By: Dr. Oscar Tejeda, M.Sc., Ph.D.
Assistant Professor of Poultry Science, SAU Department of Agriculture
Introduction and generalities of nutrition
Nutrition accounts for 65% of the total production costs in most poultry species. It also plays a crucial role in providing the building blocks necessary to obtain quality of products such as meat and eggs. Nutrition is the process by which the animal will be able to use components of the external environment to furnish cells inside their bodies that yield products such as fresh eggs and meat. Essential nutrients need to be provided at all times to guarantee the best performance of the flock. There are 6 essential nutrients, namely: water, carbohydrates, protein, fat, vitamins, and minerals. The requirements for nutrients vary in different stages of growth and the balance between nutrient requirements and nutrient intake has profound effects on production efficiency and production costs. The cheapest way to feed poultry is feeding them based on their nutritional requirements. Therefore, requirements of the flock need to be kept in mind to ensure maximum production at the minimum cost.
Water
Due to the abundance of water, this nutrient tends to be overlooked in most poultry production systems. Water is one of the most important nutrients that is part in every biochemical reaction occurring in the animal’s body. One of the biggest concerns with water is the origin of it. There are different sources of water that can be used in poultry production. Some sources include rivers, lakes, city water and wells. Natural sources such as rivers and lakes can be a problem serving as a transporter in the dissemination of avian diseases given the fact that wild birds will use such sources. City water can be expensive, specially when you have farms consuming 120,000 gallons of water per farm per day. Therefore, most poultry farms will have their own wells that supply enough for the requirements. Since water serves as the universal solvent, it is important to evaluate the quality of water being used, to prevent diseases and increase production performance.
Table 1. Total solids or “salinity” of water
| Salinity, mg/L | Comments |
| <1,000 | Safe for any species |
| 1,000-2,999 | May cause diarrhea |
| 3,000-4,999 | Poor for poultry |
| >5,500 | Should not be used for poultry |
Ideally, salinity levels should be less than 1,500 to prevent immune and metabolic problems in the flock. In cases when salinity levels are too high, alternative water sources should be used or the farm should be moved to another location where the quality of water is better.
Under normal conditions, the water intake is 2-3 times that of feed intake. Therefore, using water-meters at the farm can serve as an indirect measurement of feed intake and general welfare of the flock.
Table 2. Water intake of broilers at different ages
| Age | 10 days | 20 days | 30 days | 40 days | 50 days | 60 days |
| Gallons/1,000 birds/ day1 | 200 | 570 | 950 | 1,350 | 1,800 | 2,150 |
1Water intake increases with temperatures higher than 70 °F, specially when birds are older than 21 days.
Finally, making sure that water filters are being constantly changed can also help ensure that birds are receiving enough water.
Energy
Energy is considered the flame of life and it is considered that an animal (under normal conditions) will eat to satisfy their energy requirements first. Most diets are formulated based on energy levels. When diets are high in energy, the animal is expected to eat less, therefore, the nutrient density should be increased. The opposite is also true. Energy is measured in kilocalories per kilogram (Kcal/kg). The requirements for energy vary depending on the breed, age, environmental temperature, and level of production. There are three sources of energy: carbohydrates, lipids (fats), and protein. Carbohydrates should be the main source of energy in the diet and when energy levels cannot be reached using carbohydrates, fats can help increase energy density due to their high energetic value (2.25 times that of carbohydrates).
Table 3. Energy requirements for broilers
| Phase | Energy requirement, Kcal/kg |
| Broiler, starter (d0-14) | 2,975 |
| Broiler, grower (d15-28) | 3,025 |
| Broiler, finisher (>d29) | 3,050 |
Table 4. Energy requirements for laying hens
| Phase | Energy requirement, Kcal/kg |
| 0-6 weeks | 2,850 |
| 7-12 weeks | 2,850 |
| 13-18 weeks | 2,900 |
| >18 weeks | 2,900 |
Carbohydrates
Carbohydrates are the main source of energy and the most abundant component in typical poultry diets. Carbohydrates can be divided in 2 main groups: starch and non-starch polysaccharides (NSP). Starch is the main source of energy in poultry diets since this is highly digestible. On the other hand, NSP or also known as dietary fiber has a poor digestibility. Most energy comes from cereal grains in typical poultry diets. Different feed ingredients provide different energy levels (Table 1) that is important to consider whenever feeding the flock because the feed intake in the flock will be directly affected by the energy level.
