Effects of physical form of starter and forage provision to young calves on blood metabolites, liver composition and intestinal morphology

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The development of the gastrointestinal tract in young ruminants is a complex process that involves interactions between nutritional and physiological signals (Baldwin et al., 2004). Initiation of solid feed intake is considered as the main stimulator of rumen development which makes early weaning possible (Lesmeister and Heinrichs, 2004). Maturation of the gastrointestinal tract, associated organs and physiological processes in calves are affected by dietary strategies, weaning methods and feeding management early in life (Khan et al., 2011). For example, variations in the type (forage and concentrate) and physical form of solid feeds to young calves can affect cellular proliferation in the gastrointestinal tract (Khan et al., 2016).
Calf starter feeds may come in pelleted, mashed or textured forms with the latter consisting of a mix of coarsely rolled or ground grains, whole grains and some pellets (Khan et al., 2016). The physical form of starter feed (e.g. pelleted, mashed, or textured) may affect animal intake (Coverdale et al., 2004) and/or performance (Franklin et al., 2003); it can therefore potentially have indirect influences on the developmental processes, physiological responses or growth performance of calves (Khan et al., 2011, 2016). For example, finely ground starter feed that is high in rapidly fermentable carbohydrates could reduce starter intake, ruminal pH and growth performance (Ghassemi‐Nejad et al., 2012). Bateman et al. (2009) reported that processing starters to reduce their fine particle content increased feed intake and resulted in improved performance of dairy calves. Bach et al. (2007) concluded that pelleted starters, compared with multiparticle ones, might result in lower levels of dry feed intake and ADG around the weaning time in calves.
It has been observed that pelleting can reduce particle size of starter feeds and could, therefore, negatively influence rumen fermentation and feed intake (Bach et al., 2007). Textured starter feed contains heat‐processed grains and is commonly believed to yield better performance in calves than finely ground starter feeds (Warner, 1991). The Warner (1991) and Porter et al. (2007) suggested that approximately 80% or more of the particles in a complete starter should be greater than 1190 μm in diameter, while the weighted mean particle size should be approximately 2000 μm or greater. Bateman et al. (2009) and Hill et al. (2008) also recommended textured starters with a mean particle size of approximately 2000 μm. It is well known that the inclusion of chopped forage in starter rations not only stimulates the physical abrasion of feed particles on rumen papilla (Beiranvand et al., 2014; Omidi‐Mirzaei et al., 2015) but also maintains the integrity and the health of the rumen wall (Suárez et al., 2007). Many reports have recently recommended improved particle size via forage inclusion to stimulate rumen development, DMI and ADG in calves (Terré et al., 2013; Jahani‐Moghadam et al., 2015; Nemati et al., 2015a,b). In contrast to these studies, Hill et al. (2008) concluded that adding low energy fibrous feeds (soyhulls as forage source) to the starter feed (with adequate coarseness; approximately 2000 μm) reduced ADG in weaned calves.
Although evidences showed that the physical form of starter feeds influences the health and growth performance of young calves (Bach et al., 2007; Hill et al., 2008; Bateman et al., 2009; Terré et al., 2015), not much information is available on the effects of different physical form of the starter with identical ingredients and nutrient compositions on blood metabolites and gut histomorphology in dairy calves.
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