title: Response of saliva Na/K ratio to changing Na supply of lactating cows under tropical conditions.
abstract: 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-1dry 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-1DM for 5 weeks did not restore salivary Na/K ratio to values of >6.
  
  
  CONCLUSIONS
  A daily Na intake of heat-stressed lactating cows to a ration intake of 1.6 g Na kg-1DM 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.
authors.affiliation: Department of Large Animal and Wildlife Clinical Sciences, Faculty of Veterinary Medicine, Kasetsart University, Kamphaengsaen, Nakhon Pathom, Thailand.
authors.forename: Wandee
authors.initials: W
authors.lastname: Thiangtum
authors.affiliation: Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.|Department of Agricultural Technology and Environment, Faculty of Sciences and Liberal Arts, Rajamangala University of Technology Isan, Nakhon Ratchasima, Thailand.
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Schonewille
authors.affiliation: Department of Animal Sciences, Wageningen University, Wageningen, The Netherlands.
authors.forename: Martin Wa
authors.initials: MW
authors.lastname: Verstegen
authors.affiliation: Department of Large Animal and Wildlife Clinical Sciences, Faculty of Veterinary Medicine, Kasetsart University, Kamphaengsaen, Nakhon Pathom, Thailand.
authors.forename: Supot
authors.initials: S
authors.lastname: Arsawakulsudhi
authors.affiliation: Department of Large Animal and Wildlife Clinical Sciences, Faculty of Veterinary Medicine, Kasetsart University, Kamphaengsaen, Nakhon Pathom, Thailand.
authors.forename: Theera
authors.initials: T
authors.lastname: Rukkwamsuk
authors.affiliation: Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.|Department of Animal Sciences, Wageningen University, Wageningen, The Netherlands.
authors.forename: Wouter H
authors.initials: WH
authors.lastname: Hendriks
mesh_terms: D000818:Animals; D002417:Cattle / Q000378:metabolism*; D005260:Female; D007774:Lactation; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D011188:Potassium / Q000032:analysis / Q000378:metabolism*; D012463:Saliva / Q000737:chemistry* / Q000378:metabolism; D012964:Sodium / Q000032:analysis / Q000378:metabolism*; D014329:Tropical Climate
chemical_list: D012964:Sodium; D011188:Potassium
keywords: lactating cows; saliva Na/K; sodium; tropical conditions