Rye contains considerable quantities of intrinsic phytase and the presence of phytase in rye may result in an increased P digestibility in pigs without using exogenous phytase. It is possible that the endogenous phytase in rye also increases P digestibility in other plant feed ingredients by releasing P from the phytate. However, to our knowledge, no data demonstrating this effect have been published. Therefore, the objective of this experiment was to test the hypothesis that inclusion of rye in diets containing corn and soybean meal (SBM) without or with microbial phytase improves the apparent total tract digestibility (ATTD) of P and Ca and thus the ATTD of P is not additive in the mixed diet.

Experimental design

Forty-eight growing barrows with an average initial body weight of 39.5 ± 7.7 kg were housed individually in metabolism crates equipped with a nipple drinker, a feeder, a slatted floor, and a screen floor for fecal collection. Pigs were allotted to 6 dietary treatments with 8 pigs per treatment. Fecal output was collected during 4 d after a 5 d adaptation period.

A corn and SBM-based basal diet, a rye-based diet, and a mixed diet containing corn, SBM, and rye were formulated. Each diet was formulated without or with microbial phytase (500 unit/kg; Quantum Blue^®, AB Vista, Marlborough, UK). Therefore, a total of 6 diets were used. Vitamins and minerals except Ca and P were included in all diets to meet or exceed current requirement estimates (NRC, 2012).

Results

The rye used in this experiment had an endogenous phytase activity of 2,300 FTU/kg, but corn and SBM had phytase activity that was less than 70 FTU/kg (Table 1).

There was no interaction between ingredient and phytase effects on the ATTD of P and Ca (Table 2). Addition of microbial phytase to the diets improved (P < 0.01) the ATTD of P and Ca in all diets.

Measured values for the ATTD of P in the mixed diet containing corn, SBM, and rye with no phytase tended to be greater (P = 0.086) compared with the ATTD that was predicted from the corn-soybean meal diet and the rye diet (Table 3). The measured ATTD of P in the mixed diet supplemented with phytase was greater (P = 0.004) compared with the predicted value. These results demonstrate that the endogenous phytase in rye acts on the phytate in other ingredients in the diet and therefore increases digestibility of P in a mixed diet.

In conclusion, as expected supplementation of microbial phytase improved the ATTD of P and Ca regardless of the feed ingredients used in the diets. The intrinsic phytase present in rye also increased P digestibility in corn and SBM, which resulted in a greater digestibility of P in the diet containing corn, soybean meal and rye, than what was predicted from the separate diets.

Key points

• Supplementation of microbial phytase improved the ATTD of P and Ca regardless of the feed ingredients used in diets.
• Intrinsic phytase in rye increased the ATTD of P in corn and SBM.

Table 1. Calcium, P, phytate-P, and phytase in corn, soybean meal, and rye¹

Table 2. Apparent total tract digestibility (ATTD) of P and Ca in experimental diets

¹C = corn; S = soybean meal.

²Mixed = diet containing corn, soybean meal, and rye.

³Ing = effect of ingredients; Phy = effect of microbial phytase.

Table 3. Difference between determined and predicted values for ATTD of P in the mixed diets

¹Mixed diet contained corn, soybean meal, and rye.

²Difference was calculated by subtracting predicted values for ATTD of P from determined values.