Measurement of urine pH and net acid excretion and their association with urine calcium excretion in periparturient dairy cows

Abstract

Urine pH (U pH ) and net acid excretion (NAE) are used to monitor the degree of systemic acidification and predict the magnitude of resultant hypercalciuria when feeding an acidogenic ration to control periparturient hypocalcemia in dairy cattle. The objectives of this study were to evaluate the diagnostic performance of urine dipstick and pH paper for measuring U pH , and to characterize the U pH -NAE relationship and the association of urine Ca concentration ([Ca]) with U pH and NAE. Urine samples (n = 1,116) were collected daily from 106 periparturient Holstein-Friesian cows fed an acidogenic ration during late gestation. Net acid excretion was measured by titration, and U pH was measured by a glass-electrode pH meter (reference method), Multistix-SG urine dipsticks (Siemens Medical Solutions Inc., Ann Arbor, MI), and Hydrion pH paper (Micro Essential Laboratory Inc., Brooklyn, NY). Diagnostic performance was evaluated using Spearman correlation coefficient (r s ), Bland-Altman plots, and logistic regression. Urine pH measured by urine dipstick (r s = 0.94) and pH paper (r s = 0.96) were strongly associated with U pH . Method-comparison studies indicated that the urine dipstick measured an average of 0.28 pH units higher, and pH paper 0.10 pH units lower, than U pH . Urine [Ca] was more strongly associated with U pH (r s = −0.65) than NAE (r s = 0.52). Goals for controlling periparturient hypocalcemia under the study conditions were U pH <6.22 and <6.11, based on achieving urine [Ca] ≥5 mmol/L and estimated urinary Ca excretion ≥4 g/d, respectively. Urine pH was as accurate at predicting urine [Ca] as NAE when U pH >6.11. We conclude that pH paper is an accurate, practical, and low-cost cow-side test for measuring U pH and provides a clinically useful estimate of urine [Ca].

Technical note: Evaluation of a colorimetric point-of-care test for measuring urine ammonium concentration in periparturient dairy cattle

“…We developed a physicochemical equation for urine that demonstrated urine pH is re- where c ≈ 6.1 and TA ≈ 0 with an estimated value of 2.6 mmol/L in bovine urine [95% confidence interval (CI), 0.6 to 4.6 mmol/L; Constable et al, 2009]. Equation [2] confirmed widely held impressions that urine pH provides a clinically useful insight into the degree of systemic acidification in animals consuming acidogenic rations, in that low urine pH is associated with increased NAE and systemic metabolic acidosis, and therefore the possibility of over-acidification and systemic acidemia (Constable et al, 2009(Constable et al, , 2019. We made an interesting and unexpected finding when Eq.…”

“…Feeding an acidogenic ration during late gestation is a practical and effective approach for decreasing the incidence of periparturient hypocalcemia in dairy cattle (Constable et al, 2017;Lean et al, 2019). Ingestion of an acidogenic ration induces a strong ion (metabolic) acidosis that promotes aciduria, hypercalciuria, and increased Ca absorption from the gastrointestinal tract (Grünberg et al, 2011;Megahed et al, 2018;Constable et al, 2019). The marked hypercalciuria provides additional calcium that can be readily reabsorbed at parturition; however, it is important to minimize the development of excessive systemic acidification, as this results in decreased dry matter intake (Hu and Murphy, 2004).…”

“…The marked hypercalciuria provides additional calcium that can be readily reabsorbed at parturition; however, it is important to minimize the development of excessive systemic acidification, as this results in decreased dry matter intake (Hu and Murphy, 2004). The urinary system excretes acid via 3 main pathways: (1) increased excretion of ammonium ions, resulting in increased urine ammonium concentration ([NH 4 + ]); (2) increased proton excretion by H + -K + -ATPase and H + -ATPase in tubular epithelial cells, resulting in decreased urine pH and increased titratable acidity (TA), with TA representing protons in the urine in the form of a weak acid; and (3) increased excretion and decreased reabsorption of phosphate, resulting in increased urine phosphate concentration and buffering capacity (Hamm and Simon, 1987;Lemann et al, 2003;Constable et al, 2019). A gradual increase in urinary ammonium excretion is the major method employed by vertebrates to address nutritionally induced systemic acidification (Hamm and Simon, 1987;Koeppen, 1998Koeppen, , 2009Lemann et al, 2003).…”

“…Urinary excretion of acid has traditionally been quantified by calculating the net acid excretion (NAE) from the urinary [NH 4 + ], TA, and bicarbonate concentration ([HCO 3 − ]; Constable et al, 2009Constable et al, , 2019:…”

Orientações a Proprietários De Equídeos De Trabalho E Lazer Em Bandeirantes E Região, Visando a Prevenção De Doenças, Acidentes No Trânsito, E Melhoria Do Bem-Estar Humano E Animal

“…Para prevenção da hipocalcemia pós-parto, utiliza-se a dieta acidogênica, e sua eficiência pode ser monitorada através da mensuração do pH da urina da vaca (CONSTABLE et al, 2019), sendo relacionado com o metabolismo do cálcio.…”