Colin Musara, Vati Ndjoze, Ophelia Chuma Matomola
et al.
Abstract Urine pH and specific gravity represent the routine objectively verifiable parameters in urinalysis. Urinalysis is presently an underutilised analytical tool in ovine medicine but holds the same potential for predictive, diagnostic and prognostic use in sheep as it does in human and small animal medicine. Urine pH and specific gravity were measured as a health screening tool to ascertain normal physiological ranges in sheep on free-range summer pastures with free access to drinking water. Both sexes, different ages and various breeds including Dorper, Karakul, Damara and cross-breeds were recruited into the study to investigate possible sources of variation. Experimental animals were selected through stratified random sampling using farm records from a population of 69 rams, 135 ewes and 115 lambs. Samples of urine were collected from 60 rams, 60 ewes and 60 lambs by free catch following induction of micturition by transient apnoea. Urine pH was measured by a pH metre whilst urine specific gravity was evaluated with an optical refractometer. The urine pH ranged from 6.81 to 9.08, with a mean of 8.52 ± 0.02 (se). Only one animal had a urine pH value below the existing reference level (7.4–8.5). Concurrent abnormalities of the urine in dipstick analysis included proteinuria and glucosuria. Urine specific gravity varied from 1.003 to 1.050 with a mean of 1.021 ± 0.001 (se). Four sheep, all of them lambs, had urine-specific gravity values above the existing reference level (1.015 to 1.045). The high urine specific gravity was associated with diverse pathological findings including proteinuria, pyuria and glucosuria as well as the presence of urine sediment. Urine pH was influenced by gender and breed and specific gravity by age. The results affirmed that sheep naturally produce alkaline urine and aciduria points to an underlying pathological problem. An association between high urine specific gravity and systemic/urinary system disorders was evident in lambs. Isosthenuria and hyposthenuria were frequently encountered in healthy adult sheep and were considered indices of positive water balance rather than renal dysfunction. Collated data confirmed existing reference levels but revised the upper limit of normal urine pH to 9 instead of 8.5, and the lower limit of normal urine specific gravity to 1.003 instead of 1.015.
Spectrophotometric procedures allow rapid and precise measurements of the pH of natural waters. However, impurities in the acid–base indicators used in these analyses can significantly affect measurement accuracy. This work describes HPLC procedures for purifying one such indicator, meta-cresol purple (mCP), and reports mCP physical–chemical characteristics (thermodynamic equilibrium constants and visible-light absorbances) over a range of temperature (T) and salinity (S). Using pure mCP, seawater pH on the total hydrogen ion concentration scale (pHT) can be expressed in terms of measured mCP absorbance ratios (R = λ2A/λ1A) as follows:where −log(K2Te2) = a + (b/T) + c ln T – dT; a = −246.64209 + 0.315971S + 2.8855 × 10–4S2; b = 7229.23864 – 7.098137S – 0.057034S2; c = 44.493382 – 0.052711S; d = 0.0781344; and mCP molar absorbance ratios (ei) are expressed as e1 = −0.007762 + 4.5174 × 10–5T and e3/e2 = −0.020813 + 2.60262 × 10–4T + 1.0436 × 10–4 (S – 35). The mCP absorbances, λ1A and λ2A, used to calculate R are measured at wavelengths (λ) of 434 and 578 nm. This characterization is appropriate for 278.15 ≤ T ≤ 308.15 and 20 ≤ S ≤ 40.