Effects of graded levels of dietary microbial 6-phytase on performance, intestinal histomorphology, caecal microbial population and short-chain fatty acid composition of Lohmann white-classics

1. This study was conducted to determine the effects of graded levels of phytase on the performance, egg quality and gut health of white laying hens. 2. Treatments consisted of a negative control (NC) diet containing 0.14% available phosphorus (avP), positive control (PC) diet containing 0.35% avP provided via dicalcium phosphate (DCP) and DCP replaced in the PC by with three graded levels of phytase derived from Komagataella phaffii at 500 (PC-500), 750 (PC-750) and 1000 (PC-1000) FTU/kg which provided 0.176%, 0.188% and 0.200% of avP, respectively. 3. Egg production, feed intake, feed conversion ratio and jejunal morphometry were negatively affected in NC-fed birds (p < 0.05). Considering the whole period, birds fed a diet supplemented with graded levels of phytase shared the same egg production and feed intake levels with PC birds (p < 0.05). Feed conversion ratio was significantly lowered by 4.9%, 1.6% and 7.6% in hens fed on diets PC-500, PC-750 and PC-1000, respectively compared to those fed the PC (p < 0.05). 4. Neither of the dietary treatments affected cracked eggs, dirty eggs, eggshell breaking strength and eggshell thickness. Dietary supplementation of phytase significantly increased villus surface area by 15%, 36% and 40% in PC-500, PC-750 and PC-1000 birds, respectively compared to PC (p < 0.05). 5. A significant increase in lactobacillus count was observed in line with increasing the level of phytase (p < 0.05). Dietary treatments had no effect on the caecal coliform or aerobic populations. Furthermore, phytase supplementation significantly increased the concentrations of total caecal short-chain fatty acid (SCFA; p < 0.01). 6. In conclusion, along with improving performance parameters, the inclusion of phytase in laying hen diets can ameliorate intestinal morphology and stimulate caecal microflora and increase SCFA concentrations.