The effects of high dose of microbial
phytase and an emulsifier on the performance, apparent metabolisable energy (
AME) and
nitrogen (N) retention in broilers fed on diets containing different fat sources were examined in a 5-week trial. Two fat sources (soy oil and
tallow), two inclusion levels of E. coli
phytase (500 or 1000
phytase units (FTU)/kg diet) and two inclusion levels of
lysolecithin emulsifier (0 or 3.5 g/kg of diet) were evaluated in a 2 × 2 × 2 factorial arrangement of treatments. Throughout the 5-week trial, soy oil supplementation improved
weight gain and feed per gain compared with
tallow, but had no effect on feed intake. The high dose of
phytase increased the
weight gain and feed intake and lowered the feed per gain during d 1-21, but had no effect on performance parameters over the whole trial period. An effect of emulsifier was observed for feed intake during d 1-21 and over the whole trial period. Addition of emulsifier increased feed intake compared with diets without emulsifier. During weeks 1, 2, 3 and 5, birds fed on soy oil-based diets had higher
nitrogen-corrected
AME (AMEN) compared with those fed on
tallow-based diets. During weeks 2, 3 and 5, the effect of
phytase was significant for AMEN, with the high dose increasing the AMEN. During week 2, AMEN was increased with emulsifier addition. During weeks 1, 2, 3 and 5, birds fed on soy oil-based diets had higher fat retention compared with those fed on
tallow-based diets. The high dose of
phytase improved the retention of fat during week 5 and the addition of emulsifier resulted in higher fat retention during week 1. During weeks 2, 3 and 5, an interaction between fat source ×
phytase × emulsifier was observed for N retention. In soy oil-based diets, emulsifier plus 1000 FTU/kg
phytase increased N retention compared with other groups, while in
tallow-based diets, emulsifier addition increased N retention in diets with 500 FTU/kg, but not in 1000 FTU/kg diet. Overall, the present data suggest that the
dietary fat source influenced performance, AMEN and fat retention in broiler chickens. There is opportunity to improve bird performance during d 1-21, AMEN and fat retention with higher doses of microbial
phytase. Addition of the emulsifier increased the AMEN during week 2 and tract retention of fat during week 1, but this effect was not translated into improvements in performance.