title: Impact of iodine supplementation of dairy cows on milk production and iodine concentrations in milk.
abstract: OBJECTIVE
  To determine the effect of iodine supplementation on milk production and iodine concentrations in milk for pasture-fed, seasonally calving dairy cows.
  
  
  METHODS
  The study was run over two consecutive seasons on the same dairy farm. In Trial One, 294 Friesian dairy cows were either untreated or injected intramuscularly three times with iodised oil (2,370 mg iodine/dose) at the start of lactation (Day 1) and at about 100-day intervals thereafter. Iodine concentrations in milk were determined prior to each injection on Days 1, 98 and 210, and milk, fat and protein yields measured on Days 43, 98, 176 and 238. In Trial Two, 234 Friesian dairy cows were either untreated or injected intramuscularly with iodised oil (2,370 mg iodine/dose) in early lactation (Day 1) and 99 days later. Iodine concentrations in milk were determined prior to treatment on Days 1, 55 and 161. Serum thyroxine (T4) and triiodothyronine (T3) concentrations were determined in the latter two samples and milk, protein and fat yields were determined on Days 25, 119, 182 and 221. In both trials, pasture was sampled at 1- or 3-monthly intervals and iodine concentrations in herbage measured.
  
  
  RESULTS
  Iodine concentrations in pasture averaged 0.24 mg/kg dry matter (DM) in both seasons and varied little over the experimental period. Iodine concentrations in milk from unsupplemented cows were <20 microg/L in both trials. Three iodine injections at about 100-day intervals increased iodine concentrations in milk to 58 microg/L for at least 98 days after each treatment. Two iodine injections at about 100-day intervals raised milk iodine concentrations to 160 microg/L and 211 microg/L at least 55 days after each treatment, but had no effect on serum thyroid hormone concentrations. Iodine supplementation had no significant effect on milk, milkfat or milk protein yield.
  
  
  CONCLUSIONS
  Pastures in New Zealand that contained 0.24 mg iodine/kg DM appeared to provide an adequate iodine intake for dairy cows. Intramuscular injections of iodine resulted in significant increases in iodine concentrations in milk.
  
  
  CONCLUSIONS
  Increasing iodine concentrations in milk via intramuscular injection of iodine could provide a method for significantly increasing iodine intakes of humans, in particular, children.
authors.affiliation: AgResearch Grasslands Research Centre, Private Bag 11008, Palmerston North, New Zealand. neville.grace@agresearch.co.nz
authors.forename: N D
authors.initials: ND
authors.lastname: Grace
authors.forename: G C
authors.initials: GC
authors.lastname: Waghorn
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000502:physiology*; D003612:Dairying; D019587:Dietary Supplements; D005260:Female; D007273:Injections, Intramuscular / Q000662:veterinary; D007455:Iodine / Q000008:administration & dosage* / Q000378:metabolism*; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood; D016896:Treatment Outcome; D014284:Triiodothyronine / Q000097:blood
chemical_list: D014284:Triiodothyronine; D007455:Iodine; D013974:Thyroxine