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Poult Sci 2007. 86:1690-1695
© 2007 Poultry Science Association
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METABOLISM AND NUTRITION

Effects of Dietary Metabolizable Energy and Crude Protein Content on the Activities of Digestive Enzymes in Jejunal Fluid of Peking Ducks

F. Zhao1, S. S. Hou, H. F. Zhang and Z. Y. Zhang

The State Key Laboratory of Animal Nutrition, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing 100094, China

1 Corresponding author: zsummit{at}hotmail.com


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
The response of digestive enzymes activities in the jejunal fluid of Peking ducks to dietary ME and CP content was investigated. In experiment 1, jejunal digesta from 24 cannulated male white Peking ducks of 18 wk of age were collected for 1 h out of every 4 h beginning at 0930 h on d 16, 18, and 20 of the experiment. The activities of amylase, trypsin, and chymotrypsin in jejunal fluid were determined. In experiment 2, 72 male cannulated ducks were randomly sorted into 4 groups. Four treatments consisted of combinations of 3,050 and 2,800 kcal/kg of ME, and 17.50 and 14.40% CP content were available ad libitum. Jejunal digesta samples were collected for 1 h every 4 h from 0930 to 1830 h on d 31, 33, and 35 of the experiment according to the results of experiment 1. The activities of amylase, trypsin, chymotrypsin, lipase, sucrase, and maltase in jejunal fluid were determined. In experiment 1, significant differences were found in the average activities of amylase and chymotrypsin among days. The collection time significantly affected the 3 enzyme activities, and average enzyme activities during the day were higher and more stable than during the night. In experiment 2, the effect of dietary ME content on the 6 digestive enzymes activities was not significant. But the dietary protein content significantly changed amylase, trypsin, and chymotrypsin activities.

Key Words: jejunal fluid • digestive enzyme • duck


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
The small intestine is the main site of carbohydrate, protein, and fat digestion in birds. The digestive enzymes activities in intestinal fluid play an important role in dietary nutrient hydrolyzation for absorption, and they could be a limiting factor in food intake, digestion, and subsequent growth in broiler chicks (Nitsan et al., 1991; Nir et al., 1993). Overfeeding and dietary nutrients level such as ME and CP content had effects on the total activities of amylase, lipase, trypsin, chymotrypsin, and disaccharidase in pancreas or intestinal digesta of chicks (Imondi and Bird, 1967; Kokue and Hayama, 1972; Siddons, 1972; Nitsan et al., 1974; Nir et al., 1978; Maiorka et al., 2004), which meant dietary nutrients were mediating these endogenous digestive enzyme levels, but few were reported in ducks. Recent studies showed that the TMEn values of naked oats, corn, and soybean in ducks were about 15% higher than that in broiler chickens (King et al., 1997; Fan, 2003), which could contribute to the higher digestive enzymes activities in intestinal fluid of ducks (Fan, 2003). Because energy and protein are the main macronutrients in poultry diets, research to determine the response of digestive enzymes activities in the intestinal fluid of Peking ducks to dietary ME and CP content will be warranted for explaining energy and protein utilization of ducks. However, in intestinal fluid, the digestive enzymes from pancreatic fluid, intestinal glands, and mucosal cells are variable in a 24-h cycle, and sampling site in intestine significantly affected the activities of digestive enzymes in chicks and roosters (Siddons, 1969; Bird, 1971). In many studies for measuring digestive enzymes in poultry gastrointestine, samples were collected through slaughtering. Such a method allows for only 1 sample at a certain time per animal and makes it difficult to get a representative sample. Therefore, some study conclusions about the relationship between dietary nutrients and digestive enzymes activities in chickens made by the slaughter method could be questionable and may not be applicable in ducks. The continuous sample collection method for duck jejunal digesta (JD) by cannula (Zhao et al., 2006) provides a potent means for in vivo repetitive sampling. The method collects digesta samples from the same relative site of intestine. However, few studies have determined digestive enzyme activities over a 24-h period and the scheme of representative samples, which shows physiological value of digestive enzymes activities. Therefore, our objective was to determine digestive enzyme activities in jejunal fluid (JF) collected by cannula from ducks over a 24-h period and to create a scheme of representative samples in terms of variation in the cycle of digestive enzyme activities to determine the response of digestive enzymes activities in the JF of Peking ducks to dietary ME and CP content. Four different diets consisted of 2 ME levels (3,050 and 2,800 kcal/kg) and 2 CP levels (17.50 and 14.40%) designed for estimating the relationship between dietary macronutrients and digestive enzyme activities.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
Birds and Diets
The objective of experiment 1 was to determine the representative JF collection scheme by simple T-type cannula according to the variation of digestive enzymes activities. Twenty-four male white Peking ducks of 18 wk of age fitted with a T-type jejunal cannula were allotted into 6 replicates with 4 birds per replication and placed in individual cages (0.45 m x 0.38 m x 0.51 m). The cages were housed in a temperature-controlled room at 25°C with a 12L:12D period. Water and typical diet (Table 1Go) designed to satisfy the recommendations of NRC (1994) were available ad libitum. The digesta were collected for 1 h every 4 h beginning at 0930 h on d 16, 18, and 20 of the experiment.


