THE RELATIONSHIP AMONG DIETARY UNDETERMINED ANION, ACID-BASE-BALANCE,AND NUTRIENT METABOLISM IN SWINE

Dietary undetermined anion (dUA) reflects, in part, the net acid load contributed by the diet. Although dUA is known to influence performanc e and nutrient metabolism of swine, a lack of knowledge impairs its ap plication to diet formulation. This study was undertaken to separate t he effects of dUA from the individual electrolytes that constitute its calculation. Eighteen 35-kg pigs were fitted with indwelling venous c atheters and fed one of three barley and soybean meal-based diets: a c ontrol diet (C), an acidogenic diet containing calcium chloride (A), o r a compensated acidogenic diet containing alkaline salts of sodium an d potassium, as well as calcium chloride (CA). Compared with diet C, d iet A lowered (P < .05) blood pH, bicarbonate, and base excess and inc reased (P < .05) urinary ammonium, titratable acid (TA), and net acid excretion (NAE). Diet CA returned blood acid-base values to normal and reduced urinary ammonium, TA, and NAE relative to diet A. Total nitro gen balance was unaffected by diet. Diet CA increased (P < .05) water intake and urine output. Diet A, but not CA, increased (P < .05) serum ionized Ca and Cl. Apparent Ca and S digestibility and retention were reduced by diet A, but not by CA. Sodium retention was enhanced (P < .05) by diets A and CA; potassium retention was impaired (P < .05) by CA. Dietary UA altered systemic and renal acid-base balance in pigs. M ineral, but not nitrogen, metabolism was affected by both dUA and spec ific ion effects.