Poultry nutrition

Poultry nutrition Poultry convert feed into useful nutrients quickly and efficiently. They have a relatively low envir They are required for various functions within the bird.

Proteins & Amino Acids
The dietary requirements for protein are actually requirements for the amino acids found in dietary protein. Poultry use these amino acids to fulfil a number of functions, including using them to make up the bulk of their structural and protective tissues such as skin, feathers, bones and ligaments. Amino acids also help form the soft tissues including the organs and muscles

, as well as playing an important role in the metabolisation of feed into energy. Failure to provide adequate protein in your bird’s diet will result in a number of structural and health problems for your flock, as well as reducing yield of meat or eggs. However, it’s important to remember that poultry protein and amino acid requirements can vary considerably, depending on the rate of growth or level of egg production of the individual bird. Turkey poults and broiler chickens have high amino acid requirements so they can meet the necessary rapid growth, for instance, and the mature rooster requires fewer amino acids than the laying hen, even though its body size is greater and feed consumption similar. The percentage requirements of protein and amino acids must also increase if you keep your flock in warmer environments, when metabolisation is far quicker. In general, protein and amino acid percentages are some of the trickier nutritional balances to get right for poultry production, so it’s best to fully research the breed you’re working with, and tailor your feed to them specifically. Fats
Generally speaking, fat is usually added to the feed for meat-type poultry to increase overall energy concentration, and thereby improve productivity and feed efficiency. Feed-grade fat tends to come from different sources, including grease from restaurants, the rendering of animal carcasses, and the refuse from vegetable oil refining. Nevertheless, all feed fats should be stabilised by an antioxidant to preserve unsaturated fatty acids, and when animal tallow is added to feed at a low level, it might be nutritionally beneficial to blend it with a small amount of vegetable oil. This is because the metabolic value of a fat blend is better than a singular addition. Corn is a particularly advantageous fat source because its fatty acids are mostly unsaturated, and it usually constitutes a large portion of existing poultry feed regardless. Minerals
Minerals are the inorganic parts of feed or tissues. For example, calcium and phosphorous are vital in the formation of the skeleton, and sodium, potassium, magnesium and chloride function to stabilise the pH levels throughout the body. In the diet of growing birds calcium is used for bone formation, whereas the bulk of calcium rations in laying hens is usually used to form the eggshell. If a hen does not receive sufficient calcium in its diet for eggshell production, it may use reserves of calcium from its skeleton, but this resource will be rapidly depleted and the hen will stop laying. Backyard producers often use oyster shells or ground limestone to add calcium to their flock’s diet . It is easy to find general mineral supplements for addition to poultry feed, although again, it’s best to research your specific breedin a more in-depth way before working out percentages. Vitamins
Vitamins tend to be classified under two different categories: fat soluble vitamins, A, D, E, and K, and water-soluble vitamins, including the B-complex and vitamin C. Ensuring layers are well supplied with the vitamin A precursors known as carotenoids gives the golden yellow yolk that consumers demand from their eggs. Vitamin C isn’t usually required as an additional dietary supplement for poultry, as it’s already synthesised by them. However, it has been suggested that poultry under stress respond well to its addition in the diet. Dietary supplements for poultry tend to contain high levels of vitamins that are considered well in excess of the minimum requirements, so as long as your flock is receiving adequate supplement to their feed, it is unlikely they will be deficient in any of the main components.

Feeding poultry for optimum growth and production requires that the birds consume appropriate, balanced diets. Nutrient ...
25/02/2023

Feeding poultry for optimum growth and production requires that the birds consume appropriate, balanced diets. Nutrient recommendations are different for each species and the purpose of the birds (meat versus eggs), as well as the stage of growth and production. Cross feeding, such as feeding laying hens a diet that is intended for broiler chickens, is not advised. Therefore, raising mixed flocks should be done with caution.

Table 1, located at the end of this webpage, illustrates guidelines for some of the major nutrient requirements for poultry. The table does not contain information regarding vitamins and most of the minerals, but vitamins and minerals are important for proper growth and development of the birds.

