Abstract: 【Objective】To promote the growth of piglets and nutrient digestibility, high copper and/or phytase additives are usually added to weaned piglet diets. However, the effects of high dietary copper on the phytase application are not very clear. This study was conducted to determine the effects of supplementation of phytase on nutrient apparent digestibility (AD), growth performance, fecal copper (FCu) and fecal phosphorus (FP) in piglets with high copper diets, and the effects of reducing copper dosage on the phytase application. 【Method】Total of 180 Landrace ´ Yorkshire piglets with initial body weight of 9-10 kg were randomly assigned to three dietary treatments group, 5 replicate pens of 12 piglets in each group. The diets based on corn-soybean meal meet or exceed NRC (1998) nutrient requirements. For the first group (control group, Group 1), 180 mg·kg^-1 copper from copper sulfate addition was added to the diet without phytase. For the second and third group (phytase treatment groups, Group 2 and Group 3), 180 and 120 mg·kg^-1 copper from copper sulfate addition was added to the diets with 500 IU·kg^-1 phytase, respectively. Feed and water were provided ad libitum throughout the three weeks of experimental period, following by three days of adaptation. Feed consumption and diarrhea were checked daily, and body weight was recorded at the beginning and end of the experiment to calculate average daily bodyweight gain (ADG), average daily feed intake (ADFI), feed conversion ratio (F/G) and diarrhea frequency. At the last week, fececs were spot sampled for three consecutive days from each pen. Every 100 gram of feces was immediately added with 10 mL of 10% ethanol and stored at -20°C until required for further analysis. Nutrients apparent digestibilities were calculated using acid-insoluble ash as an index in feed and fecal samples. 【Result】 The results showed that adding phytase to high copper level diet increased phosphorus (P) apparent digestibility by 21.12% (Group 2 to Group 1, P＜0.05), decreased FCu by 4.41% (P=0.09) and diarrhea frequency by 19.22 % (P=0.35). No significant difference was observed in apparent digestibility of dry matter (DM) and crude protein (CP), ADFI, ADG or F/G. Compared with two phytase treatment groups, reducing the copper supplement from 180 mg·kg^-1 to 120 mg·kg^-1 increased the apparent digestibility of calcium (Ca) and P by 13.74% and 9.79% (Group 3 to Group 2, P=0.02 and P=0.01), decreased FP by 18.86% (P＜0.01) and diarrhea frequency by 25.24% (P=0.25). No significant difference was observed in digestibility of DM, CP, ADFI, ADG or F/G. In contrast to high copper diet without phytase addition, lower copper diet with phytase addition showed higher apparent digestibility of DM, CP, Ca and P by 1.80%, 2.84%, 17.20% and 32.98% (Group 3 compare with Group 1, P=0.02, P=0.04，P＜0.01 and P＜0.01) and lower diarrhea frequency by 39.6% (P=0.04). 【Conclusion】Results of the current experiment indicate that reducing copper supplementation in the corn-soybean meal basal diet from 180 mg·kg^-1 to 120 mg?kg^-1 could prevent severely diminishing phytase’s positive effects on Ca and P apparent digestibility and FCu and FP content.

Key words: phytase, piglets, performance, digestibility, fecal copper