Sodium requirements of lactating ewes

At parturition, lactation ewes were given ad libitum one of 6 diets containing either a basal level of sodium (200 ppm Na) or basal plus 12.5, 25, 37.5, 50, or 100% of the National Research Council (NRC) allowance of sodium for lactating ewes (equivalent to 0.5% of the ration as sodium chloride). Deionized water was supplied to the ewes with a sodium concentration of less than 0.5 ppm. The parotid Na⁺:K⁺ ratio was taken as an index of sodium adequacy. At 4, 6, and 8 wk postpartum, there was a positive rectilinear relationship between the Na⁺:K⁺ ratio of the parotid saliva and level of sodium in the diet up to 37.5% of the NRC allowance. The Na⁺:K⁺ ratio of parotid saliva from ewes consuming 37.5% or greater of the NRC allowance was not affected by the level of sodium in the diet. It was concluded that the NRC allowance for sodium for lactating ewes was excessive, and an allowance of 870 mg/kg diet was adequate for the maintenance of a normal Na⁺:K⁺ ratio of the parotid saliva.