WHEAT: COMPOSITION AND FEEDING VALUE FOR POULTRY - Soybean and Wheat Crops: Growth, Fertilization, and Yield - page 253

factors suggested to explain variation between individual birds within the same treatment
group include diurnal rhythms, water intake patterns and pancreatic serous secretion output
(Bedford and Schulze, 1998).
E NDOSPERM H ARDNESS AND THE N UTRITIVE V ALUE
Hardness is one of the important characteristics of wheat grain that determines whether a
wheat variety is classified as hard or soft and this depends on the strength of adhesion
between the protein matrix and the starch granules in the endosperm. Endosperm hardness is
an important aspect in determining the milling outcomes of wheat cultivars. A hard
endosperm gives larger irregular shaped particles (Rose et al ., 2001) which are easy to handle
(GreVeuille et al ., 2006). Due to the hard texture, the endosperm requires more energy to
grind into flour, resulting in a greater level of starch damage during the milling process than
experienced with soft wheats. This also results in increased water absorption during
processing, for example, during the pelleting process. In the baking industry, hard wheat
flours are used for bread-making, while soft wheat flours are using for biscuit and cakes.
Despite the wide use of wheat in poultry diets, studies on the effect of wheat endosperm
hardness on broiler performance are limited. Harder wheat produces larger particle size
flours, which may account for the better broiler performance reported using mash diets based
on hard wheats (Rose et al ., 2001; Pirgozliev et al ., 2003). In pelleted diets, Salah Uddin et
al . (1996) compared two wheat cultivars selected to be similar in nutrient composition but
differing in hardness value. They found no effect of wheat hardness on broiler performance
either in ground or whole grain form. Similarly, Hetland et al . (2007) found no relationship
between wheat hardness and broiler performance.
A negative relationship between wheat hardness and the digestibility of starch in pelleted
diets has been reported (Carre et al ., 2002; 2005; Peron et al ., 2006). This effect of hardness
was attributed to larger particulate size reducing the surface area and accessibility for
digestive enzymes (Carre et al ., 2005). In support of this theory, Peron et al . (2005) found
that fine grinding of hard wheat improved starch digestibility in broilers fed pelleted diets.
Similarly, Short et al . (2000) found that the hard wheat endosperm was associated with lower
amino acid digestibility. It has been suggested that the interaction between the starch granules
and the surrounding protein matrix may act to obstruct enzyme hydrolysis of starch in hard
wheat (Guerrieri et al ., 1997; Peron et al ., 2006). Conversely, Salah Uddin et al . (1996) found
that the AME of pelleted wheat diets was not affected by endosperm hardness in broilers.
This lack of a relationship between grain hardness and AME or starch digestibility in wheat-
based mash diets has been reported by several workers (Rogel et al ., 1987; Rose et al ., 2001;
Pirgozliev et al ., 2003).
W HOLE W HEAT I NCLUSION IN P OULTRY D IETS
The need to reduce feed costs renewed the interest within the feed industry in whole grain
feeding, which was a common practice at early days of commercial poultry production.
Wheat is the common cereal considered in whole grain feeding and, only limited studies have