European reference method of in vivo determination of metabolisable energy in poultry: reproducibility, effect of age, comparison with predicted values.

1. Apparent metabolisable energy corrected to zero-nitrogen retention (AMEn) was measured using the European reference procedure in 9 European laboratories. Seven pelleted diets were evaluated. AMEn was measured with adult cockerels and young birds. 2. Between-laboratory standard deviations were for dry matter (DM) 12.5 g/kg, gross energy 0.085 MJ/kg DM, Kjeldahl nitrogen 0.768 g/kg DM, AMEn (adults) 0.256 MJ/kg DM, and AMEn (young) 0.337 MJ/kg DM. Corresponding coefficients of variation between laboratories were 1.42, 0.45, 2.15, 1.88 and 2.60% respectively. 3. AMEn values of experimental diets were always significantly lower when measured with young birds. This effect was more pronounced when diets contained added fat. 4. Tallow or soyabean oil were incorporated into two basal diets at 40 g/kg inclusion rate. No significant differences were observed between AMEn values of either diet with adults or young birds, suggesting that AMEn energy values of these fats are indistinguishable at this inclusion rate. 5. Similar AMEn values were obtained in young birds by estimating nitrogen accretion, either by the difference between intake and excreta nitrogen or by measuring body weight gain. Determined AMEn values were very similar to those predicted using three different regression equations.