Responses in Peking Ducks

Over the last decade, the market for poultry meat has grown considerably, particularly for duck meat. Weight gain and feed conversion potential of the Peking duck has improved substantially. In 1998, ducks produced in Germany achieved a body weight of 3650 g and a feed conversion ratio of 2.10 kg kg-1 within only 7 weeks (Bons, 2000). Breast meat yield as a percentage of carcass increased from 9.0% to 16.6%. This enormous genetic progress, especially in meat or protein deposition, should be reflected in feed formulation, particularly in adjusted amino acid supply. Published information on this topic is scarce, therefore a set of experiments conducted at the University of Halle, Germany (Bons, 2000), is reported here in order to put them into perspective with the concept developed for the broiler data.

The biological data obtained from this project were recalculated, including important economic parameters such as cost of feed and amino acids to predict how amino acid supply might affect overall profitability. In each experiment, a total of 240 male 21-day-old ducklings were distributed to six dietary treatments includ-

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Fig. 25.9. Relative responses to graded dietary Thr levels (two broiler late finisher experiments, approx. 42-56 days of age), (a) Weight gain; (b) feed to gain ratio; (c) breast meat yield (% of live weight).

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  1. 0 g kg-1 Thr Feed cost US$160 H
  2. 9 g kg-1 Thr Feed cost US$140 H
  3. 7 g kg-1 Thr Feed cost US$120 H
  1. 50 -| 2.40 -2.30 -2.20 -2.10 -2.00 -1.90 -1.80 -
  2. 0 g kg-1 Thr Feed cost US$160 H
  3. 9 g kg-1 Thr Feed cost US$140 H
  4. 7 g kg-1 Thr Feed cost US$120 H
Thr Thr cost US$ 3.80 kg-1

Minimum = 6.9 g kg-1 Thr Thr cost US$ 3.30 kg-1 -1-1-

Minimum = 6.9 g kg-1 Thr Thr cost US$ 3.30 kg-1 -1-1-

Fig. 25.10. Effect of increasing Thr levels on feed cost kg-"1 breast meat in late finishing broilers 42-56 days of age at changing prices for feed or L-Thr. (a) Feed cost kg-"1 breast meat, feed cost set at US$120/140/160 ton-1, (b) Feed cost per kg-"1 breast meat, cost of supplemental L-Thr set at US$2.80/3.30/3.80 kg-1.

ing one basal diet and five diets with graded inclusion levels of the respective amino acid. The diets were generally maize-wheat-soybean meal-based. Crude protein and energy content of the grower diets were about 205g kg-1 and 12.6 MJ ME kg-1, respectively.

As shown in Figs 25.13-25.18, birds consistently responded to increasing dietary amino acid content, confirming the deficiency of the basal diets for the respective amino acid. Following the 'law of diminishing returns', performance improved non-linearly with increas ing supplementation level. The magnitude of the responses was different between the trials, indicating a varying degree of deficiency of the basal diets. The strongest increase in weight gain due to supplementation was found in the Lys trials, whereas growth rate in the Met trial showed only a slight effect. However, whereas the basal diet was only slightly deficient in ducks aged 21-42 days with respect to weight gain, the asymptote for feed conversion ratio was not even achieved at the highest Met+Cys level (Fig. 25.13).

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| | cost kg-1 feed | | cost kg-1 live bird | H cost kg-1 breast meat Fig. 25.11. Effect of different dietary Met+Cys levels on overall profitability in an integrated broiler operation.

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0.8983

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cost kg-1 live bird

  1. 5 g kg-1 Lys cost kg-1 breast meat
  2. 25.12. Effect of different dietary lysine levels on overall profitability in an integrated broiler operation.

The results of the carcass evaluation performed with birds in the Met+Cys experiment are presented in Fig. 25.14. There was a relevant response to dietary Met+Cys, however, with some variation resulting in the weakest R2 of 0.56 within this data set.

