Supplemental fat continues to be a
practical means of sustaining energy intake in high producing
cows. However, the economic success of using supplemental fat
depends not only on proper selection of fat sources, but also on
knowing how much fat to feed and when to feed it. Today, we know a
lot more about feeding fat than just a few short years ago.
Unfortunately, the selection of fat source(s) has not gotten any
easier due to the growing number of supplemental fat products on
the market. In fact, the majority of research and information
available about feeding fat is now driven almost entirely by the
commercial sector. Although industry support has rapidly advanced
our understanding of the role of fats in dairy nutrition, the
marketing spin used to promote fat products sometimes makes it
difficult to “see the forest for the trees.” What really is the
economic value of rumen bypass fat? Do fatty acids really play
that much of a role in digestibility, reproduction, or milk fat
composition? Do cows prefer one bypass fat source over another? At
times, the differences seem very subtle.
Many excellent general reviews of feeding fat to dairy cattle are
available in printed literature and on the internet. Compared with
natural, high-fat feeds, the cost of rumen bypass fat sources is
very significant. Consequently, this article will focus primarily
on:
Why Feed Fat?
In North America, most dairy cows have very high levels of milk
production and would classify as “energy challenged.” In early
lactation, most cows will actually lose a considerable amount of
weight, because energy intake is less than that needed to meet the
nutrient demands of milk production. As a result, the cow
mobilizes body nutrient reserves, particularly body fat, to meet
energy demand. Considering its energy density, fat is a logical
choice for boosting ration energy density. In fact, one pound of
fat is roughly equivalent to the energy value of three pounds of
shelled corn. The additional advantage of feeding supplemental fat
is that the detrimental effects (including acidosis and laminitis)
of feeding high levels of grain can be avoided. Improving forage
quality will always be the most economical and nutritionally safe
way to balance high production rations. However, supplemental fat
almost always has a place in the ration when high-quality forages
are not readily available.
Why Limit Natural,
High-fat Feeds?
Most dietary fat is in the form of triglycerides – three fatty
acids connected to a glycerol molecule. It is the fatty acids that
create a special problem for rumen bacteria. Although the bacteria
can use the glycerol portion of the triglyceride for energy, they
cannot ferment the long fatty acids chains and therefore simply
release them into the rumen environment. These long-chain fatty
acids are inhibitory to many microbial species. Although some
bacteria can partially “detoxify” the unsaturated fatty acids by
saturating them with hydrogen, the fatty acids are still
particularly harmful to fiber-digesting bacteria. Therefore, as
fat availability (unprotected) in the rumen increases, fiber
digestion decreases. Just 2% vegetable oil in the diet can
dramatically reduce rumen fiber digestion.
Limiting the negative impact of natural feed fats in the rumen
(i.e., fats coming from vegetable sources such as whole/roasted
soybeans, whole cottonseed, and distillers grains) is the basis
for the sometimes complex restrictions related to feeding
supplemental fat to dairy cattle. Feeding natural fat sources at
levels higher than recommended is almost always a mistake. Once
feeding limits on starch and natural fat are reached, rumen bypass
fats become a logical option to push ration energy levels higher.
What is a Rumen
Bypass Fat?
Rumen bypass or “protected” fats are essentially dry fats that are
processed to be easily handled and mixed into all animal feeds.
Because dry fats naturally have high melting points, they are
mostly insoluble at rumen body temperature. In essence, dry fats
are not as much “protected” as completely insoluble in the rumen
such that they have little impact on rumen fermentation. Today,
there are only three methods of producing dry fats for animal
feeds. The method that produces the least desirable product for
the cow, partial hydrogenation of tallow, is seldom used for dairy
rations and will not be discussed further. One acceptable method
for producing a bypass fat is to hydrolyze the fatty acids from
tallow, partially hydrogenate them, and then prill them in a
spray-chilling tower (e.g., Energy Booster®* 100, Milk Specialties
Dundee, IL). The most widely used and effective method for
producing a rumen bypass fat is to react vegetable fatty acids
with calcium oxide to form insoluble calcium soaps (Enertia®, ADM;
Megalac®*, Church and Dwight Co., Inc.). Within the feed industry,
these calcium soaps, or salts, appear on feed labels as “calcium
salts of long chain fatty acids.” Fatty acids distilled from palm
oil processing are most commonly used to make calcium salts,
because these fatty acids are produced in the greatest quantity
worldwide. By far, calcium salts of palm fatty acids (PFA) are the
highest quality and best understood bypass fat for dairy cattle.