Table 5. Common feed ingredients and their metabolizable energy content
| Ingredient | Crude fiber, % | ME1, Kcal/Kg |
| Corn | 1.9 | 3,373 |
| Wheat | 3.0 | 3,170 |
| Barley | 5.0 | 2,750 |
| Milo (sorghum) | 2.0 | 3,310 |
| Rye | 2.8 | 2,710 |
| Oats | 10.5 | 2,550 |
| Millet | 1.8 | 3,240 |
| Rice | 2.8 | 2,940 |
| Triticale | – | 3,150 |
| Rice bran | 13.0 | 2,040 |
1ME = metabolizable energy
The metabolizable energy of a feedstuffs is inversely related to the fiber content as shown in table 1. When ingredients high in fiber are to be fed to the flock, it is necessary to provide endogenous enzymes to prevent intestinal problems and improve nutrient digestibility and performance. Some Examples of enzymes are shown in the table below:
Table 6. Carbohydrases and different feed ingredients (From Raza et al., 2019)
| Enzyme1 | Feed ingredient | Inclusion rate, units/Kg |
| Glucanases | Barley | 52.5 |
| Xylanase |amylase | Corn/soy/wheat | 2,000 | 200 |
| Xylanase | cellulase | β-galactosidase | Rice bran | 4,520 | 4,060 | 2,700 |
| Xylanase | glucanase | cellulase | Wheat | – |
1Please see product’s label to determine the adequate inclusion rate for different enzymes.
Table 2 shows some enzymes that can be used with different feed ingredients. It is important to point out the fact that enzymes are substrate-specific which means that enzymes that may work with wheat may not work with barley. Therefore, before using any carbohydrase (carbohydrate-breaking enzymes) be sure to use the specific enzyme for the specific feed ingredient. The use of “enzyme cocktails” is also gaining popularity due to the synergistic activity of some carbohydrases and the positive effects obtained.
Carbohydrates are the most expensive nutrient, as a total, because they are the most abundant in the diet. Therefore, the use of by-products allows for the reduction of production costs
Protein
Protein is used by poultry species after the process of digestion where large polymers (i.e. proteins) are broken down into smaller peptides and amino acids, providing the building blocks for the synthesis of body tissues (i.e. meat, eggs). Just like other monogastric animals, poultry species do not have a requirement of protein per se but they have a requirement for amino acids. Amino acids are the most expensive nutrient on a weight basis. Therefore, amino acids/protein should be provided at the adequate levels to support growth but levels added must always be evaluated to prevent waste. Different factors can affect the requirements for amino acids including:
- Breed
- Age
- Type (meat vs egg)
- Production level
- Environmental stressors
There are 20 different amino acids that are used for protein synthesis. From those 20 amino acids, 10 are considered “nutritionally essential” which means that we need to make sure that such amino acids are present in the diet at adequate levels, otherwise, protein synthesis (i.e. meat accretion) will be impaired. From the 10 nutritionally essential amino acids there are about 5 amino acids that are found in extremely low amounts in typical poultry diets (corn-soybean meal). Those 5 amino acids receive the name of “first limiting amino acids” because they are the most likely to be deficient in the diet. Muscle accretion will happen at the level of the first limiting amino acids. Therefore, first limiting amino acids are the main focus whenever we formulate diets for poultry species to guarantee that all amino acids are being used at the highest efficiency.
