Effects of addition of protease with or without fructo-oligosaccharide to low protein diet on growth performance, nutrient digestibility, and fecal ammonia emission in growing-finishing pigs

This study was conducted to determine the effects of supplementating protease with or without fructo-oligosaccharide (FOS) to a low-protein diet on growth performance, nutrient digestibility, and fecal ammonia emission in growing-finishing pigs. A total of 160 pigs (Duroc × [Landrace × Yorkshire]) with an average initial body weight (BW) of 57.70 ± 1.16 kg were randomly allotted into 1 of 4 dietary treatments based on initial BW and sex (10 replicate pens per treatment, 2 barrows and 2 gilts per pen). Dietary treatments included: 1) PC: a positive control diet (15.97% CP); 2) NC: a negative control diet (12.94% CP); 3) PRO: NC supplemented with 0.05% protease; 4) PROFOS: NC supplemented with 0.05% protease and 0.1% FOS. Apparent total tract digestibility (ATTD) was determined by mixing chromic oxide (0.2%) as an indigestible marker in the diet during the last wk of the experiment. All experimental data were analyzed as a completely randomized block design using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC). The pen was considered as the experimental unit. Differences among treatments were separated by Tukey’s range test. Pigs fed the NC (2961 g/d) diet had higher average daily feed intake (ADFI) than those fed PC (2838 g/d) and PRO (2815 g/d) diets during wk 5 to 9 (P < 0.05). Pigs fed the NC (0.293) diet had lower gain:feed ratio (G:F) compared to those the PC (0.321), PRO (0.312), and PROFOS (0.313) diets during wk 1 to 9 phase. Compared to the PC (74.30%), PRO (73.65%), and PROFOS (73.81%) groups, ATTD of CP was lower (P < 0.05) in pigs offered the NC (71.97%) diet. Ammonia emission was reduced (P < 0.05) in pigs fed NC (16.55 ppm) and PRO (16.14 ppm) diets compared with those fed the PC (18.50 ppm) diet, but no difference was observed between pigs fed the NC diet and those fed the PRO diet. Additionally, pigs fed PROFOS (14.98 ppm) diet had lower (P < 0.05) ammonia emission compared to pigs offered the NC and PRO diets. In conclusion, supplementation of protease to a low-CP diet improved growth performance and increased ATTD of protein. Dietary supplementation with protease and FOS in a low-CP diet improved growth performance, increased ATTD of CP and decreased fecal ammonia emission in growing-finishing pigs.