Effect of Grain Source and Exogenous Phytase on Phosphorus Digestibility in Dairy Cows

Abstract

Two experiments were conducted to determine P digestibility in lactating dairy cows fed corn or barley as grain sources. The first experiment utilized a replicated incomplete 5 x 4 Latin square design with 8 lactating Holstein cows fed diets containing either corn alone or corn in combination with one of 4 barley varieties that differed in chemical composition. Total tract digestibility of P ranged from 11 to 29% for diets containing the barley varieties and was approximately 35% for the corn diet. A second experiment compared P digestibility in cows fed diets containing corn or barley when exogenous phytase was added to the diets. Lactating Holstein cows (n = 16) were arranged in 4 replications of a Latin square with 2 grains (barley or corn), fed separately or with added exogenous phytase (427 phytase units/kg of total mixed ration and 4 periods of 21 d. Phytate P comprised about 50% of the total P (0.46% P) in the total mixed ration. The concentration of serum inorganic P was higher in cows fed diets with exogenous phytase (5.8 vs. 6.5 mg/dL in cows fed barley diets and 5.5 vs 6.0 mg/dL in cows fed corn diets). Using acid detergent lignin as an internal marker, hydrolysis of phytate P was increased by the exogenous phytase, and total P digestibility tended to be increased. In contrast to Experiment 1, in Experiment 2 there was no effect of grain source on P digestibility and total fecal P. Dry matter intake and efficiency of milk production were not affected by exogenous phytase or grain type. Although phytase activity occurs in the rumen, physical properties of the diet and ruminal passage rates may prevent total hydrolysis of phytate in the rumen of lactating cows. Thus, exogenous dietary phytase might improve P digestibility in dairy cows in some dietary situations.

Animal production for efficient phosphate utilization: from optimized feed to high efficiency livestock

“…Microbial phytase can be added to diets to increase availability of phytate bound P. The most common microbial phytase used in swine and poultry diets are from fungi (Aspergillus niger and Peniophora lycii) and bacteria (Escherichia coli) [22]. The activity of phytase depends mainly on pH, temperature, dose, and diet composition [24][25][26][27]. Phytase supplementation has mostly been studied in monogastric animals, and improvement of the P digestibility has been observed in Animal production for efficient phosphate utilization Kebreab, Hansen and Strathe 873 [33,34] poultry [21,28 ] and swine [22,29].…”

“…However, there is a wide variation in the effect of phytase added at the same phytase dose and type of diet [30], contributing to its unreliability in diet formulation. Addition of phytase to dairy cow and goat diets has also been shown to improve P availability [23,[25][26]. Owing to differences in pH of the digestive tract of ruminants and monogastric animals, different types of phytases are required for ruminants [31 ].…”

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

“…This indicates that, irrespective of the dietary phytate content, the rumen microbial phytase readily hydrolysed phytate P. In addition to microbial phytase, high intrinsic phytase activity, associated with the barley grain (Yingran et al, 2005), may increase the extent of ruminal phytate P hydrolysis. As such, intrinsic or exogenous phytase may ameliorate measurable differences in total-tract P digestibility (Kincaid et al, 2005). Substantially lower water-soluble P was available in Harrington barley based diets.…”

“…The extent of phytate-P hydrolysis in ruminants varies considerably and may be incomplete resulting in undegraded phytate entering the small intestine. Dietary feed type , intrinsic and endogenous phytase (Bravo et al, 2002;Kincaid et al, 2005), feed processing (Park et al, 2000), and decreasing forage:concentrate ratio (Bravo et al, 2003) may alter phytate-P hydrolysis in ruminants. Phytate can bind and inhibit digestive enzymes (Bedford, 1996) or complex with proteins (Gifford and Clydesdale, 1990) and micronutrients (Maenz et al, 1999), impairing digestion.…”

“…Considering that undegraded phytate may appear in the chyme of ruminant animals consuming high-grain diets Park et al, 2000;Bravo et al, 2003;Kincaid et al, 2005), inclusion of mutant low-phytate grains may be a strategy for reduc-ing total dietary phytate, while maintaining recommended daily P need. Our objectives for this study were to determine the extent of phytate degradation through the digestive tract using phosphorus-31 nuclear magnetic resonance spectroscopy ( 31 P NMR) and to assess apparent P, Ca, Fe, Mg, and Zn absorption in wethers fed high-grain diets containing either the low-phytate mutant-M 955 or the non-mutant Harrington variety barley grain.…”