The crude protein recommendations are estimations for amino acid requirements. Crude protein can vary somewhat and still allow the birds to grow. Birds cannot utilize all forms of phosphorus in feeds; therefore, recommendations in the table are based on available phosphorus. Although total phosphorus concentrations appear on feed bags, appropriate adjustments are made when diets and supplements are formulated.

04/08/2022

Vitamin D plays an essential role in calcium homeostasis, bone metabolism, immune function, muscle growth and gene expression. Although animals are capable of synthesizing vitamin D through skin exposure to ultraviolet light; animals housed in confinement or without adequate direct exposure must receive dietary supplements of vitamin D activity. Whether derived from ultraviolet light exposure or the diet, vitamin D (cholecalciferol) is converted in the liver to the main circulating and storage metabolite, 25-hydroxycholecalciferol (25-OH-D3). When active vitamin D is required in the body, it is converted into 1,25-dihydroxycholecalciferol (1,25-(OH)2-D3) in the kidney. A number of other tissues are capable of converting 25-OH-D3 to the active form, including muscle, lymphoid and intestine tissues. As the main circulating metabolite, 25-OH-D3 is the indicator to assess vitamin D status in humans, other mammals and poultry.

Dietary vitamin D3 vs 25-OHD3
In the chicken, absorption of dietary 25-OH-D3 and vitamin D3, takes place in the upper jejunum. The increased intestinal absorption of 25-OH-D3 compared to vitamin D3 is likely associated with the greater polarity of the 25-hydroxylated metabolite, allowing it to be absorbed via non-micelle-dependent transport. This greater efficiency of absorption may contribute to increased circulating 25-OH-D3 status in young birds with limited ability to digest and absorb fat, or birds with impaired liver function compared to those fed vitamin D3.
In young broiler chicks, blood levels of 25-OH-D3 are low following hatch, either due to poor efficiency of fat absorption, limited conversion of vitamin D3 to 25-OH-D3, or a combination of the two. In broiler chicks fed vitamin D3, blood 25-OH-D3 levels decreased from 2 days post-hatch to 6 days, and increased from 10 to 28 days of age, but did not increase between 28 and 41 days of age. When chicks were fed 25-OH-D3 at an equivalent level of vitamin D activity as 25-OH-D3, plasma 25-OH-D3 did not decrease from hatch to 10 days, and the increase from 10 to 28 days paralleled that of the vitamin D3 -fed chicks, but at a higher level. Switching chicks from dietary vitamin D3 to dietary 25-OH-D3 increased, and switching from 25-OH-D3 to vitamin D3 decreased, serum 25-OH-D3. The chicks with the highest level of plasma 25-OH-D3 had the greatest body weights at 41 days of age. Interestingly, the chicks fed 25-OH-D3 from 0 to 41 days, and those supplemented from 1 to 10 days of age had the greatest breast meat yield, suggesting that early supplementation of 25-OH-D3 is crucial.

Providing 25-OH-D3 in the diet eliminates the need for liver conversion of vitamin D, and prevents the reduction in blood 25-OH-D3 during the early part of the chick’s life. In addition, direct supplementation of 25-OH-D3 could reduce some of the negative effects of liver damage that reduces vitamin D metabolism, as occurs with some mycotoxins.

Systemic effects of dietary 25-OHD3 supplementation
At low levels of supplementation relative to typical commercial levels, 25-OH-D3 exhibits a greater potency to prevent tibial dyschondroplasia in broilers. Importantly, at commercially-relevant levels of supplementation the additional advantages of 25-OH-D3 relative to vitamin D3 also includes increased bone mineralization, breast muscle yield, reduced systemic effects of inflammation (i.e. reduced growth rate following an inflammatory challenge) and increased intestinal integrity. In the studies where plasma levels of 25-OH-D3 have been measured, the supplementation of 25-OH-D3 resulting in these physiological effects also results in an increase in plasma levels of 25-OH-D3.

