Effect of microbial phytase on digestibility and utilisation of phosphorus and protein in pigs fed wet barley protein with fibre

Effect of microbial phytase supplementation on apparent ileal and total tract digestibility, utilisation of phosphorus (P) and protein in wet barley protein with fibre (WBPF), a by-product of the integrated starch–ethanol process, was studied in six ileal cannulated pigs (live weight 89–120 kg). Three dietary treatments containing microbial phytase either 0, 250 or 500 FTU kg−1 dry matter (DM) were assigned using a two-period change-over design. WBPF was the sole source of P and protein in semi-purified experimental diet. WBPF phosphorus and crude protein contents were 5.4 and 237 g kg−1 DM, respectively. No inositol hexa- or pentaphosphates were found in WBPF, while only 1 g of P was in the form of inositol tetra- or triphosphates. Lysine, threonine, methionine and cystine contents in WBPF protein were 2.4, 2.8, 1.3 and 1.8 g 16 g−1 N, respectively. Microbial phytase supplementation improved apparent ileal P (p<0.10) and calcium (p<0.05) digestibility in WBPF diets with no effect on total tract digestibility. No significant differences were found in the degradation of phytates in WBPF at the ileal or total tract level. Phytase supplementation tended to improve apparent ileal ash digestibility (p<0.10) and depressed that of ether extract in WBPF diets (p<0.05). Apparent ileal and total tract P digestibility in WBPF was very high even without microbial phytase supplementation (ileal digestibility: 58.3% and total tract digestibility: 59.3%). Daily P retention was the same for all treatments. Microbial phytase supplementation had no effect on apparent ileal or total tract crude protein digestibility (means 79.5 and 83.5%, respectively) in WBPF. Apparent ileal cystine digestibility tended to decline after phytase supplementation (p<0.10), but otherwise the amino acid digestibilities in WBPF were similar. Average apparent ileal digestibilities of lysine, threonine, methionine and cystine in WBPF were 74.1, 73.1, 83.2 and 81.6%, respectively. No differences were found in daily nitrogen retention between treatments.