Energy in food for cats is valuated on the basis of metabolizable energy. To
predict the energy content, some estimation formulas exist. Aim of this
stud y was to compare these formulas with trial based results.
Nine metabolic trials with 8 cats each were conducted. After 7 days
prefeeding period a 7 days collection period followed, where total faeces as
well as total urine were collected. Gross energy was anal yzed from the food
and faeces samples. The urine of cats was slowl y dried b y adding a special
amount every day until enough dry substance was available to determine the
energy using a bomb calorimeter.
Digestibilit y and metabolizabilit y of energy of wet food was significantl y
higher compared with dry food. Deviations between calculated (NRC, 2006)
and the trial based results of ME were between -10.3 and 18.7 %, the
correlation between both was 0.707 (Pearson). Digestibilit y and
metabolizabilit y were significantl y correlated with the fat content and
negativel y with the fibre content. Mean loss of energy by urine was
significantl y higher when dry food was given compared with wet food.
The content of crude protein in the diet was onl y weakl y correlated with the
loss of urine energy per g protein.
The mean urine loss determined in these trials was lower than that
calculated with the equation, nevertheless, the value of 3.1 kJ/g protein
prevents overestimation of energy in food. Digestibilit y of fibre seems to be
an unknown factor, whereas fat seems to have an essential influence on