Analysis of on-farm serum samples for 25-OHD3
In published studies in which serum 25-OH-D3 has been measured, dietary supplementation of 25-OH-D3 increases plasma levels accordingly; those increased levels are often associated with increased bone strength, intestinal barrier function, immune function and muscle growth and meat yield. Therefore, on-farm assessment of serum 25-OH-D3 may allow producers to assess whether there is an impaired absorption or metabolism of vitamin D (inefficient absorption, reduced liver function), or whether levels associated with increased physiological function, health and production parameters have been achieved. For such a system to be practical for commercial use, a simple, economical, rapid and accurate test must be available, and clinical serum 25-OH-D3 ranges to achieve various functions need to be established. Currently, blood can be collected on farm using Dried Blood Spot sampling for easy sample collection, storage and transport, followed by liquid chromatography-tandem mass spectrometry analysis. Establishment of clinical ranges upon which to make adjustments to dietary supplementation is underway.
Conclusions
Dietary supplementation of 25-OH-D3 is an effective means of increasing circulating levels of this important vitamin D metabolite in poultry. The ability to assess vitamin D status in commercial poultry in a timely manner that allows corrective action to be taken if necessary can lead to increased performance and bird health.

29/07/2022

Nutrition and feeding
In terms of cost, feed is the most important input for intensive poultry production, and the availability of low-priced, high-quality feeds is critical for the expansion of the poultry industry. For maximum performance and good health, poultry need a steady supply of energy, protein, essential amino acids, minerals, vitamins and, most important, water. Recent advances in poultry nutrition have focused on three main areas:
developing an understanding of nutrient metabolism and nutrient requirements;
determining the availability of nutrients in feed ingredients; and
formulating least-cost diets that bring nutrient requirements and nutrient supply together.
Practical poultry diets are formulated from a mixture of ingredients, including cereal grains, cereal by-products, fats, plant protein sources, vitamin and mineral supplements, crystalline amino acids and feed additives. Increasing costs and decreasing supplies of traditional feedstuffs (due in part to food-feed competition and population growth) are expected to affect the future expansion of poultry production. This highlights the urgent need to make greater use of a wide range of alternative feeds (e.g. insect meals, food waste, agro-industrial byproducts) and to use fewer human-edible components in poultry diets. The use of most alternative feedstuffs is currently negligible, owing to constraints imposed by nutritional, technical and socio-economic factors. In many circumstances, feed resources are either unused and wasted, or used inefficiently.
A major nutritional problem in developing countries is the biological and chemical contamination of poultry feeds, which may have serious consequences on bird performance and the safety of poultry products for humans. Of the potential contaminants, mycotoxins are the most widespread, particularly in hot, humid conditions, and mycotoxin decontamination must be a part of feeding strategies.
Did you know?
Among traditional livestock species, poultry are the most efficient feed converters.
Poultry and swine production account for over 70 percent of the grain used for feeding livestock.
Improving feed efficiency is a key factor in reducing the environmental impact of poultry production.
Poultry feed is largely derived from cereals and legumes that could be used directly for human consumption.

Poultry Nutrient RequirementsPoultry diets must be formulated to provide all of the bird’s nutrient requirements if opti...
15/04/2022

