Protein requirements for growth, feed efficiency, and meat production in growing mule ducks

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1 2012 Poultry Science Association, Inc. Protein requirements for growth, feed efficiency, and meat production in growing mule ducks E. Baéza,* M. D. Bernadet, and M. Lessire * * INRA, UR83 Recherches Avicoles, F Nouzilly, France; and INRA, UE89 Palmipèdes à Foie Gras, Artiguères, F Benquet, France Primary Audience: Poultry Feed Manufacturers, Flock Supervisors, Broiler Managers, Researchers SUMMARY The objective of this study was to determine the protein requirements of female mule ducks during the starting (0 to 3 wk), growing (4 to 7 wk), and finishing (8 to 10 wk) periods. We performed 1 trial for each period. Five increasing dietary protein levels were tested for each period. All diets had the same ME content (12.12 MJ of ME/kg of feed), and the ratios between the main amino acids and lysine and the lysine-to-protein levels were similar. Six pens of 22 or 25 ducks were used per treatment. By adjustment with the more accurate model, the evolution of average BW, FCR, and weights of breast muscle and thighs with shanks was evaluated according to the protein level in the diets for each period. On the basis of our findings, 23.5, 15.4, and 13.8% CP levels could represent optimal levels in the starting, growing, and finishing diets, respectively. Increasing the protein level in diets for the starting, growing, and finishing periods from 15.4 to 25.3%, 10.8 to 16.6%, and 10.2 to 18.0%, respectively, decreased the efficiency of body protein deposition from 54 to 42%, 47 to 42%, and 79 to 45%, respectively. As a consequence, the nitrogen content in feces increased by 1.5-, 2.0-, and 1.9-fold, following a linear relationship with dietary nitrogen content. Key words: duck, feed efficiency, growth, meat yield, protein requirement 2012 J. Appl. Poult. Res. 21 : DESCRIPTION OF PROBLEM To date, dietary protein levels for the growing mule duck (a crossbreed between a male Muscovy duck, Cairina moschata, and a common female duck, very often Pekin, Anas platyrhynchos) have been derived from protein requirements measured in the Muscovy duck [1]. In practice, female mule and Muscovy ducks reared for meat production are usually slaughtered at the same age, 10 wk. However, only male mule ducks are used for fatty liver production in France, and the females are reared for meat production. Leclercq and De Carville [2] studied the effects of different protein levels in diets during the finishing period (4 to 9, 10, or 11 wk) on growth performance, carcass presentation, and meat yield of female mule ducks. In addition, Robin et al. [3 5] and Robin and Castaing [6] analyzed the consequences of reducing protein levels and modifying lysine and methionine levels in the growing diet on the growth performance of male mule ducks. To optimize FE and to reduce nitrogen excretion, we 1 Corresponding author: Elisabeth.Baeza@tours.inra.fr

2 22 JAPR: Research Report believe it is important to determine the specific feeding requirements of the mule duck, whose body development occurs earlier than that of the male Muscovy duck [7]. The objective of our study was to determine the protein requirements of growing mule ducks for growth, FE, and meat production for each rearing period (starting, growing, and finishing). The effect of dietary protein content on nitrogen excretion was also analyzed. MATERIALS AND METHODS Three trials were conducted, corresponding to the starting (0 to 3 wk), growing (4 to 7 wk), and finishing (8 to 10 wk) periods. The dietary protein levels were chosen according to the recommendations for the Muscovy duck [1]. First, we determined the average value. We then tried to have 2 levels higher and 2 levels lower than this average value, with the aim of reaching a plateau with the highest values and to deteriorate the growth performance with the lowest values. For each period, all diets were calculated to contain the same ME content, MJ of ME/ kg of feed (the average ME value actually used in diets for ducks in France), to analyze only the effect of modulating the dietary protein level. All