Under normal conditions, poultry species have requirements for amino acids as shown below
Table 7. Amino acids requirements for broilers1
| Phase | Protein, % | TSAA3, % | Lysine, % | Threonine, % | Tryptophan, % | Valine, % |
| Broiler, starter | 22 | 0.95 | 1.28 | 0.86 | 0.20 | 0.96 |
| Broiler, grower | 19 | 0.87 | 1.15 | 0.77 | 0.18 | 0.87 |
| Broiler, finisher | 17 | 0.83 | 1.06 | 0.71 | 0.17 | 0.81 |
1Digestible amino acids as a % of the diet
2Starter = 1-14 days of age; Grower = 15- 28 days of age; Finisher = 29- 42 days of age
3TSAA = total sulfur amino acids (Methionine + cysteine)
Amino acid levels vary in breeders depending on the production level and the breed.
Table 8. Protein requirements for female broiler breeders in different stages of production
| Age, weeks | 0-8 | 9-17 | 18-45 | 46-72 |
| CP, % | 22% | 15% | 15% | 15% |
Table 9. Amino acid requirements for female broiler breeders during production
| TSAA3, % | Lysine, % | Threonine, % | Tryptophan, % | Valine, % |
| 0.70 | 0.77 | 0.72 | 0.19 | 0.75 |
There are 2 main sources of protein: one is vegetable protein and the other one is animal by-products of by-products of the processing plant. Most sources of proteins are by-products of oil extraction or oilseed meals. Animal proteins tends to have an amino acid profile that better resembles the amino acid profile of the animal consuming the feed.
Table 10. Sources of protein and their amino acid levels
| Ingredient | Crude protein, % | Met, % | Lys, % | Thr, % | Trp, % |
| Soybean meal | 48 | 0.70 | 3.02 | 2.0 | 0.70 |
| Cottonseed meal | 41 | 0.52 | 1.65 | 1.32 | 0.47 |
| Canola meal | 38 | 0.77 | 2.02 | 1.50 | 0.46 |
| Peanut meal | 47 | 0.50 | 1.52 | 1.12 | 0.42 |
| Sesame meal | 42 | 1.48 | 1.37 | 1.71 | 0.82 |
| Meat and bone meal | 50 | 0.67 | 2.60 | 1.70 | 0.26 |
| Meat meal | 55 | 0.75 | 3.00 | 1.81 | 0.35 |
| Poultry meal | 57 | 0.91 | 2.25 | 1.88 | 0.50 |
| Blood meal | 80 | 1.0 | 6.9 | 3.8 | 1.00 |
| Casein | 80 | 2.7 | 7.0 | 3.8 | 1.00 |
In general, cereal grains provide 75% of the energy and 25% of protein (AA) and oilseed meals provide 75% of protein (AA) and 25% of energy.
In case levels of first limiting amino acids have not been met using conventional feedstuffs, crystalline amino acids are used as purified sources that increase levels of individual amino acids without affecting the level of the rest, increasing production efficiency and reducing waste. The most common crystalline amino acids include: D/L methionine, L-lysine, L-tryptophan, L-threonine, L-valine or their respective analog whenever convenient.
Table 11. Price of lysine from different sources
| Source | % lysine | $/ lbs. of digestible lysine1 |
| Soybean meal | 3.02 | 8.56 |
| Corn | 0.25 | 55.12 |
| Cotton seed meal | 1.65 | 16.29 |
| Canola meal | 2.02 | 11.14 |
| Poultry byproduct | 2.25 | 4.48 |
| L-lysine | 78 | 0.90 |
Lastly, more than total protein content is the amino acid profile and the digestibility of amino acids present in the protein source. Information about amino acid profile and digestibility of different feed ingredients can be found in sources such as NRC (swine, poultry, cattle).
Lipids
Lipids or fats are the densest source of energy in animal diets. Triglycerides are the most important lipid in terms of nutrition providing 2.25 times the energy of carbohydrates per unit of weight. Addition of lipids have several benefits in poultry diets:
- Increase of energy of the diets
- Provides essential fatty acids
- Provides fat-soluble vitamins
- Reduces wear-out of equipment during mixing
Lipids include two major groups: fats that are solid at room temperature and oils that are liquid at room temperature. Poultry diets typically contain up to 0.5-2% lipids and can vary based on the nutrient density of the diet. In the diet, lipids can come directly from added ingredients (i.e. corn has 3.5% fat) or it can be added separately (i.e. soybean oil). During summer time, birds decrease feed intake due to the heat increment associated to nutrient metabolism. Therefore, increases in the energy and nutrient density can be an alternative to prevent loss of the body condition in broilers, or decreases in egg production in laying hens and breeders, specially during the summer time or in places with high temperatures. During the winter time, a higher feed intake is expected, therefore, diets are generally formulated to have relatively lower energy levels compared to summer time.
