D i e t f o r m u l at i o n
Adding a feed or oil ingredient supplies the animal
with essential fatty acids, needed for production and
growth. But the digestibility of the fatty acids can
vary between animal species and age groups. The
effectiveness of including a fat or oil also depends
on the total feed formulation. In this article we
explain what nutritionists should consider.
By Jannes Doppenberg, Ph.D. and Dr Piet J. van der Aar, Schothorst
Feed Research and Carine van Vuure, MSc. Darling Ingredients Inc.
the Netherlands
I
n the past feed grade animal fat was derived as a slaughter by-product as well as from dead (recycled) animals.
Nowadays in the EU (category 3) animal fat is only
derived from pre and post slaughter inspected animals.
Also the major streams of animal fat are separated
(coming from designated slaughtering facilities) resulting in
tallow, lard and poultry fat. Extracted animal fat does not contain animal protein and therefore does not pose a risk of TSE.
From this perspective animal fat and specifically poultry fat
and lard are safe to use in animal feeds.
Compositions of different oils
In Table 1, the fatty acid composition of common fats and oils
is shown. The major differences are that coconut, palm kernel
and palm oil are highly saturated fats (ratio between unsaturated and saturated fatty acids (u/s ratio) < 1.5). In addition,
coconut (and palm kernel) oil are high in medium chain fatty
acids, specifically C12:0 (lauric acid). Palm oil is high in palmitic acid (C16:0) and oleic acid (C18:1). The other plant oils
Photo: Fotopersbureau Bert Jansen.
Animal fat: Nutritious
ingredient for animal diets
Close up of lard. Lard has a higher
fat digestibility than palm oil when
used in pig and poultry diets.
are high in unsaturated fatty acids: Rapeseed oil is high in
C18:1 (n-9), sunflower seed, soybean (and maize) oil are high
in C18:2 (linoleic acid, n-6) and linseed oil is high in linolenic
acid (C18:3, n-3). The u/s ratio is typically very high (>5).
Tallow is low in polyunsaturated fatty acids (PUFA) due to biohydrogenation in the rumen. The end product of fatty acid
synthesis from volatile fatty acids is mainly C16:0 and C18:1.
Consequently the content of C16:0, C18:0 and C18:1 is high in
tallow. Butterfat (and sow milk fat) on the other hand contains
some medium chain fatty acids. Lard is higher in C16:0 and
C18:1 than poultry fat since these two fatty acids are the primarily end products of fatty acid synthesis from starch and
consequently deposited as body fat in pigs. The fatty acid composition of non-ruminants (lard, poultry fat and fish oil) is
largely influenced by the amount and type of fat that has been
fed to the animals.
Specific fatty acid usage
The fatty acid composition of fats and oils determines the
nutritional and economical value in several ways. First of all
there is a need to supply the essential omega 3 (or n-3) and
omega 6 (or n-6) fatty acids via the feed. This is in general limited to the polyunsaturated fatty acids linoleic (C18:2, n-6) and
ALL ABOUT FEED Volume 23, No. 5, 2015
9
D i e t f o r m u l at i o n
linolenic acid (C18:3, n-3). A minimum requirement for C18:2
is in general easily met by the addition of fat rich grains or
grain by-products and lard or poultry fat in combination with
plant oils like soybean oil (layer feeds). On the other hand if
for carcass (e.g. bacon) quality a maximum restriction of C18:2
(and/or C18:3) is used the inclusion rate of the highly unsaturated plant oils or fat rich grains and grain by-products have to
be limited. If n-3 rich animal products need to be produced, a
maximum n-6/ n-3 ratio should be used in at least the finisher
feed. In practice a source of linseed oil (rich in C18:3) will has
to be added. The inflammatory response is regulated in the
animal by the ratio between the long chain polyunsaturated
fatty acids (LC-PUFA) archidonic (AA C20:4, n-6) and eicosapentanoic (EPA C20:5, n-3). AA is pro-inflammatory and EPA
anti-inflammatory. The ratio of AA/EPA can be influenced by
the direct addition of EPA and DHA from algae and deep sea
fish oil (salmon oil) or by the C18:2/C18:3 ratio in the feed
since LC-PUFA are synthesised from these in the animal (by
elongation and desaturation). Docosahexanoic (DHA C22:6,
n-3) rich oils are often used sow feeds to reduce crushing of
piglets and increase fertility. Medium chain fatty acid (MCFA)
sources like coconut or palm kernel oil (mainly C12:0) or the
extracted fatty acids of these (PKFAD often C6:0, C8:0 or
C10:0) offer specific benefits in terms of maintaining gut
health and litter quality while improving average daily gain
(ADG) and feed conversion ratio (FCR) in young animals. The
energy value of MCFA are lower than of long chain fatty acids
(LCFA). The anti-microbial effects are increased when used in
combination with organic acids or essential oil.
