An attempt to define the sodium requirement of lactating dairy cows in a tropical environment

BACKGROUND: Lactating dairy cattle in the tropics may require more sodium (Na) owing to the hot and humid climatic conditions. It is unknown whether the current recommendations on Na for lactating cows can be quantitatively used in tropical countries. This study attempted to define the Na requirement of lactating dairy cows under tropical conditions by measuring Na levels in saliva, milk and faeces. RESULTS: The concentrations of Na and potassium (K) in milk, faeces and serum were not affected by dietary treatments. The amount of Na absorbed by cows fed the basal (low‐Na) diet containing 0.4 g Na kg^?1 dry matter (DM) was equal to the amount of Na lost in the milk, showing that these animals were fed an Na‐deficient ration. This observation was corroborated by salivary Na and K levels, with the cows on the low‐Na diet having salivary Na concentrations below 120 mmol L^?1 in combination with salivary K concentrations above 20 mmol L^?1 (P < 0.05). CONCLUSION: Consumption of a daily ration formulated to contain the current Na requirement set by the NRC appears to provide too much Na for lactating cows under tropical conditions. A tentative value of 1.2 g kg^?1 DM is proposed as the Na requirement for dairy cows under tropical conditions. Copyright © 2011 Society of Chemical Industry