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Impact on growth performance and carcass characteristics of “super-dosing” phytase in growing pig diets
Previous research has shown that super-dosing phytase may improve pig performance; however the response in grow-out has been inconsistent. This experiment was conducted to determine if performance could be improved by feeding phytase at super-dosed levels, and whether this response would be achieved if energy and amino acids were limiting. Two thousand two hundred pigs (36.6 ± 1.0 kg) were split by sex and blocked by initial BW, and randomly allotted to 5 dietary treatments (10 pens per treatment per gender): a fully balanced positive control (PC; SID lysine set at 98% of asymptote; 250 FTU Quantum Blue 5G/kg), a negative control (NC; PC with 15% less SID lysine and 1.5% lower NE), and 3 super-dosing treatments applied to the NC for a total of 1,000, 1,750, and 2,500 FTU/kg. Feed and water were available ad libitum. Data were analyzed using the PROC MIXED procedure of SAS (9.4) with pen as the experimental unit and treatment as a fixed effect. Barrows grew faster than gilts (1.06 vs 0.90 kg/d; P < 0.05), were heavier at marketing (123.6 vs 120.6 kg; P < 0.05) and had a higher dressing percent (74.4 vs 73.8%; P < 0.05). Barrows ate more feed (3.09 vs 2.62 kg/d; P < 0.05) and were less feed efficient than gilts on PC (0.347 vs 0.360) but not on NC diets (0.338 vs 0.335 kg/d; Interaction: P < 0.05). Barrows responded to super-dosed phytase with improved feed conversion while gilts did not (interaction: P < 0.05). Compared to the NC, pigs on the PC were heavier at marketing (125.2 vs 120.1 kg; P < 0.05) and grew faster (1.01 vs 0.96 kg/d; P < 0.05). There was no difference in feed intake between the PC and NC (P > 0.10). Super-dosing phytase tended to improve final body weight compared with the negative control (P = 0.058). There was no effect of super-dosing phytase on growth rate, feed intake or carcass yield (P > 0.10). Super-dosing phytase tended to improve gain:feed on a liveweight basis (P = 0.08) although the interaction between treatment and sex was significant (P < 0.001): barrows (0.338, 0.339, 0.343, 0.344) vs gilts: (0.335, 0.338, 0.337, 0.336 for NC, 1,000, 1,750 and 2,500 FTU/kg, respectively); this was also true when feed efficiency was expressed on a carcass basis. In conclusion, super-dosing phytase tended to improve efficiency of gain, suggesting possibly enhanced energy and/or nutrient utilization.
Keywords: super-dose phytase, barrows, gilts