experimental procedures were performed in accordance with the French National Guidelines for the Care and Use of Animals for Research Purposes (Certificate of Authorization to Experiment on Living Animals No , Ministry of Agriculture and Fish Products, Paris, France). Starting Period A total of 750 female mule ducks of the Hytop 74 genotype [8] were reared on wood shavings. From 1 d of age, ducks were distributed into 2 similar contiguous rooms, each containing 15 pens (6 m 2 /pen and 25 ducks/pen). In each room, 5 groups were allocated to 5 different diets, with 15.4, 18.6, 20.5, 21.8, and 25.3% protein levels. The ratios between the main amino acids and lysine and the lysine-to-protein levels were similar between the groups. All ducks were wing banded and weighed at 1 and 21 d of age. Feed consumption was determined per pen. At 3 wk of age, 4 ducks per pen representing the average BW of the pen were killed by decapitation, and the skin was removed with feathers. The weights of the breast muscle and thighs with shanks were determined. For groups at 15.4, 20.5, and 25.3% CP, 8 other ducks representing the average BW of the group were killed by pentobarbital injection, plucked, weighed, and frozen at 20 C before being ground and lyophilized to determine the carcass protein content using the Kjeldahl procedure [9]. These 3 groups were chosen according to the effect of CP level on BW (2 extremes and 1 average value). In each pen, all excreted feces were collected during the last 3 d of the starting period and mixed. A fecal sample of 200 g per pen was then frozen at 20 C and lyophilized. After lyophilization, samples were kept at 4 C to analyze the nitrogen content using the Kjeldahl procedure [9]. Growing Period The same experimental schedule was used as described previously for the starting period. During the starting period, all ducks (750 females) received the same diet (12.12 MJ of ME/kg of feed and 23.5% CP) according to the findings of the previous trial. At 21 d of age, ducks were distributed into 5 groups corresponding to 5 different dietary protein levels: 10.8, 13.1, 14.5, 16.6, and 18.7% CP. All ducks were weighed at 1, 21, and 49 d of age. The feed consumption per pen was determined at the same ages. To determine the body composition at 49 d of age, 4 ducks per pen representing the average BW of the pen were slaughtered, and the carcasses were cut up after 24 h of storage at 4 C. The carcass protein content was measured as described previously for the groups fed diets containing 10.8, 13.1, and 16.6% CP and chosen as described previously for the starting period. In each pen, all excreted feces were collected during the last day of the growing period and mixed. A fecal sample of 200 g per pen was then frozen at 20 C and lyophilized. After lyophilization, samples were kept at 4 C to analyze the nitrogen content using the Kjeldahl procedure [9]. Finishing Period The same experimental schedule was used as described previously for the starting period. Only 660 female mule ducks were reared, which

3 Baéza et al.: PROTEIN REQUIREMENTS OF MULE DUCKS 23 Table 1. Main calculated characteristics (g/kg) of the experimental diets for the starting, growing, and finishing periods Item Group 1 Group 2 Group 3 Group 4 Group 5 Starting period ME, MJ/kg CP Lysine Sulfur amino acids Tryptophan Threonine Calcium Available phosphorus Growing period ME, MJ/kg CP Lysine Sulfur amino acids Tryptophan Threonine Calcium Available phosphorus Finishing period ME, MJ/kg CP Lysine Sulfur amino acids Tryptophan Threonine Calcium Available phosphorus Crude protein levels were measured according to the Kjeldahl procedure [9]. were distributed into 30 pens, with each pen containing 22 ducks. During the starting and growing periods, all ducks received the same diets (12.12 MJ of ME/kg of feed and 23.5% CP, and then 15.4% CP) according to the findings of the previous trials. At 49 d of age, ducks were distributed into 5 groups corresponding to 5 different dietary protein levels: 10.2, 12.0, 14.0, 16.0, and 18.0% CP. All ducks were weighed at 1, 21, 49, and 70 d of age. The feed consumption per pen was determined at the same ages. To determine