Live performance, carcass characteristic and blood metabolite responses of broilers to two distinct corn types with different extent of grinding

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The predominant feed grain used in poultry diets worldwide is corn. Corn breeding programs have produced many high‐yielding hybrids, with different agronomic characteristics, as well as differences in grain composition and texture. The two types of corn used to feed livestock are dent (soft) and flint (hard) corn, the texture of which is mainly defined by the ratio between vitreous and starchy endosperm (Phillippeav and Michalet‐Doreau, 1997). The predominant endosperm in dent corn is mealy or porous, while that of flint corn is vitreous or hard. Compared with soft corn, hard corn requires more energy for grinding in feed milling, and higher concentrations of digestive enzymes for hydrolysis (Silva et al., 2006). As for nutritional value, the metabolizable energy (ME) content of corn can vary by more than 400 kcal/kg in poultry (Gehring et al., 2013), which may be partially explained by endosperm type (the proportions of horny and floury endosperm). The contents of protein, fat and starch, and the levels of amylose and amylopectin may also vary with corn texture, which directly affect nutrient and energy availability (Duarte et al., 2005; Cantarelli et al., 2007; Vieira et al., 2007). Modern broilers are extremely precocious and there is a need to know the real capacity of their use of different corn types during the short production cycle, in order to achieve the best performance results.
Preparing corn by grinding before incorporating it into a compound diet improves broiler performance (Reece et al., 1986; Lott et al., 1992). Smaller corn particle size has a greater surface area to volume ratio, increasing exposure to digestive enzymes and presumably decreasing energy needed for mechanical digestion (Jurgens, 1993). Feeding large‐particle corn may produce beneficial effects similar to reports of whole grain feeding. Whole grain feeding has been associated with increased gut development and health, that is a heavier muscular gizzard and less occurrence of proventricular dilatation (Jones and Taylor, 2001). Greater development of the broiler gastrointestinal tract suggests that feed may be retained in the upper digestive tract for a longer period allowing for increased enzymatic digestion (Jones and Taylor, 2001; Hetland et al., 2002). Many studies have been published on the broiler responses to varying corn particle size, but with conflicting results. Reece et al. (1986) and Lott et al. (1992) reported improved broiler performance when corn particle size decreased from 1289 to 987 μm and from 1173 to 710 μm respectively. Further decreases (900–300 μm) have also resulted in improved performance (Healy, 1992). In contrast, Nir et al. (1994a) has shown that increasing corn particle size from 525 to 897 μm increased broiler performance. The type of corn used in different studies likely explains the different findings, namely that the feeding value of a particular type of corn is probably related to specific particle size. From the foregoing, it was hypothesized that the optimal extent of grinding of corn may well change with different types.
In the present study, two popular corn hybrids in traditional Chinese farming, a dent type (Ludan No. 50, LD50) containing more floury endosperm and a flint variety (Nongda No. 108, ND108) having more horny endosperm, were assessed for feeding value to broiler chickens when ground into large or small particles, in terms of growth and carcass composition. To expose the underlying causal mechanisms, some relevant metabolites were also measured in plasma.
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