Studies on the inevitable nitrogen losses of White Pekin ducks

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1 Studies on the inevitable nitrogen losses of White Pekin ducks O. A. AKINDE 1, H. KLUTH 1 and M. RODEHUTSCORD 1 * 1 Institut für Ernährungswissenschaften, Martin-Luther-Universität Halle-Wittenberg, Halle (Saale), Germany *Corresponding author: markus.rodehutscord@landw.uni-halle.de It was the objective to estimate inevitable N losses of White Pekin ducks and to investigate the effect of a crude fibre supplementation and body weight. Experiment 1 followed a 5 2 factorial arrangement of treatments with 5 CP levels (5, 9, 13, 17, and 21 %) with identical CP composition and 2 crude fibre levels (3 and 8 %) achieved by α-cellulose supplementation. Six to twelve ducks 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 of the functions to zero N intake was not significantly different between the two levels. The joint estimate for the inevitable N loss for both crude fibre levels was 469 (SE 63) mg N/kg BW and day. In Experiment 2, 101-d old ducks (mean BW 3.48 kg) were used. The experimental protocol was similar as in Exp. 1. Treatments comprised 3 CP levels (2, 6, and 10 %) and 2 crude fibre levels (3 and 8 %) achieved by varying α-cellulose supplementation. The excretion of N was highly significantly affected by crude fibre supplementation (P< 0.01), but not by N intake (P = 0.088). 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 125 (SE 15) mg N/kg BW and day. We conclude that the inevitable N loss, 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. Key words: inevitable losses; nitrogen; crude fibre; starting and adult ducks Introduction There is an ongoing need to study and estimate the minimum nutrient need of farm species. This is in line with economic and environmental considerations. With regards to dietary nitrogen, the needs to evaluate feedstuffs more accurately and the increasing tendency to estimate requirements and formulate diets based on maintenance and desired performance levels have added more impetus to this direction in nutrition research (Morgan and Fuller, 2003; Rodehutscord, 2005). The inevitable nitrogen (N) losses are an integral component of the total animal requirement that result from basal nitrogen metabolism. Inevitable N losses of ducks are not reported in the literature. This study was undertaken to investigate the inevitable losses of nitrogen and, by extension, the maintenance N requirements of Pekin ducks. Special attention was given to the roles of crude fibre and body weight or age on these losses. Ducks were used in these studies because of the ongoing improvements in ducks breeding and production (Timmler and Jeroch, 1999; Pingel, 2004).