the body composition at 70 d of age, 4 ducks per pen representing the average BW of the pen were slaughtered, and carcasses were cut up after 24 h of storage at 4 C. The carcass protein content was measured as described previously for the groups fed diets with 10.2, 14.0, and 18.0% CP and chosen as described previously for the starting period. In each pen, all excreted feces were collected during the last day of the finishing period and mixed. A fecal sample of 200 g per pen was then frozen at 20 C and lyophilized. After lyophilization, samples were kept at 4 C to analyze the nitrogen content with the Kjeldahl procedure [9]. The main characteristics of the experimental diets are detailed in Table 1. Statistical Analysis and Modeling The effect of dietary protein level on the different measured parameters was tested by ANOVA, with P < To estimate the protein requirements for growth, FE, and meat production for each growing period, we used the more accurate model (presenting the highest correlation coefficient) determined using CurveExpert software ( and by cross-linear regressions according to the method of Schwartz [10]. The pen was our experimental unit for all parameters. For each rearing period, we calculated the efficiency of protein deposition as follows:

4 24 JAPR: Research Report amount of protein ingested (API) = % of CP in the diet total feed consumption, amount of protein deposited (APD) = average BW % of protein in the carcass (without feathers), amount of protein excreted (APE) = API APD, efficiency of protein deposition = (APD/API) 100. We also calculated linear regressions between dietary protein level and nitrogen content in feces. The regression slopes were compared between periods by using a t-test with P < BW RESULTS AND DISCUSSION For all periods, the increase in dietary protein level increased the average BW by 38, 11, and 6% between the extreme values of protein levels for the starting, growing, and finishing periods, respectively (Table 2 and Figure 1). However, for the starting period, no plateau was reached. Adjusting the evolution of average BW per pen, measured at 3 wk according to the protein level in the diet using a Gaussian model {y = a exp[( b x) 2 /(2 c 2 )], a = ; b = 26.78; c = 14.11; r = 0.93; P < 0.05}, showed that 23.2% might be optimal (Figure 1). Adjusting the evolution of average BW per pen, measured at 7 wk according to the dietary protein level using an exponential association model {y = a[1 exp( bx)], a = 3,123.37; b = 0.18; r = 0.84; P < 0.05} and linear regressions, showed that 15.1% CP might be optimal (Figure 1). Adjusting the evolution of average BW per pen, measured at 10 wk according to the dietary protein levels by using an exponential association model {y = a[1 exp( bx)], a = 3,832; b = 0.29; r = 0.62; P < 0.05} and linear regressions, showed that 13.6% CP might be optimal (Figure 1). FCR For all periods, the increase in dietary protein level improved the FCR by 14, 24, and 6% Table 2. Effect of dietary protein levels (%) on the growth performance and muscle development of female mule ducks for the starting, growing, and finishing periods (mean ± SEM; n = 6) Starting period protein Item BW 3 wk, g 637 ± 109 e 742 ± 122 d 795 ± 97 c 834 ± 99 b 877 ± 114 a FCR 0 to 3 wk 1.79 ± 0.07 a 1.67 ± 0.02 b 1.61 ± 0.03 c 1.59 ± 0.06 cd 1.54 ± 0.02 d Breast weight, g 4.73 ± 1.22 e 5.93 ± 1.67 d 6.82 ± 1.40 c 7.88 ± 1.56 b 9.00 ± 1.77 a Thigh with shank weight, g ± 9.90 d ± c ± 8.98 bc ± b ± 8.74 a Growing period protein BW 7 wk, g 2,702 ± 275 c 2,802 ± 248 b 2,947 ± 260 a 3,002 ± 272 a 3,008 ± 288 a FCR 4 to 7 wk 3.58 ± 0.10 a 3.26 ± 0.15 b 2.83 ± 0.05 c 2.77 ± 0.07 c 2.71 ± 0.11 c Breast weight, g 59 ± 12 d 75 ± 17 c 89 ± 21 b 100 ± 14 a 104 ± 22 a Thigh with shank weight, g 298 ± 35 b 311 ± 22 ab 324 ± 37 a 322 ± 34 a 323 ± 32 a Finishing period protein BW 10 wk, g 3,623 ± 400 c 3,726 ± 378 b 3,717 ± 417 bc 3,760 ± 416 ab 3,830 ± 350 a FCR 8 to 10 wk 7.72 ± ± ± ± ± 0.63 Breast weight, g 186 ± 33 b 205 ± 27 ab 206 ± 46 a 204 ± 37 ab 219 ± 21 a Thigh with shank weight, g 329 ± ± ± ± ± 40 a e Means between groups having different superscript letters differ significantly (P < 0.05).

