WHAT IS ENDOGENOUS FAT? HOW IT GIVES EXTRA CALORIC ENERGY?
Do you know if fully absorbed in the lumen it increases net
ME (metabolized energy) thus net gain in extra caloric value?
For proper digestion and assimilation of
endogenous fat which is primarily saturated fatty acids such as palmitic and
stearic supported by oleic and linoleic acids- just the same as found in
balanced blend of Fat. BROFAT RHT II does that job efficiently. That is why we
have numerous satisfied customers willingly endorsing the product.
For details read the comment section of the article. How
BROFAT RHT II can help absorb the endogenous fat for improved ME of the diet?
Digestion and Absorption of Fat by Chicken
By Dr. Sanjib Kumar
Pratihar-G.M.Technical-Rnk Agro & Chemicals P.Ltd. Brofat Division
How Fats Work and
Chicken Digestive System?
Two excellent reviews on
the digestion of fats in poultry are available (Freeman, 1984; Krogdahl, 1985)Poultry (chickens, geese, turkeys etc) have a distinctive
digestion system, which has some clear differences to the digestion of
ruminants or other monogastric animals. Their digestive system is comparatively
short, so each food particle remains only approximately 6 hours in the
digestive system.
In such a short time the chicken must be able to absorb as much nutrients
as possible from its feed. It's also interesting to note that the digestive
system of a chicken develops very fast: a chick can digest fibers as well as an
adult chicken.
Poultry
have no teeth or soft palate. They peck food with their beaks, and especially
chickens have no problem eating hard or stringy material. All food particles
are swallowed whole without chewing. The saliva has no active amylases so no
digestion happens in the mouth or esophagus. In breeder and layer birds,
Farmers cut the beaks of the chicks, which is effective in preventing the birds
from pecking each others in frustration.
The digestive tract
consists of the beak, the esophagus which widens into crop,
Lower esophagus, proventriculus, gizzard, duodenum, jejunum and ileum, caeca, large intestine and cloaca.
From the beak, food slides
down into esophagus, after swallowing and covers approximately 35 cm long, covering 17 % of the
length of the entire digestive tract. It secretes mucus which lubricates the
esophagus.
The
crop is not a stomach, it is simply a small sac used to store and moisten feed.
The crop secretes enzymes which digest starch and proteins, and has some
microbial activity as well, resulting in formation of lactic acid and acetic
acid.
After
the crop is moist, partially digested food mass enters the proventriculus (glandular
stomach). Like crop, the proventriculus is found only in birds. The
proventriculus secretes HCI, pepsin and mucus, which start the actual enzymatic
digestion. Food travels through the proventriculus very fast: it is covered in
gastric juices, but doesn't stay in the proventriculus to be digested. For
actual digestion and mechanical breaking food enters the actual stomach,
the gizzard. The gizzard is surrounded by strong muscles, which
contract pendulum like and break food particles. The muscles are set in two
pairs, thick and thin pairs of muscle. Muscle contractions (Smulikowska, 1998) also mix the enzymes well with
the food mass. The internal wall of the gizzard has koilin fibres, which stick
out from the wall like tiny teeth, further aiding in breaking food particles
mechanically.
This
state of food is called Digesta which shuttles between the
proventriculus and gizzard to optimize enzymatic and mechanical digestive
actions.
This
liquid digesta is then pushed through pylorus into the duodenum (klasing, 1999). In chickens the reflux process
is continuous, enabling penetration of the gizzard by duodenal contents during
the contractile period of the gizzard and proventriculus (Sklan et.al.1978).
