Studies on inevitable losses of amino acids and nitrogen in the Pekin duck and their consequences for maintenance nitrogen requirement

Questions relating to the inevitable losses (IL) and maintenance requirements of nitrogen as well as the inevitable precaecal losses (IPL) of nitrogen and individual amino acids (AA) were the key objectives of this study. The estimates were to be generated under the influences of both dietary and physiological conditions. Physiological conditions studied were the effects of age or body weight of the animals. Dietary inputs under investigation were changes in dietary crude fibre levels achieved by supplementary a-cellulose or corn cob meal as well as dietary levels of soybean oil. These were done using either N balance or precaecal flow experiments. Efficiency with which ingested nitrogen was utilised was also studied. All experiments were carried out with White Pekin ducks. Diets were formulated to contain graded levels of protein having identical AA composition and adequate levels of all other essential nutrients. Protein pre-mixes were used for all studies and were pre-formulated to have AA composition nearly close to a calculated ideal balance for the respective age phase. The protein concentrations in the basal diets were always very low in order to allow an unbiased extrapolation of nitrogen excretion or amino acids flow to zero intake. Studies on the recovery rate of TiO2 were included as side objectives. Two balance experiments each with ducklings and adult ducks were carried out to estimate inevitable N losses at excreta level (IL) and N maintenance requirements using different crude fibre (CF) concentrations. Experiment 1 followed a 5 2 factorial arrangement of treatments with 5 CP levels (50, 90, 130, 170, and 210 g/kg) with identical crude protein (CP) composition and 2 CF levels (30 and 80 g/kg) achieved by a-cellulose supplementation. Six to twelve ducklings with an average BW of 0.79 kg were allocated to each diet and individually kept in specially designed balance crates. Excreta were quantitatively collected for 5 days beginning on day 19 of age. The N excretion was, without a significant interaction, highly significantly affected by CP and by crude fibre inclusion. N excretion nonlinearly increased with N intake. The estimate for N excretion in relation to body weight determined by extrapolation to zero N intake was not significantly different between the two CF levels. The joint estimate for the inevitable N losses for both crude fibre levels was 469 (SE 63) mg N/kg BW and day. In Experiment 2, 101-d old adult ducks (mean BW 3.48 kg) were used. The experimental protocol was similar as in Experiment 1. Treatments comprised 3 CP levels (20, 60, and 100 g/kg) and 2 crude fibre levels (30 and 80 g/kg) achieved by varying a-cellulose supplementation. The excretion of N was highly significantly affected by N intake (P< 0.01), but not by CF supplementation (P = 0.867). Again, the estimated N excretion at an extrapolated zero N intake was not significantly different between the two crude fibre levels, and the joint estimate was 128 (SE 20) mg N/kg BW and day. It was concluded that the inevitable N losses, and consequently the maintenance CP requirement, expressed in relation to BW, is affected by BW in ducks, but not by the level of crude fibre. Analysis of data when expressed in relation to DM intake gave the same results. Utilisation of dietary nitrogen showed diminishing efficiency with increasing N intake. Estimated cumulative efficiency was between 63 % to 67 % for ducklings and between 55 to 104 % for adults ducks, depending on crude fibre intake.