Exogenous protease supplementation of poultry by‐product meal‐based diets for broilers: Effects on growth, carcass characteristics and nutrient digestibility

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Soybean meal has an established nutritional significance, but countries, which import this commodity, face fluctuation in its price and supply. Thus, the usage of indigenous protein sources in broiler diets will not only reduce dependency on soybean meal, but it can also add versatility to poultry feed ingredients, thus adding it to national feed inventory. The poultry by‐product meal (PBM), a locally manufactured protein source, has the potential to replace vegetable protein sources with superior animal protein. However, there are certain bottlenecks especially inconsistent results, variable nutritive composition, low digestibility values and its appropriate dietary level in poultry feed.
The PBM is the by‐product of poultry, which is produced by processing the inedible parts of poultry carcasses (Senkoylu, Samli, Akyurek, Agma, & Yasar, 2005) such as feathers, viscera, heads and feet. These waste products are converted to PBM and are used in many countries as protein source in diets of mono‐gastric animals (Aimiuwu & Lilburn, 2006). The crude protein content of PBM ranges from 58.4 to 62% (NRC 1994). The raw material especially feathers, bones and processing methods contribute mainly to the variation in composition of PBM (Johnson & Parsons, 1997).
Bhargava and O'Neil (1975) reported that PBM can be an effective replacement of soybean protein up to 10% of the diet in broilers. Hassanabadi, Amanloo, and Zamanian (2008) reported that PBM can be included up to 5% in the diets of broiler without deleterious effect on bird performance. Higher inclusion rates beyond 5% have led to reduction in growth rate and feed efficiency as compared to corn–soybean diets (Jafari, Ebrahimnezhad, Janmohammadi, Nazeradl, & Nemati, 2011). This inconsistency in previous studies results about the inclusion level of PBM in poultry diets necessitates that some more studies be conducted to figure out the correct picture.
Nowadays, exogenous enzymes usage in animal feed industry is a common practice. Exogenous proteases dietary supplementation perhaps improves the feeding value of feed ingredients by complementing bird's endogenous protease system, enhancing the hydrolysis of certain proteins, which are otherwise unresponsive to endogenous enzymes (Classen, Graham, Inborr, & Bedford, 1991). Bacterial keratinase isolated from Bacillus licheniformis a PWD‐1 strain has been reported to improve ground feathers and commercial feather meal digestibility from 30% to 66% and 77% to 90% respectively (Shih, 1993). Therefore, this study was planned to examine the influence of exogenous protease on broiler's growth performance, nutrient digestibility and carcass characteristics fed PBM‐based diets from 1 to 35 days post‐hatch.
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