5 Baéza et al.: PROTEIN REQUIREMENTS OF MULE DUCKS 25 Figure 1. Effects of dietary protein levels on the BW of female mule ducks at the end of the starting, growing, and finishing periods (n = 6). Color version available in the online PDF.

6 26 JAPR: Research Report Figure 2. Effects of dietary protein levels on the FCR of female mule ducks for the starting, growing, and finishing periods (n = 6). Color version available in the online PDF.

7 Baéza et al.: PROTEIN REQUIREMENTS OF MULE DUCKS 27 between the extreme values of protein levels for the starting, growing, and finishing periods, respectively (Table 2 and Figure 2). For the starting period, adjusting the evolution of average FCR per pen, measured according to the protein level in the diet using a growth-rate saturation model [y = ax/(b + x), a = 1.25; b = 4.62; r = 0.90; P < 0.05] and linear regressions, showed that 21.4% might be optimal (Figure 2). For the growing period, adjusting the evolution of average FCR per pen, measured according to the dietary protein level using the Weibull model {y = (a b) [exp( c x d )], a = 3.99; b = 1.48; c = ; d = 4.40; r = 0.94; P < 0.05} and linear regressions, showed that 14.8% might be optimal (Figure 2). For the finishing period, adjusting the evolution of average FCR per pen, measured according to the dietary protein level using a growthrate saturation model [y = ax/(b + x), a = 6.41; b = 1.96; r = 0.32; P < 0.05] and linear regressions, showed that 13.8% might be optimal (Figure 2). Meat Production For all periods, the increase in dietary protein level increased meat production (Figures 3 and 4). Adjusting the evolution of average breast muscle weight per pen, measured at 3 wk of age according to the protein level in the diet using a reciprocal quadratic model [y = 1/(a + bx + cx 2 ), a = 0.67; b = 0.04; c = ; r = 0.93] and linear regressions, showed that 23.1% might be optimal (Figure 3). Adjusting the evolution of average thigh with shank weight per pen, measured at 3 wk of age according to the protein level in the diet using a Gaussian model {y = a exp[( b x) 2 /(2 c 2 )], a = 85.04; b = 27.19; c = 12.70; r = 0.95; P < 0.05} and linear regressions, showed that 23.5% might be optimal (Figure 4). Adjusting the evolution of average breast muscle weight per pen, measured at 7 wk of age according to the protein level in the diet using a logistic model {y = a/[(1 + b) exp( cx)]; a = ; b = 18.87; c = 0.26; r = 0.91; P < 0.05} and linear regressions, showed that 15.4% might be optimal (Figure 3). Adjusting the evolution of average thigh with shank weight per pen, measured at 7 wk of age according to the protein level in the diet using an exponential association model {y = a[1 exp( bx)], a = ; b = 0.21; r = 0.57; P < 0.05} and linear regressions, showed that 15.4% might be optimal (Figure 4). Adjusting the evolution of average breast muscle weight per pen, measured at 10 wk of age, according to the protein level in the diet using an exponential association model {y = a[1 exp( bx)], a = ; b = 0.22; r = 0.32; P < 0.05] and linear regressions, showed that 13.8% might be optimal (Figure 3). Adjusting the evolution of average thigh with shank weight per pen, measured at 10 wk of age according the protein level in the diet using an exponential association model {y = a[1 exp( bx)], a = ; b = 0.40; r = 0.17; P < 0.05}, showed that 12.5% might be optimal (Figure 4). Nitrogen Excretion For all periods, the increases in dietary protein level induced linear increases in the nitrogen content of feces of 1.5-, 2.0-, and 1.9-fold between the extreme values of protein levels for the starting, growing, and finishing periods, respectively (Figure 5). The slopes of the 3 linear regressions were not different (P > 0.05). Efficiency of Protein Deposition Between 0 and 3 wk of age, the efficiency of protein deposition decreased from 54 to 42% when the protein level in the diet increased from 15.4 to 25.3% (Figure 6). Between 4 and 7 wk of age, it decreased from 47 to 42% when the protein level in the diet increased from 10.8 to 16.6% (Figure 6). Between 8 and 10 wk of age, it decreased from 79 to 45% when the protein level in the diet increased from 10.2 to 18.0% (Figure 6). Starting Period (0 to 3 wk) On the basis of our results, 23.2, 21.4, 23.1, and 23.5% CP in the starting diet could optimize BW at 3 wk of age, FCR, breast muscle development, and thigh muscle development, respectively. However, no plateau was reached. We should have chosen intermediate values for protein levels in the diet closer to optimal values or a value higher than 25.3% CP to reveal a plateau effect. Therefore, our observations and conclusions for this phase need to be confirmed

8 28 JAPR: Research Report Figure 3. Effects of dietary protein levels on the weight of breast muscle of female mule ducks at the end of the starting, growing, and finishing periods (n = 6). Color version available in the online PDF.

