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

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 α-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 α-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 α-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.

Precaecal flow studies were further conducted to study dietary effects on estimates of inevitable precaecal losses (IPL) and precaecal digestibility by regression (PDR) of nitrogen and individual amino acids in adult ducks. In study I, male and female ducks were used to study the effects of crude fibre intake mainly in the form of α-cellulose supplementation. A 2×3 factorial design of two crude fibre levels (30 or 80 g/kg) and CP (20, 60 and 100 g/kg) was implemented. Dietary treatments were randomly allotted to 24 pens with each diet been replicated twice for each sex making a total of 4 pens per diet. Birds were fed for 5 days, killed in a CO2 chamber, and digesta collected on pen basis from the last 2/3 of the small intestinal section between Meckel’s diverticulum and 2 cm anterior to the ileo-caeco-colonic junction. To investigate if natural crude fibre supplementation will alter estimates of IPL, precaecal study II was undertaken with a similar experimental protocol (2×3 factorial). Diets were fed to male adult ducks at 57 days of age with average body weight of 4.0 kg. In this study, the CF supplementation was achieved with corn cob meal. A study on the effect of additional fat intake on IPL was undertaken with male adult ducks with another 3 diets containing 100 g/kg dietary concentration of soybean oil were compared with initial 3 basal protein diets (20, 60 and 100 g/kg) each of which contained 40 g/kg soybean oil. Similarly, 57 day old male ducks with average body weight of 4.0 kg were used. For all precaecal studies, response in precaecal flow to increased nitrogen intake was linear. The estimated (y) intercept value was subsequently interpreted as inevitable precaecal losses while PDR was measured as the slope of the regression lines relating digested nitrogen (mg/d) to intake (mg/d).

For CP and AA, results indicated that estimated intercepts were unrelated to crude fibre intake whether increments in crude fibre intake was mainly as synthetic α-cellulose (precaecal study I) or in the form of corn cob meal as natural crude fibre source (precaecal study II). Also the level of dietary oil supplementation did not alter estimated IPL (precaecal study II). Ranking of individual AA in amounts of IPL found for adult ducks was:
Glutamic acid>aspartic acid>leucine>threonine>proline>serine>lysine>glycine>
alanine>valine>arginine>isoleucine>phenylalanine>cystine>methionine>
tryptophan. Means of pooled estimates of IPL ranged between 13.0 mg/kg BW d-1 (tryptophan) to 130.0 mg/kg BW d-1 (glutamic acid). Estimated means of IPL of CP were between 33256 to 95875 mg/kg DMI (1163 to 1275 mg/kg BW d-1).

Response in PDR for all amino acids and CP was essentially similar if the dietary crude fibre level was elevated mainly by synthetic cellulose supplementation (precaecal study I) but strongly reduced when increment in the level of crude fibre in the diets was achieved by corn cob meal supplementation as a natural crude fibre source. This indicates that the type of crude fibre supplementation modifies PDR in adult ducks and that results with one type of crude fibre source should not be generalised for all crude fibre types. The PDR was similarly not influenced by the level of soybean oil in the diet.

The recovery rate of TiO2 was found to be high in both ducklings and adult ducks and amounted to 93 % in ducklings and 91 % in adult ducks. However, watery nature of adult ducks excrements may make it difficult to accurately quantify the marker excretion at this age phase.