CONCEPT OF ENERGY(C) & PROTEIN(P) –C:P RATIO IN POULTRY RATION

CONCEPT OF ENERGY(C) & PROTEIN(P) –C:P RATIO IN POULTRY RATION

Compiled & Edited by-DR RAJESH KUMAR SINGH, JAMSHEDPUR, 9431309542,rajeshsinghvet@gmail.com

Protein and energy are two important components of food that generates a lot of interest and challenges to nutriationists ,Because of the ability of poultry to adjust their feed intake to accommodate a wide range of diets with differing energy content.

When feeding poultry, we have to look at what are some of the factors that can affect nutrient requirements. Can we feed a single standard diet to all birds? Can you? We cannot. Why? Because our goals are different. Our goals are different, as well as our birds are different.

Genetic makeup of the birds are not the same. For example, broilers versus layer birds. Broiler birds are raised for six weeks, maximum of 42-48 days, they are selected for maximum growth. Layer birds are raised for 70-72 weeks, selected for the egg production. The two birds, totally different body makeup, totally different genetic makeup, one selected for growth and one selected for egg production. The metabolic makeup is controlled by genetic material passed on by parents. We cannot feed a broiler feed to a layer and expect to get the same results. In broiler birds, we look for weight gain, we look for feed efficiency, we look for the carcass composition. In layer birds, we look for egg production, we look for egg size, we look for shell quality, we may also look into feed intake.

When feeding these two classes of poultry energy content of the diet is very, very important. The most important thing about energy that you need to understand is birds eat to meet their energy requirement. Chickens cannot identify between different nutrient components, but it takes feed to meet their energy requirements. Energy is needed to do the work. Work, in this case, for broilers, is muscle accretion or muscle growth. Work in layer birds is egg production, egg size. When we talk about energy, in poultry, we use the word ME or metabolizable energy. For example, the metabolizable energy of 2,600 kilocalories, the feed consumed will be around 102 grams. If you increase the metabolizable energy to 2,800, feed consumption comes down to 98 grams. This simply shows that as the energy content or the energy density of the diet goes up, total feed consumed comes down. This is a very important concept in nutrition. As the volume of the feed comes down, it has to be highly balanced to meet all the nutrient requirements. It has to be nutritionally balanced so that the birds can get all the nutrient requirements. Again, in poultry, as I mentioned, their gut size is very small. Chicken eats anywhere from, laying chicken for example, eat anywhere from 90-110 grams a day, such a small amount. That small amount we have to make sure it meets all the necessary nutrients. And also, unlike in other ruminant animals, gut microbial synthesis is very limited or none. We have to make sure all the minor vitamins are all included in the poultry diet.

Again, environmental temperature stress, heat stress vs. cold pen. Heat stress is more common in the southern part of India During heat stress, birds tend to eat less. When birds tend to eat less, we have to make sure their diet is well balanced. At the same time, in a cold pen, birds tend to eat more. Again, we have to make sure, as the volume of the feed goes up, cost also goes up.

What are some of the factors that affect the nutrient requirements of poultry?

Number one factor is availability of the nutrients. When I say availability, just because the nutrients are in the gut that does not mean it is available to the bird. Unless the nutrients are digested, absorbed and passed across the intestinal villi into the cells, it is of no use to the bird. Sometimes, some of the nutrients are bound tightly, they cannot be liberated by endogenous enzymes. When I say endogenous, means enzymes within the animal body. For example, phosphorus is a typical example. Some of the phosphorus in the cereal grains is bound with phytate, so it is not available to the bird. Availability comes down when nutrients are bound with other components. Processing can also limit the availability of nutrients. Heat, for example, denatures the proteins so that the proteins cannot be digested and absorbed as amino acids. Heat can also destroy some of the B vitamins.

Another important factor that can affect nutrient requirements is nutrient interrelationship. Two terms I would like to introduce here are antagonism and synergism. Presence of one nutrient interfering with the absorption of another nutrient is called antagonism. Antagonism is seen more in amino acids and vitamins. Synergism occurs when the presence of one nutrient enhances the absorption of another nutrient. For example, animal fat when included in the animal diet versus a combination of animal fat and vegetable fat or commonly called as an animal-vegetable blend. The digestibility and absorption of animal-vegetable blend is much higher, about 90%, with tallow alone it could be under 80%. Simply shows that presence of one nutrient or one component in the animal tallow plus combination of animal tallow versus animal-vegetable blend increasing the digestibility. Usually, because of this, animal-vegetable blends are more used in poultry diets.

Age and stage of growth is again another important factor. Digestibility of certain nutrients are very limited in young chicks. Stage of growth, for example, laying chickens. We need to provide, at sexual maturity in laying chickens, we need to increase certain nutrients so that it can get up for proper egg production. All these important factors are needed for an optimum egg production.

Feed contributes about 70% of poultry production cost, out of which about 95% cost is used to meet protein and energy requirements. Among macro nutrients, crude protein (CP) and ME is the key element in formulationof diet for broilers in terms of cost (Kamran et al., 2004). As broilers are fast growing birds so demand a high CP diet to meet amino acids requirement and consequently increasing the overall cost of finished product (Kamran et al., 2004). However, CP level can be lowered up to certain level if optimum amino acid contents needed for growth and muscle development is providedLow CP diet with optimal levels of amino acids is better as birds are unable to utilize excess dietary amino acids efficiently and excessive amino acids are de-aminated and nitrogen is excreted as uric acid (Kamran et al, 2004). In contrary, birds fed on marginal CP level consume more feed in order to acquire the required nutrient level for growth resulting in increased carcass fat and decreased feed efficiency (Thomas et al., 1978) which can be voided if diet contains optimal levels of metabolisable Energy (ME) and amino acids. In addition, increasing environmental concern due to N excretion is also driving the nutritionists to formulate diets with low protein profiles (Moran et al., 1992; Kamran et al., 2004). If the amino acid levels and ME meet the bird’s requirements, excessive can be avoided and maximum protein utilization may be achieved with low protein diets .

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 (AME_n) and the true metabolizable energy (TME_n). AME_n 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 TME_n 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. AME_n and TME_n 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. 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.

Concepts of C:P ratio and its importance

It ensures adequate protein intake at all possible dietary metabolizable energy  levels.

• wider C: P ratio – Higher fat deposition of corcass, hence using in broiler finisher  Stage.
• narrower  C:P ratio:- lower fat and higher protein deposition on the caress hence sing  for  lean meat production.

The recommended C:P ratio for various classes of chicken

The relationship between protein and energy requirements has been discussed by many researchers around the world. It is clear that protein requirements have little meaning unless energy requirements have been considered .Several workers have chosen to expressed these nutrient requirements in terms of protein and energy ratios. The performance of broilers were evaluated  and reported that 23% crude protein (CP) with either 2800 or 3000 kcal/kg metabolizable energy (ME) was adequate as the requirement for broiler starters, while  recommended 22% CP and 2900 kcal/kg ME. On the other hand, a range of 23 – 24% CP and 2800 – 3000kcal/kg ME for starter broiler and 19 – 21% CP with same energy level for the finisher phase was recommended .The physiological and practical implications of the interaction between energy intake and protein metabolism and between protein intake and energy metabolism must then be considered when the dietary requirements for either nutrient is assessed.

CONCEPT OF PROTEIN & NPN SUBSTANCE FEEDING TO DAIRY CATTLE FOR BETTER PRODUCTION & REPRODUCTION

Reference-On Request

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