title: Hypovitaminosis A in extensively grazed beef cattle.
abstract: METHODS
  Vitamin A deficiency was diagnosed in a herd of 97 19-month-old Braford heifers in the Mitchell Grass Downs (Astrebla spp.) bioregion of Hughenden in north-western Queensland during November 2015. Two heifers died after a 48-h history of sternal recumbency and of the 19 that had neurological signs, 7 were blind. Histological changes in the optic nerves of the two necropsied cattle were consistent with vitamin A deficiency. This diagnosis was supported by vitamin A concentrations in fresh liver samples of 5 and 6 mg/kg wet tissue (reference range, 100-175 mg/kg) despite treatment of the cattle with twice the recommended dose of parenteral vitamin A 3 weeks prior to sampling. Rainfall on the property during the 2 years before the outbreak was less than the annual rainfall average of 464 mm, with a total of 281 mm in 2014 and 117 mm from January to November in 2015, most of this falling in January.
  
  
  CONCLUSIONS
  Plant assays for both β-carotene and crude protein concentrations in dry matter (DM) were less than the recommended dietary requirements for beef cattle (0.30 mg/kg DM and 56 g/kg, respectively).
authors.affiliation: College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland, Australia.
authors.forename: E M
authors.identifier: http://orcid.org/0000-0003-4846-1925
authors.initials: EM
authors.lastname: Parker
authors.affiliation: College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland, Australia.
authors.forename: C P
authors.initials: CP
authors.lastname: Gardiner
authors.affiliation: College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland, Australia.
authors.forename: A E
authors.initials: AE
authors.lastname: Kessell
authors.affiliation: College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland, Australia.
authors.forename: A J
authors.initials: AJ
authors.lastname: Parker
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000175:diagnosis / Q000453:epidemiology*; D003937:Diagnosis, Differential; D055864:Droughts; D011793:Queensland / Q000453:epidemiology; D014802:Vitamin A Deficiency / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology / Q000662:veterinary*
keywords: cattle medicine; nutritional disease; ruminant nutrition; vitamin A deficiency