Poultry Nutrient Requirements
Poultry diets must be formulated to provide all of the bird’s nutrient requirements if optimum growth and production is to be achieved. There are six classes of nutrients:
Carbohydrates – the major source of energy for poultry. Most of the carbohydrate in poultry diets is provided by cereal grains.
Fats – provide energy and essential fatty acids that are required for some bodily processes.
Proteins – required for the synthesis of body tissue (particularly muscle), physiological molecules (such as enzymes and hormones), feathers and for egg production. Proteins also provide a small amount of energy.
Vitamins – organic chemicals (chemicals containing carbon) which help control body processes and are required in small amounts for normal health and growth.
Minerals – inorganic chemicals (chemicals not containing carbon) which help control body processes and are required for normal health and growth.
Water.
Factors Affecting The Nutrient Requirements Of Poultry
The nutrient requirements of poultry are affected by a large number of factors, including:
Genetics (the species, breed or strain of bird) – Different species, breeds or strains of birds have different average body sizes, growth rates and production levels and will absorb and utilise nutrients from feed with different levels of efficiency. Therefore, they will require feed with different nutrient compositions. The genetics of commercial poultry is constantly changing, and as a result, so are their nutrient requirements. Consequently, breeders of commercial poultry provide information on the specific nutrient requirements for the birds they sell.
Age – nutrient requirements are related to both body weight and the stage of maturity in bird.
S*x – prior to s*xual maturity, the s*xes have only small differences in their nutrient requirements and males and females can usually be fed the same compromise diet to achieve acceptable growth rates. Differences in nutrient requirements are larger following the onset of s*xual maturity and significantly different diet formulations are then required for each s*x.
Reproductive state – the level of egg production in hens and s*xual activity in males will affect nutrient requirements.
Ambient temperature – poultry have increased energy requirements to maintain normal body temperature in cold ambient temperatures and the opposite in hot ambient temperatures. Food digestion processes produce body heat, the amount of which will vary according to the nutrient composition of the diet. This is called the heat increment of the diet. In cold temperatures it may be desirable to formulate a diet with a higher heat increment and the opposite in hot temperatures.
Housing system – the type of housing system will influence the level of activity of the birds and therefore their energy requirements.
Health status – birds experiencing a disease challenge may benefit from an increase in the intake of some nutrients, most commonly vitamins.
Production aims – the optimal nutrient composition of the diet will vary according to production aims, such as optimising weight gain or carcass composition, egg numbers or egg size. Poultry that are raised for breeding purposes may need to have their energy intake restricted to ensure that they do not become obese.
Feed Intake
Barn layer system
The nutrient intake of poultry is affected by both the nutrient composition of the diet and the amount of feed eaten or feed intake. The optimum nutrient intake for poultry raised commercially will depend on the commercial goals of the poultry enterprise.
The goals in feeding poultry differ between different classes of poultry. In general, for poultry raised to provide meat, such as broilers, the aim is to produce the maximum body weight gain for the minimum cost of feed while controlling the amount of fat on the carcass. For egg laying birds, the aim is to maximise egg production for the minimum cost of feed while controlling the egg size and egg quality. For mature egg laying birds this generally entails maintaining a relatively stable body weight. These different goals, along with differences in digestion and absorption of nutrients, require different levels of nutrients to be provided to different classes of poultry.
The nutrient intake of poultry can be controlled by limiting the amount of feed available to be eaten, by adjusting the nutrient content of the diet to match voluntary feed intake or by manipulating the lighting program through increasing or decreasing the duration of darkness. Allowing poultry to eat as much as they want is called ad libitum feeding.
There are a range of factors that can affect the voluntary feed intake of poultry, these include:
Breed or strain
Age
Nutrient balance of the diet
Ambient temperature
Health and welfare status of the birds
Accessibility of the feed
Flock density
In addition, certain feed ingredients, poor feed quality or feed contamination can have adverse effects on voluntary feed intake due to poor palatability or the presence of toxic factors.
Suppliers of commercial poultry provide information on the optimum nutrient and feed intakes for their birds throughout the production cycle. Feed intake and production performance of flocks should be monitored and adjustments made to the diet composition where required to keep performance on track. In particular, feed intake is readily affected by ambient temperature, with feed intake increasing at lower ambient temperatures and decreasing at higher ambient temperatures. In such cases, the diet may need to be reformulated to adjust nutrient intake to match changes in voluntary feed intake as a result of changes in ambient temperature. As an example, in high ambient temperatures, a more concentrated diet can compensate for the decreased nutrient intake occurring as a result of lower voluntary feed intake. Accessibility to feed is sometimes overlooked as a limiting factor and can be caused through inappropriate or poorly adjusted feeding equipment or inadequate feeding space due to overstocking of facilities. The height of the feeders should be adjusted according to the flock age to provide easy access to the feed for all the birds.
Water Consumption Rates For Chickens
Water is an essential nutrient for life. Water consumption can be limited if the water is too hot or is contaminated with excess minerals. Water and food consumption rates are interdependent, so reduced water intake can also lead to reduced food intake. There are other factors that affect water intake, with temperature being the most obvious one. For example, chickens drink between 30-50% more water when the environmental temperature is above 32oC compared with when it is 21oC. Water intake is also affected by the type of drinkers used. The rule of thumb for water intake is that water intake is usually 1.5 to 2 times feed intake. Tables 1 and 2 provide data on typical water consumption levels for layers and broilers, respectively, at 21oC.