2 Materials and Methods Two experiments were conducted at the research facilities of the Institute of Nutritional Sciences, University of Halle-Wittenberg with improved male White Pekin ducks. They were reared in an environmentally controlled duck house in accordance to standards prescribed for the ducks and handled in accordance to German Animal Welfare regulations. Prior to commencement of the experiments, birds were fed standard starter and adult diets. From pools of similar age and hatch, different birds were selected for the two experiments. Experimental design, diets and measurements Experiment 1 was conducted with starting ducks and followed a 5 2 factorial arrangement of treatments with 5 CP levels (5, 9, 13, 17, and 21 %) having identical AA composition and 2 crude fibre levels (3 and 8 %) achieved by α-cellulose supplementations making a total of 10 dietary treatments. A 3 2 factorial design was implemented in Experiment 2 for adult ducks, in which CP levels corresponding to 2, 6 and 10 % were fed in the presence of 3 or 8 % crude fibre achieved with α-cellulose. Again, the protein used was of identical AA composition. Tables 1 and 2 show the final dietary compositions for both experiments. Experiment 1 involved the selection of six to twelve 12-d old ducks with an average BW of 0.79 kg out of a pool of 200. They were individually kept in specially designed balance crates and fed standard starter diets to 14-d of age when they were randomly allocated to one of the dietary treatments. Excreta were quantitatively collected for 5 days beginning on day 19 of age after a 4-day adjustment to the experimental diets. Daily feed allowance was 110 g which was 95% of the ad libitum intake determined during the adaptation period. Diets were offered in three equal meals at 06:00, 14:00 and 22:00 h during which times excreta were collected and stored at 18 C for each bird. In Experiment 2 the protocol was similar to Experiment 1 but a total of 3 balance periods was carried out using the same adult ducks. From a pool of d old Pekin ducks, birds were selected and individually penned. Two to three birds were assigned to each treatment on a BW basis. Each balance period consisted of 2-3 d pre-experimental feeding of standard adult ration while already in the cages, followed by a 4-d adjustment period to the experimental diets. For the following 4 d feeding was restricted to 95% of the ad libitum intake measured during the adjustment period, during which excreta were collected at 06:00, 14:00 and 22:00 h and stored at 18 C. Feed restriction was g/d during excreta collection to minimise variations in feed intake due to feed refusal resulting from feeding highly diluted diets. Feed refusals were recorded on a daily basis. Chemical and statistical analysis, calculations and curve fitting Excreta samples were analysed for dry matter and total nitrogen content. Samples of diets were analysed for proximate composition according to the VDLUFA official methods (Naumann and Bassler, 1976). Nitrogen intake and nitrogen excretion were expressed in relation to body weight of the animals. ANOVA was carried out using the GLM protocol of SPSS 12.0 software package for windows. To determine inevitable losses of nitrogen and to elucidate the effects of dietary fibre and body weight on these losses, the course of nitrogen excretion was described by a second order polynomial function: y = a + bx + cx 2, implemented by Graph Pad Prism 4.0, where x = intake of nitrogen (mg/kg BW d -1 ), y = nitrogen excretion (mg/kg BW d -1 ). F-test of Graph Pad Prism 4.0 was used to test for the main effects. Results and discussions As shown in tables 3a and 3b, the excretion of N by starting ducks was highly significantly affected by N intake (P<0.001, table 3b) which was expected because the efficiency of utilisation of dietary

3 nitrogen drops as intake levels get close or beyond physiological requirement. In adult ducks, the effect of nitrogen intake on N excretion was related to the level of crude fibre, indicated by an interaction between CP and crude fibre levels (P = 0.016). The data trend for fibre effects showed a similar response in both age periods. N excretion (P<0.01) was strongly influenced by dietary fibre at both age periods indicating that we had effective dosage of fibre in both experiments. The average body weight during the experiments for the starting ducks was kg and 3.48 kg for the adult ducks at d and d. Starting ducks accreted weight to between 18 and 62 g/d. Adult ducks lost weight up to 18 to 40 g/d, which was due to the low amount of feed intake (50 63 g/d) necessitated by the methodological approach. For valid estimation of inevitable losses, certain preconditions have to be met or assumed. The most important being that nitrogen intake has to be as near as possible to zero. In the present experiments we came close to this, because the minimum CP level taken together for both experiments was between 2 and 5 %. When the calculated second order polynomial function (Figure 1) was extrapolated to the basal condition of zero intake (y intercept), the daily inevitable losses of nitrogen in starting ducks at high and low levels of crude fibre were 403(±80) and 542 (±97) mg/kg BW. Upon comparing these two values by F-test, it was found that there was no significant difference (P = 0.27), indicating that crude fibre had no effect on inevitable N loss. Therefore, a pooled value of 469 (±63) mg/kg BW d -1 was computed as the inevitable loss in starting ducks. Similarly, the calculation and comparison of the intercept values of the calculated functions for adult ducks (Figure 2) showed that the extrapolated intercepts of 122 (±14) mg for low crude fibre and 142 (±42) mg for high crude fibre were not different (P = 0.29). Therefore the joint intercept value was calculated to be 125 (±15) mg/kg BW d -1. Although the estimates from the two experiments cannot be compared statistically, they indicate a high effect of BW on the inevitable N losses of ducks. When these losses were adjusted for the cost of utilisation of absorbed nitrogen calculated to be 61% using our data for starting ducks, the maintenance requirements were estimated to be 4.7 g CP/kg BW d -1 and 1.3 g CP/kg BW d -1 for starting and adult ducks, respectively. On the basis of these data, we conclude that the inevitable N loss, and consequently the maintenance CP requirement, expressed in relation to BW, is affected by BW in ducks, but not by the crude fibre level within the range of intake and diet studied. It can only be speculated why we could not demonstrate the effect of crude fibre on basal nitrogen losses, given the preponderance of information to the contrary. Perhaps, it was due to the type of fibre used which was mainly in the form of synthetic cellulose. Further studies are being conducted to factorise the inevitable N losses into its precaecal and postileal components.