As most monogastric animals, poultry species have two essential fatty acids: linoleic acid and α-linolenic acid. Such requirements are higher for broiler breeders due to embryonic requirements.
There are different sources of lipids that vary in their chemical composition, digestibility, and price. Some of those sources are by-products of the rendering plan or by-products of restaurants.
Table 12. Digestibility of different sources of fat
| Source | Metabolizable energy (kcal/kg) |
| Corn oil | 9,220 |
| Soybean oil | 9,220 |
| Sunflower oil | 8,690 |
| Rapeseed oil | 8,800 |
| Poultry fat | 9,000 |
| Tallow | 8,500 |
| Lard | 8,400 |
| Animal/vegetable blend | 8,000 |
Since the gross energy of any lipid (fat or oil) is 9 kcal/gram, the digestibility is directly associated to the total metabolizable energy per kilogram. Looking at the previous table, it is clear that the digestibility of animal fats is lower compared to vegetable oils due to the higher content of saturated fatty acids. In fact, it is not recommended to use tallow and solid fats in diets of younger animals because the lipase activity (enzyme that breaks fats) is low in newly hatched birds. To decrease production costs while maintaining an adequate performance, it is recommended to use an animal/vegetable (50:50) blend that maintains performance and decreases production costs.
The energy content (i.e. digestibility) of lipids is related to the quality of fat. Different saturated: unsaturated lipid ratios, the presence of free fatty acids, presence of double bonds can affect the digestibility and stability of different lipids. Therefore, because of the susceptibility of lipids to peroxidation (rancidity), there are different methods that can be used to analyze the quality of the lipid being used.
- Free fatty acids: Measures the presence of not attached to glycerol. Free fatty acids are less stable and more susceptible to peroxidation compared to those attached to glycerol. Higher levels indicate higher potential for peroxidation.
- Unsaponifiable: Measures compounds that are not split into glycerol and fatty acids by KOH hydrolysis. Higher levels indicate lower lipid quality
- Iodine value: Indicates the degree of unsaturation. The more double bonds, the more susceptible to peroxidation. Higher levels indicate higher potential for peroxidation.
- Fat stability: Measures the propensity of lipids to rancidity. Saturated fatty acids tend to be more stable compared to unsaturated.
- Color: variations from the pure white indicate peroxidation and poor lipid quality.
- Unsaturated/saturated ratio: This indicates the ratio between the total content of unsaturated fatty acids and the total content of saturate fatty acids. Higher ratios indicate higher propensity for peroxidation.
Table 13. Typical specifications of common animal fats
| Lipid | Free fatty acids | Unsaponifiable | U/S ratio |
| Tallow | 6% | 1% | 1.2% |
| White grease | 4% | 1% | 1.8% |
| Poultry fat | 15% | 2% | 2.6% |
| Blended animal | 15% | 1% | — |
| Vegetable/animal | 30% | 1% | — |
It is important to point out the fact that animal sources are more stable than vegetable sources, however, despite the higher propensity to peroxidation, vegetable sources are more digestible than animal sources.
Minerals
Minerals are the inorganic portion of the diet and can be classified into two major groups: macrominerals and microminerals. Macrominerals are used in relatively larger amounts and are usually expressed as a % of the diet. The 6 macrominerals of importance include: calcium, phosphorus, magnesium, sodium, chloride, and potassium. Most macrominerals play important structural and metabolic functions. Under normal conditions supplementation of calcium, phosphorus, sodium, and chloride is necessary using inorganic sources. The requirements for the rest of macrominerals can be covered by the vegetable ingredients being provided in the diet.