9 Baéza et al.: PROTEIN REQUIREMENTS OF MULE DUCKS 29 Figure 4. Effects of dietary protein levels on the weights of thighs with shanks of female mule ducks at the end of the starting, growing, and finishing periods (n = 6). Color version available in the online PDF.

10 30 JAPR: Research Report Figure 5. Effects of dietary protein levels on the average total nitrogen content of feces of female mule ducks collected at the end of the starting, growing, and finishing periods (n = 6). because we may have underestimated the protein requirements. These dietary protein levels are higher than those determined by Leclercq and De Carville [11] for the Muscovy duck, of 17.7% for females and 19.3% for males, with a diet containing MJ of ME/kg of feed. For the Muscovy duck, Jeroch [12] recommended 20% CP for a diet containing 12.0 MJ of ME/kg of feed. For common ducks, Leclercq et al. [1] recommended 18.4% CP for a starting diet containing MJ of ME/kg of feed, and Jeroch [12] recommended 18% CP for a starting diet containing 11.0 MJ of ME/kg of feed. On the other hand, Rukmangadhan et al. [13] reported that the optimal protein level in the starting diet (0 to 3 wk) for growth in common female ducks of the Khaki Campbell genotype was 24%. However, a high dietary protein level increased Figure 6. Effects of dietary protein levels on carcass deposition or excretion of proteins of female mule ducks during the starting, growing, and finishing periods. the nitrogen content of feces and decreased the efficiency of protein deposition as the ME:CP ratio decreased. For common female ducks of the Shaoxing genotype, Chen and Jiang [14] showed that the efficiency of protein deposition decreased from 51 to 43% when the dietary protein level increased from 14.3 to 21.5% between 0 and 4 wk of age. Distributing diets containing 15.4 and 18.6% CP during the starting period also affected FCR during the growing and finishing periods and the breast muscle weight at 10 wk of age, but not the BW at 10 wk of age

11 Baéza et al.: PROTEIN REQUIREMENTS OF MULE DUCKS 31 because ducks were able to attain compensatory growth [15]. Growing Period (4 to 7 wk) On the basis of our results, 15.1, 14.8, 15.4, and 15.4% CP in the growing diet could optimize BW at 7 wk of age, FCR, breast muscle development, and thigh muscle development, respectively. These dietary protein levels are equivalent to those recommended by Leclercq and De Carville [11, 16] for the Muscovy duck with a diet containing MJ of ME/kg of feed. Leclercq et al. [1] recommended 14% CP for a diet containing MJ of ME/kg of feed for the common duck. For Pekin and Muscovy ducks, Jeroch [12] recommended diets containing, respectively, 16% CP and 11.5 MJ of ME/ kg of feed and 18% CP and 12.5 MJ of ME/kg of feed. Robin et al. [3] found no effects on the growth of mule ducks between 5 and 10 wk of age when comparing diets containing 15 or 17% CP and MJ of ME/kg of feed. Moreover, Rukmangadhan et al. [13] recommended 18% CP in the growing diet (4 to 8 wk) for common female ducks of the Khaki Campbell genotype. However, a high dietary protein level increased the nitrogen content of feces and decreased the efficiency of protein deposition as the ME:CP ratio decreased. Modulating the dietary protein level had less impact on the efficiency of protein deposition for the growing period than for the starting period. For common female ducks of the Shaoxing genotype, Chen and Jiang [14] also showed that the efficiency of protein deposition decreased from 58 to 45% when the dietary protein levels increased from 14.9 to 18.2% between 3 and 9 wk of age. Distributing diets containing 10.8, 13.1, and 14.5% CP during