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  		Table 1. Composition and nutrient content of the experimental diets
 
Experiment 2 was conducted to determine the effect of dietary ME and CP content on the activities of digestive enzymes in the JF of Peking ducks. The experiment used a randomized complete block design. Seventy-two cannulated male white Peking ducks of 18 wk of age were sorted by weight and placed in individual cages. Factorial treatments of 2 energy levels (2,800 or 3,050 kcal of ME/kg) and 2 protein levels (14.40 or 17.50 CP) were based on the range of ME and CP level of Peking duck diets across China (Table 1Go). There were 6 replicates for each of 4 treatments, and each replicate contained 3 cannulated ducks. The typical diet was used to feed all ducks from d 1 to 15 of the experiment. From d 16 to 35 of the experiment, the ducks from 4 treatments were fed diets 1, 2, 3, and 4, respectively. The JD samples were collected for 1 h out of every 4 h from 0930 to 1830 h on d 31, 33, and 35 of the experiment based on the results of experiment 1. The diets were analyzed for DM, CP, CF, ether extract, and ash using standard laboratory procedures (AOAC, 1990).

Cannulation Procedure
The cannulation procedure described by Zhao et al. (2006) for ducks was adapted and used in this study. The cannulas were made from a medical silicone elastomer as a T-type cannula. Peking ducks at 15 wk of age and weighing between 3.80 and 4.20 kg were used in the study. They were fasted for 16 h and then given 20 mg of sodium pentobarbital/kg of BW. The anesthetized duck was placed with its abdomen up, the feathers were removed from the cannulation site, which is the center between xiphoid and cloaca, and the area was disinfected with 2% iodine tincture, then deiodinated with 75% alcohol. A 3-cm incision along the abdomen midline was made through the abdominal skin and muscle layers. After disruption of the air sacs, the duodenal loop was brought up to the surface of the incision with a pair of forceps, and then the jejunum with Meckel’s diverticulum was brought up to the surface. At the same time, the duodenal loop was drawn back. About 2 cm from Meckel’s diverticulum, a 9-mm longitudinal incision was made in the antimesenteric side of the jejunum. The T-type cannula was inserted into the intestine with forceps, and the incision was closed with #4 (size 4) medical suture. A Murphy purse-string suture was made in the intestine around the barrel of the cannula. The cannulated intestine was returned to the abdominal cavity to prevent tissue from drying. The incision of muscular layer and skin was closed by suture separately. When completed, the barrel of the cannula projected about 2.5 cm outside the skin.

Digesta Collection
To minimize the influence of environment temperature on the digesta collected by jejunal cannula, a sampling bottle that chilled the digesta was designed. The bottle was made from 2 polypropylene plastic bottles. One was 100 mL with a diameter of 4.8 cm and a height of 7 cm. Another was 45 mL with a diameter of 3.7 cm and height of 5.5 cm. About 0.4 cm from the bottom of the large bottle, a vertical cut was made, the little bottle was placed in the large one and surrounded with steel wool, and then the cut section of the large bottle was glued on the bottom of the large bottle with liquid and solid adhesive. At least about 3 h before sampling, the section between the 2 bottles was filled with water by an injector and chilled at –20°C.