Liver and pancreas excrete
important digestive enzymes. The relatively large liver of a chicken has two
segments. Bile is excreted directly from the left segment of the liver to
duodenum (beginning of the small intestine). The right segment has a duct to
the gall bladder, which again has a duct to duodenum. Pancreas is located near
duodenum, and excretes lipolytic, protelytic and amylolytic enzymes. It is
interesting to note that chickens produce no lactase, because their nutrition
does not include milk derivatives. Chickens also lack the enzymes needed to
digest cellulose, hemicelluloses and beta glucans. Commercially available
enzymes can be added to chicken feed to enhance digestibility. The bile salts
in the gizzard are amphipatic which means they are both hydrophobic
(water fearing) and hydrophilic (water loving) as showninFig1
Bile
consists of water, bile pigments, bile salts, phospholipids such as lecithin,
and neutral fats such as cholesterol, glycerides and inorganic ions. No
published data are available on the composition of bile of poultry and other
animals but in the chicken it has been reported that high level of
glycolithocholic acid, followed by taurocholic acid (Yeh and Hwang, 2001) are found.
When
the concentration of bile salts in the lumen is at or above “critical micelle
concentration”, they arrange themselves on the surface of lipid digestion
particles as shown in Fig.2.with their hydrophobic ends inwards and hydrophilic
ends outwards (such as FFA, monoglyceride, cholesterol and lysolecithins)
forming “Mixed Micelles”(Garrett and Young, 1975) to get their lipid contents absorbed actively. This process is also called
fat emulsification, which is necessary for the subsequent stages of
digestion and absorption in the duodenum and jejunum.
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| Fig 1 |
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| Fig 2 |
The
shuttling of digesta between the gizzard and duodenum also increases the time
the feed is exposed to the digestive enzymes and favors fat absorption in
the upper parts of small intestine (Smulikowska, 1998).
The
presence of Fat in the duodenum stimulates the secretion of cholecystokinin
which in turn regulates secretions of pancreatic enzymes and bile (krogdahl, 1985). The bile salts are released from
the gall bladder to emulsify fat in the chime. Pancreatic lipase acts as
a catalyst to hydrolyze fat with the aid of co lipase (Erlanson et.al.1973). The pancreatic lipase activity
can be inhibited by the high concentration of bile salts. Co lipase binds to
the surface of the lipid droplets and acts as an anchor for lipase allowing
pancreatic lipase to digest Triglycerides (Borgstrom, 1980). Triglycerides are hydrolyzed by the action of pancreatic
lipase as in Figure 2. One of the products of this hydrolysis is Free fatty
acid (FFA) which including other products such as Lysolecithins
and long chain fatty acids, medium chain fatty acids, monoglyceride and
phospholipids, mix to form Micelles with bile salts as shown in Figure 3. These
micelles are then transported to the mucosal surface and pass through the brush
border membrane (krogdahl,
1985)
Some
researchers have reported that activity of lipase can be inhibited by Free
fatty acids (Van
Kuiken and Behnke 1994) but they further qualified this statement by adding that Unsaturated
fatty acids increased lipase activity but long chain fatty acids
particularly Stearic acid (present in high % in Palm oil and Animal fat such as
Tallow/Lard) inhibited lipase activity.Thus FFA consisting mostly of unsaturated fats does not inhibit Lipase
activity than FFA having more % of Saturated fat.
After the gizzard the food enters the small intestine, which is
short compared to mammals. Most nutrients are digested and absorbed in the
small intestine. The intestine has two kinds of glands: intestinal glands
secrete lipolytic, protelytic and amylolytic enzymes, and glands of the mucous
membrane secrete maltase, isomaltase, peptidase, saccharase and palatinase. The
small intestine of chickens is divided to two, duodenum and ileum, compared to
the three-part intestine of mammals. Ileum alone is 120 cm long, and comprises
nearly 60 % of the length of the entire digestive system.
Chickens
have two caeca (singular: caecum), which assist in digesting
fibers and non-starch polysaccharides. Caeca are approximately 8 cm
long. Caeca are full of microbes, and they are located in the junction of
the small and large intestine. The large intestine is very short,
and ends in a cloaca. Together they are about 6 cm long (5 % of the length of
the digestive tract). The oviduct and uric acid are also secreted to the
cloaca, so both feces, uric acid and eggs come out from the cloaca, which ends
in the anus.
