Introduction
Energy is the costliest part of broiler diets, and recent high feed costs have led nutritionists to optimize the caloric efficiency of feed ingredients. The broiler industry is witnessing higher prices of oil; therefore, one should critically evaluate the same. Hence, in this article nutritive value and quality evaluation of fat/oil are discussed.
Fats/oils are types of lipids (substances soluble in non-polar organic solvents such as chloroform and ether and insoluble in water). Refer table 1 for the different types of lipids.
Fats/oils are triglycerides made of different fatty acids. Fats are solid at room temperature, while oils are liquid. Both are esters of glycerol. Various fat/oil sources are used in poultry diets. Commonly used sources include crude oil from single vegetable sources, blended oil of different edible oil refinery byproducts (acid oils) to optimize fatty acid profile and other parameters, and tallow.
Important functions
Lipids play a crucial role in broiler nutrition, significantly impacting the growth, health, and overall performance of poultry. As an essential component of the diet, fats/oils provide concentrated sources of energy, enhance the absorption of fat-soluble vitamins, pigments (for yolk and shank color) and contribute to the palatability of feed.
Extra calorific value of fats/oils is attributed to its role in lowering digesta passage rate thereby improving digestibility of the other nutrients like amino acids and carbohydrates, ultimately leading to increased feed utilization efficiency (lower FCR). However, high calcium and fats/oils may hamper the digestibility of each other by forming soaps.
Essential fatty acids, such as linoleic and linolenic acid, cannot be synthesized by the birds and must be obtained through the diet. These fatty acids are integral components of cell membranes, play a role in hormone production, and are involved in inflammatory and immune responses. By ensuring an adequate supply of essential fatty acids, fats/oils support the overall metabolic health and functionality. They also play a critical role in follicle development and ovulation in layers.
In summer, diverting part of feed energy from carbohydrates to lipids reduces the heat increment of nutrient metabolism ultimately lowering the body heat production and stress.
Also, it is crucial in pellet feed manufacturing for proper lubrication (saving energy cost at pellet mill level), avoiding excessive heating and hardness of pellets. Minimum 3.5% fat/oil is recommended for pellet feed manufacturing.
Estimation of Energy value of fats/oils for broilers
AME estimation can be done using the empirical equation developed by Professor Wiseman, with adjustments made for the presence of energy-diluting components, such as MIU.
E =[A+B * FFA+C * eD(U/S)] * (1 – MIU/10)
FFA= % of free fatty acids
U/S= Ratio of unsaturated to saturated fatty acids
MIU- % of total non-nutritional materials – Moisture+Impurities / Insolubles+Unsaponifiables
e= Exponential function
The nutritional value fat/oil is measured as apparent metabolizable energy (AME) for young broilers and older broilers separately, because young birds’ efficiency of fat/oil utilization is compromised because of insufficient lipase and bile production. An increase in FFA content lowers the energy value due to the negative B value. Parameters C and D negatively impact energy value when saturated fatty acids are higher.
While the equation doesn’t explicitly state “chain length,” the U/S ratio is highly influenced by the types of fatty acids present. Longer-chain fatty acids, especially those with varying degrees of unsaturation, contribute to this ratio. Saturated FA with chain length below or equal to C12 are considered as unsaturated and trans C18:1 isomer is considered as saturated.
Use of emulsifiers may increase the energy value of fats/oils calculated by using above equation and oxidation may lower it (shown in table 2).
Quality evaluation of the fats/oils
Sampling is very crucial and first step for accurate quality evaluation, please follow correct sampling design and take equal quantity from upper, middle and bottom portion of the container.
Following are the parameters to be considered for physical quality, composition and impurities of oil/fat, which directly affects its energy value.
- Color- Quantified relative to the Fat Analysis Committee (FAC) standard, ranging from 1 (light) to 45 (dark).
- Fatty acid profile- Relative amounts of individual fatty acids in a sample. Actual analysis of fatty acid profile using Gas Chromatography is desirable rather than using book data. This is helpful in designing a diet for fortified/designer poultry products (meat, egg) rich in omega 3 fatty acids or with desirable U/S ratio. WHO recommends that the ratio of polyunsaturated fatty acids (PUFAs) to saturated fatty acids (SFAs) in the human diet be 0.8 to 1. The WHO also recommends that the ratio of omega-6 to omega-3 fatty acids be 5 to10 in human diet.
