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Section A

Que 1: Write short notes on the following:

  • Biological value
  • Feeding of breeding boars
  • Essential Amino Acids Index (EAAI)
  • Use of Indicators for digestibility determination
  • Flushing and steaming-up.

Ans 1:

Biological value:

Biological value (BV) is a measure of the proportion of absorbed protein from a food which becomes incorporated into the proteins of the organism’s body. It captures how readily the digested protein can be used in protein synthesis in the cells of the organism.

Proteins are the major source of nitrogen in food. BV assumes protein is the only source of nitrogen and measures the proportion of this nitrogen absorbed by the body which is then excreted. The remainder must have been incorporated into the proteins of the organisms body. A ratio of nitrogen incorporated into the body over nitrogen absorbed gives a measure of protein “usability” – the BV.

Feeding of breeding boars:

A breeding boar requires 2-2.5 kg concentrate per 100 kg weight depending on the age, condition and breeding demand. Feed allowances should be so adjusted that the pig is neither fatty nor run down. Greens should be provided if kept indoors. Year-round pasture is excellent if it could be provided from the stand point of providing both the needed exercise and valuable nutrients.

Nutrition guidelines for feeding breeding boars | WATTAgNet

Essential Amino Acids Index (EAAI):

  • The level of individual essential amino acids in the test materials are assessed and the results are interpreted as follows:
  • Is defined as the geometric mean of the egg ratios of essential amino acids.
  • Advantage : Predicting the effect of supplementation in combination of proteins.
  • Disadvantage:Protein having different amino acid profile may have same or a very similar index.

Use of Indicators for digestibility determination:

  1. In some circumstances the lack of suitable equipment of the particular nature of the trial may make it impracticable to measure directly either food intake or faeces output, or both. For instance, when animals are fed as a group it is impossible to measure the intake of each individual.
  2. Digestibility can still be measured, however, if the food contains some substance which is known to be completely indigestible.
  3. If the concentrations of this indicator substance in the food and in small samples of the faeces of each animal are then determined, the ratio between these concentrations gives an estimate of digestibility.
  4. For example, if the concentrations of the indicator increased from 1% dry matter to 2% in the faeces, this would mean that 50% of the dry matter had been digested and absorbed.
  5. The indicator may be a natural constituent of the food or be a chemical mixed into it. It is difficult to mix chemicals with foods like hay, but an indigestible constituent such as lignin may be used.
  6. Other indicators in use today are fractions of the food known as indigestible acid-detergent fibre and acid insoluble ash (mainly silica) and also some naturally occurring n-alkanes of long chain length (C25– C35).
  7. The indicator most commonly added to foods is chromium in the form of chromic oxide, Cr2O3.Chromic oxide is very insoluble and hence indigestible; moreover, chromium is unlikely to be present as a major natural constituent of foods.
  8. For non-ruminants, titanium dioxide may be added to foods as an indicator.
  9. Chromic oxide may be used as an indicator in a different way, to estimate faeces output rather than digestibility.
  10. In this application the marker is given for 10 -15 days in fixed amounts ( eg. administered in a gelatine capsule) and once its excretion is assumed to have stabilised its concentration in faeces samples is determined. Faeces dry matter output (kg/day) is calculated as follows:
  11. Marker dose (g per day)/ Marker concentration in faeces DM (g/kg). For example, if an animal was given 10 g of chromic oxide per day and the concentration of the marker was found to be 4 g/kg faeces DM, faeces output would be calculated as 10/4 =2.5 kg DM/day. If food intake was known, dry matter digestibility could be calculated in the usual way.

Flushing and steaming-up:

Is the additional feed given to gilts or sows before breeding or mating to increase the chances of conception 2 wks before the breeding or mating day.

Flushing is a management term for providing high quality feeds, usually grains prior to the start of the breeding to increase reproductive performance. Flushing has been used in the swine industry to increase the number of ovulations in sows.

ls the additional feed rich in protein offered to sows or gilts 2 wks before farrowing or giving birth in attempt to promote maximum milk production and increase piglets birth weight.

Steaming up is the feeding of a pregnant animals such as a dairy cow with a high plane of nutrition 6 to 8 weeks before calving/ giving birth. The feed should be of a good quality concentrate plus some good quality forage.

Que 2: Write the chemical nature, physiological functions and deficiency symptoms of vitamin A in animals.

Ans 2:

Vitamin A and its metabolites play diverse roles in physiology, ranging from incorporation into vision pigments to controlling transcription of a host of important genes. Health depends on maintaining vitamin A levels within a normal range, as either too little or too much of this vitamin lead to serious disease.


