Comparison between steeping and pelleting a mixed diet at different calcium levels on phytate degradation in pigs

Abstract

The degradation of phytate (inositol hexaphosphate) in the stomach, small intestine and colon was studied in 36 female pigs. A comparison was made between steeped (9 h, room temperature, feed:water 1:2.5) and pelleted diets with or without calcium carbonate supplementation (12.5 g kg−1). The diet was composed of barley, rapeseed cake and peas in the proportion 70:15:15. Dietary and intestinal content of phytate and its hydrolysis products (inositol penta-, tetra- and triphosphates) were determined using HPLC ion-pair chromatography. Steeping the feed for 9 h at room temperature reduced the phytate content by 45% and increased the amount of free phosphorus threefold. Pelleting the diet reduced phytate content by 7%. Supplementation with Ca decreased dietary phytate reduction. Steeping of the diet reduced ileal phytate content by 40% compared with pelleting. Apparent phosphorus absorption from ileal digesta was 10% lower when pigs were fed the pelleted diet, as compared to the steeped diet. Calcium carbonate supplementation impared inositol hexaphosphate degradation in the colon of pigs, but did not affect phytate degradation in the stomach and small intestine. Calcium carbonate supplementation, moreover, depressed apparent P uptake in the stomach/small intestinal region, as well as in the total gastrointestinal tract, for all feed treatments. Key words: Phytate degradation, inositol phosphates, steeping, pelleting, calcium, pigs