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Response of saliva Na/K ratio to changing Na supply of lactating cows under tropical conditions
Author(s) -
Thiangtum Wandee,
Schonewille J Thomas,
Verstegen Martin WA,
Arsawakulsudhi Supot,
Rukkwamsuk Theera,
Hendriks Wouter H
Publication year - 2017
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.8063
Subject(s) - polydipsia , zoology , sodium , chemistry , dry matter , saliva , polyuria , lactation , endocrinology , medicine , biology , pregnancy , biochemistry , genetics , organic chemistry , diabetes mellitus
BACKGROUND Factorial determination of the sodium (Na) requirement of heat‐stressed lactating cows is hindered by accurate estimates of the Na losses through sweat. Direct studies, therefore, may be needed requiring information on the time course of healthy animals to become Na depleted and the subsequent rate of repletion. The rate of Na depletion and subsequent rate of Na repletion with two levels of dietary Na to lactating dairy cows housed under tropical conditions were investigated using the salivary Na/K. RESULTS The 12 lactating cows (salivary Na/K ratio 14.6) rapidly developed clinical signs of Na deficiency, including pica, polyuria and polydipsia, reduced body weight and reduced milk yield when fed a low‐Na ration (0.33 g kg −1 dry matter ( DM )) for 3 weeks. Deficiency symptoms were associated with a rapid decrease in salivary Na/K ratio to <4.3 from 7 to 21 days. Subsequent repletion of the cows with NaCl to a ration concentration of 1.1 or 1.6 g Na kg −1 DM for 5 weeks did not restore salivary Na/K ratio to values of >6. CONCLUSION A daily Na intake of heat‐stressed lactating cows to a ration intake of 1.6 g Na kg −1 DM was insufficient to restore Na deficiency. One week was sufficient to deplete heat‐stressed lactating cows of Na, allowing for rapid dose–response studies utilizing the salivary Na/K ratio as a parameter for Na status of cows under tropical conditions. © 2016 Society of Chemical Industry