Three in vitro experiments were carried out to determine the effect of temperature, moisture
content, duration of incubation, Ca level, soaking with water or citric acid onphytate degradation
in a wheat–barley–rye–soybean meal-based broiler diet. In experiment 1, phytase
activity of individual feed ingredients and 4 low-P broiler diets, containing 2, 4, 8, and 12 g
Ca per kg diet, respectively, were measured in the presence or absence of sodium phytate
or soybean meal. By using sodium phytate as substrate, phytase activity of rye, wheat, barley
and soybean meal was 3350, 1170, 580 and 30 FTU/kg, respectively (P<0.001). Calcium
level had no effect on the activity of intrinsic phytase of diets (P>0.05). In experiment 2, the
effect of 2 moisture levels (0.25 and 50%), 3 temperatures (70, 75 and 80 ◦C) and 3 durations
of incubation (2, 4, and 8 min) on the residual phytase activity of diet 1 (basal diet) were
evaluated as a 2
×
3
×
3 factorial arrangement with 3 replicates per treatment. The loss of
activity of intrinsic phytase increased from 0.25 at 70 ◦C to 0.61 at 80 ◦C (P<0.001). Increasing
duration of incubation from 2 min to 8 min increased the loss of activity from 0.27 to
0.52 (P<0.001). By increasing the moisture content, loss of activity of intrinsic phytase also
significantly increased from 0.25 at 25% moisture to 0.53 at 50% moisture. In experiment
3, the effects of 4 dietary Ca levels (2, 4, 8, and 12 g/kg), 2 types of soaking (with water or
citric acid solution) and 4 duration times of soaking (2, 4, 8 and 24 h) on the amount of P
released from the complete diet were determined as a 4
×
2
×
4 factorial arrangement with
3 replicates per treatment. Increasing Ca level of the diet from 2 to 12 g/kg decreased the
amount of released P from 1.19 to 0.97 g/kg of diet (P<0.001). As time of soaking increased,
the difference in released P due to soaking with citric acid comparison to soaking with
deionized water became more prominent (interaction soaking
×
time; P<0.05).
In conclusion, soaking of a broiler diet, especially in a citric acid solution one day before
feeding, may increase available P and decrease the need of supplemental inorganic P to
these diets, thus improving the sustainable use of P resources.
