Effect of particle size and whole grain feeding on growth performance and gut health of broilers

M. Ali*, P. Krishnan and G. Channarayapatna

Nutrition & Care,  Animal Nutrition, Evonik (SEA) Pte Ltd, Singapore

Grinding, mixing and  pelletization are  the  key processes in poultry  feed  production. These  processes have direct  effect on  feed  quality,  feed  intake  (FI) and  poultry  performance. Grinding  is most typically associated with the size reduction of  cereal  grains.  It is extensively studied  that  particle  size and grinding  of raw  materials  have major  impact  on mixing and pellet  quality.  Particle  size also plays important role  on the  development of gastrointestinal tract  (GIT) and growth performance  of  broilers.  Generally, reduction  in  particle size leads  to higher  ingredient surface  area  to interact with digestive acids and enzymes which ultimately  improves digestibility.  The   practice    of   feeding  whole    grains   to broilers  along with balanced concentrate is increasing acceptance  in  certain   regions,  including   Europe, Canada, Australia and New  Zealand. The main driver  of this practice is  the  potential of  reducing feed  cost  by  eliminating the grinding  step.  It has also positive  effects  on  poultry  health and welfare. This review  summarizes the results  of different trials on  effect  of particle  size  and  whole  grain  feeding on growth performance and gut health  of broilers.

Effect of particle size  and feed form on growth performance

Importance  of   particle   size   in   poultry    diets   has   been recognized because of  its benefits associated with  gizzard development and improvement in growth performance (Abdollahi et  al.,  2018). Various  studies  over  the  last few decades  demonstrated  that   the   particle   size  has  positive impact on the FI of broilers  fed mash diets. The FI in broilers fed  mash  diets  can be  increased by increasing particle  size and the effect  varied with the age of birds and type of grain (Table 1).  Attawong et  al.  (2014)  recommends that  corn particle  size  of around 805  microns  is enough for younger birds (<28 days).  However, with advancement of age larger corn  particle  size  is likely required. The  FI of crumbled or pelleted diets  was  not  affected by particle  size  of maize  or wheat (Table 2).  Weight gain  (WG) and  feed  efficiency (FE) improved with  increase  in particle  size of grains  either in  mash   or  pelleted  diets,   but   results   are   contradictory (Tables  1  and  2).  Auttawong et  al.  (2013)  tested two dietary   levels   of   coarse   corn   (0   or   35%)  on   broiler performance and  reported improvement in FE with  coarse corn (1080 microns) with ad libitum feeding  over restricted feeding.  Similarly,  Xu  et   al.  (2015)  reported improved zootechnical parameters and  digestive functions  of  broiler birds  when   crumble-pelleted diets  contained 50%  coarse corn.  The  authors reported  improvement in  body  weight (130 g) and feed conversion ratio (12 points) in 42 days old broilers.  This  correlates  well  with   the   increased  gizzard weight  (2.75  mg/g   body    weight),   increased  digesta retention time (0.78 h) and increased apparent ileal digestibility  of  energy (8.2%)  and  nitrogen (12.4%)  in broilers  fed diets  with  50% coarse  corn  compared to those fed without coarse  corn.

Effect  of  particle   size  reduction  of  commonly   used   by- products in poultry  feed  such  as distillers  dried  grains  with solubles  (DDGS)  and  soybean meal  (SBM)  has  also  been investigated. Pacheco  et  al. (2014) evaluated the  effect  of particle   size  of  SBM  (410 or  1025  microns) and  DDGS (480 or 745  microns) on live performance. The inclusion  of fine  SBM  (410  microns) improved pellet  quality  whereas coarse   SBM  (1025  microns) had  positive   effect   on  live performance. Fine  DDGS  (480  microns) increased FI and body   weight  without  any  impact   on  the   FE.  However, coarse   DDGS   (745   microns) in   broiler    diet   increased gizzard  weight. Therefore, coarse  particle  size of DDGS and SBM in broiler  diets results  in better growth performance. Physical  form   of  feed   has  significant   impact   on  growth performance of broilers  (Dozier et al., 2010). Many studies have  reported  improvement in  broiler   performance when fed  pelleted feed  compared to  mash  feed  (Amerah et  al., 2008; Chewning et  al., 2012; Mingbin  et  al., 2015). Use of crumble  or pellet  form  of feed  reduces the  feed  wastage and   prevents  particle    selection.   Pelleting   process    also improves  palatability  and increases nutrient digestibility (Mingbin et  al.,  2015). Zang  et  al.  (2009) also  reported improvement in  FI,  WG  and  FE when   broilers   were   fed pelleted diet.  Mingbin  et  al. (2015)  conducted a study  to evaluate the effects  of feed  form (mash and crumble-pellet) and   feed   particle    size   (fine,    medium    and   coarse)  on performance  and   GIT  development  of   broilers.  Results showed  that   feed   form   had   greater  effect   on   broiler performance and  GIT development than  feed  particle  size. Figure 1 shows  effect  of feed  form and feed  particle  size on growth performance of broilers.

