Mineral availability from barley low phytic acid grains in rainbow trout (Oncorhynchus mykiss ) diets

Abstract

Phosphorus storage within plant seeds occurs mainly as phytic acid, which has profound implications on the use of seeds as food material. Phytic acid phosphorus is unavailable to non-ruminants, leaches ionic minerals during digestion, and is excreted at elevated levels as a waste product. This presents a problem in nonruminant livestock production including current efforts to develop renewable grain and legume products for use in fish feeds. The development of lines of several cereal grain species that have reduced seed phytic acid concentration provides a novel approach to dietary and environmental problems associated with seed phytic acid. Utilizing four isogenic strains of barley (one normal for seed phytic acid, and three low phytic acid lines that produce seeds with approximately 50, 70 and 95% reductions in phytic acid) the apparent digestibility of nutrients in formulated diets containing these barleys at a level of 30% was measured using rainbow trout (Oncorhynchus mykiss). Also examined was the apparent availability of several minerals including phytate phosphorus and total phosphorus. Results from these studies corresponded well with the results of other animal studies that evaluated low phytic acid cereal grains. With increasing reductions in seed phytic acid, seed available phosphorus increased and faecal phosphorus was reduced by up to 50%. Calcium availability increased, copper and sulphur decreased, and the other tested minerals demonstrated either increased or decreased availability in a manner uncorrelated to grain phytic acid concentration.