Bird performance in the commercial poultry industry has shown a consistent improvement over the past few decades. This change has occurred due to improved genetics, well balanced nutrition and better farm management practices. The industry has undergone a remarkable change and growth over the last 30 years, such that today we see 3 Kg broilers before 40 days of age and white egg layers are capable of producing nearly 340 eggs in 52 weeks of lay. Among the above factors, nutrition plays a vital role in supporting the desired growth and production performance of birds. Provision of a good quality feed with all essential nutrients must be ensured. Also, the nutrients supplied through feed have to be effectively digested, absorbed and assimilated. If the nutrients are not absorbed within the time limit, they are attacked by the bacteria in the large intestine or excreted as waste, defeating the purpose for which they are fed and is reflected in terms of inefficient growth and productivity.
Feed accounts for 65-70% of the total costs in animal production. With the rise in feed costs internationally; the birds’ ability to absorb nutrients optimally is a very important aspect of overall performance efficiency. Nutritionists are therefore increasinglyemphasizing tooptimise the feed efficiency and reduce feed cost.
Besides having a superior emulsification property, Lysophospholipids (LPLs) are proven to be very effective in enhancing the flux rate of nutrients across the gut membrane, thereby improving the absorption and reducing the nutrient loss through feces.
Membranes define the boundaries of the cell and its organelles and act as permeability barriers.One remarkable feature of all biological membranes is their flexibility; their ability to change shape without losing their integrity and becoming leaky. The“Fluid-Mosaic” model (Singer & Nicolson, 1972)of cell membrane indicates that membranes are made up of lipid bilayer and membrane proteins (peripheral and integral).
The lipid component of the membrane is a two dimensional fluid in which the constituent molecules are free to move laterally. TheLipid bilayer functions as both; a solvent for integral proteins and as a permeability barrier.Peripheral membrane proteins are anchored to the surface of the membrane, while integral membrane proteins contain trans-membrane regions that pass completely through the bilayer.These two classes of membrane proteins contribute to the “mosaic” aspect of the fluid-mosaic model.
Phospholipids (PLs) are the most abundant lipids found in membranes. These are amphipathic in nature, having hydrophilic as well as lipophilic properties. PLs are characterized by a glycerol backbone to which a polar hydrophilic Phosphodiester(head) group and two lipophilic hydrocarbon tails are linked. The tails are usually fatty acids derived acyl residues thatcan differ in length (normally contain 14 to 24 carbon atoms).
Along with phospholipids, the animal cell membrane also contains significant amounts of sterols, mainly cholesterol, which is necessary for maintaining and stabilizing the membrane by acting as a fluidity buffer. Though the lipid bilayer structure is quite stable, its individual phospholipid and sterol molecules have some freedom of motion. Lysophosphatidylcholine (LPC) like molecules affect the fluidity of the cell membrane by modifying cholesterol levels in the membrane and thereby dynamics of the membrane.
Lysophospholipids (LPLs) are glycerophospholipids in which one acyl chain is lacking as compared to PLs and therefore only one hydroxyl group of the glycerol backbone is acylated. LPLs which include lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), lysophosphatidyl inositol (LPI) and Lysophosphatidylserine (LPS) are prepared by enzymatic hydrolysis of natural soy lecithin by phospholipase A2.
Each membrane at equilibrium contains pores and holes – these are best thought as gaps or vacancies where phospholipids are missing from the lattice structure. Sometimes there are clusters of these vacancies of various sizes. When additional LPLs are introduced, it is this distribution that is affected, which results in an increase in both the number and the size of pores. Through the normal passive transport processes, nutrients of larger molecular weights can then pass more readily across the membrane. When the membrane comes into contact with a certain ratio of LPLs, these exogenous LPLs quickly get interdigitated into the bilayer membrane. The close packing between the PLs is disrupted and the lipids go from an order to disorder state and the membrane becomes more fluid i.e. the gaps or pores in the membrane form big clusters or larger vacancies in the matrix causing an increase in the number and size of pores. This means that the nutrient absorption profile of the gut is beneficially altered with the passive flux hurdle temporarily lowered.
Also, LPLs have the ability to change the attraction between lipids and displace calcium ions. With this increased freedom of movement, lipids can aggregate closer together making existing holes larger so that larger molecules are easily absorbed.A pre-determined ratio has to be maintained between PLs and LPLs, and also between different LPLs to observe a consistent and desired end result.
The above describes how Lysophospholipids (LPLs) act as a membrane fluidity modulator. They increase the number and size of pores by altering the mechanical properties of the membrane, thereby enhancing the flux rate at which nutrients of various molecular sizes pass across the membrane of the gut and thereby act as an absorption enhancer. This is one of the key applications of LPLs in animal nutrition as it is possible to extract more nutrient value from every kilogram of the diet and thereby optimize feed efficiency and therefore feed cost.