Urolithiasis is a common disease of males of small ruminant species, with the most common urolith compositions in grain-fed animals being struvite (magnesium ammonium phosphate) and apatite (calcium phosphate).1, 2 Urolith formation and subsequent obstruction have a multifactorial pathogenesis, with major factors being urine pH and urine concentration.1–5 Struvite crystallization occurs only at a pH range of 7.2 to 8.8, and dissolution occurs at pH < 6.5.4, 6 Apatite uroliths develop at a urine pH of 6.6 to 7.8.6, 7 Urine supersaturation by calculogenic materials, including electrolytes, minerals, and mucoproteins, allows precipitation of urolith components.4,8–10 Because of the large role of urine pH and urine concentration of urolith components in calculogenesis, considerable prophylactic and therapeutic focus has been placed on the production of acidic urine and inducing diuresis to promote dilution of urine.
Anionic salts, primarily ammonium chloride, have been used extensively for prevention of urolithiasis because they induce acidic urine and cause an increase in water intake and diuresis.1–3,9 Their use, however, has led to inconsistent results in lowering urine pH and the rate of urolithiasis.8,10–12 The cause of these inconsistencies is unknown; however, the most likely explanations involve the multifactorial nature of urolith production and high-potassium diets that interfere with urine acidification in animals fed anionic salts.8, 13
Dietary cation anion difference is defined as the difference between the summation of the major biological cations and anions of a diet. It is traditionally illustrated as ([Na+K] – [C1+S]), expressed in milliequivalents per kilogram of feed.14 The addition of anions to a ration induces metabolic acidosis from a compensatory increase in extracellular hydrogen ions. The excess H+ is excreted by the kidney to maintain electroneutrality, producing urine of a lower pH.15, 16 A chart correlating DCAD and urine pH exists for dairy cattle,9 but no such estimation exists for goats.
The establishment of a target DCAD in goats could potentially increase effectiveness of urinary acidification as well as prevent overacidification of diets, which may be equally undesirable. Negative effects of anion administration include reduced palatability1,8,12,17 and bone loss attributable to long-term ingestion.18–22,a For these reasons, it would be advantageous to establish a target DCAD that effectively acidifies and dilutes the urine for prevention of urolithiasis, yet avoids harmful adverse effects of overadministration. Determination of the time required from the start of DCAD treatment until optimal pH reduction occurs would provide additional assistance to those attempting to treat and prevent recurrence of urolithiasis and monitor herd response to preventive measures.
The purposes of the study reported here were to determine correlations between DCAD and urine pH, USG, and blood pH in goats and determine a DCAD that induces production of urine with a pH from 6.0 to 6.5. We sought to determine appropriate urine sampling times to monitor effectiveness of DCAD balancing. Our hypothesis was that the DCAD of a ration is positively correlated with urine pH, USG, and blood pH in goats.
Dietary cation anion difference
Urine specific gravity
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