“Effects of Enhancing Lipids in Beef Cattle Diets”
Honors Presentation
Genag 515
Nicole Roberson
Advisor: Dr. Jim Drouillard
Effects of Enhancing Lipids in Beef Cattle Diets
Dr. Drouillard helped me plan the research experiment. We used
several pieces of background information to develop our thought process.
First we know that polyunsaturated fatty acids (PUFAs) are toxic to rumen
microbes, especially the protozoa. In an effort to detoxify the PUFAs rumen
microbes, especially bacteria, biohydrogenate the unsaturated fatty acids.
Therefore, it can be expected for feeding high levels of PUFAs to exceed
capacity for ruminal hydrogenation. This could in turn become toxic to the
microbes and decrease the population. We also know that while in the rumen
fermentation occurs which releases heat and methane causing energy losses.
However, if we can bypass the rumen the abomasum posterior functions like
the monogastric gut. Also, monogastric animals are more efficient then
ruminants, partly because of the rumen fermentation. Since monogastric
animals do not hydrogenate unsaturated fatty acids they will deposit fatty
acids akin to that in their diets. Because of their lower melting point
unsaturated fats are softer than saturated fats, and softer fats may be more
desirable in some markets, for example one of the Japanese main criticisms
of beef is that the fat is too hard. Furthermore, PUFAs especially omega-3
fatty acids may be preferred by health conscious consumers, as omega-3
fatty acids offer certain health benefits when compared to omega-6 fatty acids
(Drouillard).
Based upon these pieces of background information we hypothesized
that feeding a diet containing high levels of PUFAs will become toxic to rumen
microbes, shifting digestion to the lower GI tract, thereby increasing growth
efficiency and absorption of PUFAs. We choose to use flaxseed. Flaxseed is
about 40-45% oil and of that 55-60% is in the form of linolenic acid. Linolenic
acid is an 18 carbon omega-3 fatty acid with three double bonds. The
objectives of the experiment were to create a toxic environment to the
microorganisms in the rumen, and decrease the population. This would then
allow us to bypass the rumen and increase digestion in the post ruminal tract.
Accomplishing this would allow the cattle to escape fermentation and become
more efficient. Also, it would prevent biohydrogenation and increase the
amount of unsaturated fatty acids absorbed.
We started with 27 yearling crossbred heifers that weighed
approximately 650 pounds. We weighed them prior to starting the trial and
stratified their body weights. We then randomly assigned them to pens and
one of three diets. Our control diet was a steam flaked corn and alfalfa ration;
our intermediate, Flax-10, diet was steam flaked corn, alfalfa, and 10%
ground flaxseed, and our hi-fat, Flax-50, diet was an extruded diet with 50%
ground flaxseed, hi protein about 26% to compensate for an expected
decrease in intake, and no roughage. The control diet was about four percent
fats, Flax-10 was about seven percent fats, and Flax-50 was about twentyone percent fats. We individually fed the heifers once a day, and adapted
them to their final diets over a period of 38 days. Bunks were read each
morning to determine the amount of feed that would be sufficient to result in
only trace amounts left on the following day. Any excess feed was removed
and analyzed for dry matter, which was subtracted from the amount offered to
determine the actual dry matter intake. The heifers were weighed four times
through the study. Average daily gain was computed for each period. And,
efficiency was calculated as gain to feed and reported as feed to gain. We
also took blood samples on each weigh day via the jugular vein. After
centrifuging we placed the plasma into microcentrifuge vials to analyze the
fatty acids by gas chromatography.
Yet, unfortunately the blood samples perished during a freezer
malfunction so my data is limited to performance only. All the diets showed to
be different with a probability of less than 0.05 with respect to average daily
gain. While the Flax-10 cattle gained about 3.33lbs/day and the Control cattle
gained about 2.88lbs/day, the Flax-50 cattle unfortunately only gained
approximately 1.85 lbs/day. However, there was no real difference between
the diets for dry matter intake, but the Flax-50 showed a tendency to eat
about a pound per day less. This left the Flax-50 heifers being the least
efficient cattle with a feed to gain ratio of 7.54 compared to Flax-10 which was
4.32 and the Control which was 5.16 with all diets being different from each
other (Roberson). Data was ran through SAS to determine whether or not the
diets were different and the standard error. We also noticed that the fecal
material from the Flax-50 cattle was gray and had a soapy appearance. In
addition, all of the Flax-50 cattle showed bloat to some extent during the trial,
but none were severe.
After completing the trial we placed the cattle into three pens and
stepped up onto a common diet. During this time one of the heifers that had
been on the Flax-50 diet expired from overeating. During the trial she had an
average dry matter intake of 22.74 lbs/day, an average daily gain of 1.76
lbs/day, and a feed to gain ratio of 12.91. The rest of the cattle on the Flax-50
diet were able to make up a lot of compensatory gain before slaughter. The
hot carcass weights showed the Flax-10 was different from Flax-50 and
Control, but Control and Flax-50 were not different. No real differences
showed on any other carcass attributes probably because there was such a
small number of cattle being processed (Roberson).
To summarize the Flax-10 diet improved all areas of performance.
However, Flax-50 decreased average daily gain, decreased intake, resulted
in poorer feed efficiency, and increased bloat. So in conclusion based on
these results, feeding high levels of lipid to “bypass” rumen digestion is not a
feasible method for improving efficiency.
Works Cited
Drouillard, Dr. James. “Advising Sessions”. March 2006- June2006.
Roberson, Nicole. “Roberson/Drouillard, Enhanced Lipids, 2006-08” June
2006- September 2006.