Submitted to: Animal Feed Science And Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2006
Publication Date: 7/6/2007
Citation: Leytem, A.B., Taylor, J.B., Raboy, V., Plumstead, P.W. 2007. Dietary low-phytate mutant-M 955 barley grain alters phytate degradation and mineral digestion in sheep fed high-grain diets. Animal Feed Science and Technology. 138:13-28. Interpretive Summary: Greater demands for food products from high-performance ruminant animals require increased dietary inclusion of high-energy feeds. Grains and oil seeds are most commonly used to enhance diet energy density of ruminant diets. However, use of such feeds proportionally increases the amount of phytate phosphorus in the diet, which the ruminant may not be able to fully utilize. Our objectives for this study were to determine the extent of phytate degradation and mineral digestion in wethers fed high-grain diets consisting of either a normal- or low-phytate barley grain. The results of this study indicate that dietary inclusion of the mutant-M 955 low-phytate barley grain, in place of the wild-type Harrington variety, in finishing diets fed to wethers decreased the amount of undegraded phytate passing into the duodenum and seemed to increase mineral absorption and retention. Based on these results, we conclude that less supplemental calcium, iron, magnesium, and zinc may be needed in ruminant finishing diets formulated with low-phytate grains.
Technical Abstract: Our objectives for this study were to determine the extent of phytate degradation and mineral digestion in wethers fed high-grain diets consisting of either a normal- or low-phytate barley grain. In two separate experiments, mature Columbia wethers (n = 7) fitted with rumen and duodenal cannulas and Columbia × Polypay wether lambs (n = 8) were individually fed one of two finishing diets formulated with either normal-phytate Harrington (HARR) variety or low-phytate mutant-M 955 (M955) barley grains. Repeated samples were obtained from the rumen, duodenum, and rectum of each mature wether on day-25 of treatment. Total daily feces and urine were collected from wether lambs on days 10 through 15 of treatment. Total-phosphorus intake was similar (P = 0.46 to 0.70) between the M955 and HARR treatments for mature (5,756 and 5,550 mg/d, respectively) and lamb (5,207 and 4,894 mg/d, respectively) wethers. Dietary water-soluble phosphorus was 3.6 times greater in M955 than HARR treatment diets. Apparent total-phosphorus digestion was similar between M955 and HARR treatments (P = 0.83 to 0.88). More monoester phosphorus was identified in the duodenal chyme of mature wethers fed HARR treatment diet, presumably due to incomplete hydrolysis of phytate phosphorus in the rumen. Inclusion of the low-phytate M 955, as opposed to the Harrington variety, barley grain resulted in greater (P < 0.05) apparent partial-tract digestion of calcium and total-tract digestion of magnesium, iron, and zinc in mature wethers and apparent total-tract digestion of magnesium and iron and retention of magnesium, iron, and calcium in wether lambs. These results indicate that phytate in wild-type Harrington grain diet may not be fully digested in the rumen, and subsequent passage of partially digested phytate from the rumen may interfere with mineral digestion in wethers fed finishing diets. Based on these results, we conclude that less supplemental calcium, iron, magnesium, and zinc may be needed in ruminant finishing diets formulated with low-phytate grains.