Transcript Document

Dr. Katharine
Knowlton
Reducing the environmental
Department of Dairy Science
[email protected]
Sarah Marpet and Dr. Burt Staniar, Dept
of Animal and Poultry Science;
impact of horse farms through dietary nutrient management
Dr. Katharine Knowlton, Dept of Dairy
Science
Hypothesis
We hypothesize that efficiency of phytic acid digestion will be greater in the horses fed the high fat/high fiber
feed because of increased retention time of digesta in the hindgut as well as diet-induced differences in gut
microbial population
Methods
Background
In spring of 2006, three groups of open mares were offered pasture and hay, a high fat/fiber feed to
supplement pasture and hay, or a traditional high starch feed with pasture and hay. Feed and feces were
collected.
In summer of 2006 two different groups were sampled, open mares and mares with standing foals . The
open mares were fed pasture only while the mares with foals were fed the high fat/fiber feed and pasture.
Feed, pasture, feces, and urine were collected.
Total P (nitric/perchloric digestion with Pi release measured colorimetrically with molybdovanadate) was
measured in samples from both studies, while phytate P (low pressure ion chromatography/molbydate
blue) was measured only in the spring 2006 samples. Fractionation was confirmed on a subset of samples
using NMR spectroscopy.
Federal regulations to address nutrient losses from
concentrated animal feeding operations now explicitly
include horse farms. These regulations increase the
amount of land needed for manure application. While
many horse farms have limited land base for manure
application, nutrient losses from horse farms have not
been an area of focus. Similarly, little is known about
factors affecting P excretion.
Our research focuses on digestion of phytic acid.
Phytic acid P is unavailable for digestion and use by
simple stomached animals, because they do not
possess the enzyme phytase. Ruminants and hind-gut
fermentors are thought to be able to digest phytic acid
as a result of the microbes within their GI tract that
secrete phytase. Unknown as are the factors which
affect phytic acid digestion.
• Figure 1. Digestibility of phytic acid was increased in non-lactating, non-pregnant mares fed a
sugar-starch grain compared to those fed a fat-fiber diet or pasture only.
Objectives
• Figure 2. In lactating mares , feeding a fat-fiber diet decreased digestibility of phosphorus. This is
contrary to our hypothesis.
Implications
This work will help identify dietary strategies to
reduce potential nutrient losses from land-limited
horse farms.
Phytic acid analysis
Results
Figure 1
Figure 2
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Total P digestibility
%
• We evaluated the effect of high fat/fiber feeds
formulated to increase growth and performance while
optimizing health as compared to high starch feeds or
traditional pasture-only diets.
Phytic acid
PA digestibility, %
• To quantify excretion of total and phytate P by
grazing mares (open or with foal at side).
Nitric/perchloric acid digestion
Sugar-Starch
Pasture
Fat-Fiber
Summary
• Non-lactating, non-pregnant mares with low
nutrient needs excreted all consumed P.
• In non-pregnant, non-lactating mares, the
sugar-starch diet increased digestibility of
phytic acid. This suggests increased
microbial phytase activity in the hindgut and
may be due to:
• Increased supply of desired substrate.
Starch-fermenting bacteria have greater
phytase activity than fiber-digesting
bacteria.
• Decreased pH in the hindgut, giving
these starch fermenters with high phytase
capacity a competitive advantage over
fiber digesting bacteria.
• In both studies, our hypothesis that the
increased retention time observed with the
fat-fiber diet would increase digestion of
phytate P was not supported.
• Urinary P was measured and is negligible (1
to 5 ppm, < 1 g/day)
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Acknowledgements
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• The Middleburg Agriculture Research &
Extension Center
• Cathy Parsons, Tzu-Hsuan Yang, and Karen Hall,
Dept of Dairy Science; Dr. Chao Shang, Dept of
Crop and Soil Environmental Sciences
• The John Lee Pratt Animal Nutrition Foundation
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Fat-Fiber
Pasture