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Abstract
1. There are few studies on the effect of dietary protein content on pulmonary hypertension syndrome (PHS) in broiler chickens. Conflicting results from these studies prevent a clear conclusion on the effects of reduced-protein diets on development of the syndrome.
2. To obtain an understanding of the mechanisms involved, the current study, conducted at a high altitude (2100 m above sea level), evaluated the effect of three treatments that varied only according to dietary protein (CP) levels. One treatment with dietary CP advocated by National Research Council (1994) acted as a control. Two reduced-protein diets were also prepared with CP reduced 20 and 40 g/kg relative to the CP of the control, which were designated as LCPD2 and LCPD4, respectively. A total of 180 d-old male broilers (Ross 308) were randomised across 15 floor pens measuring 1.5 m2 (12 birds per pen). Five such pens (replicates) were allotted to each dietary treatment. The protein treatments were applied from 1 to 42 d of age in which growth performance was measured and the mortality from PHS was monitored. At the end of trial (42 d), blood sampling was done and carcase characteristics were recorded.
3. Birds receiving LCPD4 gained more weight throughout the trial and had increased right ventricular weight ratio (RV:TV), relative liver weight, haematocrit, and heterophil: lymphocyte ratio at the end of the trial compared to the control. Plasma concentrations of nitric oxide (NO) and uric acid, however, were significantly lower in birds fed on LCPD4 than in those receiving the control diet.
4. Mortality from PHS was increased in birds fed the reduced-protein diets, which may have been associated with reduced concentration of plasma NO and increased haematocrit and RV:TV. In conclusion, feeding reduced-protein diets to broilers subjected to hypobaric hypoxia was associated with the development of PHS.
Acknowledgment
The Authors appreciate Shahrekord University, Shahrekord, Iran for supporting the research (Grant No. 90-2589).