The thickness and increase the nutrient demand
The smallintestine is a vital organ involved in absorption of nutrients and goodintestinal health in broiler is the key factor to achieve desirable growthrates and feed conversion efficiency. The integrity of gastrointestinal tract mucosais of utmost important in production animals as it is the first tissue that comesin contact with ingested dietary ingredients. Hence assessing the intestinal morphology grossly and microscopicallycan indicate response of the intestinal tract to active substances in feeds. Theresult of current study showed that the length of the small intestine was notsignificantly affected by the dietary treatments however there was a numerical increasein length upon inclusion of PAB in diet. The results on body weight gain andsmall intestine length also revealed that there is a relationship betweenlength of intestine and body weight gained that longer the gut length, more thetime for digesta to pass through gut which leads to better nutrient absorptionand resulted in a heavier body weight. Supplementation of PAB at 400 g/ton alsoresulted in decrease in weight of small intestine.
The reduction in intestinalweight was due to thinning of intestinal wall (Gunal et al., 2006) which increasednutrients’ digestion and absorption as well. In the present study, the reduction in small intestineweight observed in birds supplemented with PAB at 400 g/ton may be associatedwith a reduction in muscularis layer thickness.
Accumulation of lymphocytesduring infection to kill the pathogens cause inflammation, which in turn increases muscular layer thickness and increase the nutrient demand bythe gut-associated lymphoid tissues. Supplementation of phytogenic feedadditive containing Andrographispaniculata, Emblica officinalis and Punicagranatum was previously known to reduce the level of acute phase protein, ?1- acid glycoprotein, a marker for gut inflammation (Feed – X ref) which is suggestive of ananti-inflammatory effect of the phytogenic additives and possibly caused significantreduction in density of jejunum by suppressing the intestinal inflammation inthe present study. Furthermore, it issensible to investigate the microscopic structure of intestinal tract inresponse to the supplementation of PAB since microvilli plays a pivotal role inabsorptive functions. Generally, shortened villi decreases the surface area forabsorption of available nutrients, while increased crypt depth indicates fast tissueturnover in response to cellular sloughing or inflammation and can lead tolower the overall performance parameters in birds.
Conversely, long villi are usually associatedwith better absorptive functions of the intestine as a result of increased absorptive surface area, expression of brushborder enzymes, nutrient transport systems (Caspary, 1992), resulted in healthier intestinal tractof chickens (Alfaro et al., 2007) and anincreased body weight gain (Zijlstra et al., 1996). In the presentinvestigation, supplementation of PAB at 400 g/ton significantly increased thevilli height, villi surface area and villi height/crypt depth ratio in theileum. Hence supplementation of PAB improved the body weight gain and feedconversion efficiency possibly by enhanced absorption of dietary nutrients andreduced tissue turnover that might leave the energy conserved for lean muscle synthesis.Besides nutrientsabsorption, the intestine is believed to have barrier functions, which usually protectthe gut from external insults. The epithelial surface of the intestinal tractis covered by a layer of mucus predominantly of mucin glycoproteins that aresynthesized and secreted by goblet cells (Smirnov et al., 2004).
This layer canact as a barrier between the luminal contents and the absorptive system of theintestine and protects the epithelial surface from invasion of enteric bacteria,bacterial and environmental toxins (Forstner and Forstner, 1994). The resultsof this study showed that increased goblet cells count in the villi of ileum couldcaused large release of mucus and formation of thick mucus layer on the wall ofgut in the birds fed on diets with PAB. This can partially help to explain the villi-relatedprotective properties of the phytoactives which reduced the possibility ofadhesion of E. coli, Clostridiumperfringens, Salmonella and fungi in intestinal content to epithelium (Jamroz et al., 2005) and reduced the inflammation ofintestinal tract.
Intestinal alkalinephosphatase, a membrane-bound glycoprotein which is more sensitive to change inmembrane than other brush border enzymes. The change in its activity levels mayreflect the degree of maturation of enterocytes and function of intestinalepithelium (Ghafoorunissa, 2001; Iji et al., 2001; Jeurissen et al.
, 2002).Birds supplemented with PAB exhibited significantly higher ileal alkalinephosphatase activity in the present study demonstrated that dietary inclusionof PAB has a beneficial effect on the gut by favouring the maturation and functionof intestinal epithelium. The enhanced maturation of intestinal epithelium inbirds supplemented with PAB could be due to favorable alterations in thenumbers of enteric bacteria and depression of the activity of bacterial enzymein the small intestinal digesta of broilers (Xu et al., 2003). This increasedALP activity in ileum is also parallely equated with the morphologicalmeasurements of increased villi height, villi surface area and villi height/cryptdepth ratio which ultimately leads to better absorption and utilization ofdietary nutrients.