Research Note Predicting Metabolizable Energy of Normal Corn from its Chemical Composition in Adult Pekin Ducks F. Zhao,1 H. F. Zhang, S. S. Hou, and Z. Y. Zhang The State Key Laboratory of Animal Nutrition, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing 100094, China ABSTRACT Two experiments were conducted to establish an ME content prediction model for normal corn for ducks based on the grain’s chemical composition. In Experiment 1, observed linear relationships between the determined ME content of 30 corn calibration samples and proximate nutrients, acid detergent fiber (ADF), and neutral detergent fiber (NDF) were used to develop an ME prediction model. In Experiment 2, 6 samples of corn selected at random from the primary corn-growing regions of China were used for testing the accuracy of ME prediction models. The results indicated that the AME, AMEn, TME, and TMEn were negatively correlated with
crude fiber (r = −0.905), ADF (r = −0.915), and NDF (r = −0.95) contents, and moderately correlated with gross energy (GE; r = −0.55) content in corn calibration samples. In contrast, no significant correlations were found for CP, ether extract, and ash contents. According to the stepwise regression analysis, both NDF and GE were found to be useful for the ME prediction models. Because the maximum absolute difference between the in vivo ME determinations and the predicted ME values was 61 kcal/kg, it was concluded that, for White Pekin ducks, the latter could be used to predict the ME content of corn with acceptable accuracy.
Key words: duck, corn, metabolizable energy, prediction model 2008 Poultry Science 87:1603–1608 doi:10.3382/ps.2007-00494
INTRODUCTION In 2005, the total yield of Chinese corn was >130,000,000 t. Corn is the principal energy source for ducks, comprising >40% by weight of the duck diet in China. To produce an accurate evaluation of the ME content of corn for poultry diet formulation, a considerable number of studies have been conducted to predict the ME content of corn based on its physical characteristics or chemical composition. Using the adult rooster as a test animal, many researchers have shown that the ME content of corn was correlated with its bulk density or chemical composition (Conner et al., 1976; Leeson et al., 1977; Mollah and Annison, 1981; Dale, 1994; NRC, 1994; Lessire et al., 2003). These results also indicated that the ME value of corn could be predicted, but few studies have been reported with ducks. In general, models that are based on chemical composition and used to predict ingredient ME value are more accurate than models based upon physical characteristics of the test ingredient. However, there has been no uniform model predicting the ME content of corn for birds based
©2008 Poultry Science Association Inc. Received December 4, 2007. Accepted April 9, 2008. 1 Corresponding author:
[email protected]
on the chemical composition. Several factors can affect the accuracy of ME prediction models, which subsequently influences their successful use. One such factor is the sample size for regression analysis; another is the representativeness of samples for the feedstuff as a whole. In some experiments aimed at predicting the ME content of raw materials, more than 25 samples were included in the regression analysis (Dale, 1994; Lessire et al., 2003). However, in other studies, the number of samples was less than 15 (Mollah and Annison, 1981). Prediction models from smaller sample sizes may have greater R2 and less residual standard deviation (RSD), but may not be as accurate as other models developed with a greater number of samples (Carre´, 1990). On the other hand, the range of ME and chemical composition contents of samples obviously affect the accuracy of the prediction model. For example, low variation in the ME and chemical composition contents of calibration sample set might provide an incorrect prediction model (Carre´, 1990). Because the ME from corn contributes more than 40% of the total dietary ME content in diets typically fed to ducks in China, research to establish a model for predicting the AME and TME contents of corn for ducks should improve the accuracy of calculating ME in diet formulations for ducks. Therefore, this study utilized a series of calibration samples comprising corn and corn plus corn gluten meal, corn hulls, corn germ, and corn starch to establish an ME prediction model for White Pekin ducks.
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Table 1. Composition and nutrient content of the corn-soybean mealbased diet fed during the wash-out period between ME determinations Item
m) in a temperature-controlled room (25°C) and provided with 12 h of light daily.
%
Ingredient Corn Soybean meal Soybean oil Sodium chloride Limestone Calcium phosphate DL-Methionine LysineⴢHCl Vitamin-mineral premix1 Analyzed nutrient content DM CP Crude fiber Ether extract Ash Calculated nutrient content ME,2 kcal/kg Lys Met Calcium Total phosphorus
Experimental Design 70.87 23.37 1.42 0.30 1.23 1.70 0.07 0.04 1.00 89.68 16.79 3.07 4.12 5.66 2,950 0.82 0.32 0.90 0.60
1 Supplied per kilogram of diet: vitamin A (retinyl acetate), 2,500 IU; vitamin D3, 400 IU; vitamin E (DL-α-tocopheryl acetate), 10 IU; vitamin K3, 0.50 mg; thiamin, 1.80 mg; riboflavin, 4 mg; pyridoxineⴢHCl, 3 mg; vitamin B12 (cobalamin), 7 g; D-Ca pantothenate, 11 mg; nicotinic acid, 55 mg; folate, 0.50 mg; D-biotin, 0.12 mg; choline chloride, 750 mg; copper (CuSO4ⴢ5H2O), 8 mg; iron (FeSO4ⴢ7H2O), 80 mg; zinc (ZnSO4), 40 mg; manganese (MnSO4ⴢH2O), 60 mg; selenium (Na2SeO3), 0.15 mg; iodine (KI), 0.35 mg. 2 Calculated value according to the AME of roosters.
MATERIALS AND METHODS Duck ME Assay All procedures were approved by the animal care and welfare committee of Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing. The method of ME determination was similar to the TME bioassay described by Sibbald (1976) and partly modified to account for the difference in digestive physiology between rooster and duck as shown by studies in our lab (Fan, 2003). The modifications to Sibbald’s bioassay include feed withdrawal of all birds for 36 h before feeding test samples, use of 60 g of feedstuff for force feeding, and a 36-h period of excreta collection. In a 14-d wash-out period between ME trials, water and a corn-soybean mealbased diet (Table 1) were available for ad libitum consumption. Endogenous energy losses were determined using 4 replicates of 3 ducks per replicate during each ME trial. Four kilograms of each sample were made and ground through a 2-mm screen before pelleting. Pellets, 4 mm in diameter and 6 mm long, were prepared by regulating the ratio of water to feedstuff with a laboratory nonsteam press pellet mill, and were then air-dried until the water content was