Responses to Lys were very consistent with the exponential response functions (Figs 25.15 and 25.16). It is important to note that, as opposed to the responses in broilers, the feed conversion response in ducks was steeper than the growth response. In other words, further increases in growth at intermediate Lys levels (7.0-9.0 g kg-1) were triggered by extra feed intake without changing the feed : gain ratio. Breast meat responses appear closely correlated to growth rate as judged from the shapes of the corresponding curves.

Thr in the diet had only a small effect on growth rate, but a substantial effect on feed conversion (Fig. 25.17) and breast meat yield (Fig. 25.18).

The economics were determined by a calculation similar to the analysis of the broiler data. To calculate feed cost per kg weight gain or per kg breast meat, feed conversion ratio was multiplied with the feed cost assuming a grower feed price of US$170.00 t1. Prices of supplemental Lys-HCl, Met and Thr were kept at 2.50, 2.00 and US$3.30 kg-1, respectively.

y=2.818-2.473x(1-e-°034x(*-60)) R2=0.95

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Fig. 25.13. The effect of graded levels of dietary Met+Cys on weight gain (♦) and feed conversion ratio

(A) in Peking ducks 21-49 days of age. (Bons, 2000.)

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Fig. 25.14. The effect of graded levels of dietary Met+Cys on breast meat yield (% of carcass) in Peking ducks 21—49 days of age. (Bons, 2000.)

The results shown in Fig. 25.19 give an impression of how different the economic optima can be depending on the limiting amino acid and the parameters included in the calculation. For Met+Cys, the continuous improvement in feed conversion even beyond the dietary levels in the test diets prevents the determination of a definite optimum, disregarding whether cost per kg gain or cost per kg breast meat is used. A dietary content of Met+Cys higher than 8.5 g kg-1 is considerably higher than the NRC (1994) recommended level of 5.5 g kg-1 for 2-7 weeks of age.

The economics of Lys vary significantly with the response parameters (Fig. 25.19b). Given the steep response in feed conversion, the minimum feed cost per kg live weight gain would occur at only 7.8 g kg-1, while the extra responses in breast meat yield will minimize feed cost kg-1 breast meat at 9.5 g kg-1 dietary Lys. This is a very substantial difference when specifying dietary target values, and both values are much higher than the NRC (1994) figure of 6.5 g kg-1. Even more, the extra growth rate at dietary levels beyond those that minimize feed cost per kg

Fig. 25.15. The effect of graded levels of dietary Lys on weight gain (♦) and feed conversion ratio (A) in Peking ducks 21-49 days of age. (Bons, 2000.)

10.5

11.5

2.70

2.60

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Fig. 25.15. The effect of graded levels of dietary Lys on weight gain (♦) and feed conversion ratio (A) in Peking ducks 21-49 days of age. (Bons, 2000.)

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  • 11.69+4.59x(1-e_0 94x<*-6 2)) fl2=0.97
  • 1-1-1-1—

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11.5

Fig. 25.16. The effect of graded levels of dietary Lys on breast meat yield (% of carcass) in Peking ducks 21-49 days of age. (Bons, 2000.)

live weight gain would be expected to give additional profit due to higher weight at a given age at kill.

Finally, Thr economics are less conflicting to Interpret. Curves reported in Fig. 25.19c show again that the optimum dietary content to minimize feed cost per kg breast meat (7.2 g kg-1 Thr) is higher than to minimize feed cost per kg live weight gain (6.8 g kg-1), but the difference is less than with Lys. For Thr, NRC (1994) does not state a recommendation.

Overall, the response data in Peking ducks show many similarities to the far more extensive data available for broilers. It appears that the exponential functions give an acceptable fit and allow further processing of predicted results towards economics.

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Fig. 25.17. The effect of graded levels of dietary Thr on weight gain (♦) and feed conversion ratio (A) in Peking ducks 21-49 days of age. (Bons, 2000.)

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  2. 0 4.5 4.0

Fig. 25.18. The effect of graded levels of dietary Thr on breast meat yield (% of carcass) in Peking ducks 21—49 days of age. (Bons, 2000.)

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