Salt supplementation of dairy cows

Abstract

Supplementation of salt to dairy cows on a pumice soil at Waikite, Rotorua gave a 12.8% increase in milk yield with unaltered composition. The response was immediate and occurred over a 3- month trial period. The result was obtained on ryegrass/clover pastures averaging 0.05% Na whereas the recommended concentration for dairy cows is 0.12% Na. Two methods of diagnosing Na deficiency were examined in the trial namely saliva Na: K ratios and pasture Na content. In the case of the former, practical sampling problems and a lack of a production response calibration indicates that of the two methods, pasture analysis will probably be the most simple and reliable means of diagnosing deficiency. Salt supplementation in a Na-deficient situation is likely to be economically very viable. If the 12.8% milk production response in the current trial was extended to the full lactation period this would give an additional income of $129/cow (at $3.50/kg milk solids) at a cost of $2.84/cow increased. Sodium deficiency is likely to become more prevalent in the future as outputs of Na on farms exceed inputs and potassium fertiliser continues to be applied at rates in excess of maintenance. Further work is required to determine critical Na levels for production responses, the best methods of supplementation, the rates of application required and how well salt dissolves and mixes with other drenches. Keywords: dairy cows, milk yield, salt supplementation, sodium response