Barley Particle Size and Supplemental Enzymes: Influence on Growth Performance and Nutrient Utilisation of Broiler Starters

Cereal grains are ground prior to feed mixing to reduce the particle size with the aim of modifying their physical characteristics. This facilitates handling, mixing and further processing (extrusion and pelleting) and increases the exposure of nutrients in the endosperm to digestive enzymes (Amerah et al., 2011). Available recommendations regarding optimum particle size are contradictory, due to the confounding effects from several factors including grain type, feed form, complexity of the diet, endosperm hardness, grinding method and particle size distribution (Amerah et al., 2007a). The influence of grain particle size on growth performance and nutrient utilisation of poultry fed maize- (Amerah and Ravindran, 2009; Naderinejad et al., 2016) and wheat- (Amerah et al., 2007b; Abdollahi et al., 2019) based diets has been examined, but corresponding studies with barley are lacking.

In addition to the commonly used carbohydrases that target non-starch polysaccharides, phytases are usually added to cereal-based diets to facilitate the release of phytate-bound phosphorus and to minimise the phosphorus effluent from intensive poultry production (Ravindran et al., 1995). Several researchers (Ravindran et al., 1999; Wu et al., 2004) have evaluated the individual and combined supplementation of carbohydrases and phytases to cereal-based diets and reported inconsistent effects requiring further elucidation. Moreover, only a limited number of studies were conducted to evaluate the interactions between different particle sizes of maize (Kasim and Edwards, 2000; Amerah and Ravindran, 2009) and wheat (Amerah et al., 2008) and supplemental enzymes. However, the findings from these studies are contradictory and, to the authors’ knowledge, corresponding studies with barley are not available. Accordingly, the present study was conducted to assess the potential interactive influence of barley particle size and carbohydrase and phytase addition, individually or in combination, on growth performance and nutrient digestibility of broiler starters offered pelleted diets.

 

A hulled barley cultivar (Fortitude; Amylopectin, 343 g/kg; Amylose, 267 g/kg; Perera et al., 2019) was ground in a hammer mill to pass through 2.0 and 8.0 mm screens, to achieve fine and coarse barley particles, respectively. Nutrient composition, nitrogen (N)-corrected apparent metabolisable energy and standardised digestible amino acid contents of barley, determined in a previous study (Perera et al., 2019), were used in formulating a basal diet that contained an adequate concentration of non-phytate phosphorus (4.8 g/kg). Two diets, mixed using fine or coarse barley, were developed into eight dietary treatments using a multi-component non-starch polysaccharide-degrading enzyme (Ronozyme® Multigrain) and a phytase (Ronozyme® HiPhos). Four methods of enzyme supplementation were employed: non-supplemented (control), carbohydrase (0.15 g/kg of feed; Carb), phytase (0.10 g/kg; Phy) and combination of carbohydrase and phytase (0.15 and 0.10 g/kg, respectively; Carb + Phy) were used in this study. The average analysed activities of phytase, endo-1,3 (4)-β-glucanase and endo-1,4-β-xylanase from enzyme-supplemented diets were 775, 80.5 and 212 IU/kg, respectively. The diets contained 5.0 g/kg of titanium dioxide as an indigestible marker. Each of the eight dietary treatments was offered ad libitum to six replicate cages (eight birds per cage). Body weights and feed intake were recorded at weekly intervals throughout the 21-d trial. On d 21, ileal digesta were collected for determination of the coefficient of apparent ileal digestibility (CAID) of dry matter (DM), N, starch and fat.

 

Enzyme supplementation tended (P = 0.056) to increase the weight gain of birds with a synergetic effect from the combined use of enzymes (Table 1). A significant (P < 0.05) barley particle size × enzyme interaction was observed as Phy increased feed intake only in fine barley diets, partly due to the poor nutrient digestibility of birds fed fine barley diets. Both coarse particle size and supplemental carbohydrase, either individually or in combination with phytase, reduced feed per gain (F/G; P < 0.001). Coarse particles reduced F/G by 2.1 points, whilst Carb and Carb + Phy reduced the F/G by 2.9 and 2.1 points, respectively. The improvement in F/G due to coarse grinding in the current study is in contrast to previous research (Amerah et al., 2007b; Chewning et al., 2012) reporting no effect of grain particle size on performance of birds fed pelleted diets. Based on the lack of effect from grain particle size in pelleted diets, previous studies hypothesised that pelleting can mask the influence of particle size. However, the present results suggest that the effects of feed particle size on performance might be maintained even after pelleting.

The main effects of barley particle size and supplemental enzyme on nutrient digestibility are summarised in Table 2, as there was no significant interaction between particle size and enzyme. The improvements (P < 0.01 to 0.05) of 3.1, 3.2 and 4.3% in CAID of DM, N and fat, respectively, in coarsely-ground barley diets are contrary to the findings of Naderinejad et al. (2016) and Abdollahi et al. (2019), who reported no effect of maize and wheat particle size, respectively, on ileal digestibility of DM, N and fat. Well-developed gizzards in birds fed coarse barley diets (data not reported) might have contributed to the improved digestibility of DM, N and fat through extensive grinding, mixing and lower pH (Svihus, 2011). Moreover, coarse particles can reduce the digesta passage rate through the gizzard and therefore are retained longer than finer particles in the digestive tract (Amerah et al., 2007a) increasing the exposure time of nutrients to digestive enzymes.

Enzyme supplementation, regardless of barley particle size, improved (P < 0.05) the DM, starch and fat digestibility. Carb, Phy and Carb + Phy improved CAID of DM by 5.7, 4.2 and 5.9%, respectively. Moreover, Carb and Carb + Phy enhanced the starch digestibility by 1.5 and 1.8%, respectively and, fat digestibility by 4.7 and 5.7%, respectively. In this study, however, no effect of supplemental enzymes on jejunal digesta viscosity was observed (data not shown). Therefore, the improvement in CAID of nutrients due to supplemental Carb might be attributed to the degradation of endosperm cell walls by added Carb, consequently releasing encapsulated nutrients and allowing better interaction with digestive enzymes (Kim et al., 2005). Phytate in wheat and barley is largely located in the aleurone layer (Eeckhout and De Paepe, 1994). The improvement in CAID of DM due to supplemental Phy, at least in part, was caused by the action in disrupting cell wall and consequent release of encapsulated nutrients in a manner similar to that of Carb (Ravindran et al., 1999). In conclusion, the present study showed that feeding coarse barley particles and supplementation of Carb improved feed efficiency and nutrient utilisation in broiler starters fed pelleted diets. The effect of grain particle size was preserved even after pelleting, as indicated by feed intake, feed efficiency and DM, N and fat digestibility values. The combination of Carb and Phy tended to improve weight gain, but caused no further improvements in nutrient utilisation.