Because large amounts of dietary fat will eventually reduce feed
intake of any animal species, feeding guidelines for feeding
bypass fats are generally in the range of 1 to 2 lb per cow daily.
Performance goals and ration cost will generally be the dominant
factors in determining how much bypass fat to feed.
Purchasing Bypass
Fats . . . What Really Matters?
Digestibility Determines Energy Content The energy content of a
bypass fat is determined almost entirely by its intestinal
digestibility. According to the 2001 Dairy NRC (Table 1), the
intestinal digestibility of pure fat sources can vary
considerably. Extensive research suggests that reduced fat
digestibility is most closely associated with a high stearic acid
content. Vegetable fats, including palm fatty acid salts, have
much lower stearic acid levels than animal fats or bypass fat
derived from tallow. Calcium salts of long-chain fatty acids
(usually assumed to be derived from palm oil processing) have the
highest intestinal digestibility among rumen bypass fats. Because
of their calcium content, calcium salts of fatty acids contain
slightly less total fat than other rumen bypass fats. However,
because of their high digestibility, calcium salts also have the
highest net energy content per unit of fat.
Because it is still primarily energy that is being purchased, it
is important to understand how different types of bypass fats
differ in their energy content. In addition, when comparing fat
sources, it is critical to make “apples to apples” comparisons in
energy levels. That is, all reported energy levels should come
from the same database and be calculated in the same way. For
example, the 2001 NRC Nutrient Requirements for Dairy Cattle would
be considered the “gold standard” for energy values for feedstuffs
fed to dairy cattle.
It is very important to understand that the 2001 Dairy NRC changed
the method of calculating the energy value of feeds and moved the
energy values for most dairy feedstuffs DOWN. The 2001 Dairy NRC
indicated that calcium salts of PFA have a typical Net Energy of
Lactation value of 2.3 Mcal/lb. On literature pieces for bypass
fat products, suppliers often report out-dated or independently
calculated energy values. These are often unrealistically high
when compared to other high-fat feedstuffs. Meaningful comparisons
are easier to make when using the NRC values, such as those shown
in Table 1.
Table 1
2001 Dairy NRC Suggested Energy Values for Fat Sources for
Dairy Cows
|
Fat
source
|
Fat, % |
Digestibility, % |
Net energy, Mcal/lb |
Net energy, Mcal/lb of fat |
|
Calcium salts of fatty acids (bypass) |
84 |
86 |
2.30 |
2.67 |
|
Hydrolyzed tallow fatty acids (bypass) |
98 |
79 |
2.46 |
2.51 |
|
Partially hydrogenated tallow (bypass) |
100 |
43 |
1.30 |
1.30 |
|
Vegetable oil (unprotected) |
100 |
86 |
2.57 |
2.57 |
|
Tallow (unprotected) |
100 |
68 |
2.06 |
2.06 |
Fatty Acids Should Be
Considered
Although the primary reason for feeding fat is for its energy
density, it is becoming increasingly evident that essential fatty
acids supplied by fat may have an important role in the nutrition
of the high-producing cow. Unfortunately, fatty acid metabolism in
the dairy cow is quite complex. It may be some years before it is
accurately known which and how much fatty acid to feed, in order
to manipulate milk composition, reproduction, or other health or
metabolic parameters in the cow. However, a few generalizations
can be made regarding fatty acids:
-
Vegetable fats have more value than
animal fats.
-
Animal fats have more saturated
fatty acids, such as the aforementioned stearic acid, that are
associated with reduced fat digestibility.
-
Compared to animal fats, vegetable
fats have very low levels of stearic acid and much higher levels
of the key essential fatty acids, linoleic and linolenic acid.
Linoleic acid particularly, has been shown to have possible
favorable effects on reproductive performance.
