Performance and carbon turnover in fast- and slow-growing broilers submitted to cyclic heat stress and fed on high-protein diets.

Two experiments were conducted to test the hypothesis that when using similar protein/amino acid diets and environment temperature conditions, the performance and carbon turnover in muscle and liver tissues, as measured by the incorporation of stable isotopes ((13)C/(12)C), must be different between fast-growing Cobb 500® and slow-growing Label Rouge broilers. For both experiments (Cobb and Label Rouge), 21-d-old birds were distributed in a completely randomised, 3 × 3 factorial design; three environmental temperatures (cyclic heat stress ad libitum, 22°C ad libitum, and 22°C restricted) and three crude protein concentrations (189.1, 210 and 220 g/kg CP) were used. The Cobb 500® had better performance with higher concentrations of crude protein. Cyclic heat stress (a temperature factor), negatively affected this genetic strain's performance. For the Label Rouge birds, the crude protein concentrations in the diet presented inconsistent results and cyclic heat stress did not affect the performance. The carbon turnover rate was affected in the Cobb 500® strain, with a high protein content reducing carbon turnover in the evaluated tissues (liver and muscles). Feed intake had a greater impact on carbon turnover rates than cyclic heat stress. The Label Rouge birds were not affected by the evaluated factors, suggesting that genetic improvement has a leading role on tissue carbon turnover. There is a genetic influence on carbon turnover in the liver and muscle tissues of broiler chickens. In addition, genetically fast-growing broilers are more susceptible to variations in diet composition and environmental temperature than less rapidly growing animals.

Effects of corn replacement by sorghum in broiler diets on performance and intestinal mucosa integrity.

The effect of replacing corn with low-tannin sorghum on broiler performance, carcass yield, integrity of mucosa of small intestine segments, and activity of membrane enzymes of the jejunum is investigated. A total of 594 male Cobb-500 broiler chicks were randomly assigned to 3 dietary treatments: 100% corn (control), 50% corn replacement with low-tannin sorghum (low sorghum), and 100% corn replacement with low-tannin sorghum (high sorghum). Body weight gain, feed consumption, feed conversion, and carcass yield were determined at 7, 21, and 42 d, and segments of the small intestine were collected. Feed conversion and weight gain were impaired at d 42 in broilers fed the high-sorghum diet, but no differences were observed for carcass yield among the treatments (P > 0.05). Crypt cell mitotic index of the jejunum and ileum at d 21 and 42 was lower in broilers fed the control diet than in those fed low- and high-sorghum diets (P < 0.05). Aminopeptidase activity was higher in broilers fed the control diet than in those fed low- and high-sorghum diets irrespective of age (P < 0.05). Conversely, intestinal alkaline phosphatase activity in the small intestine did not differ among the dietary treatments (P > 0.05). Our results indicate that 50% corn replacement with low-tannin sorghum is suitable for broiler diets, whereas 100% corn replacement with low-tannin sorghum had negative effects on the intestinal mucosa and performance of broilers at 42 d.