The large
intestine is very short, and ends in a cloaca. Together they are about
6 cm long (5 % of the length of the digestive tract). The oviduct and uric
acid are also secreted to the cloaca, so both feces, uric acid and eggs come
out from the cloaca, which ends in the anus.
Absorption of fats
How do Fats get
absorbed?
Fats or triglycerides are
enzymatically digested by lipase into a monoglyceride and two free fatty acids.
Most of Fatty acids derived after lipase hydrolysis are insoluble, the
solubilisation of these lipolytic products is required which is established
through micelle formation. The micelle formation is the aggregation of
hydrophobic components (fatty acids) brought together by ampiphatic molecules
such as bile salts and monoglyceride. In addition to these physiological
amphipatic molecules sometimes feed added exogenous emulsifiers have
also the properties to display this effect. In the process of micelle
formation, amphipatic molecule, which comprises both hydrophilic
(water-attracting) and hydrophobic (water repelling) properties in one
molecule, functions as a bridge between fat and water, around which hydrophobic
fatty acids can orientate themselves. The hydrophilic “heads “of the fatty
acids will face the aqueous environment of the digesta, leaving hydrophobic
“tails” of the fatty acids to format the core of the micelle (fig2.). These
spherical micelle structures are able to solubulise fatty acids in the
intestinal tract together with other fat soluble components like phospholipids,
cholesterol and fat-soluble vitamins.
Micellar solubulisation can
increase the aqueous concentration of fatty acids and monoglyceride in the
small intestine up to a thousand times. It is assumed that most of absorption
of the micelle contents by the enterocytes takes place through passive
diffusion.
By now we know that Fat digestion and
absorption takes place in the small intestine (Freeman, 1976; Hurwitz et.al.1973; Krogdahl, 1985) However, some researchers’ claim
differently making it a controversial issue. We stop at this and proceed to
show through a diagram (Fig.4) below the process of fat digestion and
absorption.
After
the digestion short chain fatty acids and monoglyceride are absorbed passively
from the intestinal lumen to mesentery blood vessels via intestinal cells (pond et.al.2005). Whereas long chain saturated
fatty acids, diglycerides, fat soluble vitamins and cholesteryl esters require
solubilisation in the hydrophobic cores of mixed micelles, which are then
transported to the intestinal cells. Some researchers realize that movement of
fatty acids are influenced by proteins which have highest affinity for
unsaturated fatty acids than for the saturated fatty acids and almost no
affinity for short and medium chain fatty acids.(Davenport,1980; Ockner et.al.1972; katongole and
March, 1979; Ockner and Manning,1974.).Inside intestinal cells, monoglyceride and long chain
fatty acids are rebuilt into triglycerides and together with cholesterol, lipoproteins
and lysolecithins, are assembled into portomicrons (Stevens, 2004). Around 15% of fatty acids
present in the lumen are catabolised in the mucosal epithelium towards the maintenance
energy requirement (Noy and Sklan, 1996). Short chain fatty acids and free glycerol are absorbed directly through
passive uptake (Gropper
et.al.2008). The
portomicrons, short chain fatty acids and free glycerol are transported through
the portal venous system to the liver since the bird’s lymphatic system is not
as developed as the mammals (Bensadoun and Rothfield, 1972). Very low density lipoproteins carry triglycerides from
the liver to the extra hepatic tissues like the ovary (for egg yolk synthesis)
or muscle (for energy) (Phan and Tso, 2001)
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| Digestion of Lipid |
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Absorption of Lipid
Endogenous Fat
Secretion:
Apart from lipid
absorption of extraneous dietary fat, the animal also extracts fat through continuous secretion of endogenous lipids into the
lumen of the intestinal tract. The primary sources of this endogenous fat are
bile and scraped intestinal epithelial cells (Clement, 1980). These endogenous
lipids mix with dietary lipids and are partially digested and absorbed. The
unabsorbed fraction passing beyond the ileum is considered loss to the animal,
and measurement of these losses is essential to calculate the true
digestibility of the lipids.
