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Abstract
Wheat is a common ingredient in poultry diets, especially in Europe. Due to its low protein and high starch levels, wheat is essentially used as an energy supplier. Nutritional values of wheat samples vary according to their nutrient content and digestibilities. Variations of nutrient contents may be associated with cultivars and environmental conditions. Digestibility variations in growing chicks may be associated with these factors, and also, with technological treatments of diets and genetic origin of birds.
Total nutrient content (starch, protein, lipids and sugars) is strongly related to fibre content through a negative relationship. A large part of fibre content variations of wheat samples depends on their cultivar origin. Wheat protein content depends both on cultivar and environmental conditions. High yield cultivars are often associated with low protein content.
Lipid and starch digestibilities of wheat diets given to growing birds may sometimes be rather low.
The main reason of the low lipid digestibility values observed with some wheat samples is the high viscosity of water-extract induced by their water-soluble arabinoxylans. This viscosity results from a combination of several variables including the potential applied viscosity value (PAV as mL/g) of the wheat cultivar, the endogenous and exogenous xylanases, and the endogenous anti-xylanase contents. Environmental conditions and technological treatments are major factors acting on xylanase and anti-xylanase contents.
A part of wheat starch digestibility variations may be related to accessibility problems in coarse particles due to hard wheat cultivars and coarse grinding. However, coarse particles may be positive for stimulating feed intake of mash diets, and protecting against intestinal transit disorders.
In growing chicks, genetic origin of birds may result in very large variations in the digestibility of wheat diets, as observed with the divergent D+ and D- “Digestion” lines selected on the digestion ability of a wheat diet. In 3 w old chickens selected over 4 generations, the AMEn value of a Rialto wheat diet was 13% lower in D- than in D+ birds (P=0.0001). D- birds showed 10% variations in AMEn values between four cereal diets (P=0.0003), while D+ birds showed only 4% variations (P=0.0006). In D+ birds, AMEn values of wheat and maize diets were the same (14,488 vs. 14,538 J/g DM), while, in D- birds, AMEn values of wheat diets were 5% lower (P=0.015) than the maize diet value (13,106 vs. 13,809 J/g DM).
