Liveweight response following sodium chloride supplementation of beef cows and their calves grazing native pasture

Abstract

Hereford cattle grazing native pastures on the eastern Darling Downs, Queensland, were deemed sodium (Na) deficient on the basis of salivary Na and potassium (K) levels. Common salt (NaCl) was offered ad libitum to one half of the animals. Cows receiving the supplement had significantly better rates of liveweight increase (0.35 v. 0.14 kg head-1 day-1, P < 0.01) than unsupplemented cows. Calves of supplemented cows grew significantly faster than calves of unsupplemented cows (0.77 v. 0.62 kg head-1 day-1, P < 0.01). After 21 days of Na supplementation, cows in the supplemented group had mean saliva values of 139.1 m-equiv l-1 Na and 7.4 m-equiv l-1 K; these values are considered normal. Corresponding values in the unsupplemented group were 60.2 m-equiv l-1 Na and 71.7 m-equiv l-1 K, which are indicative of severe Na deficiency. Levels of this magnitude remained throughout the duration of the experiment. Blood and milk concentrations of Na and K were not affected by Na intake. Urinary levels of Na and K were attered by Na intake but were extremely variable.