the growing period also affected FCR during the finishing period [17]. Only the diet containing 10.8% CP affected the breast muscle weight at 10 wk of age, whereas the BW at 10 wk of age was similar for all groups [17]. Breast muscle development was less affected by dietary protein level during the growing period than during the starting period because the greatest increase in the weight of the pectoralis major muscle occurs during the first week posthatch [18]. Finishing Period (8 to 10 wk) In the finishing period, 13.6, 13.8, 13.8, and 12.5% CP in the finishing diet was able to optimize BW at 10 wk of age, FCR, breast muscle development, and thigh muscle development, respectively. These dietary protein levels are slightly higher than those recommended by Leclercq and De Carville [11, 16] for Muscovy ducks with a diet containing MJ of ME/ kg of feed, and were close to the recommendations of Jeroch [12] (18% CP for a diet containing 12.5 MJ of ME/kg of feed). Leclercq et al. [1] recommended 14% CP for a diet containing MJ of ME/kg of feed for common ducks. The effect of dietary protein levels on the nitrogen content of feces was similar for all periods because the slopes of the linear regressions were not different. The effect on the efficiency of protein deposition was much higher for the finishing period than for the starting and growing periods. However, this efficiency also decreased with increasing dietary protein level, confirming the previous observation of Chen and Jiang [14] for common female ducks of the Shaoxing genotype between 3 and 9 wk of age. Distributing diets containing 10.2, 12.0, and 14.0% CP during the finishing period affected BW, compared with the diet containing 18% CP [19]. Only the diet containing 10.2% CP affected the breast muscle weight at 10 wk of age [19]. For the male Muscovy duck, in which breast muscle development occurs later than in the mule duck, the breast muscle weight at 12 wk of age was affected by diets containing 10.6 and 12.0% CP compared with a diet containing 13.4% CP [11]. For the finishing period, the variability in each measured parameter was high, and the correlation parameters for the nonlinear regressions were moderate. Therefore, our observations and conclusions for this phase need to be confirmed. CONCLUSIONS AND APPLICATIONS 1. For the starting and growing periods, the protein requirement for optimizing FCR was slightly lower than that for BW, whereas the reverse was observed for the finishing period. For the starting and

12 32 JAPR: Research Report growing periods, the protein requirement for optimizing meat production was the same as or higher than the requirements for FCR and BW. This was true only for breast muscle weight in the finishing period because breast muscle development occurred later than development of the thigh and shank. 2. For each period, adjustment of the evolution of average BW, FCR, and weights of the breast muscle and thighs with shanks according to the protein level in the diet when using the more accurate model showed that 23.5, 15.4, and 13.8% CP might be optimal levels in the starting, growing, and finishing diets, respectively. With these dietary protein levels, the predicted nitrogen content in feces would be 6.36, 5.43, and 4.63%, respectively. 3. The gap between the starting and growing periods for dietary protein level was quite high. Therefore, one intermediate period between the starting and growing periods could be proposed to allow a more gradual decrease in the protein level of diets with age. 4. The different regression models determined for all periods and all parameters could be used to predict growth performance, meat production, and nitrogen excretion for a given dietary protein level. REFERENCES AND NOTES 1. Leclercq, B., J. C. Blum, B. Sauveur, and P. Stevens Alimentation des canards à rôtir. Pages in L alimentation des animaux monogastriques: Porc, lapin, volailles. Ed. INRA, Paris, France. 