Studies on the inevitable losses of nitrogen in Pekin ducks.

By definition, inevitable losses of nitrogen (N) refer to the hypothetical condition of zero N intake. This loss is the minimum net requirement for N and forms part of the maintenance requirement. Investigations regarding inevitable losses are needed because they are part of the total protein requirement, and such data are needed in systems that model the necessary protein supply in animal diets (OWENS and PETTIGREW, 1989; FULLER, 1994), especially when the factorial approach is used. In the literature, age or body weight (BW) (MISKI and QUAZI, 1981; RAVINDRAN and HENDRIKS, 2004) and crude fibre (CF) intake (DE LANGE et al., 1989) are mentioned as possible factors that could modulate inevitable N losses. To our knowledge, their effects have not been studied in ducks although the contribution of duck meat to the poultry meat market has continuously increased (TIMMLER and JEROCH, 1999; FAO, 2009) and duck farms often operate on a high level of production intensity. It is known that the development of the digestive tract during growth is different between broilers and waterfowl (JAMROZ et al., 2001, 2002, 2004), and differences exist in the precaecal digestibility of amino acids between broilers and ducks (KLUTH and RODEHUTSCORD, 2006). This indicates that existing broiler data on N metabolism of the gut may not be applicable to ducks. The main objective of this study was to investigate whether the dietary CF level and the BW affect the inevitable N losses and consequently the maintenance protein requirement in the White Pekin duck. An approach referred to as the regression approach (NYACHOTI et al., 1997) was used.