeogenesis, but many more studies will be required to obtain a complete understanding.
199 citations
"Energy metabolism in the digestive ..." refers background in this paper
...Ruminants are eminently capable of gluconeogenesis to meet their metabolic needs (Young, 1977)....
[...]
166 citations