title: An attempt to define the sodium requirement of lactating dairy cows in a tropical environment.
abstract: 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Large Animal and Wildlife Clinical Sciences, Faculty of Veterinary Medicine, Kasetsart University, Kamphaengsaen, Nakhon Pathom 73140, Thailand. fvetwdr@yahoo.com
authors.forename: Wandee
authors.initials: W
authors.lastname: Thiangtum
authors.forename: Adisorn
authors.initials: A
authors.lastname: Yawongsa
authors.forename: Jan Thomas
authors.initials: JT
authors.lastname: Schonewille
authors.forename: Theera
authors.initials: T
authors.lastname: Rukkwamsuk
authors.forename: Chalermpon
authors.initials: C
authors.lastname: Yuangklang
authors.forename: Martin W A
authors.initials: MW
authors.lastname: Verstegen
authors.forename: Wouter H
authors.initials: WH
authors.lastname: Hendriks
mesh_terms: D000465:Algorithms; D000818:Animals; D002417:Cattle / Q000502:physiology*; D003433:Crosses, Genetic; D003612:Dairying; D005243:Feces / Q000737:chemistry; D005260:Female; D017408:Guidelines as Topic; D007408:Intestinal Absorption; D007774:Lactation / Q000097:blood / Q000378:metabolism*; D008892:Milk / Q000737:chemistry; D009751:Nutritional Requirements; D011188:Potassium / Q000032:analysis / Q000097:blood; D011897:Random Allocation; D012463:Saliva / Q000737:chemistry; D012964:Sodium / Q000032:analysis / Q000097:blood; D012982:Sodium, Dietary / Q000008:administration & dosage / Q000009:adverse effects / Q000378:metabolism*; D014329:Tropical Climate
chemical_list: D012982:Sodium, Dietary; D012964:Sodium; D011188:Potassium