It was reported that the
endogenous fatty acid losses in the ileal digesta and excreta of birds fed by
balanced oil diet were lower than the ones fed with imbalanced or high acidic
poor quality oil mixture diet.
The endogenous fatty acid
profile contained mainly Palmitic, Stearic, Oleic and Linoleic acids (generally
present in blended fat in a more balanced way).
References:
1.
Freeman C.P.
(1984) The digestion, absorption and transport of fats-non ruminants in
Wiseman, J.(Ed), Fats in Animal Nutrition, Butterworths, London, U.K.
2.
Krogdahl, A.(1985)
Digestion and absorption of lipid in poultry, Journal of Nutrition
3.
Smulikowska, S.(1998)
Relationship between the stage of digestive tract development in chicks and the
effect of viscosity reducing enzymes on fat digestion, Journal of Animal and
Feed sciences
4.
Klasing K.C.(1999)
Avian gastrointestinal anatomy and physiology, Proceedings of seminar in
avian and exotic pet medicine.
5.
Sklan,
D.Shachaf,B. Baron, J. and Hurwitz, S.(1978) Retrograde movement of digesta
in the duodenum of the chick; extent,frequency, and nutritional implications,
journal of nutrition.
6.
Yeh , Y.H. and
Hwang, D.F.(2001) High-performance liquid chromatographic determination for
bile components in fish, chicken and duck, Journal of chromatography B:
biomedical Sciences and Applications
7.
Garrett, R.L.
and Young, R.J.(1975) Effect of micelle formation on the absorption of
neutral fat and fatty acids by the chicken, Journal of Nutrition
8.
Erlanson,C,
Fernlund, P. and Borgstrom, B(1973), Purification and characterization of
two proteins with co-lipase activity from porcine pancreas, Biochemica et
Biophysica Acta
9.
Borgstrom, B. (1980) Importance of
phospholipids, pancreatic phospholipase A2, and fatty acid for the digestion of
dietary fat: in vitro experiments with the porcine enzymes, Gastroenterology.
10.
Van Kuiken,
B.A. and Behnke,W.D. (1994) The activation of porcine pancreatic lipase by
cis-unsaturated fatty acids, Biochemica et Biophysica Acta (BBA)-lipids and
Lipid metabolism.
11.
Piyamas
Tancharoenrat, 2012, A thesis presented for Doctor of philosophy in poultry
nutrition at Massey Universit, Palmerston North, New Zealand, Factors
influencing fat digestion in Poultry.
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Freeman C.P.
(1976) Digestion and Absorption of fat. In Boorman, K.N. and Wiseman, J.(Ed)
Digestion in the Fowl.
13.
Hurwitz, S., Bar,
A., Katz, M.Sklan,D. and Budowski, P.(1973). Absorption and secretion of
fatty acids and bile acids in the intestine of the laying fowl. Journal of
Nutrition
14.
Pond, W.C.,
Church, D.C., Pond, K.R. and Schoknecht, P.A.(2005) Basic animal nutrition
and feeding (5th ed.)John Wiley & Sons Inc., USA
15.
Murugusen, Dr.
G.R., Iowa University, Understanding the effectiveness of blended fats and
oils in poultry diet.
16.
Davenport,
H.W. (1980) Physiology of the digestive tract, The year book Medical
Publishers, Inc. London
17.
Katongole,
J.B.D. and March, B.E. (1979), Fatty acid binding protein in the intestine
of the chicken, Poultry science
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Ockner, R.K.,
Manning, J.A., Poppenhausen, R.B. and Ho, W.K.L. (1972), A binding protein
for fatty acids in cytosol of intestinal mucosa, liver, myocardium and other
tissues, Science.
19.
Stevens ,L.(2004) Avian
Biochemistry and Molecular Biology, Cambridge Univ. Press
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Gropper, S.S.,
Smith, J.L., Groff, J.L. (2008) Advanced nutrition and Human metabolism,
Wadsworth Pub.Co.
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Bensadoun, A.,
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domesticus.
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Tso.P, (2001) Intestinal lipid absorption and transport Front
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