- - - Department of Animal Science, Faculty of Agriculture, University of Zanjan, Zanjan, Iran.
- - - Department of Animal Science, Faculty of Agriculture, University of Zanjan, Zanjan, Iran.

This study investigated the effect of reducing dietary metabolizable energy (ME) and crude protein (CP and amino acids) or decreasing only dietary CP [and amino acids, except first limiting amino acids (i.e. lysine, methionine+cystine, and threonine)] on mortality and performance of broilers raised in a farm ۱,۷۰۰ m above sea level. Two hundred and fifty-two Ross ۳۰۸ male broiler chicks were distributed into ۳ treatments with ۶ replicates per each from ۱ to ۳۸ d of age. Dietary treatments were: control) a diet met or exceeded nutritional recommendations; DMC) a diet with the dilution of ME and CP (and amino acids), and DC) a diet with the dilution of CP (and amino acids, except lysine, methionine+cystine, and threonine). Mortality was higher in control compared to that of other treatments from ۲۵ to ۳۸ and ۱ to ۳۸ d of age. There was a higher relative weight of the right ventricle in control compared to that in DMC, and DC was being intermediate. During ۱ to ۳۸ d of age, control and DC improved average daily gain and adjusted feed conversion ratio compared to those of DMC. But in respect of the unadjusted feed conversion ratio and European poultry efficiency factor, DC improved these parameters compared to those of other treatments. In conclusion, decreasing CP content without any reductions in ME, lysine, methionine+cystine, and threonine concentration reduces mortality and enhances European poultry efficiency factor without any negative effects on feed efficiency or weight gain in broilers reared at a high-altitude area.

Energy, Mortality, High-altitude, Crude protein, Broiler chicken