Assessment of sodium deficiency and polyuria/polydipsia in dairy cows

Abstract

Sodium (Na) deficiency was observed as a cause of decreased production and associated with polyuria/polydipsia (PU/PD) in a herd of dairy cows. Subsequent investigations revealed other herds experiencing milk loss due to Na deficiency, however PU/PD was not observed in all cases. To further study Na deficiency and diagnostic tests to confirm a diagnosis of NaCl deficiency, sixteen mid-to-late lactation dairy cows were divided into 2 groups for a 30 day Na depletion study. The control group (C) received 0.75% NaCl in their concentrate while the deficient group (E) was fed a ration without supplemental Na. There was a significant difference in production decline (9.5% vs. 29.3%) between C (25.1 to 22.7 kg) and E (18.8 to 13.3 kg). A significant difference in urine Na was observed between C vs. E (29.7 to 21.4 vs. 43.4 to 1.8 mEq/L) and in faecal excretion of Na (FENa) of C vs. E (0.357 to 0.205 vs. 0.329 to 0.016%). A significant decline in serum K was demonstrated between C vs. E (4.43 to 4.61 to 1.8 mEq/l, P<0.01), while FEK increased (39.27 to 36.68 vs. 39.47 to 50.78%). There were no significant differences observed in serum Na or other serum parameters between groups. The diagnostic values of FENa and urine Na determinations was very high. A significant difference between control and depleted animals in both determinations was observed in both experimental and field conditions. Therefore the simple determination of urinary Na concentration in a herd of lactating dairy cows can be used to diagnose Na deficiency. Sampling of 5 high producing cows could be recommended since they would be at greatest risk of deficiency in borderline salt supplementation situations.