Diagnosis of sodium status in small ruminants

Existing techniques of determining the Na status of ruminants were evaluated in goats and sheep that had widely varying intakes of Na (3-86 mmol/day) and K (20-780 mmol/day). The experiments involved the examination of relationships between Na balance, plasma aldosterone and renin, Na content of faeces and urine, and salivary Na:K ratio in these animals. The variables were measured at monthly intervals for 6 months in goats receiving low or high Na diets, and during 1 month in sheep offered a low Na and low K diet alone or supplemented with 1.5 or 3.0% K. Aldosterone was closely correlated with salivary Na, K and Na:K ratio for both goats and sheep, but there was little relationship indicated between aldosterone and the other variables, either by the raw or logarithmically transformed data. Sodium balance was poorly correlated with all variables, probably because of the unavoidable inaccuracies in measuring Na intake and output. Therefore it was assumed that aldosterone was the best indicator of Na status, since it is the major hormone regulating Na conservation. Stepwise multiple linear regression of all the data with aldosterone as the dependent variable yielded the equation: In (aldosterone) = 5.7-0.87 in (saliva Na:K). Coefficient of multiple determination (R2) was 0.93. In both species aldosterone levels increased markedly when salivary Na:K ratio was less than 4:l. It is concluded that the ratio of Na:K in saliva is a reliable indicator of Na status and a ratio of less than 4 is diagnostic of an incipient Na deficiency