The digesta collection method was similar to that described by Adeola et al. (1997) in the determination of ME content of feed ingredients for ducks. Each time after JD collected, about 5 mL of JD was transferred to a 10-mL centrifuge tube while shaken by hand. The JF was made by centrifuging JD samples for 10 min at 1,250 x g and 4°C according to procedure described by Furuya et al. (1979). In each replicate, 1 mL of supernatant JF was transferred to 5-mL centrifuge tube and vortexed. The sample was stored at –30°C for enzyme activities determination.

Digestive Enzyme Assay
The frozen sample was thawed in 4°C water for enzyme activities determination. The {alpha}-amylase was measured with soluble starch as substrate according to procedures described by Dahlquist (1962). One unit of amylase was defined as the activity liberating starch corresponding to 1 µmol of maltose per min at 25°C, pH 6.9. Trypsin was measured using Na-p-Toluolsulfonyl-L-arginine methyl ester hydrochloride (T 4626, Sigma Chemical Co., St. Louis, MO) as a substrate; chymotrypsin was measured using N-Benzoyl-L-tyrosine ethyl ester (B 6125, Sigma Chemical Co., St. Louis, MO) as a substrate according to procedures described by Wirnt (1974a,b). One unit of trypsin was defined as the activity hydrolyzing 1 µmol of substrate per min at 25°C, pH 8.1. One unit of chymotrypsin was defined as the activity hydrolyzing 1 µmol of substrate per min at 25°C, pH 7.8. Lipase was determined using Randox reagent box (LI 188, Randox Laboratories Ltd., Antrim, UK). One unit of lipase was defined as the activity hydrolyzing 0.1 µmol of triolein to diolein per min at 37°C, pH 8.9. The maltase and sucrase were measured with maltose and sucrose as a substrate at pH 6.0 using the original method by Dahlquist (1968). One unit of sucrase was defined as the activity hydrolyzing 1 µmol of sucrose per min at 37°C, pH 6.0. One unit of maltase was defined as the activity hydrolyzing 1 µmol of maltose per min at 37°C, pH 6.0. All digestive enzymes activities were expressed as units per milliliter (U/mL) of JF.

Statistical Analysis
Statistical analysis of the data was done by using the GLM procedures of the SAS program (SAS Institute, 1990). Treatment means were separated for statistical significance (P < 0.05) by the Duncan’s difference test.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
The results of experiment 1 showed changes of amylase, trypsin, and chymotrypsin activities in JF of Peking ducks with day and time (Table 2Go). There were significant differences in the average activity of amylase and chymotrypsin. But, the trypsin was stable in a different collection day. Collection time in a day cycle significantly affected the activities of amylase, trypsin, and chymotrypsin. No interactions between collection day and time were found. The present results show the activities of digestive enzymes in JF of ducks fluctuate with time. Similar phenomena have also been reported in the pancreatic fluid of pigs and geese (Low, 1982; Thaela et al., 1998, Ai et al., 2003), as well as in the intestinal fluid of pigs (Low, 1982). The main reason for this fluctuation is probably that most digestive enzymes in JF come from pancreatic secretions, which are affected by the presence or absence of feed in the intestine (Kokue and Hayama, 1972; Nitsan et al., 1974; Pierzynowski et al., 1988; Thaela et al., 1998; Keller and Layer, 2002). In our study, regarding 0930 to 1830 h as day and 2130 to 0630 h as night, the average activities of 3 digestive enzymes during the day were higher than during the night (Table 2Go). This result was supported by the finding of Ai et al. (2003), who observed more volume of pancreatic fluid and higher activities of trypsin, amylase, and lipase in pancreatic fluid of geese in day than night. The result is also supported by the findings of Borgo et al. (1968), who reported less pancreatic fluid of chicks excreted during night than day and Savory (1976) who found the birds under ad libitum feeding conditions subjected to 12-h photoperiods seldom eat during darkness, which made the flow of pancreatic juice steady in day and intermittent in night (Chawan et al., 1978). Those indicated that the difference of food intake frequency between day and night lead to unbalanced pancreatic fluid and intestinal fluid secretion. According to the difference of digestive enzymes activities in JF of ducks between day and night (Table 2Go), it can be deduced that the digestive efficiency is likely higher in the day.