Microminerals are added in smaller amounts to poultry diets and they are generally expressed as part per million (ppm). Essential microminerals include: manganese, zinc, iodine, cupper, iron, and selenium. Microminerals are generally supplemented using mineral premixes that are specific for different poultry species.
Table 14. Common sources of minerals
| Mineral | Supplementation | Inorganic source | Composition |
| Calcium | Common | Limestone | 40% Ca |
| Phosphorus | Common | Mono-calcium phosphate | 16% Ca and 21% P |
| Phosphorus | Common | Di-calcium phosphate | 28% Ca and 18.5% P |
| Sodium | Common | Salt (NaCl) | 40% Na |
| Chloride | Common | Salt (NaCl) | 60% Cl |
| Micromineals | Common | Mineral pre-mix | – |
There are small variations in the requirements for minerals in broilers. Most diets for broilers will contain 0.80-0.90% of calcium and 0.45-0.50% of phosphorus at a ratio of 2 ca to 1 phosphorus. However, there are large variations in the mineral requirements in laying hens and breeders in different stages of growth due to the higher physiological needs associated with egg production (See table x).
Table 15. Calcium and phosphorus requirements for laying hens
| Mineral | 0-3 wk | 4-6 wk | 7-12 wk | 13-15 wk | 16-18 wk | Peak |
| Calcium, % | 1.05 | 1.00 | 0.95 | 0.90 | 2.50 | 4.0 |
| Phosphorus1, % | 0.48 | 0.47 | 0.45 | 0.40 | 0.43 | 0.43 |
1Available phosphorus
Phosphorus is the second costliest nutrients (after amino acids) on a weight basis. There are 2 main types of plant phosphorus: phytate phosphorus that is indigestible by poultry species, and the non-phytate phosphorus that is digestible for birds. About 30% of the total vegetable phosphorus is found in the indigestible form which requires the use of phytases to break down chemical bonds and render phosphorus available for the animal. The use of enzymes such as phytase helps to reduce the excretion of phosphorus by the flock and reduces environmental problems such as eutrophication.
Formulation of the adequate calcium to phosphorus ratio is crucial to ensure the adequate grow of the flock. There are changes in the amounts of Ca and P being used in the diet based on different stages of growth of the flock. When vegetable ingredients fail to provide all the phosphorus in the diet, inorganic sources such as monocalcium phosphate and dicalcium phosphate allow us to cover P requirements.
Vitamins
Vitamins are a group of complex organic compounds made of chemically different functional groups. Vitamins can be classified as fat-soluble which includes vitamins A, D, E, and K. The second group is water-soluble vitamins that includes 8 vitamins of the B complex. Under normal production conditions, all vitamins need to be supplemented either individually or using a vitamin pre-mix specific for the requirements of the flock. Requirements for vitamins A and D are higher compared to the rest of vitamins.
Fat-soluble vitamins occur as precursors and their supplementation is highly dependent on the precursor being fed.
Table 16. Vitamin requirements per kilogram of feed (Ross 2019; Hy-line 2021)
| Specie | Vitamin A, IU | Vitamin D, IU | Vitamin E | Vitamin K |
| Broilers | 10,000-15,000 | 3,000-5,000 | 80-100 IU | 3-5 IU |
| Laying hens | 8,000-10,000 | 3,000-4,000 | 25 ppm | 3.5 ppm |
Most of the time, vitamins are supplemented in higher amounts than required because they are relatively cheap and is safer to supplement higher levels to offset environmental stressors that may increase the requirements and result in reduced performance. Finally, the exact requirements for some vitamins are have not been publish due to the constant changes in genetics, changes in feed ingredients, and feed additives that impact directly the requirements for vitamins.
Table 17. Functions of vitamins and signs of deficiency
| Vitamin | Function | Signs of deficiency |
| A | Sight, epithelial tissues, reproduction | Soft epithelium becomes keratinized, lower hatchability |
| D | Ca and P metabolism, bone integrity | Rickets, beak and claws become soft |
| E | Antioxidant | Encephalomalacia, muscle dysfunction |
| K | Coagulation | Constant bleeding |
| B-complex | Energy metabolism, protein metabolism | Fatty liver, anemia, stunted growth |