title: The isoflavone content of commercially-available feline diets in New Zealand.
abstract: OBJECTIVE
  To identify and quantify concentrations of the isoflavones genistein, daidzein, biochanin A and formononetin in commercially- prepared feline diets sold in New Zealand.
  
  
  METHODS
  Feline diets (n=138) were collected from supermarkets, pet stores and veterinary clinics in New Zealand. Diets were classified into five categories based on the following criteria: the presence/absence of soy, the presence/absence of non-soy plant material, and dry matter (DM) content. A high performance liquid chromatography (HPLC)-based assay was developed and validated to identify and quantify concentrations of the isoflavones genistein, daidzein, biochanin A and formononetin.
  
  
  RESULTS
  Isoflavones were detected in all categories of diet, and at quantifiable concentrations in 104/138 (75%) of the diets tested. More dry diets (127/138; 92%) contained isoflavones at quantifiable concentrations than moist diets (83/138; 60%, p<0.001). Of the isoflavone-positive diets, moist diets that contained soy had the highest median isoflavone content (71.1 mg/kg DM and 0.018 mg/kcal metabolisable energy; ME) whilst moist meat-only diets had the lowest (3.24 mg/kg DM and 0.0004 mg/kcal ME). Isoflavone contents varied similarly between categories of diet whether evaluated on a DM or ME basis. High isoflavone contents were associated with diets containing soy and those of low cost. Biochanin A and formononetin were found at concentrations above the detection limit of the assay in 25/138 (18%) and 7/138 (5%) of the diets analysed, respectively. The estimated median daily isoflavone exposure for cats consuming feline diets sold in New Zealand ranged from 0.03 mg/kg bodyweight (BW) for moist meat-only diets to 1.47 mg/kg BW for moist diets containing soy, whilst the diet with the highest isoflavone content would provide daily exposure of 8.13 mg/kg BW.
  
  
  CONCLUSIONS
  Isoflavones are present in commercially-prepared feline diets sold in New Zealand at concentrations that have elicited physiological responses in the reproductive, endocrine, and immune systems of other mammalian species. Since isoflavones appear to be a common constituent of feline diets, further investigation of the biological activities of these dietary compounds in cats is warranted.
authors.affiliation: Institute of Food, Nutrition and Human Health, Massey University, Private Bag 11222, Palmerston North, New Zealand. k.m.bell@massey.ac.nz
authors.forename: K M
authors.initials: KM
authors.lastname: Bell
authors.forename: S M
authors.initials: SM
authors.lastname: Rutherfurd
authors.forename: W H
authors.initials: WH
authors.lastname: Hendriks
mesh_terms: D000821:Animal Feed / Q000032:analysis* / Q000592:standards; D000824:Animal Nutritional Physiological Phenomena; D000827:Animal Welfare; D000818:Animals; D002415:Cats; D002851:Chromatography, High Pressure Liquid; D008401:Gas Chromatography-Mass Spectrometry; D007529:Isoflavones / Q000032:analysis* / Q000502:physiology; D009520:New Zealand; D013025:Glycine max
chemical_list: D007529:Isoflavones