Materiales para la RM

Dry diets were defined as those containing >90% DM and moist diets defined as those containing <25% D M . No diets of intermediate D M content were analysed. Residual data was tested for normality with the Anderson-Darling test and found not to be normally distributed. Diets found to contain any isoflavone above the limit of detection of the assay were termed 'positive' for either genistein or daidzein.

Data were analysed according to the content of genistein, daidzein and total isoflavone, as well as retail price of each diet (NZ$/kg D M). Data are expressed either on a DM or metabolisable energy (ME, kcal) basis. The ME of each diet was calculated using the modified Atwater factors (crude protein x 3 . 5, crude fat x 8.5, and carbohydrate x 3 . 5),

where the proportions of protein, fat and carbohydrate in each diet were recorded according to the manufacturer's labelling. Where the content of carbohydrate was not reported, it was estimated by subtraction (AAFCO 2004) .

All statistical analyses were performed with SAS (version 8, SAS Institute Inc, Cary NC, USA). Univariate procedures were used to describe the median and quartiles of the data, s ince the data were not normally distributed and calculation of the mean was therefore inappropriate (Glantz 2005). Median and quartile data included diets with a zero value, unless otherwise specified. Proportions of isoflavone-positive diets in each category were calculated and compared for equality. N on-parametric analyses of variance were performed on isoflavone-containing diets within each group using the Kruskal-Wallis test statistic ( H ; p<0.05).

Daily intake of isoflavone was estimated according to the total content of i soflavone of each diet per unit of ME (kcal) . According to the National Research Council (NRC

1 986), active domestic cats have an approximate daily ME requirement of 80 kcal/kg BW. Based on this assumption, the total isoflavone content found in 80 kcal of each diet is equivalent to the total content of i soflavone consumed by a domestic cat per kg BW.

2. 1 .3. Results

An HPLC-based assay was developed to identify and quanti fy the concentrations of the isoflavones genistein, daidzein, biochanin A and formononetin in domestic cat diets. Absorbance was linear over the range of 0. 1 25 11g/ml to 625 11g/ml for all isoflavones tested ( R2 ranged from 0 .943 for biochanin A to 0 .998 for gen istein). Glycitein could not be adequately separated and could not, therefore, be quantified. Mass spectrometry suggested that glycitein, if present, occurred only in trace amounts.

The limit of detection of the assay was 1 .56 11g/g, as defined by evaluation of the linearity of standard curves following serial dilutions of i soflavone standards and the peak signal­ to-noise ratio in preliminary trials. Samples w ith concentrations of i soflavone below the limit of detection were assigned a value of zero. For the purposes of comparison of diet

isoflavone content between diet categories, only isoflavone-positive diets, i.e. those diets containing isoflavones above the limit of detection, were included. The average intra­ assay coefficient of variation (CV) was 1 0% for daidzein, 7% for genistein, 9% for biochanin A and 1 1 % for formononetin (n = 3). The inter-batch CV, determined by

repeated analysis of triplicate samples of the soy protein isolate at regular intervals throughout the period of analyses of the diets, was 7%. The mean (± standard error of the mean, S EM) content of isoflavone of the soy protein isolate was 700 (± 26. 3 ) mg/kg DM, which is within the reported range of 373 - 1 875 mg/kg DM for soy protein isolate (Mazur 1 998).

No category of diet was devoid of isoflavones. lsoflavones were detected at quantifiable concentrations in 1 04/ 1 3 8 (75%) of all diets tested. More dry diets ( 1 27/ 1 3 8 ; 92%) contained isoflavones at quantifiable concentrations compared with moist diets (831 1 3 8 ; 60%, p < 0.0 1 ) . Overall, the most common isoflavone was daidzein, which was quantifiable in 97/ 1 3 8 (70%) of all diets, followed by genistein (661 1 3 8 ; 48%), biochanin A (25/1 3 8 ; 1 8%) and formononetin (7/ 1 3 8 ; 5%).

When comparing diet categories, the moist with-soy category was found to have the greatest proportion of isoflavone-containing diets (7 /7; 1 00%). Significant differences were detected between isoflavone occurrences within diet categories. The lowest proportion of isoflavone-positive diets was found in the moist meat-only category (see Table 2 . 1 ).

No significant differences were found between dry diets with- and without-soy as an ingredient on the label. When categories of diet were assessed according to the proportion of genistein- and daidzein-positive diets in them, the same pattern of greatest to lowest incidence of isoflavones and significant differences between categories was observed, with the exception that no significant difference was evident between daidzein-positive

Of the isoflavone-positive diets, 3 3/ 1 04 (32%) contained daidzein and no detectable genistein. Of these, 3 0/33 (9 1 %) were devoid of soy in their ingredient list and the remainder were in the dry with-soy category. Conversely, only 2/1 04 (2%) of isoflavone­ positive diets contained genistein but no detectable daidzein, one of which contained soy in its ingredient list and one of which did not. Only 1 / 1 04 ( 1 %) of isoflavone-positive diets contained formononetin without its precursor, daidzein.

Category of diet• n Genistein-positive Daidzein-positive diets (%)

diets (%)

Moist meat-only 23 1 7' 39'

Moist without-soy 43 26x 53x

Dry without-soy 52 63z 9QY

Moist with- soy 7 J QQY I QQY

Dry with-soy 1 3 85yz 85y

Table 2 . 1 . Percentage of domestic cat diets within defined categoriesa that contained detectable amounts of genistein and daidzein. Values with different super-scripts, within columns, were significantly different (p < 0.05)

A greater proportion of diets (8/ 1 04; 8%) contained biochanin A without its precursor, genistein, and biochanin A was found in 3/ 1 04 (3%) diets containing genistein but not daidzein.