Abstract
The aim of this study was to evaluate the effect of dietary metabolizable energy levels on the performance and carcass yield of free-range broiler chickens from 1 to 84 days of age. A total of 900 male day-old naked neck lineage chicks were distributed in a completely randomized design between six levels of metabolizable energy (2,700; 2,800; 2,900; 3,000; 3,100 and 3,200 kcal.kg-1 diet) with six replications of 25 birds each. The increase in levels of dietary metabolizable energy resulted in a linear reduction of the feed intake, crude protein and digestible lysine intakes, as well as in the protein body deposition and protein efficiency and linear improvements in the feed conversion ratio of chickens in all experimental phases. The carcass yield, wing and abdominal fat weight and percentage of abdominal fat reduced linearly by increasing the level of dietary metabolizable energy. The diet including 2700 kcal.kg-1 of metabolizable energy in the diet of free-range broiler chickens in phases 1 to 28, 28 and 56 and 57 to 84 days of age does not interfere in the broilers performance and results in a better carcass yield in the final period of production.
Highlights
The production of free-range broiler chickens results in differences in flavor, softness, and coloring as well as a lower fat content
The Ministério da Agricultura, Pecuária e Abastecimento (MAPA), is responsible for the regulation of the free-range broiler chickens, through the circular letter n°. 07 of 1999, that lays down the following conditions for this category: 1) feed should contain only vegetable products; 2) it is prohibited to use any type of growth promoter ; 3) the animals may be reared in a chicken house up to 25 days of age, after which period the birds must be released in a pasturage area of 3m2per bird; 4) slaughter must be carried out after at least 85 days of age; 5) the lineages used should be suitable for this purpose, the use of commercial lineage of broilers being prohibited (Brasil, 1999)
There is still no established energy requirement for that animal category in its different phases of production, some studies suggest that free-range broiler chickens require lower amounts of metabolizable energy and a lower energy: protein ratio in the diet compared with commercial lineage (Mendonça et al, 2008; Moreira et al, 2012)
Summary
The production of free-range broiler chickens results in differences in flavor, softness, and coloring as well as a lower fat content. There is still no established energy requirement for that animal category in its different phases of production, some studies suggest that free-range broiler chickens require lower amounts of metabolizable energy and a lower energy: protein ratio in the diet compared with commercial lineage (Mendonça et al, 2008; Moreira et al, 2012). High amounts of energy provide an increase in deposition of abdominal fat in broilers (Santos et al, 2014)
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