Pharmacological levels of Zn (i.e., 2,000 to 3,000 mg/kg) is often included in diets for weanling pigs to prevent post-weaning diarrhea. However, pharmacological levels of Zn may reduce microbial phytase efficacy by chelating the phytate molecule, which subsequently prevents access for phytase. However, it is possible that this effect can be reduced by adding more phytase to diets. Therefore, an experiment was conducted to test the hypothesis that inclusion of increasing levels of phytase increases pig growth performance and mineral digestibility in diets with 3,000 mg/kg of Zn.
Experimental design
A positive control (PC) diet that met nutrient requirements and a negative control (NC) diet that was deficient in total Ca (-0.16%), digestible P (-0.14%), metabolizable energy (-50 kcal/kg), and digestible amino acids (-0.02%) were formulated. Eight additional diets were formulated by adding 500, 1,000, 1,500, or 2,000 phytase units/kg of a novel bacterial 6-phytase (PhyG) or a commercial Buttiauxella phytase (PhyB) to the NC diet. A randomized complete block design with 400 weanling pigs (initial body weight: 5.82 ± 0.70 kg), 10 diets, 4 pigs per pen, and 10 replicate pens per diet was used. Pigs were fed the experimental diets for 28 d. Fecal samples were collected from 1 pig per pen on d 26 to 28. Linear and quadratic effects of PhyG and PhyB on pig growth performance and mineral digestibility were determined using polynomial contrast statements. Contrast statements were used to compare effects of PC diet with NC diet, and to compare effects of PhyG diets with PhyB diets.
Results
Overall, pigs fed the NC diet had reduced growth performance (P < 0.05) compared with pigs fed the PC diet (Table 1). Linear (P < 0.01) and quadratic (P < 0.05) increases in overall average daily gain and average daily feed intake of pigs were observed as dietary concentrations of PhyG or PhyB increased. Gain:feed of pigs increased (quadratic, P < 0.01) as the level of PhyG increased, whereas a tendency for a quadratic increase (P < 0.10) in gain:feed of pigs was observed as PhyB increased in the diets. Increasing levels of PhyG or PhyB linearly increased (P < 0.01) the apparent total tract digestibility (ATTD) of P and Ca. PhyG increased ATTD of P more (P < 0.05) than PhyB.
Key points
- Inclusion of increasing levels of phytase to diets increased pig growth performance and ATTD of minerals
- The novel consensus phytase increased the ATTD of P more than the Buttiauxella phytase.
Table 1. Overall growth performance of pigs and apparent total tract digestibility (ATTD) of minerals in experimental diets1
1Data are least squares means of 10 observations per treatment.
2ADG = average daily gain; ADFI = average daily feed intake; G:F = gain to feed ratio.
3PC = positive control; NC = negative control; FTU = phytase units.