4 Table 1 Compositions of diets in Experiment 1 (g/kg of diet as fed) Ingredients T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 Corn Wheat Soya bean meal Wheat gluten Corn gluten L-lys-HCl DL-met L-thr L-try α-cellulose Corn starch Soya oil DCP (CaHPO 3 ) CaCO NaCl Premix TiO Analysed nutrients Dry Matter ,3 896,8 CP CF Ash Lipids Table 2 Composition of diets in Experiment 2 (g/kg diet as fed) Ingredients T1 T2 T3 T4 T5 T6 Corn Wheat Soya bean meal Wheat gluten Corn gluten L-lys-HCl α-cellulose Corn starch Soya oil DCP (CaHPO 3 ) CaCO NaCl Premix TiO Analysed nutrients Dry Matter CP CF Ash Lipids

5 Table 3a Nitrogen metabolism of ducks in response to varying levels of dietary crude protein and crude fibre LOW FIBRE (3%) HIGH FIBRE (8%) Starting ducks Starting ducks 5 % 9 % 13 % 17 % 21 % 5 % 9 % 13 % 17 % 21 % DM intake, g/d N intake, mg/d N excretion, mg/d Adult ducks Adult ducks 2 % 6 % 10 % 2 % 6 % 10 % DM intake, g/d N intake, mg/d N excretion, mg/d Table 3b Factorial effects on metabolic response parameters in ducks P (ANOVA) Parameters Crude fibre Crude protein CF CP Starting ducks DM intake, g/d < N intake, mg/d < N excretion, mg/d < Adult ducks CP DM intake, g/d N intake, mg/d < N excretion, mg/d N excretion, mg/kg BW d Low Fibre High Fibre N intake, mg/kg BW d -1 ylow Fibre = 403.1(±80.18) x x 2 ; r 2 : 0.96; s y.x : 67.4 yhigh Fibre =542(±96.64) x x 2 ; r 2 : 0.95; s y.x : 77.4 Figure 1. N excretion (y) of starting ducks in response to N intake (x) at low and high levels of crude fibre.

6 N-excretion, mg/kg BW d Low Fibre High Fibre N-intake, mg/kg BW d -1 ylow Fibre = (±13.89) x x 2 ; r 2 : 0.67; s y.x : 31.3 yhigh Fibre =142.2(±41.45) x x 2 ; r 2 : 0.13; s y.x : 42.2 Figure 2. N excretion (y) of adult ducks in response to N intake (x) at low and high levels of crude fibre. REFERENCES MORGAN, P. J. and FULLER, M.F. (2003). Modelling amino acid metabolism and the estimation of amino acid requirements, in: Amino acids in animal nutrition. 2 nd edition (J. P. F. D Mello ed.). PINGEL, H. (2004). Ducks and geese production, World Poultry 20: RODEHUTSCORD, M. (2005). Towards an optimal utilisation of phosphorus sources in growing meat ducks. Proceedings 15 th European symposium on poultry nutrition, Balatonfüred, Hungary, September, TIMMLER, R. and JEROCH, H. (1999).Nutrition of meat type Pekin ducks-latest advances and developments trends. Proceedings 1 st World waterfowl congress, Taiwan, pp