How much acid in the gut is too much?

Transcription

1 81 How much acid in the gut is too much? J.B. Rowe Animal Science, University of New England, Armidale NSW 2351 Summary Introduction Is the gut adapted for acidic conditions? Recent Advances in Animal Nutrition in Australia, Volume 12 (1999)

2 82 Rowe, J.B. How can acidity of the gut contents affect the host? Effects of increased absorption of acid from the gut Absorption of acid Fermentative metabolic acidosis Rapid carbohydrate fermentation Acid accumulation in the rumen and/or hindgut Direct effect of acid on the gut wall Effect of acid on bacteria in the gut Figure 1 Summary of the pathways linking intake of starch and sugar with the major ways that acid in the gut can adversely affect the host animal.

3 How much acid in the gut is too much? 83 Absorption of acids Fermentative metabolic acidosis Altered balance of anions/cations and acid/base Altered acid/base and cation/anion balances Phosphorus Calcium Ammonium Udder oedema Osteoporosis Osteochondrosis Arthritis Mobilisation of Ca and P from bone Increased Ca and P excretion Lameness Figure 2 Summary of the ways in which absorbed acids may have adverse effects on anion/cation as well as acid/base balances within the host animal. (a) Blood Renal tubule cell Renal tubule lumen Urine H 2 O + CO 2 H 2 CO 3 HCO - 3 HCO H + H + H 2 PO - 4 HPO 2-4 (b) Blood Renal tubule cell Renal tubule lumen Urine H 2 O + CO 2 H 2 CO 3 HCO - 3 HCO H + H + NH 4 + Amino acids Amino acids NH 3 NH 3 Figure 3 Summary of the pathways in the renal tubule cells responsible for acid excretion in the form of (a) phosphoric acid and (b) ammonium ions (from Baggott 1992).

4 84 Rowe, J.B. Urine phosphorus, urine ph and rumen ph Titratable acid 30 Phosphorus Urine ph Rumen ph Figure 4 Relationship between the urine titratable acid (ml N NaOH against 24 hour urine excretion) and the excretion of phosphorus (g/d), urine ph and rumen ph in cattle fed high levels of maize grain (Topps et al. 1966). 35 Direct effect of acid on the gut wall Direct effect of acid on the gut wall Inflammation and tissue damage Compromised resistance to pathogens and parasites Leakage Swine dysentry Laminitis in horses & behavioural problems Stimulation of cytokines Increased disease risk Figure 5 Direct effects of acidic digesta contents on the gut wall and the likely consequences for domestic animals.

5 How much acid in the gut is too much? 85 Bacterial population Consequences of acidic damage to the gut wall Cytokines Matrix metalloproteinases

6 86 Rowe, J.B. Leakage of toxins and bacteria from the gut Effect of acidity on microbes within the gut Endotoxin production Acid resistant pathogens Effect of acid on bacteria in the gut Endotoxins/proteinase Altered microbes Facilitatory bacteria Acid resistant pathogens Immune stimulation and tissue damage Increased disease risk Figure 6 Effects of acid accumulation during anaerobic fermentation on bacteria in the gut.

7 How much acid in the gut is too much? 87 Facilitating bacteria Interaction and synergism of the adverse effects of fermentative acidosis Log (% survival) Colonic ph Figure 7 The relationship between ph of digesta in the colon of cattle fed different amounts of rolled maize and the survival of acid resistant E. coli excreted in the faeces (from the data of Diez Gonzalez et al. 1998) Rapid carbohydrate fermentation Absorption of acids Fermentative metabolic acidosis Altered balance of anions/cations and acids/bases Altered acid/base and cation/anion balances Phosphorus Calcium Ammonium Udder oedema Osteoporosis Osteochondrosis Arthritis Acid accumulation in the rumen and/or hindgut Direct effect of acid on the gut wall Inflammation and tissue damage Compromised resistance to pathogens and parasites Leakage Stimulation of cytokines Lameness Swine dysentry Laminitis Behavioural problems Increased disease risk Respiratory diseases Effect of acid on bacteria in the gut Endotoxins/proteinase Altered microbes Facilitatory bacteria Acid resistant pathogens Stomach parakeratosis and ulcers Increased disease risk Figure 8 Summary of the direct and indirect effects of acid accumulation in the rumen and/or hind gut. The dotted lines indicates likely interactions and the solid lines those effects already well documented.

8 88 Rowe, J.B. Conclusion Acknowledgement References

9 How much acid in the gut is too much? 89

10 90 Rowe, J.B.