Effect of dietary protein level on retention of nutrients, growth performance, litter composition and NH3 emission using a multi-phase feeding programme in broilers.

Three experiments were conducted to study the effect of dietary protein level on the retention of nutrients, growth performance, litter composition and NH3 emission in broiler chickens kept under laboratory conditions (housed in cages, Exp.1) or in commercial conditions (in pens, Exp.2; or whole houses of a farm, Exp.3). All the trials were performed according to a factorial experimental design, involving a 4-stage feeding programme and two levels of dietary crude protein (CP) for each period: control vs. low crude protein (CP reduced by 1.5%). In Exp.1, the coefficients of total tract apparent retention of dry matter and CP were higher in the birds fed the low CP diet (p<0.05). On average, reducing the CP of the diet led to a 4.8% reduction in the nitrogen excreted per CP intake. In Exp.2, the feed conversion ratio was higher in birds fed the low CP diet from 22 to 35d (p<0.05), from 35 to 42d (p<0.01), and over the whole experimental period (p<0.01). In Exp.3, low CP diets decreased the nitrogen content of the litter in the finisher period (p<0.05). The average NH3 concentration and emission from 33 to 42d were lower in the low CP house (p<0.01), with a 16% decrease in the cumulative NH3 emission. Therefore, the reduction in dietary CP content by 1.5% reduced the potential environmental impact, although it had a negative effect on the feed efficiency of broilers.