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.

Fig 1

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)

Digestion of Lipid

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.

12.     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 (5^th 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

18.     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

20.     Gropper, S.S., Smith, J.L., Groff, J.L. (2008) Advanced nutrition and Human metabolism, Wadsworth Pub.Co.

21.     Bensadoun, A., Rothfeld A.,(1972) The form of absorption of lipids in the chicken, Gallus domesticus.

22.     Phan, C.T., Tso.P, (2001) Intestinal lipid absorption and transport Front

23.     Clement, J, (1980) Intestinal absorption of triglycerols, reproduction Nutrition Development


POULTRY TECHNOLOGY -PUBLISHED ABOVE ARTICLE IN APRIL 2016 ISSUE

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