MineralsMinerals are the inorganic parts of feed or tissues.They are required for various functions within the bird.For ...
15/04/2022

Minerals
Minerals are the inorganic parts of feed or tissues.
They are required for various functions within the bird.
For example, calcium and phosphorous are vital in the formation of the skeleton, and sodium, potassium, magnesium and chloride function to stabilise the pH levels throughout the body.
In the diet of growing birds calcium is used for bone formation, whereas the bulk of calcium rations in laying hens is usually used to form the eggshell.
If a hen does not receive sufficient calcium in its diet for eggshell production, it may use reserves of calcium from its skeleton, but this resource will be rapidly depleted and the hen will stop laying.
Backyard producers often use oyster shells or ground limestone to add calcium to their flock’s diet .
It is easy to find general mineral supplements for addition to poultry feed, although again, it’s best to research your specific breedin a more in-depth way before working out percentages.
Vitamins
Vitamins tend to be classified under two different categories: fat soluble vitamins, A, D, E, and K, and water-soluble vitamins, including the B-complex and vitamin C.
Ensuring layers are well supplied with the vitamin A precursors known as carotenoids gives the golden yellow yolk that consumers demand from their eggs.
Vitamin C isn’t usually required as an additional dietary supplement for poultry, as it’s already synthesised by them. However, it has been suggested that poultry under stress respond well to its addition in the diet.
Dietary supplements for poultry tend to contain high levels of vitamins that are considered well in excess of the minimum requirements, so as long as your flock is receiving adequate supplement to their feed, it is unlikely they will be deficient in any of the main components.

FatsGenerally speaking, fat is usually added to the feed for meat-type poultry to increase overall energy concentration,...
15/04/2022

Fats
Generally speaking, fat is usually added to the feed for meat-type poultry to increase overall energy concentration, and thereby improve productivity and feed efficiency.
Feed-grade fat tends to come from different sources, including grease from restaurants, the rendering of animal carcasses, and the refuse from vegetable oil refining.
Nevertheless, all feed fats should be stabilised by an antioxidant to preserve unsaturated fatty acids, and when animal tallow is added to feed at a low level, it might be nutritionally beneficial to blend it with a small amount of vegetable oil. This is because the metabolic value of a fat blend is better than a singular addition.
Corn is a particularly advantageous fat source because its fatty acids are mostly unsaturated, and it usually constitutes a large portion of existing poultry feed regardless.

Water is an essential part of life for all poultry and livestock, but the amount required for adequate health and produc...
15/04/2022