Vitamin A or retinol has a structure depicted to the right. Retinol is the immediate precursor to two important active metabolites: retinal, which plays a critical role in vision, and retinoic acid, which serves as an intracellular messenger that affects transcription of a number of genes. Vitamin A does not occur in plants, but many plants contain carotenoids such as beta-carotene that can be converted to vitamin A within the intestine and other tissues.

Physiologic Effects of Vitamin A

Vitamin A and its metabolites retinal and retinoic acid appear to serve a number of critical roles in physiology, as evidenced by the myriad of disorders that accompany deficiency or excess states. In many cases, precise mechanisms are poorly understood. Some of the well-characterized effects of vitamin A include:

  • Vision: Retinal is a necessary structural component of rhodopsin or visual purple, the light sensitive pigment within rod and cone cells of the retina. If inadequate quantities of vitamin A are present, vision is impaired.
  • Resistance to infectious disease: In almost every infectious disease studied, vitamin A deficiency has been shown to increase the frequency and severity of disease. Several large trials with malnourished children have demonstrated dramatic reductions in mortality from diseases such as measles by the simple and inexpensive procedure of providing vitamin A supplementation. This “anti-infective” effect is undoubtedly complex, but is due, in part, to the necessity for vitamin A in normal immune responses. Additionally, many infections are associated with inflammatory reactions that lead to reduced synthesis of retinol-binding protein and thus, reduced circulating levels of retinol.
  • Epithelial cell “integrity”: Many epithelial cells appear to require vitamin A for proper differentiation and maintenance. Lack of vitamin A leads to dysfunction of many epithelia – the skin becomes keratinized and scaly, and mucus secretion is suppressed. It seems likely that many of these effects are due to impaired transcriptional regulation due to deficits in retinoic acid signalling.
  • Bone remodeling: Normal functioning of osteoblasts and osteoclasts is dependent upon vitamin A.
  • Reproduction: Normal levels of vitamin A are required for sperm production, reflecting a requirement for vitamin A by spermatogenic epithelial (Sertoli) cells. Similarly, normal reproductive cycles in females require adequate availability of vitamin A.

Sources of Vitamin A

Vitamin A is present in many animal tissues, and is readily absorbed from such dietary sources in the terminal small intestine. Liver is clearly the richest dietary source of vitamin A.

Plants do not contain vitamin A, but many dark-green or dark-yellow plants (including the famous carrot) contain carotenoids such as beta-carotene that serve as provitamins because they are converted within the intestinal mucosa to retinol during absorption.

Vitamin A is stored in the liver, predominantly within stellate cells, as retinyl esters and, when needed, exported into blood, where it is carried by retinol binding protein for delivery to other tissues.

Vitamin A Deficiency and Excess States

Both too much and too little vitamin A are well known causes of disease in man and animals.

Vitamin A deficiency usually results from malnutrition, but can also be due to abnormalities in intestinal absorption of retinol or carotenoids. Deficiency is prevalent in humans, especially children, in certain underdeveloped countries. In herbivores such as cattle, vitamin A deficiency is usually due to lack of green feed, such as in animals coming off of dry summer pastures or those fed poor quality hay. Because the liver stores rather large amounts of retinol, deficiency states typically take several months to develop. Some of the more serious manifestations of vitamin A deficiency include:

  • Blindness due to inability to synthesize adequate quantities of rhodopsin. Moderate deficiency leads to deficits in vision under conditions of low light (“night blindness”), while severe deficiency can result in severe dryness and opacity of the cornea (xeropthalmia).
  • Increased risk of mortality from infectious disease has been best studied in malnourished children, but also is seen in animals. In such cases, supplementation with vitamin A has been shown to substantially reduce mortality from diseases such as measles and gastrointestinal infections.
  • Abnormal function of many epithelial cells, manifest by such diverse conditions as dry, scaly skin, inadequate secretion from mucosal surfaces, infertility, decreased synthesis of thyroid hormones and elevated cerebrospinal fluid pressure due to inadequate absorption in meninges.
  • Abnormal bone growth in vitamin A-deficient animals can result in malformations and, when the skull is affected, disorders of the central nervous system and optic nerve.

Vitamin A excess states, while not as common as deficiency, also lead to disease. Vitamin A and most retinoids are highly toxic when taken in large amounts, and the most common cause of this disorder in both man and animals is excessive supplementation. In contrast, excessive intake of carotinoids are not reported to cause disease – you cannot use the excuse of potential vitamin A toxicity to avoid eating carrots or green vegetables!

