Phosphorus digestibility of alternative feed ingredients for pigs

Oilseeds and oilseed meals also provide phosphorus to the diet. However, most of the phosphorus in these sources is bound to phytate, and is not available to pigs.

An experiment was performed to determine the standardised total tract digestibility (STTD) of phosphorus in canola, cottonseed, and sunflower products, and to discover how the addition of phytase influences the STTD of phosphorus.

The apparent total tract digestibility (ATTD) of calcium and the effect of adding phytase on ATTD of calcium were also measured.

Trial setup
A total of 84 growing barrows with an average initial body weight of 13.7 kg were randomly allotted to 14 diets with 6 replicate pigs per diet.

Seven diets were formulated by mixing cornstarch and sucrose with canola meal, canola seeds, cottonseed meal, sunflower seeds, sunflower meal, dehulled sunflower meal, or soybean meal.

Another seven diets were formulated that were identical to the initial seven diets with the exception that 500 units of phytase were added to each diet. The test ingredients provided all of the phosphorus in each diet.

The STTD of phosphorus in each ingredient was calculated by correcting ATTD values for the endogenous loss of phosphorus, which was assumed to be 200 mg/kg dry matter intake as per a previous experiment.

Results
Values for ATTD and STTD for phosphorus in soybean meal and canola meal were greater than the ATTD in canola seeds, cottonseed meal, dehulled sunflower meal, and sunflower meal.

The ATTD and STTD values for phosphorus in sunflower seeds were not different from the ATTD in soybean meal, canola meal, and canola seeds, but greater than for cottonseed meal, sunflower meal, and dehulled sunflower meal.

Canola seeds also had greater ATTD and STTD of phosphorus compared with sunflower meal.

For all ingredients, the ATTD and STTD of phosphorus increased when phytase was added to the diets. The addition of phytase did not have more of an effect on phosphorus digestibility in some ingredients than others, and therefore no interaction between ingredient and phytase was observed.

The ATTD of calcium was greater in canola meal diets than in diets containing dehulled sunflower meal, sunflower seeds, sunflower meal, or cottonseed meal.

For all diets, the ATTD of calcium increased when phytase was added to the diets. No interaction between diet and phytase was observed.

Key points

• The STTD of P was greater in canola meal, sunflower seeds, and soybean meal than in canola seeds, cotton seed meal and sunflower meal.

• The ATTD of calcium was greatest in diets containing canola meal.

• Adding microbial phytase increased both the ATTD and STTD of phosphorus and the ATTD of calcium in all ingredients tested.

This report is based on unpublished research by D. A. Rodriguez, R. C. Sulabo, J. C. González-Vega, and H. H. Stein.