Feeding value of fats and oils
The ratio between unsaturated and saturated fatty acids (u/s) in
the complete feed influences the fat digestibility to a large
extend. The degree of saturation of a fatty acids strongly influences the melting temperature and therefore the ability to be
emulsified in the gut lumen by bile acids. Since saturated fatty
acids <C16:0 and the LC-PUFA are highly digestible, the u/s
ratio is limited to (C16:1 + C18:1 + C18:2+C18:3)/(C16:0+C18:0).
For practical purposes a minimum u/s ratio for young animal
feeds in the range of 2.25-2.50 should be maintained to ensure
adequate fat digestion, while for older animals the ratio can be
between 2.0-2.25. By maintaining a minimum u/s ratio (in the
complete feed) the inclusion of saturated fatty acid sources like
palm oil, palm oil fatty acids, tallow and to a lesser extend lard
will be restricted. Poultry fat usage is in general not restricted
by using minimum u/s ratios in poultry and pig feed.
Effect of digestibility
Fat digestibility is species dependent (lower for poultry than
for pigs), age dependent (lower for young animals) and strongly influenced by gut health (dysbacteriosis, mycotoxins etc).
However the energy density of feeds for young animals and
broilers is in general considerably higher leading to higher
additions of fats and oils. Intact fats (tryglycerides) can form
monoglycerides which aid the emulsification of hydrolysed free
fatty acids. For sensitive species and young animals the amount
of (added) free fatty acids as a ratio of the total fat content in
the feed should be maximised (leading to restrictions on the
usage of PFAD and fatty acid mixtures). The gross energy content and digestibility of the different fats and oils has the
strongest influence on the nutritional and economical value.
Although e.g. the gross energy content of medium chain fatty
acid sources like coconut or palm kernel oil is lower than that
of longer chain fatty acids, the digestibility is very high.
Resultantly the ME or NE is comparable. As mentioned the u/s
ration in the finished feed is a determining factor for fat digestibility. With the usage of a minimum u/s ratio, different fats
and oils can be combined in feed formulation upgrading the
digestibility of otherwise low digestible saturated fats (like tallow and palm oil). The position of the saturated fatty acid on
the triglyceride also determines fatty acid digestibility since the
absorption of saturated fatty acids like C16:0 and C18:0 as
Table 1 – Fatty acid composition (% of fatty acids) of common fats and oils.
Coconut oil
Butter fat Linseed oil
Palm oil Rapeseed oil Soybean oil Sunflower oil
Fish oil
Tallow
Lard
Poultry fat
C4-10
159
C12:0
473
C14:0
1610111183
2 1
C16:0
926 740 4 8 61626
24 19
C16:1
1211211114
3 5
C18:0
21255243321
15 7
C18:1
62518465328261438
39 33
C18:2
2 218 7225555 2 3
11 22
C18:31551116111
1 2
C20:41
C20:59
C22:66
U/s ratio*
0.80.87.81.214.77.59.21.81.0
1.4 2.4
*U/s ration is (C16:1 + C18:1 + C18:2 + C18:3)/(C16:0 + C18:0)
10
ALL ABOUT FEED Volume 23, No. 5, 2015
monoglycerides (on the sn-2 position) is greatly enhanced over
that of free fatty acids hydrolysed from the sn-1 and sn-3 position of triglycerides by lipase. Lard has therefore a 7% higher
fat digestibility than palm oil for pigs and 14% for broilers,
although the fatty acid pattern is similar.
