EFFECTS OF SUPPLEMENTARY ASPERGILLUS-NIGER PHYTASE ON THE AVAILABILITY OF PLANT PHOSPHORUS, OTHER MINERALS AND NUTRIENTS IN GROWING PIGS FED ON HIGH-PEA DIETS

The effect of Aspergillus niger phytase on phytin-phosphorus utilizati on in barley-pea diets was measured with eight pigs (28-75 kg live wei ght) in a digestibility and balance experiment using a 2 x 2 x 2 facto rial arrangement of treatments in a 6 x 8 cyclic change-over design. T he experimental factors were pea level, phosphorus (P) level and phyta se addition. The diets were composed of ground barley (500 or 750 g) a nd peas (500 or 250 g) and were supplemented with methionine, vitamins and minerals. A semi-leafless, white-flowered pea variety, 'Pika', wa s used in the experiment. The calculated total P content of high-P die ts was 6.5 g/kg (the estimated digestible P, dP, 4.0 g/kg) and low-P d iets 3.9 g/kg (1.4 g dP/kg) on average. Each diet contained 8.0 g/kg o f calcium (Ca). The phytase supplementation, 1000 PU/g diet, was carri ed out with Finase(R) FP500. On low-P diets, the average improvement i n ash digestibility due to phytase was 0.05 units, and 0.02 units on h igh-P diets. Phytase enhanced the digestibility of dry matter (DM, p < 0.01), organic matter (p < 0.05), crude protein (p < 0.05), crude fat (p < 0.001) and acid-detergent fibre (p < 0.05) on low-P diets. It al so improved both P absorption (p < 0.001) from 0.40 to 0.56, and P ret ention (p < 0.001) from 0.40 to 0.55, and decreased P excretion in fae ces by 0.25 (p < 0.001). The effects of phytase were less pronounced o n high-P diets. On low-P diets, phytase supplementation increased Ca a bsorption by 0.08 units (p < 0.01) and Ca retention by 0.09 units (p < 0.01). Phytase did not affect Ca balance on high-P diets. The digesti bility of P from peas was higher than from barley (0.47 vs. 0.36) and phytase improved it, in peas by 0.22 and in barley by 0.12 units. The digestibility coefficient for organic matter in peas was 0.93 and the digestible crude-protein content 194 g/kg DM. The NE-value for peas wa s 11.11 MJ/kg DM. On the basis of these results, supplementation of a barley-pea diet with microbial phytase seems to be an effective way of improving the utilization of vegetable P and consequently of decreasi ng the faecal output of P in growing pigs. The 'Pika' pea variety appe ars to be a good source of energy and protein for growing pigs.