World duck meat production is still increasing which emphasises the need for knowledge about nutrient requirements for feed formulations allowing efficient meat production. Data from research with broilers cannot be used for formulating duck diets, Ariane Helmbrecht of Evonik told the World Poultry Congress in Salvador, Brazil. Her overview on the current knowledge of amino acid nutrition of ducks pointed out where information is lacking.
By Ariane Helmbrecht, Evonik Industries, Hanau, Germany
Like the meat production of all poultry species the world duck meat demand and production is still increasing. In 2009, 3.8 million tonnes of duck meat was produced, this is about one million more than 2000. The core market for duck meat is still Asia with 84% of world production. Although worldwide duck meat production volume is close to that of turkey meat, the knowledge about nutrient requirement and digestibility of feedstuffs is poorer for waterfowl than for the big American land bird. This difference in knowledge is emphasised by comparing the background for the amino acid recommendations. The NRC (1994) recommendations for crude protein and amino acid supply, for instance, are for 38% backed by research in turkeys but just for 20% in ducks.
Differences between poultry species
Between various poultry species there are anatomical, physiological and metabolic differences in the intestinal tract. For example, the weight of the small intestine compared to its metabolic body weight in ducks is lower than in broilers, but higher than in turkeys.
German researchers found significant differences between strains as well as between sexes when they determined the body composition of Pekin ducks, Muscovy ducks, crossbred Mulards and geese with the non-invasive magnet resonance tomography (MRT). They too discovered differences in muscle and organ growth not only between species, but also between strains within the duck species, which leads to the assumption of differences in physiological functions and metabolism.
Amino acid digestibility
The differences in intestinal tract and growth suggested differences in the digestibility of nutrients. A comparison of the apparent ileal digestibility of amino acids showed in average 76, 69, and 56% for chickens, ducks and geese, respectively, while the digestibility of methionine (Met) and lysine (Lys) were resp. 70 and 72, 44 and 57, 52 and 41%. Conclusively, the amino acid digestibility in both waterfowl species is significantly lower than in the tested landfowl. However, even within the waterfowl species a difference for single amino acids was detected without a special direction.
A second comparison showed an amino acid digestibility of 72, 55, and 63% in chicken, ducks and geese, respectively. The digestibility of Met and Lys was found with 74 and 62, 55 and 41, 60 and 41%. These results demonstrated again a higher apparent amino acid digestibility in the land bird than in waterfowl, but within waterfowls higher values were generally found in geese than in ducks. The impact of single ingredients on the amino acid digestibility in waterfowl is also obvious. To achieve the true or standardised ileal amino acid digestibility, the inevitable or endogenous loss has to be subtracted from the apparent ileal digestible amino acids. The endogenous loss is known to be influenced in broilers by age and diet composition. A separate study in Pekin ducks showed that the inevitable losses of nitrogen and, by extension, the maintenance protein requirements were in line with findings in broilers. Since digestibility coefficients are significantly different between ducks and broilers, coefficients determined in broilers cannot be applied for ducks. Values for amino acid digestibility of feedstuffs in ducks are as scarce as the knowledge of the requirement for digestible amino acids, thus recommendations for the amino acid supplementation of duck diets are usually given as total amino acids.
An additional inevitable aspect is the genetic improvement of modern ducks. The final market weight of a Pekin duck in 1969 was 2400 g at 56 days of age with a breast muscle yield of 9%. Thirty years later Pekin ducks grew up to 3820 g within a 49-day growing period with a breast muscle yield of 16.6%. This rapid progress in growth performance and protein deposition is the premise of the knowledge of the amino acid requirement of this modern waterfowl.
Amino acid requirement of ducks
Interesting research has been done by Professor Hou from the Chinese Academy of Agricultural Science in Beijing. He studied the need for amino acids of ducks and found results in Pekin and Muscovy ducks and some regional grown Chinese duck strains as well as in crossbreds of these strains and of different age ranges. Table 1 shows the suggested total amino acid contents of the NRC (1994), Hou (2007) and Evonik. Due to research results Hou separated the second part of rearing into a grower and a finisher phase. Having the development of the intestinal tract in mind this is a meaningful choice.
Over time an increase of the recommended supplementation level for the sulphur amino acids and Lys is recognisable. Recommendations for the other amino acids are close together. The small differences in tryptophan, arginine and valine can be explained by the small number of research conducted on these topics after the publication of the NRC recommendations.
For the sulphur amino acids, Lys, threonine (Thr) and tryptophan (Trp) more recent data are available. In 2000 higher needs were suggested for methionine+cystine (M+C), Lys and Thr to achieve maximum growth of the modern Pekin duck for the age ranges of 1-21 and 21-49 days. By evaluating the data with exponential regression levels of 1.16 and 1.03% Lys, 0.76 and >0.87% M+C, >0.99 and 0.98% Thr and 0.21 and 0.18 % Trp were found to perform optimum body weight gain and feed conversion ratio from 1-21 days, respectively.
For the age range from 21-49 days the levels 0.83 and 0.73% Lys, 0.73 and >0.84% M+C, 0.62 and 0.62% Thr and 0.23 and 0.27% Trp were found as optimal for body weight gain and feed conversion ratio, respectively. Additionally, optima for breast meat yield were found to be 0.90% Lys, 0.77 % M+C, 0.66% Thr, and >0.28% Trp.
The optima Lys requirement for male white Pekin ducks (from 7-21 days) are 0.97% for body weight gain, 1.08% for feed conversion ratio, 1.39% for breast meat weight and 1.53% for breast meat yield.
To investigate the requirement for Met and M+C a dose-response trial was conducted by Evonik and Prof Hou. All 1,680 birds received commercial feed until start of the individual experimental feeding. Nine levels of methionine were tested in corn-peanut meal based diets providing all other amino acids 10% above recommendation of Evonik during the starter and grower phase. Energy and crude protein levels were orientated according to the suggestions of Prof Hou. The deficient Met and M+C levels in starter and grower phase were 0.28 and 0.27% as well as 0.59 and 0.55%, respectively. These levels were lifted up in eight increments each of 0.04%.
The findings suggested Met and M+C levels higher than the current NRC (1994) but close to Evonik (2010) recommendation for the starter and grower phase. Only the finishing phase of the duck meat productions indicated adjustments for the sulphur amino acids which are lower than thought before for the maximum growth and being close to the recommendations of the NRC (1994).
Supplemented amino acids
An additional conclusion of the above described trial is the possibility of using low crude protein diets in finishing Pekin ducks. In France, researchers tested low crude protein diets and balanced the first four limiting amino acids by adding L-Lysine HCl, DL-Methionine, L-Threonine and L-Tryptophan. They showed no significant modification in growth or carcass quality when the crude protein level was greater than 12.4% in diets supplemented with the four essential amino acids.
Other researchers assume a positive effect of using supplemented amino acids. One of them, the Chinese scientist Wu hypothesised that L-arginine might regulate body fat deposition in ducks from 21 to 42 days of age without affecting their fast growth rate. The results indicated that a diet with 1.00% supplemental L-arginine could reduce the fat deposition of carcass and abdominal adipose cell size (diameter and volume), enhance intramuscular fat in breast muscles, as well as increase muscle and protein gain.
Considering the current findings there is still a lack of knowledge for the best partition of the feeding phases for ducks older than 14 days. The knowledge of the requirement of starting ducks seems to be close to the requirement for maximum growth, but for the grower and finisher phase there is still a need for better understanding the nutritional requirements.