Palatability
Different classes of bypass fats may differ slightly in their
palatability. Calcium salts of palm oil have a very pungent odor
and a slightly bitter taste, and there is evidence that cows can
detect these fats when they are initially added to the ration.
Therefore, animals that have not had previous exposure to these
fats may require an adaptation period. In addition, when calcium
salts of palm oil are fed, greater care should be taken to ensure
these products are thoroughly incorporated into the ration, so
that feed intake is not affected. In general, palatability should
not be considered a criteria for determining which protected fat
source to purchase, unless that fat source will be used at low
levels in a transition ration or perhaps top-dressed onto the
ration.
Physical Form
Most classes of bypass fats are handled and mixed into dairy feeds
with relative ease. Calcium salts of palm oil tend to be favored
during very hot weather, because flowability of soy-based calcium
salts and prilled fats can be greatly reduced during warm weather.
Particle size could be a criteria for purchasing a specific class
or brand of protected fat depending on the application. Finer
particle sizes may improve mixability of the salts within mineral
mixes, but may lead to reduced flowability or excessive dustiness
in feedmills or mixer wagons. For example, calcium salts of palm
fatty acids tend to be slightly dustier, but more flowable than
prilled fatty acid products.
Special Applications of
Protected Fat
Fat and Hot Weather
It makes sense that enhancing ration energy density by utilizing
fats could be particularly beneficial during hot weather. However,
research on the effects of feeding high-fat rations during hot
weather have yielded inconsistent results. This is probably
because it is very easy to overfeed unprotected fat sources, such
as whole oilseeds, when the cow’s feed intake is significantly
reduced due to heat stress. If fat is overfed, then the negative
effects of the fat on fiber digestibility will negate any possible
gains with increased ration density. Because bypass fats do not
affect rumen fermentation, they should probably make up a greater
percentage of the total fat included in the ration during hot
weather.
Improving
Reproductive Performance
It is well-accepted that supplemental fat benefits herd
reproductive performance by minimizing body weight loss and
accelerating body weight gain after calving. In addition, research
strongly suggests that unsaturated vegetable fatty acids could
have additive effects on reproductive parameters in the cow,
including follicular size and hormone patterns. Linoleic acid has
been identified as one of the essential fatty acids that may have
direct effects on reproductive function. In fact, higher linoleic
acid levels is the basis for at least one rumen protected fat
product that is promoted within the feed industry for its
“supposed” ability to improve reproductive performance (e.g.,
Megalac®*-R, Church & Dwight Co., Inc). Although this approach to
improving reproductive performance makes biological sense, there
is currently very little supporting data to prove these products
are truly worth the money. That is, there is a large body of data
that shows that calcium salts of palm fatty acids are very
effective in statistically improving reproductive performance over
and above the benefits of tallows and other unprotected fats. What
future research must determine is whether “reproduction formulas”
are in fact statistically superior to “regular” protected
vegetable fats in enhancing reproduction.
Conclusion
Selecting the best value in bypass fat is not an easy task because
of the growing number of available fat sources. In addition, we
now understand that complicated factors, such as fatty acid
composition, can also create potentially greater value for some
bypass fats. Non-nutritional factors that will sometimes influence
which bypass fat to purchase include level of supplier trust,
storage facilities and mixing requirements, and ration feeding
method. To assure obtaining the greatest economic value from a
bypass fat, nutritional factors should be considered in this
order:
1) Digestibility – Vegetable
sources are higher than animal sources.
2) Fatty acids – Vegetable fats have more favorable fatty
acid profiles than animal fats.
3) Palatability – Although there are “preference”
differences among prilled fats and
calcium salts when these are either top-dressed or fed in
their pure form, when
properly mixed into feeds, palatability differences between
these fat types are not
typically observed.
Many specialty bypass fats are
appearing in the North American market. These include reproduction
and functional feed formulas that promote high levels of
conjugated linoleic acid in the milk. Although these “improved”
bypass fats suggest an exciting future for fatty acid nutrition in
the dairy cow, it may be a few more years before we understand how
much of these fats to feed and the economic threshold for feeding
these fats.
*Not trademarks of ADM.