Analyse total fatty acid content
Fat is in general analysed as ether extract, with or without prior
acid hydrolyses. Consequently fat soluble products (waxes, oxidised and damaged fatty acids) which cannot be used for ATP
production will dilute the (gross) energy content of the fat or
oil. It is therefore recommendable to determine the total (identifiable) fatty acid content via gas chromatographic analyses.
When correcting for the glycerol content based on the amount
of free fatty acids in the product the so-called rest fraction can
be calculated and the gross energy content be adjusted accordingly. Fat products that have been exposed to an extensive heat
treatment during extraction or distillation contain on average a
low 3% (PFAD), medium 4-5% (animal fat) or even high 7-8%
(fatty acid mixtures) rest fractions.
Total feed composition counts
The overall feed composition, feed processing and total feed
(energy) intake influences the digestibility and fate of added
fats and oils. High fibre levels in feeds (often leading to an
increased fats and oil addition because of the low energy content of fibre rich by products) will decrease fat digestion due to
increased endogenous losses. Feeds high in starch and sugars
(fed in excess of maintenance requirements) will increase de
novo fatty acid synthesis (leading to primarily C16:0 and C18:1
synthesis) and fat deposition. Feed processing will decrease
particle size and specifically increase fat digestibility in byproducts of plant oil extraction like soy bean, sunflower, palm
kernel or rapeseed meal. An increased viscosity due to the heat
treatment of grains will positively influence digestion in pigs
the first 2 weeks post weaning, but will have a negative effect in
broiler feeds. The addition of emulsifiers, generally consisting
of phospholipids, can enhance fat digestion under (gut health)
circumstances where fat digestion is compromised or poor
quality fats are used.
Considerations for feed formulations
Fats and oils are high energy sources. Consequently when fats
and oils are relatively cheap compared to starch rich grains and
grain by-products often high fibre (low energy) feedstuffs
become attractive. Feed costs can therefore be reduced when
higher amounts of fats and oils can be used in feed production.
The spraying of animal fat or plant oils with a lower u/s ratio
(to maintain pellet hardness) in either the mixer or after pelleting (coating) is often needed in order to increase the inclusion
level. From a nutritional stand point the amount of (fermentable) carbohydrates might need to be maximised and emulsifiers might be needed if the u/s ratio is low. The addition of fat
and oil can increase feed production capacity since the work as
lubricants in the die. Also a low amount of fats and oil can help
prevent dust in mash feeds. The energy value of fat and oil is
relatively higher in a Net Energy system compared to a ME or
DE system. Energy from fat is used more efficiently (for fat
deposition) than energy derived from starch, sugars or (fermentable) carbohydrates. Consequently heat production during metabolism is lower in energy derived from fat, feeds
higher in fat can be used to reduce heat stress. Therefore
when formulating pig feed based on a NE system feeds or
using a ME system for poultry upgraded for the extra caloric
effect of fat will increase the addition of fat and oil (up to
1-1.5%). This means that the quality of fat used becomes more
apparent as well as means of physically reducing and maintaining a small fat particles size (by pressure spraying of fat and/or
the use of emulsifiers).
Fat digestibility is species dependent (lower
for poultry than for
pigs), age dependent
(lower for young animals) and strongly
influenced by gut
health (dysbacteriosis,
mycotoxins etc).
For further information or references, please contact the authors
via [email protected].
ALL ABOUT FEED Volume 23, No. 5, 2015
11