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  		Table 2. Variation of digestive enzymes activities in jejunal fluid of Peking ducks, experiment 1
 
With the results of experiment 1 and the method of continuous collection of JD from ducks (Zhao et al., 2006), it is possible to develop a new sampling scheme that is capable of decreasing stress, avoiding dehydration or electrolyte depletion in intestine, and getting the digestive enzymes activities close to average physiological value. However, few research works described sampling scheme for digesta or pancreatic fluid collected by cannula in pigs, cattle, and chickens. It is obvious that sampling schemes vary depending on animal species, type of cannula, objective of individual research, and variation of tested data (Raharjo and Farrell, 1984; Wanderley et al., 1985; Jorgensen et al., 1997; Titgemeyer, 1997; Thaela et al., 1998; Montagne et al., 2000; Zhang et al., 2004). Experiment 1 showed that the activities of digestive enzymes were higher and more stable during the day than night.

Experiment 2 showed the effects of dietary ME and CP content on amylase, lipase, sucrase, maltase, trypsin, and chymotrypsin activities in JF of Peking ducks (Table 3Go). There were no obvious effects of dietary ME content on all 6 digestive enzyme activities. The amylase, trypsin, and chymotrypsin activities were significantly higher in high protein diet treatments. No interactions between dietary ME and protein content on the activities of all 6 digestive enzymes were significant. The present results show that amylase, trypsin, and chymotrypsin activities in JF of ducks adapted to the dietary CP content but not dietary ME content. However, other digestive enzymes activities were not influenced by dietary macronutrient content. As stated previously, rats, pigs, and chicks adapted endogenous digestive enzyme activities to diet (Imondi and Bird, 1967; Corring, 1980; Brannon, 1990). This might be due to hydrolyzed dietary products affecting gene expression (Brannon, 1990). In our study, the percentage of corn in 4 diets was identical and dietary ME and CP content adjusted by soybean, soybean oil, and rice hull. The difference of starch content among 4 diets was less than 0.6%, which was calculated based on the starch content in soybean being less than 7% (Van Eys et al., 2004). So, the fact that amylase activity was not influenced by dietary ME content regulated by soybean oil could be due to the difference of dietary starch content being too small to have any practical significance. In current study, the dietary macronutrient content did not influence the maltase and sucrase activities in JF. But Siddons (1972) reported the disaccharidase (maltase, sucrase, palatinase, and lactase) in the intestinal wall of chicks had adaptation to dietary disaccharide content. It was perhaps due to the disaccharidases activities in the JF less than 5% of the total activity according to disaccharidases located mainly in the intestinal wall (Siddons, 1969), and the difference of starch hydrolytic product, which was the substrate of disaccharidases from 4 diets, was too little to the activity of maltase and sucrase. However, the amylase activity was significantly increased with higher dietary CP content. This result was partly in agreement with the study of Schick et al. (1984), who reported that the dietary CP content was the main factor influencing the amylase synthesis when dietary CP content did not exceed a normal level and Johnson et al. (1977) who reported that the quality of dietary protein also affected amylase activity in the rat pancreas. In our study, the CP content of 14.40% in low protein diets (diets 2 and 4) was 1.6% lower than NRC (1994). So, the dietary protein content might be the first limiting factor for amylase activity in JF. At the same time, the dietary CP content also significantly affected trypsin and chymotrypsin activities in JF of ducks in current study. This result was agreement with the study of Imondi and Bird (1967), who reported dietary CP content affected the protease activities in chicken pancreas when dietary CP content was below 30%. So, the activities of amylase and protease in JF of ducks were mainly dependent on dietary CP content. In current study, the effect of dietary ME and CP content on lipase activity in JF was not statistically significant.


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  		Table 3. Effect of dietary ME and CP content on digestive enzymes in jejunal fluid of Peking ducks, experiment 2
 
In conclusion, increasing the dietary macronutrients content could increase the digestive enzyme activities for improving total nutrient digestion, which is also present in Peking ducks. However, in ducks, the activities of amylase and protease in JF are mainly dependent on dietary protein content but not ME content.


   ACKNOWLEDGMENTS
 
We gratefully acknowledge the financial support of the State Commonwealth Research Project (2004DIB4J152) and State Key Laboratory of Animal Nutrition Science Project (200401) in China. We also thank X. P. Tang (China Agricultural University, Beijing), Y. W. Dong, Q. J. Wang, J. T. Zhao, and Z. Y. Wang (Institute of Animal Science, Chinese Academy of Agricultual Sciences, Beijing) for cannulation operation and samples collection.

Received for publication December 3, 2006. Accepted for publication April 7, 2007.


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 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
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