Both hypovitaminosis A and hypervitaminosis A are known to cause congenital defects in animals and likely to have deleterious effects in humans.

Que 3: Give the schematic representation of partitioning of feed energy in the body of lactating cows.

Partitioning of feed energy
Schematic partition of energy in the animal (NRC, 1981 ...

Energy gained from food is partitioned for different uses. Gross energy, digestible energy, metabolisable energy and the net energy are all used for different functions.


• Gross energy is the total heat of combustion of a material as determined with a bomb calorimeter-ordinarily expressed as kilocalories per kilogram of feed or mega joule/kg dry matter.

• Roughages have gross energy values comparable concentrates, but the two differ greatly in digestible, metabolizableand net energy values.

• Fat, because of their greater proportion of carbon and hydrogen, yield 2.25 times more gross energy per kg than carbohydrates and protein

• Energy supplied by the food in excess of that needed for maintenance is used for the various forms of production.

• A young growing animal will store energy principally in the protein of its new tissues, a fattening animal stores energy in fat, and a lactating animal will transfer food energy into milk.


• This is that portion of the gross energy of a feed which does not appear in the faeces. It include metabolizable energy as well as the energy of the urine and methane.

• The undigested food nutrient present in faeces can burnt in bomb calorimeter produced enough heat. This means that considerable quantity of heat of the digested food is eliminated in the faeces.


• It is that portion of gross energy not appearing in the faeces, urine and gases of fermentation (Principally methane).

• It is digestible energy minus energy of the urine and methane. It is comparable energy of TDN minus the energy of the fermentation gases.

• Metabolizable energy = Energy in the food – (Energy lost in faeces + energy lost in combustible gases + energy lost in urine).

• Normally about 8 per cent of the gross energy intake is lost through the methane production.

• Metabolizable energy can also be calculated from the digestible energy by multiplying with 0.82 which means roughly about 18 per cent of the energy is lost through urine and methane.

• ME = DE * 0.82

Factors Affecting the Metabolizable Energy Values of Foods

• Species of animals

• Composition of feed

• Processing of food

• Level of feeding


• This is that portion of metabolizable energy which may be used as needed by the animals for work, growth, fattening, fetal development, milk production, and/or heat production.

• It differs from metabolizable energy in that net energy does not include the heat of fermentation and nutrient metabolism or the heat increment.

• Net energy is not used for heat production unless however and above that from other sources is required to keep the animal warm.

• It is important to understand that of the heat lost by the animal only a part, the heat increment of the food, is truly waste energy which can be regarded as a direct tax on the food energy.

Que 4: Differentiate between the following:

  • Basal metabolism and Fasting metabolism.
  • Curled-toe-paralysis and polyneuritis.
  • Grass staggers and Blind Staggers.
  • Net protein utilization and net protein value.

Ans 4:

Basal metabolism and Fasting metabolism:

Basal metabolism

  • The term Basal Metabolism or Basal Metabolic rate (BMR) refer to the heat production of an animal resting in a thermally neutral environment (temperature range in which environmental temperature does not stimulate normal metabolism, approximately 25oC) and in a post-absorptive state (that is after the digestion and absorption of the last food ingested has stopped).
  • During this rest period although the animal will be doing no external or digestive work nor will it have any emotional excitement, still it will carry on a variety of internal processes, which are essential to life.
  • These processes include respiration, circulation, maintenance of muscular tonus, production of internal secretions, etc.
  • In the absence of feed, the nutrients required to support these activities must come from the breakdown of body tissues itself.

Fasting metabolism

  • Fasting metabolism refers to the heat production at specified times after the last feeding. In ruminats the value determined is referred as fasting metabolism rather than as basal metabolism.This should not be confused with the term fasting catabolism,which also includes energy voided in the urine of fasting animals.
  • To avoid some of the problems associated with a four day fast in ruminants, some workers have determined heat production over a specific time period after the last feeding and have referred this value as standard metabolism.
  • The term resting metabolism has been used to denote the heat eliminated when an animal is lying at rest, though not strictly in a thermoneutral environment or in the postabsorptive state.

Curled-toe-paralysis and polyneuritis:

Curly toe paralysis is caused by riboflavin (vitamin B2) deficiency in young chicks. The condition nervous system related due to peripheral nerve damage, related to degeneration of the sciatic nerves (the nerves along the back of the chick’s leg to the foot). The damage can be reversed if treated quickly, however in longstanding cases where treatment is delayed the condition will become permanent.

