With the prices of cereal grains rising, opportunities to reduce feed costs by using alternative ingredients are being explored. One source of alternative feed ingredients is co-products from the use of corn in the production of food for humans. Only limited published information is available on the digestibility of phosphorus in corn co-products derived from the human food industry.

Phosphorus from plant sources is often bound to phytate, which decreases the availability of the phosphorus to the pigs because pigs do not produce the enzyme phytase. The addition of microbial phytase to diets containing corn and soybean meal increases phosphorus digestibility in these ingredients. However, no data have been published on the effect of adding phytase to diets containing hominy feed,  bakery meal, corn gluten meal, corn gluten feed, or corn germ meal.

Therefore, an experiment was performed to determine the apparent (ATTD) and standardized (STTD) total tract digestibility of phosphorus in hominy feed, bakery meal, corn gluten meal, corn gluten feed, and corn germ meal, and to compare these values to the values obtained for corn and DDGS. The effect of the addition of microbial phytase to the diets on the digestibility of phosphorus in the experimental ingredients was also measured.

A total of 84 barrows with an initial body weight of 13.7 kg were fed one of 14 experimental diets. Seven diets were formulated to contain corn, hominy feed, bakery meal, DDGS, corn gluten meal, corn gluten feed, or corn germ meal as the sole source of phosphorus. The other seven diets were similar to the initial seven, with the exception that of 500 phytase units (FTU) of  microbial phytase per kilogram were added to each diet.

Variability in digestibility of P among ingredients

Values for apparent and standardized total tract digestibility of phosphorus were greatest (P < 0.01) in pigs fed DDGS, corn gluten meal, and corn gluten feed (Table 1). ATTD and STTD of phosphorus in bakery meal and corn germ meal were less than in DDGS, corn gluten meal, and corn gluten feed. Values of ATTD and STTD of phosphorus in hominy feed were less than in bakery meal, but did not differ from values in corn germ meal. ATTD and STTD of phosphorus in corn did not differ from hominy feed, and was less than in all other ingredients.

Variability in phytate P and response to phytase

Due to differences in composition and processing, different corn co-products contain different proportions of phytate-bound phosphorus (Table 2). The addition of phytase to diets whose ingredients contain relatively large amounts of phytate-bound phosphorus is expected to increase phosphorus digestibility. If, however, the ingredients contain relatively little phytate-bound phosphorus, the addition of phytase to the diet is not expected to affect phosphorus digestibility.

The addition of microbial phytase to the corn, hominy feed, bakery meal, and corn germ meal diets increased (P < 0.05) the ATTD and STTD of phosphorus. Addition of phytase to the DDGS and corn gluten feed diets did not affect the ATTD and STTD of phosphorus, due to the relatively low proportion of phosphorus in these ingredients that is bound to phytate. Adding phytase also did not affect the ATTD and STTD of phosphorus in diets containing corn gluten meal.

Key points

• DDGS, corn gluten meal, and corn gluten feed have greater values for ATTD and STTD of phosphorus than corn, hominy feed, bakery meal, and corn germ meal.
• Adding microbial phytase to diets containing corn, hominy feed, bakery meal and corn germ meal increases ATTD and STTD of phosphorus.
• The addition of phytase to diets containing DDGS and corn gluten feed does not affect ATTD or STTD of phosphorus, due to the relatively low proportion of phosphorus in these ingredients that is bound to phytate. Adding phytase also does not affect the ATTD and STTD of phosphorus in diets containing corn gluten meal.

Table 1. Phosphorus content and apparent (ATTD) and standardized (STTD) total tract digestibility of P in corn and corn co-products

^a-dWithin a row, means without a common superscript differ (P < 0.05).

Table 2. Effect of microbial phytase on apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of P in corn and corn co-products

^a-bFor each ingredient, means within a row without a common superscript differ (P < 0.05).

This report is based on unpublished research by O. J. Rojas and H. H. Stein.