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 performance and nutrient metabolism of swine, a lack of knowledge impairs its application to diet formulation. This study was undertaken to separate the effects of dUA from the individual electrolytes that constitute its calculation. Eighteen 35-kg pigs were fitted with indwelling venous catheters and fed one of three barley and soybean meal-based diets: a control diet (C), an acidogenic diet containing calcium chloride (A), or a compensated acidogenic diet containing alkaline salts of sodium and potassium, as well as calcium chloride (CA). Compared with diet C, diet A lowered (P < .05) blood pH, bicarbonate, and base excess and increased (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 nitrogen 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 C1. 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. Mineral, but not nitrogen, metabolism was affected by both dUA and specific ion effects.