Gut-bone axis response to dietary replacement of soybean meal with raw low-tannin faba bean seeds in broiler chickens

It seems that faba bean (FB) seeds could be a good protein-energy component in animal feed, but the presence of anti-nutritional substances limits their use as a substitute of soybean meal. The aim of the study was to examine the influence of different concentrations of raw, low-tannin, FB seeds on the gut-bone axis in Ross 308 broilers. One-day old chickens were randomly subjected to one of the 3 dietary treatments: the control group was fed standard diet based on soybean meal and without FB seeds, and two groups were fed 8%/15% and 16%/22% of raw low-tannin FB seeds in the starter and grower, respectively. On the 35(th) day, hematological and serum biochemical analyses as well histomorphometry of the small intestine and liver tissue and bone mechanical tests were performed. The diet type had no effect on the body weight gain and feed conversion ratio. However, the basal intestinal structures were significantly reduced in birds fed the lower concentration of FB. The enlargement of nerve plexuses was dependent on the concentration used in the diet and, additionally, on the kind of plexus and location in the intestinal tract. The liver was characterized by an increase in non-hepatocytes. There was no influence of the low-tannin FB seeds on most of the analyzed serum parameters in the 35-day-old broiler chickens, except the decreased concentration of total cholesterol and Ca in both experimental groups, triglycerides in group I, and P and uric acid in group II. Furthermore, the increasing concentration of the dietary low-tannin FB did not influence the activities of AspAT (except the group fed the higher amount of FB), ALAT, and LDH. The broiler chickens had no visible leg lesions and no problem in the locomotor function, but the tibiae were lighter mainly in birds fed the higher concentration of FB seeds. Geometric analysis revealed reduction of the cross section area and wall thickness, indicating a decline in the bone midshaft, which influenced the densitometric parameters and the results of mechanical tests. In conclusion, the dietary inclusion of raw low-tannin FB seeds had no negative effects on broiler growth, but disturbed the intestine structure and tibia characteristics. Therefore, all these negative effects necessitate additional examinations before inclusion of raw low-tannin FB seed into poultry diet.