Water is an essential part of life for all poultry and livestock, but the amount required for adequate health and productivity will vary depending on the temperature in which the birds are kept, the bird’s growth rate or level of egg production, and the individual’s ability to reabsorb water through the kidneys.
Any level of water deprivation exceeding twelve hours will have an adverse effect on the growth of poultry and the egg production of layers. Water deprivation exceeding 24 - 36 hours will more often than not result in death.
It is particularly important to consider water availability for chicks. The baby chick is about 79 per cent water, and it cannot drink a lot of water at once so it has to drink often.
It’s therefore vital to provide cool, clean water for your poultry, and ensure that it’s accessible to them at all times.
Carbohydrates
Dietary carbohydrates are important sources of energy for poultry. Corn, wheat, and other cereal grains are the main carbohydrate component of most poultry diets.
The starch in these foodstuffs is readily digested by poultry, but other carbohydrates occur in varying levels of concentration in cereal grains and protein supplements.
Certain types of dietary carbohydrates aren’t easily digested by poultry, so it’s always best to add appropriate enzyme preparations to supplement diets of rye or barley and improve the nutrient absorption in a non-starch based diet.
If such diets aren’t properly supplemented, they’ll contribute very little to meeting the energy requirements of your flock.
Proteins & Amino Acids
The dietary requirements for protein are actually requirements for the amino acids found in dietary protein. Poultry use these amino acids to fulfil a number of functions, including using them to make up the bulk of their structural and protective tissues such as skin, feathers, bones and ligaments.
Amino acids also help form the soft tissues including the organs and muscles, as well as playing an important role in the metabolisation of feed into energy.
Failure to provide adequate protein in your bird’s diet will result in a number of structural and health problems for your flock, as well as reducing yield of meat or eggs.
However, it’s important to remember that poultry protein and amino acid requirements can vary considerably, depending on the rate of growth or level of egg production of the individual bird.
Turkey poults and broiler chickens have high amino acid requirements so they can meet the necessary rapid growth, for instance, and the mature rooster requires fewer amino acids than the laying hen, even though its body size is greater and feed consumption similar.
The percentage requirements of protein and amino acids must also increase if you keep your flock in warmer environments, when metabolisation is far quicker.
In general, protein and amino acid percentages are some of the trickier nutritional balances to get right for poultry production, so it’s best to fully research the breed you’re working with, and tailor your feed to them specifically.

Poultry convert feed into food products quickly, efficiently, and with relatively low environmental impact compared with...
15/04/2022

Poultry convert feed into food products quickly, efficiently, and with relatively low environmental impact compared with other livestock. The high rate of productivity of poultry results in relatively high nutrient needs. Poultry require the presence of at least 38 dietary nutrients in appropriate concentrations and balance. The nutrient requirement figures published in Nutrient Requirements of Poultry (National Research Council, 1994) are the most recent available and should be viewed as minimal nutrient needs for poultry. They are derived from experimentally determined levels after an extensive review of the published data. Criteria used to determine the requirement for a given nutrient include growth, feed efficiency, egg production, prevention of deficiency symptoms, and quality of poultry product. These requirements assume the nutrients are in a highly bioavailable form, and they do not include a margin of safety. Consequently, adjustments should be made based on bioavailability of nutrients in various feedstuffs. A margin of safety should be added based on the length of time the diet will be stored before feeding, changes in rates of feed intake due to environmental temperature or dietary energy content, genetic strain, husbandry conditions (especially the level of sanitation), and the presence of stressors (such as diseases or mycotoxins).
Water:
Water is an essential nutrient. Many factors influence water intake, including environmental temperature, relative humidity, salt and protein levels of the diet, birds’ productivity (rate of growth or egg production), and the individual bird’s ability to resorb water in the kidney. As a result, precise water requirements are highly variable. Water deprivation for ≥12 hr has an adverse effect on growth of young poultry and egg production of layers; water deprivation for ≥36 hr results in a marked increase in mortality of both young and mature poultry. Cool, clean water, uncontaminated by high levels of minerals or other potential toxic substances, must be available at all times.