- Free fatty acids- Amount of fatty acids not bound to glycerol backbone in a triglyceride. Excessively high levels may result from factors such as poor storage conditions, prolonged exposure to heat or light, or inadequate refining processes. Free fatty acids may be easily oxidized. Ideally FFA should be below 15% for young birds and below 25% for older birds.
- Insoluble/Impurity- Amount of sediment in a sample. For example, fiber, hair or soil. Impurity contents should be lower than 1%.
- Iodine value (IV)- Measure of chemical unsaturation, expressed as grams of iodine absorbed by 100 g of fat. Oils with higher IV are more digestible and less stable, vice versa for the oils with low iodine value. Ideal IV depends on the source of oil.
- Moisture- Amount of moisture in a sample. Maximum accepted values are between 0.5 and 1.0%.
- Non-elutable material- Reflects the total amount of non-nutritional material; includes moisture, impurities, unsaponifiable material, glycerol, and oxidized and polymerized fats.
- Saponification value- An estimate of the average molecular weight of the constituent
fatty acids in a sample, defined as milligrams of KOH required to saponify 1 g of lipid. The greater the saponification value, the lower the average chain length of fatty acids. - Total fatty acids- The total of both free fatty acids and fatty acids combined with glycerol.
- Unsaponifiable- A measures of material in the lipid that will not saponify (form a soap) when mixed with caustic soda (NaOH or KOH). Examples include: sterols, hydrocarbons, pigments, fatty alcohol, and vitamins. It should be below 2%.
Lipid peroxidation:
Lipid peroxidation is a complex process influenced by factors such as the degree of
saturation, temperature, and the presence of oxygen, transition metals (e.g., Cu and Fe), undissociated salts, water, and other non-lipidic compounds. Lipid peroxidation has three phases: initiation, propagation, and termination, with each step producing and consuming various compounds. Lipid hydroperoxides formed during the lipid peroxidation process can affect lipid quality and form secondary and tertiary peroxidation products (aldehydes, ketones, alcohols, hydrocarbons, volatile organic acids, and epoxy compounds) that can have detrimental effects on animal productivity and health. However, peroxides and aldehydes that are initially produced are ultimately degraded as peroxidation continues. Accurately measuring lipid peroxidation in feed ingredients is difficult due to its complexity and the various compounds involved. No single method can fully predict or describe lipid peroxidation; following multiple measures are necessary for a comprehensive assessment.
- Peroxide value (PV)- Measure of lipid peroxides and hydroperoxides. Limitation of this parameter is Peroxides may be undetectable in lipids exposed to >150°C. Should be used in conjunction with TBARS and AnV when assessing peroxidation. PV below 5 mEq/kg is desirable.
- p-Anisidine value (AnV)-Measure of the high molecular weight saturated and unsaturated aldehydes.
- Thiobarbituric acid reactive substance concentration (TBARS)- Measure of carbonyl-containing secondary lipid oxidation products formed from the decomposition of hydroperoxides. Developed to detect malondialdehyde, although other carbonyl compounds can also contribute to the TBARS values.
- Triacylglycerol dimers and polymers- Polymeric compounds formed during the late phases of peroxidation.
- Totox value- Sum of AnV (or TBARS) and 2×PV. Measures both primary and secondary peroxidation compounds. Limitation is the lack of specificity inherent with AnV (or TBARS) and PV.
- Active oxygen method stability(AOM)- A predictive method where purified air is bubbled through a lipid sample at 97.8 °C, and the PV of the lipid is determined at regular intervals to determine the time required to reach a PV of 100 mEq/kg lipid (recorded as h), or the PV of the lipid is determined at a predetermined time endpoint, such as at 20 h (recorded as mEq/kg lipid). The maximum acceptable is 20 mEq of peroxide per kg after 20h.
- Oil stability index (OSI)- A method whereupon air passes through a lipid under a specific temperature, at which point volatile acids decomposed from lipid peroxidation are driven out by the air and subsequently dissolved in water thereby increasing its conductivity. The conductivity of the water is constantly measured, and the OSI value is defined as the hours required for the rate of conductivity to reach a predetermined level.
Dr. Ravindra Jadhav, Premium Chick Feeds
