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METABOLISM AND NUTRITION |
College of Animal Sciences, Zhejiang University, Huajiachi Campus, Hangzhou 310029, P.R. China
1 Corresponding author: agchen{at}zju.edu.cn
| ABSTRACT |
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Key Words: cysteamine growth performance digestive enzyme metabolic hormone broiler
| INTRODUCTION |
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Despite the extensive research that has been conducted on the regulation of CSH on GH and SS secretion, there has not been sufficient information on the effects of CSH on the activities of digestive enzymes and metabolic hormones, especially in broiler chickens. Furthermore, most of the current research on CSH is conducted by injection or infusion once per 6 or 7 d, which proves to be useful but not practical in depleting SS. Dietary administration of CSH would be much more practical than administering it by injection, especially for broiler breeders.
Therefore, an experiment was carried out to investigate the effects of the dietary addition of CSH on growth performance, digestive enzyme activities, and the concentration of metabolic hormones in broilers.
| MATERIALS AND METHODS |
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Diets were fed from d 1 to 42 and included starter (d 1 to 21) and finisher (d 21 to 42) phases. Nutrient levels of the diets (Table 1
) were based on the NRC (1994) recommendations. Feeds were analyzed for CP, Ca, and total P, according to the methods of AOAC (1990). All chickens had free access to feed and drinking water. Temperature was maintained at 32°C for the first 5 d and then gradually reduced until a temperature of 22°C was achieved according to broiler management practices. Continuous lighting was maintained. Chickens were weighed individually at the age of 1, 21, and 42 d to determine average daily weight gain (ADG). Feed consumption on a pen basis was recorded daily, the uneaten feed was discarded, and the feeders were replenished with fresh feed. Average daily feed intake and feed-to-gain ratio were calculated. On d 21 and 42 of the feeding trial, 12 chickens per treatment (3 per pen) were slaughtered to obtain the small intestinal digesta and pancreatic tissue samples.
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-1, 4-glucan 4-glucanohydrolase, EC 3.2.1.1
[EC]
) was determined using a kit (no. 700, Sigma Chemical Co., St. Louis, MO) by the method of Somogyi (1960). Lipase activity (triacylglycerol lipase, EC 3.1.1.3
[EC]
.) was assayed using a kit (no. 800, Sigma) according to the method by Tietz and Fiereck (1966). Protease activity was analyzed using the modified method of Lynn and Clevette-Radford (1984), and all chemicals were purchased in a kit (no. 690, Sigma).
Blood Sample Collection and Analysis
On d 21 and 42, blood samples were obtained at 0, 25, 50, and 75 min after the morning feeding (0830 h) by jugular venipuncture into evacuated tubes, and then the samples were pooled to analyze the concentrations of thyroxine (T4), triiodothyronine (T3), insulin (INS), and gastrin (GAS). Blood samples were allowed to clot at 4°C and were centrifuged at 1,520 x g for 20 min before harvesting serum. Serum samples were stored at 20°C until assayed. Concentration of T4, T3, INS, and GAS were determined using the commercial RIA kit (Beifang Biotechnology Corp., Beijing, P.R. China).
Statistical Analysis
One-way ANOVA was performed using the GLM procedure of SAS software (SAS Institute Inc., 1989). Differences among dietary treatment means were compared using Duncans multiple range tests (Steel and Torrie, 1980). A significance level of P < 0.05 was used.
| RESULTS |
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| DISCUSSION |
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The growth performance of broilers was improved with the lower dose of CSH (60 and 90 mg of CSH/kg), whereas the addition at a high dose (150 mg of CSH/kg) had an adverse effect on growth performance. Little published information is available on the effect of dietary CSH on growth performance. Using growing chicks at 3 to 10 d of age and 17 to 24 d of age, Zavy and Lindsey (1988) observed that feed efficiency was significantly improved by adding 1,200 and 1,800 mg of CSH/kg, attributable to a significant decrease in feed intake. There was no difference in weight gains between chickens in the control group and those receiving 1,200 mg of CSH/kg, but a significant decrease in weight gain was observed in chickens fed 1,800 mg of CSH/kg. The dose of CSH used in this study was much lower than that by Zavy and Lindsey (1988), because our CSH was enveloped by the antioxidant. It was observed that the addition of 100 mg of CSH/kg of BW per week to the diet of broiler fowls from 21 or 32 d of age increased weight gain and food conversion but decreased abdominal fat pad weight (Han and Lin, 1992). Low doses of CSH appear to have a specific effect on SS-mediated inhibition of GH secretion, whereas high doses of CSH might disrupt GH secretion by an alternative mechanism (Millard et al., 1983; McLeod et al., 1995). In addition, high doses of CSH might result in gastric ulcers and gastrointestinal lining damage (Szabo and Reichlin, 1985; Nassar et al., 1987; Yang et al., 2002).
The activities of protease, amylase, and lipase in the pancreas and small intestinal contents of broilers were increased with the addition of CSH at 60 and 90 mg of CSH/kg, whereas they were decreased at 150 mg of CSH/kg. It is known that SS inhibits secretion of digestive enzymes from the pancreas and gastrointestine, whereas CSH can relieve the inhibition. Ai and Han (2002) reported that CSH added in the diet of geese at dosages of 100 mg/kg of BW per week increased pancreatic secretion. Amylase activity was higher in CSH-added birds than in the control birds. It might be due to the depletion of SS resulting from the addition of CSH, because depletion of SS could enhance the movement of gastrointestine, increase the enzyme secretion of the pancreas and gastrointestine, and, finally, improve the activities of digestive enzymes.
In mammals, CSH has been shown to promote the release of INS from pancreatic islets; however, greater levels of CSH are required to alter INS release than GH secretion (Patel et al., 1985; Hashimoto et al., 1987). Conversely, purified INS has been demonstrated to have similar sensitivity to SS when incubated in the presence of CSH (Hashimoto et al., 1987). In in vitro studies, CSH has been shown to promote basal and glucose-stimulated releases of INS from pancreatic islets in rats and mice (Patel et al., 1985; Petersson and Hellerstrom, 1985). Rideau et al. (1990) studied the effects of subcutaneous injection of CSH (300 mg/kg) in 5- to 6-wk-old chickens. Cysteamine increased plasma glucose and INS in the short term (1 h), but INS was not modified in a longer term (17 to 24 h). In a study with geese, Ai et al. (2004) observed that CSH decreased the plasma SS levels and increased the levels of T4 and glucagon, resulting in benefits in growth. Xiao and Lin (2003) reported that the action of CSH in stimulating GH release in vitro appeared to be mediated through hypothalamic pathways. Dietary delivery of CSH directly or indirectly stimulated endogenous GH, T3, and T4 secretion, leading to an increase in the growth rate in grass carp.
In the present experiment, adding CSH improved serum concentrations of T4 and T3 but did not affect INS. In addition, high doses of CSH significantly increased serum concentrations of GAS. The enhanced concentration of T4, T3, and INS might promote the growth of chickens, but high GAS content might result in gastric ulcers and, consequently, decrease growth performance.
In conclusion, lower doses of dietary CSH increased growth performance and enhanced activities of digestive enzymes in broilers, but higher doses of CSH appeared to decrease activities of digestive enzymes and, hence, inhibit growth performance. Adding CSH exerted effects on the concentrations of metabolic hormones.
| ACKNOWLEDGMENTS |
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Received for publication November 22, 2005. Accepted for publication March 17, 2006.
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