2. Leclercq, B., and H. De Carville Facteurs influençant la qualité des carcasses de femelles mulards. Pages in 1ères Journées de la Recherche sur les Palmipèdes à Foie Gras, Bordeaux, France. Ed. ITAVI, Paris, France. 3. Robin, N., A. Peyhorgue, and J. Castaing Effets d une réduction de la teneur protéique de l aliment sur la croissance et le gavage de canards mulards. Pages in 5èmes Journées de la Recherche sur les Palmipèdes à Foie Gras, Pau, France. Ed. ITAVI, Paris, France. 4. Robin, N., P. Larroude, and J. Castaing Effets d une variation de l apport de méthionine sur la croissance et le gavage de canards mulards. Pages in 5èmes Journées de la Recherche sur les Palmipèdes à Foie Gras, Pau, France. Ed. ITAVI, Paris, France. 5. Robin, N., P. Larroude, D. Cambeilh, and F. Skiba Effets de deux niveaux d apports en lysine et en acides aminés soufrés pour des canards mulards en phase de croissance. Pages in 6èmes Journées de la Recherche sur les Palmipèdes à Foie Gras, Arcachon, France. Ed. ITA- VI, Paris, France. 6. Robin, N., and J. Castaing Effet d une variation de l apport de lysine sur la croissance et le gavage de canards mulards. Pages in 5èmes Journées de la Recherche sur les Palmipèdes à Foie Gras, Pau, France. Ed. ITAVI, Paris, France. 7. Leclercq, B Croissance et composition corporelle du canard de Barbarie. Pages in Le canard de Barbarie. Ed. INRA, Paris, France. 8. S. A. Grimaud, Roussay, France. 9. AOAC Official Methods of Analysis, 14th ed. Assoc. Off. Anal. Chem., Arlington, VA. 10. Schwartz, D Méthodes statistiques à l usage des médecins et des biologistes. Flamarion Médecine, Paris, France. 11. Leclercq, B., and H. De Carville Influence of the protein and energy contents of the diet on the growth of young Muscovy ducklings. Arch. Geflügelkd. 40: Jeroch, H Faustzahlen zur Geflügelfutterung. Pages in Yearbook for Poultry Production. Eugen Ulmer Verlag, Stuttgart, Germany. 13. Rukmangadhan, S., R. Asha Rajini, D. Narahari, N. Ramamurthy, and R. Kumararaj Crude protein requirement of female Khaki Campbell ducklings. Indian J. Poult. Sci. 25: Chen, A. G., and Z. J. Jiang Effects of dietary protein levels on nitrogen retention rate in growing Shaoxing ducks. J. Zhejiang Agric. Univ. 25: Baéza, E., M. D. Bernadet, G. Guy, M. Lessire, and B. Carré Détermination du besoin en protéines de la canette mulard en phase de démarrage: Effet sur la croissance et les rejets azotés. Tema 2: Leclercq, B., and H. De Carville Besoin en protéines du caneton de Barbarie entre les âges de 4 et 11 semaines. Ann. Zootech. 24: Baéza, E., M. D. Bernadet, G. Guy, M. Lessire, and B. Carré Détermination du besoin en protéines de la canette mulard en phase de croissance: Effet sur la croissance et les rejets azotés. Tema 8: Chartrin, P., M. D. Bernadet, G. Guy, J. Mourot, J. F. Hocquette, N. Rideau, M. J. Duclos, and E. Baéza Do age and feeding levels have comparable effects on fat deposition in breast muscle of mule ducks? Animal 1: Baéza, E., M. Carrière, M. D. Bernadet, G. Guy, and M. Lessire Détermination du besoin en protéines de la canette mulard en phase de finition: Effet sur la croissance et les rejets azotés. Tema 17: Acknowledgments We thank the technical staff of UE89 Palmipèdes à Foie Gras (Artiguères, France) who reared, slaughtered, and cut up the female mule ducks, ground the carcasses, collected feces, and lyophilized all samples.