MINERALS IN CATTLE URINE
Minerals are dosed preferentially in the urine. Indeed, the regulations are such that the blood variations are quite low and when the concentrations are changed, it is too late for the animal.
Faced with a problem of underproduction in cattle breeding, one of the complementary examinations available to the veterinarian is the analysis of urinary macroelements. When infectious and parasitic causes have been ruled out and a feed-related problem is being considered, this analysis is an additional tool in a livestock audit or follow-up.
Urinary calcium excretion represents only a small portion of the calcium excreted by a bovine and is not dependent on blood calcium levels (MESCHY, 2010). Thus, a low urinary pH associated with elevated calciuria is a sign of metabolic acidosis.
Phosphorus is also mostly eliminated in the faeces, its urinary excretion is low. Acute ruminal acidosis increases urinary phosphorus (ENEMARK et al., 2004; NIKOLOV, 1998) and renal failure can also cause hyperphosphaturia (LUNN and McGUIRK, 1990).
The linear relationship between digestive absorption of magnesium and urinary excretion makes it a good indicator of nutritional status (MESCHY, 2010). Urinary concentration is more sensitive to magnesium deficiency than plasma concentration, making urinalysis the test of choice to diagnose magnesium deficiency. Metabolic acidosis, including that induced by low BACA in the diet, can increase renal excretion of magnesium (LUNN and McGUIRK, 1990; LEAN et al., 2006).
Urinary excretion of electrolytes (K, Na, Cl)
Urine is an interesting medium for assessing electrolyte intake given the efficiency of intestinal absorption, low faecal excretion (MESCHY, 2010) and the lack of storage in the body (APPER-BOSSARD et al., 2010). Linear relationships exist between sodium and chlorine intake and urinary elimination (APPER-BOSSARD et al., 2010). The urinary concentrations of potassium, sodium and chlorine are thus indicators of the level of dietary intake.
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