Chicks that are fed a riboflavin-deficient diet will begin to show signs at about 8 to 14 days following hatch. They will slowly develop progressive symmetrical paresis starting with initial signs of reduced growth rate (despite a good appetite), weakness and sometimes diarrhea.

Polyneuritis, or “star gazing” disease: This is caused by a thiamine deficiency.

General signs –
Lack of appetite, lethargy, head shaking or tremors, eventually convulsions

Cardinal or diagnostic signs –
“Star gazing,” meaning the birds assume a posture of looking at the sky. This is due to paralysis of the neck muscles. After star gazing develops, the birds may soon be unable to stand at all, but will lay with their heads still in the star gazing posture.

Grass staggers and Blind Staggers:

Grass staggers or Magnesium and grass tetany

Grass staggers is a metabolic disease caused by magnesium deficiency. It is also called hypomagnesaemia

Mg plays an important role in nerve and muscle function and functioning of the immune system. Although cows have significant stores of Mg in the bones, little of these stores are available to maintain levels in the blood. Therefore, the cow is dependent on the Mg supplied in the diet and from supplements to maintain blood levels.  Blood and urine tests can confirm Mg deficiency. Consult your vet. 

The initial symptoms of Mg deficiency are nervousness, ears pricked, nostrils flaring, eyes alert and head held high. Movement is stiff, like a cow is walking on stilts, and she will stagger when forced to move quickly. Cows suffer loss of appetite and reduced milk production.  Death results from a “tetany”, where the muscles contract uncontrollably, including the heart.

Blind staggers

There are two different types of chronic poisoning dependent on the chemical form of the ingested selenium. “Blind staggers” occurs when animals ingest water-soluble selenium compounds naturally found in accumulator plants. Toxicity from eating plants or grain with protein-bound, insoluble selenium is called “alkali disease.”

Blind staggers normally occurs in cattle and sheep feeding on seleniferous plants. Symptoms manifest in three stages:

  1. wandering, stumbling over objects, anorexia, visual impairment
  2. increase in the severity of the first stage, front legs seem unable to support animal
  3. blindness, paralysis of tongue and swallowing mechanism, rapid and labored respiration, salivation, and low temperature

The animal will die within a few hours from the onset of the third stage. The action of the toxicity has been documented to delay between stages. The first and second stages may be unnoticeable, and then weeks later, the animal may show signs of the third stage and die. In sheep, it is more difficult to diagnose because the stages are not as well defined as in cattle. Toxic amounts of Se can also cause birth defects in offspring from dams fed such levels.

Alkali disease is more chronic than blind staggers, often taking years to manifest itself. It is caused by feeding on plants and grain that have protein-bound, insoluble selenium. This disease can affect all livestock, but it is detected mostly in cattle and horses.

General symptoms include: lack of vitality, anemia, emaciation, stiffness of joints, lameness, rough coat, loss of long hair, and hoof sloughing and deformities. Hoof deformities are a classic sign of selenium and can cause lameness and severe pain for the animal; food and water must be provided to the animal, for it may be hesitant to walk.

Net protein utilization and net protein value.

The net protein utilization, or NPU, is the ratio of amino acid mass converted to proteins to the mass of amino acids supplied. This figure is somewhat affected by the salvage of essential amino acids within the body, but is profoundly affected by the level of limiting amino acids within a foodstuff.

As a value, NPU can range from 0 to 1 (or 100), with a value of 1 (or 100) indicating 100% utilization of dietary nitrogen as protein and a value of 0 an indication that none of the nitrogen supplied was converted to protein.

Certain foodstuffs, such as eggs or milk, rate as 1 on an NPU chart.

Net protein value or Biological Value

It has been defined as the “percentage of absorbed nitrogen retained in the body” and a complete evaluation of the dietary protein includes measurement of the Biological Value and the Digestibility. These values are obtained by measuring the fecal and urinary nitrogen when the test protein is fed and correcting for the amounts excreted when a nitrogen-free diet is fed. True digestibility is defined as the percentage of food nitrogen absorbed from the gut.

Net protein utilization is similar to the biological value except that it involves a direct measure of retention of absorbed nitrogen. Net protein utilization and biological value both measure the same parameter of nitrogen retention, however, the difference lies in that the biological value is calculated from nitrogen absorbed whereas net protein utilization is from nitrogen ingested.