Table 1: Effect of particle  size on feed intake,  weight gain and feed conversion ratio (FCR) of broilers  fed mash diets
Table 2: Effect of particle  size on feed intake,  weight gain and feed conversion ratio (FCR) of broilers  fed crumbled or pelleted diets
Figure  1:  Effect  of  feed   form  (mash   and  crumble- pellet) and feed particle  size (fine, medium  and coarse) on  average feed  intake,   average daily  gain  and  feed conversion ratio of broilers  (1-40 days).  Fine, medium and coarse  particle  sizes were achieved  by grinding the macro  ingredients (wheat, corn  and  soybean meal) in the hammer mill to pass through 2, 5 and 8 mm sieves, respectively. (Mingbin et al., 2015)

Effect of particle size  on gut development and health

Feed   particle   size  influences  the   GIT  development  to  a greater  extent  when    the   broilers    are   fed   mash   diets compared to pelleted diets.  Reducing  particle  size property of pelleting process  may results  in suboptimal gizzard development   and    changes   in    the    morphology   and microbiota profile of intestinal  tract (Zaefarian et al., 2016). Large particle  size supports gizzard  functions  and gut health development in broilers  (Svihus et al., 2004; Choct,  2009). Naderinejad et al. (2016) also found  that coarse  grinding  of maize in pelleted diets had positive  effect  on gizzard development  and   functionality   which   is   beneficial    for nutrient utilization   and  growth  performance. The  gizzard has  good  ability  to  grind  the  feed  to  a consistent particle size (Hetland et al., 2004). A well-developed gizzard improves  grinding activity and gut  motility  (Ferket, 2000). It  increases  cholecystokinin release  which   stimulates the secretion   of   pancreatic   enzymes   and    gastro-duodenal reflexes  (Duke, 1982; Svihus et al., 2004). Coarse  particles reduce the  digesta   rate  in  gizzard   and  lower   the  pH  of gizzard  (Nir et al., 1994). Low pH of gizzard  may increase pepsin  activity (Gabriel  et al., 2003) and protein efficiency. It also reduces the risk of coccidiosis (Cumming, 1994) and feed-borne pathogens (Engberg et al., 2002).

Particle  size  also affects  the  intestinal  tract  segments other than the gizzard, but results  are contradictory. Amerah  et al. (2007)  reported  non-significant change   in  villus  height, crypt  depth, and epithelial  thickness in the  duodenum with increase  in maize  particle  size.  However, Liu et  al. (2006) and  Xu  et  al.  (2015)  reported positive   effect   of  coarse maize  on  intestinal   morphology.  The  inclusion   of  coarse maize  reduced the  number of mast  cells in the  duodenum, jejunum, and ileum compared with finely ground maize (Liu et al., 2006). Reduction in mast cell in the small intestine is beneficial.  Increase   in  mast  cell  numbers reflects   Eimeria infection  in broilers  (Morris et  al.,  2004). Particle  size  of ingredients  also  affects   the   intestinal   microbiota  profile. Jacobs  et  al.  (2010)  reported change   in  cecal  microbiota profile  with  use  of  different corn  particle  sizes  (Table 3). The  Lactobacilli population was  significantly  increased (P < 0.05) when  the  largest  corn  particle  size of 1,387 μm was included  in the diet.  Increase  in Lactobacilli concentration is considered to  be  beneficial  because it can  prevent colonization of  pathogens such  as  E. coli (Engberg et  al., 2002). The Bifidobacteria population was significantly decreased with increasing corn particle  size from 557  μm to 1,387 μm. However, E. coli population was not affected by corn  particle  size.  Singh  et  al. (2014) also  found  that  the counts  of Lactobacillus and  Bifidobacteria species  increased and  those   of Clostridium,  Campylobacter   and  Bacteroides species  were decreased with  increasing inclusion  levels  of coarse  maize  (0  to 600  g/kg). Coarse  mash  diets  can also increase  the  Lactobacilli population in the  ceca  and  rectum (Engberg  et  al.,  2002).  It  can  be  concluded  that   large particle  size  not  only  influence   the  GIT development but also change  the  cecal  microbial  populations. Large  particle size  increases the  Lactobacilli counts  and  reduces the pathogenic bacteria  in the  caecum  of broilers. Gracia  et  al. (2016)  tested the   effect   of  whole   wheat  and  oat  hulls addition  in pellet  and  mash  diets  on  GIT development and Campylobacter  jejuni  in cecum.  Whole  wheat and  oat  hulls in  mash   diets   significantly   reduced  cecal   Campylobacter jejuni  colonization at  42  days  whereas no  clear  reduction was observed for pellet  diets.

