Dietary low-phytate mutant-M 955 barley grain alters phytate degradation and mineral digestion in sheep fed high-grain diets

Abstract

Greater production demands for ruminants require increased dietary inclusion of high-energy feeds. Grains and oil seeds are most commonly used to enhance diet energy density. However, use of such feeds proportionally increases the amount of dietary phytate phosphorus (P), which the ruminant may not be able to fully utilise. 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 non-mutant or low-phytate mutant 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 non-mutant Harrington (HARR) variety or lowphytate mutant-M 955 (M955) barley grains. Total-P intake was similar (P=0.46-0.70) between the M955 and HARR treatments for mature (5756 and 5550 mg/day, respectively) and lamb (5207 and 4894 mg/day, respectively) wethers. Dietary water-soluble P was 3.6 times greater in M955 Author's personal copy 14 A.B. Leytem et al. / Animal Feed Science and Technology 138 (2007) 13-28 HARR diets and phytate P was 11 times greater in HARR versus M955 treatment diets. Apparent total-P digestion was similar between M955 and HARR treatments (P=0.52-0.69). More monoester P was identified in the duodenal chyme of mature wethers fed HARR treatment diet, presumably due to incomplete hydrolysis of phytate P in the rumen. Feeding M955, compared to HARR, treatment diet resulted in greater (P<0.05) apparent partial-tract digestion of calcium (Ca) and total-tract digestion of iron (Fe), magnesium (Mg), and zinc in mature wethers and apparent total-tract digestion of Mg and Fe and retention of Ca, Fe, and Mg in wether lambs. These results indicate that phytate in diets formulated with Harrington variety barley grain may not be fully digested in the rumen. Subsequent passage of partially digested phytate from the rumen may interfere with mineral digestion in wethers fed high-grain diets.

Scientific Opinion on the potential reduction of the currently authorised maximum zinc content in complete feed

“…In sheep consuming high-grain diets, low-phytate barley decreased the amount of undegraded phytate passing into the duodenum compared with conventional barley and increased zinc absorption and retention. This effect was not seen in lambs (Leytem et al, 2007).…”

Plant cell wall chemistry: implications for ruminant utilisation

“…However, little work has been done to examine the impact of exogenous phytase on the availability of dietary P in ruminants and the results vary (Hankins-Herr et al, 2009;Long, 2016). Dietary feed type (Leytem et al, 2007), intrinsic phytase of feed ingredients, feed processing (Lakke Gowda et al, 1955;Park et al 2000), passage rate (Kincaid et al, 2005) and forage:concentrate ratios (Bravo et al, 2003) may alter phytate-P hydrolysis in ruminants. Phytase concentration in the rumen was lower in cattle fed grain than those fed forages (Turner and Leytem, 2004).…”

“…Phytase supplementation of dairy cow diets increased phytate hydrolysis and P flow from the rumen to the lower digestive tract and increased faecal excretion of P (Brask- Pedersen et al, 2013). Inorganic P released from phytate may inhibit the activity of phytase due to the presence of excessive substrate, as demonstrated for plant phytases (Gibson and Ullah, 1988;Hubel and Beck, 1996), phytases from Escherichia coli (Greiner et al, 1993), Aspergillus ficuum (Irving and Cosgrove, 1974) and most bacteria (Leytem et al, 2007;Raun et al, 1956 negative impact on phytase production. This unique ability facilitates efficient phytate hydrolysis in the rumen, even when there are high substrate levels in the rumen fluid of animals fed concentrated feed.…”

Allelic Variants of CRISPR/Cas9 Induced Mutation in an Inositol Trisphosphate 5/6 Kinase Gene Manifest Different Phenotypes in Barley

“…These lines carried mutations in genes encoding enzymes involved in PA biosynthesis, mostly inositol phosphate kinases or myo-inositol phosphate synthases. Feeding trials with poultry [16], swine [17,18], sheep [19], and rats [20] confirmed that lpa barley lines had better nutritional value, with increased mineral and phosphate digestibility. It was observed in previous studies with several lpa mutants that these plants have impaired seed or plant performance [21].…”