Energy Requirements and Feed Intake:
The energy requirements of poultry and the energy content of feedstuffs are expressed in kilocalories (1 kcal equals 4.1868 kilojoules). Two different measures of the bioavailable energy in feedstuffs are in use, metabolizable energy (AMEn) and the true metabolizable energy (TMEn). AMEn is the gross energy of the feed minus the gross energy of the excreta after a correction for the nitrogen retained in the body. Calculations of TMEn make an additional correction to account for endogenous losses of energy that are not directly attributable to the feedstuff and are usually a more useful measure. AMEn and TMEn are similar for many ingredients. However, the two values differ substantially for some ingredients such as feather meal, rice, wheat middlings, and corn distiller’s grains with solubles.
Poultry can adjust their feed intake over a considerable range of feed energy levels to meet their daily energy needs. Energy needs and, consequently, feed intake also vary considerably with environmental temperature and amount of physical activity. A bird’s daily need for amino acids, vitamins, and minerals are mostly independent of these factors. The nutrient requirement values in the following tables are based on typical rates of intake of birds in a thermoneutral environment consuming a diet that contains a specific energy content (eg, 3,200 kcal/kg for broilers). If a bird consumes a diet that has a higher energy content, it will decrease its feed intake; consequently, that diet must contain a proportionally higher amount of amino acids, vitamins, and minerals. Thus, nutrient density in the ration should be adjusted to provide appropriate nutrient intake based on requirements and the actual feed intake.
Because of the ability of poultry to adjust their feed intake to accommodate a wide range of diets with differing energy content, the energy values listed in the nutrient requirement tables in this section ( Nutrient Requirements of Growing Pullets a through Linoleic Acid, Mineral, and Vitamin Requirements of Leghorn-type Chickens a) should be regarded as guidelines rather than absolute requirements.
TABLE
Nutrient Requirements of Growing Pullets a icon
TABLE
Nutrient Requirements of Laying Hens at Different Feed Intakes a icon
TABLE
Nutrient Requirements of Broilers a icon
TABLE
Protein and Amino Acid Requirements of Turkeys a icon
TABLE
Nutrient Requirements of Pheasants a icon
TABLE
Nutrient Requirements of Bobwhite Quail a icon
TABLE
Nutrient Requirements of Pekin Ducks a icon
TABLE
Nutrient Requirements of Geese a icon
TABLE
Linoleic Acid, Mineral, and Vitamin Requirements of Leghorn-type Chickens a icon
TABLE
Linoleic Acid, Mineral, and Vitamin Requirements of Turkeys a icon
Appropriate body weight and fat deposition are important factors in rearing pullets for maximal egg production. Most strains of White Leghorn chickens have relatively low body weights and do not tend, under normal feeding, to become obese. Feed is normally provided for ad lib intake to this strain of pullets. For brown-egg strains of chickens, some degree of restriction is often practiced (~90% of ad lib feeding) to prevent precocial onset of lay. Broiler strains tend to become obese if fed ab lib; feed restriction is necessary for broiler pullets and broiler breeders. When feed restriction is practiced, the feed levels of amino acids, vitamins, and minerals must be proportionally increased to prevent deficiencies. Most large commercial breeders provide feed restriction and dietary nutrient guidelines specific for their strains.
Amino Acid Requirements:
Poultry, like all animals, synthesize proteins that contain 20 L-amino acids. Birds are unable to synthesize 9 of these amino acids because of the lack of specific enzymes: arginine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Histidine, glycine, and proline can be synthesized by birds, but the rate is usually insufficient to meet metabolic needs and a dietary source is required. These 12 amino acids are referred to as the essential amino acids. Tyrosine and cysteine can be synthesized from phenylalanine and methionine, respectively, and are referred to as conditionally essential because they must be in the diet if phenylalanine or methionine levels are inadequate. The diet must also supply sufficient amounts of nitrogen to allow the synthesis of nonessential amino acids. Essential amino acids are often added to the diet in purified form (eg, DL-methionine and L-lysine) to minimize the total protein level as well as the cost of the diet. This has the added advantage of minimizing nitrogen excretion.
Vitamins:
Requirements for vitamins A, D, and E are expressed in IU. For chickens, 1 IU of vitamin A activity is equivalent to 0.3 mcg of pure retinol, 0.344 mcg of retinyl acetate, or 0.6 mcg of β-carotene. However, young chicks use β-carotene less efficiently.
One IU of vitamin D is equal to 0.025 mcg of cholecalciferol (vitamin D3). Ergocalciferol (vitamin D2) is used with an efficiency of

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