Table 3: Effect of corn  particle  size on cecal microbial  populations in 21-d-old chicks in experiment 1 as determined by quantitative PCR1 (Adapted from Jacobs et al., 2010)

Effect of whole grain feeding on growth performance and gut health

The  primary  aims of feeding whole  grains  in broilers  is to reduce feed  cost and to improve  digestive functions (Singh et  al.,  2014). It  has  also  good   impact  on  gut  health   by encouraging  the   colonization  of  beneficial   bacterial   and reduces the incidence of coccidiosis (Cumming, 1989). Engberg et  al. (2004) reported that  whole  wheat feeding can  reduce  intestinal   numbers  of  Clostridium  perfringens which   is  important  for  prevention  of  necrotic   enteritis. Whole  grain  feeding  practice  meets  consumer demands for a  natural   feeding   system   and   good   for   animal   welfare (Gabriel   et  al.,  2008).  Whole wheat feeding under   free choice  feeding system  increased weights and  length  of the segments of small intestine (Singh  et al., 2015). Fernandes et  al.  (2013)  also  reported  increased in  small  intestine weight with  50  or  100% of  whole  sorghum grain  in the broiler  diet.  Cecum  length  was  also  significantly  increased when birds were fed diets  contained whole  sorghum grain. Intestine is the  biggest immune  organ  inside  the  bird  body which contributes further to better health  and immune response. It  has  been   reported that  whole   grain  feeding approach  helps  in  preventing  the  enlargement  of proventriculus and  atrophy of  gizzard  which  are  common problems with  pelleted diets  (Singh  et  al.,  2014). Whole wheat  given   under    free   choice   feeding  increased  the relative  gizzard  weight, irrespective of mash  or pellet  form of feed  (Singh  et al., 2014). Whole  grain feeding may also influence  starch   digestive  dynamics   and   provide    more gradually  or  slowly  digestible starch.  This effect  on  starch digestion may lead to improvement in energy utilization  and FE (Liu et  al., 2015). Wu  et  al. (2004) reported that  pre- pellet    20%   whole     grain    addition     improved   energy utilization.   Published   studies    on   whole    grain    feeding reported contradictory results. Many  studies  reported beneficial  effect  of whole  grain  feeding on  broiler performance whereas others reported no advantage or even poorer performance (Singh  et  al.,  2014). The  inclusion  of 5-15% whole  wheat in grower and finisher  diets of broilers reduced final body  weight, FCR and  breast  meat  yield  by 3.8,   3.9   and  5.7%,  respectively. Water  intake,   nitrogen excretion and  litter  weight were   decreased by  5.8,   15.5 and 11.0%, respectively (Facts and Figures,  15177).

Whole grain  can be incorporated in poultry  feed  either  pre or post steam  pelleting and offered as either  intact pellets  or as a whole  grain  pelleted concentrate blend  (Moss et  al., 2018).   In    New     Zealand,    whole     wheat   is    usually incorporated  into   broiler   diet   prior   to   steam   pelleting whereas in Australia,  whole  wheat is added  post  pelleting. Effect of pre-  and  post-pellet inclusions  of whole  wheat in broiler  diet on growth performance is presented in Figure 2 (Truong et  al.  2017). The  post-pellet inclusion  of  whole wheat in broiler  diets had greater impacts  compared to pre- pellet  inclusions.  Relative to ground grain control  diet, post- pellet   whole   wheat  inclusion   increased  relative   gizzard weight, reduced gizzard  digesta  pH and  reduced incidence of dilated  proventriculus. The FE was significantly  improved in all whole  wheat included  diets (pre- and post-pellet).

Figure 2: Effect of pre-  and post-pellet inclusion levels of whole  wheat (WW) on growth performance from 7 to 28 days post-hatch. (Truong et al., 2017)


Particle  size of grains  and  by-products used  in broiler  feed affects   growth  performance.  Particle   size   has   positive impact on the development of GIT mainly the gizzard development and functionality. Large  particle  size supports gizzard  functions   and  gut  health  development in  broilers. Impact of particle  size is clearer  for mash diets compared to pellet/crumble diets.   Use  of  large  particle   size  of  grains increases the  Lactobacilli counts  and reduces the population of pathogenic bacteria. Whole  grain feeding improves digestive functions  and encourages the colonization of beneficial  bacteria  in gut of broilers.