| The study was conducted to determine the effects of cysteamine (CS) on growth performance, digestive function and approach to the mechanism in broilers. It included two parts. In partâ… :the effects of CS on growth performance, digestive enzyme activities and serum parameter in broilers were investigated (Experiment 1). In partâ…¡: the effects were studied of optimal level of CS on small intestinal villous morphology, antioxidation function, serum somatostatin (SS) and insulin-like growth factor-â… (IGF-â… ) level in the development of broilers (Experiment 2), and SS gene expression were analyzed in hypothalamus, proventriculus, duodenum and liver tissue (Experiment 3).In partâ… :600 male broiler chickens at the age of 1 d were randomly divided into five equal groups of 120 birds each, and each of these groups was then assigned to one of five treatments. All birds were offered the same basal diets with addition of CS at levels of 0 (Control),60,90,120 and 150 mg/kg. Chickens were weighed individually at the age of 1,22 and 42 d to determine average daily weight gain (ADG) and feed conversions. On d 22 and d 42 of the feeding trial,12 chickens per treatment were chosen to collect pancreatic tissue, small intestinal digesta and blood samples. The activities of amylase, lipase and protease in pancreatic tissue and small intestinal digesta were determined. The serum concentration were analyzed for total protein, albumin, urea N, triglyceride, alkaline phosphatase (AKP), thyroxine (T4), triiodothyronine (T3), insulin and gastrin. The main results obtained were as followes.1. Compared with the control, the ADG during d 1-21 was significantly higher in the birds adding 60 mg CS/kg, but lower in those with 120 or 150 mg CS/kg; and the ADG during d 22-42 was significantly higher with 90 mg CS/kg, but lower with 150 mg CS/kg. Over the experiment, chickens fed on 150 mg CS/kg had lower ADG and feed conversions than those in other groups. The results indicated that 60 mg CS/kg during d 1-21 and 90 mg CS/kg during d 22-42 might be the optimal dose in broilers.2. The activities of protease, amylase and lipase were higher in broilers fed 60 mg CS/kg than fed 0 (control),120 and 150 mg CS/kg during d 1-21. Chickens fed with 90 mg CS/kg had higher activities of protease in pancreas as well as protease, amylase and lipase in the small intestinal digesta, compared with the control during d 22-42. Adding 150 mg CS/kg resulted in lower activities of protease than other groups during d 22-42. The results indicated that the effects of CS on digestive enzyme activities were consistent with the growth performance.3. During d 1-21, adding 60mg CS/kg significantly increased the serum concentrations of total protein and AKP as well as decreased urea N, while adding 150 mg CS/kg significantly decreased total and AKP. During d 22-42, adding 60,90 and 120 mg CS/kg significantly increased the concentration of total protein, while adding 150 mg CS/kg significantly decreased total protein.4. During d 1-21, adding 60,90,120 and 150 mg CS/kg significantly increased the serum concentrations of T4 and T3, while adding 120 and 150 mg CS/kg significantly increased the serum concentrations of gastrin. During d 22-42, adding 90,120 and 150 mg CS/kg significantly increased T4, while gastrin was significantly increased with addition of 150 mg CS/kg. The results suggested that adding CS in dietary increased the serum concentrations of metabolic hormones.In Part II:472 Avian male broilers at the age of 1 d were randomly divided into a control and a treatment group. Birds in each group were kept in 8 pens. Birds in control group were offered basal diets, while birds in treatment group were offered basal diets with addition of CS at levels of 60 mg/kg into a starter diet (d 1-21) and 90 mg/kg into grower diet (d 22-42). Chickens were weighed individually at the age of 1, 7,14,21,28,35 and 42 d, respectively, to determine ADG. At the same time,12 chickens per group were used to obtain blood, duodenum, jejunum, ileum, hypothalamus, proventriculus and liver tissue. The villous morphology in duodenum, jejunum and ileum were analyzed. The serum concentrations of glutathione peroxidase (GSH-Px), total antioxidation capability, SS and IGF-â… were determined. The SS gene expression level in hypothalamus, proventriculus, duodenum and liver tissue were determined. The main results were as described below.1. The body weight of broilers added optimal level of CS was significantly greater than that fed control on d 21,28 35 and 42. The ADG during d 14 to 21 and d 21 to 28 were increased by 9.48 (P<0.05) and 8.42%(P<0.05) compared to the control, respectively. 2. Adding 60mg CS/kg significantly decreased the duodenum villus height of broilers on d 21. No significant differences were found in intestinal villus height in d42. Addition of optimal level of CS significantly increased activity of GSH-Px on d7,14 and 21 and serum total antioxidation capability on d7. The broilers with addition of optimal level of CS had significant lower concentration of serum SS but higher IGF-I at the age of d 7,14,21 and 28 than those in control.3. No significant differences were found in hypothalamus SS mRNA level on d 7, 14,21 and 28. Hypothalamus SS mRNA of CS-added broilers were higher on d 35, while lower on d 42 than those in control. The CS-added diets significantly decreased SS mRNA level in proventriculus on d 28. The CS depressed liver SS mRNA level on d 35 while increased duodenum SS mRNA level on d 21 and 28. The results indicate the time and tissue specific of SS gene expression.In summary, dietary CS improves the growth performance and enhances the activities of digestive enzymes in broilers, but higher doses of CS appears to decrease the activities of digestive enzymes and hence inhibits growth performance. The optimal dose may be 60mg CS/kg during d 1-21 and 90mg CS/kg during d 22-42. Adding optimal level of CS decreases the concentration of serum SS but increases IGF-I. The SS mRNA level of broiler indicates the time and tissue specific. These results suggest that the CS may improve growth performance by mean of the regulation of SS and IGF-I and the activity of digestive enzyme.
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