Phosphorus digestibility in rice co-products fed to growing pigs

After corn and wheat, rice is the third most widely grown cereal grain worldwide. Most rice is processed to produce polished white rice for human consumption, and several co-products result from this processing. First, the outer husk, or hull, of the grain is removed. The dehulled grain, consisting of the bran, germ, and endosperm, is brown rice. To produce white rice, the brown rice is milled further and the bran is removed. Rice bran is high in fiber, and also contains about 15% crude protein and 14 to 20% fat. Rice bran can be fed as full fat rice bran or defatted rice bran. Rice bran is sometimes combined with rice hulls to produce rice mill feed. During milling of the rice, some kernels may get broken and cannot be used for human consumption. These broken kernels are known as broken rice or brewers rice and may also be used in animal feeding.

The phosphorus content of rice is similar to that of corn. Most of the phosphorus in rice is in the bran fraction, and 80-85% of the phosphorus in rice bran is bound to phytate, which limits its digestibility by pigs. Microbial phytase can be used in swine diets to increase the digestibility of phytate-bound phosphorus. However, limited information exists about phosphorus digestibility in rice co-products and how it is affected by microbial phytase. Therefore, an experiment was conducted to determine the apparent (ATTD) and standardized (STTD) total tract digestibility of phosphorus in brown rice, broken rice, full fat rice bran (FFRB), defatted rice bran (DFRB), and rice mill feed fed to growing pigs. A second objective of the experiment was to determine the effect of microbial phytase on phosphorus digestibility in rice co-products.

Experimental design

A total of 96 growing barrows with an average initial body weight of 19.4 kg were fed one of 12 diets. A basal diet based on corn and soybean meal was formulated. Five additional diets were formulated by adding broken rice, brown rice, FFRB, DFRB, or rice mill feed to the basal diet at the expense of corn and soybean meal, keeping the ratio of corn to soybean meal constant. The last six diets were similar to the previous six diets except that 500 FTU of microbial phytase were added to each diet. The rice co-products, corn, and soybean meal were the only sources of phosphorus in the diets.


The phosphorus content of brown rice, broken rice, full fat rice bran, defatted rice bran, and rice mill feed was 0.27% in brown rice, 0.11% in broken rice, 1.79% in FFRB, 2.58% in DFRB, and 0.63% in rice mill feed (Table 1). The percentage of phosphorus bound to phytate was 81.5% in brown rice, 54.5% in broken rice, 90.5% in FFRB, 91.5% in DFRB, and 88.9% in rice mill feed.

The ATTD and STTD of phosphorus was the greatest (P < 0.05) in broken rice, at 50.12% and 75.63% respectively in diets without added phytase (Table 2). ATTD of phosphorus in the other rice co-products ranged from 19.16% in brown rice to 30.82% in DFRB, while STTD values ranged from 26.45% in FFRB to 33.14% in DFRB.

Adding microbial phytase to the diets increased (P < 0.05) the ATTD and STTD of phosphorus in all rice co-products. Broken rice had the greatest (P < 0.05) ATTD and STTD of phosphorus at 60.79% and 79.79%, respectively. DFRB had the least (P < 0.05) ATTD and STTD of phosphorus at 35.18% and 37.61% respectively.

Key points

  • The ATTD and STTD of phosphorus were generally low in rice co-products. However, phosphorus digestibility in broken rice was greater than in brown rice, FFRB, DFRB, and rice mill feed.
  • The addition of microbial phytase increased the ATTD and STTD of phosphorus in pigs fed diets containing all rice co-products.
  • Although the digestibility of phosphorus in most rice co-products is not high, the high concentration of phosphorus in FFRB and DFRB means that these products are good sources of phosphorus if microbial phytase is added to the diets.

Table 1. Phosphorus content of brown rice, broken rice, full fat rice bran (FFRB), defatted rice bran (DFRB), and rice mill feed

Item, % Brown rice Broken rice FFRB DFRB Rice mill feed
P, % 0.27 0.11 1.79 2.58 0.63
Phytate, % 0.79 0.22 5.82 8.43 2.01
Phytate-bound P, % 0.22 0.06 1.62 2.36 0.56
Phytate-bound P, % of total P,  81.5 54.5 90.5 91.5 88.9
Nonphytate P, % 0.05 0.05 0.17 0.22 0.07
Nonphytate-bound P, % of total P 18.5 45.4 9.5 8.52 11.1


Table 2. Apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of phosphorus in brown rice, broken rice, full fat rice bran (FFRB), defatted rice bran (DFRB), and rice mill feed without or with microbial phytase




Without phytase


Brown rice



Broken rice



Full fat rice bran



Defatted rice bran



Rice mill feed



With phytase


Brown rice



Broken rice



Full fat rice bran



Defatted rice bran



Rice mill feed














Ingredient × phytase



a-gMeans within a column lacking a common superscript letter are different (P < 0.05).

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