The effect of microbial phytase and feed restriction on protein, fat and ash deposition in growing-finishing pigs

Forty-eight 35-kg-bodyweight barrows were assigned to treatments in a 2 x 2 factorial arrangement. Main factors were feed intake level (ad libitum or restricted) and supplementation of microbial phytase (with or without). Restricted pigs received 80% of the feed consumed by the corresponding ad libitum group. Phytase-supplemented diets contained 584 phytase units kg(-1). Body weight, fat, protein and ash were estimated every 2 wk by dual-energy X-ray absorptiometry. Plasma alpha-amino N concentrations were measured every 30 min during the 6 first postprandial hours at 90 and 132 d of age. Microbial phytase addition reduced feed intake by 6.8% (P < 0.05). Phytase did not affect (P > 0.05) feed, energy and protein efficiencies but it reduced protein deposition (P < 0.05) and tended to reduce ADG (P < 0.09). Ninety-day-old pigs receiving phytase had higher plasma levels of alpha-amino N during the first postprandial hours (P 0.01) as compared to control pigs. At 132 d of age these effects disappeared. Supplemental phytase may improve a-amino acid absorption in growing pigs but the phytase effect on protein deposition suggest that these effect is not necessarily associated with better growth performance when nutrient requirements are satisfied.