2. GRADIENT CALORIMETERS
INDIRECT CALORIMETRY
Because the animal body ultimately derives all of its energy from oxidation, the magnitude of energy metabolism can be estimated from the exchange of respiratory gases. Such measurements of heat production are more readily accomplished than are measurements of hear dissipation by direct calorimetry. A variety of techniques are available for measuring the respiratory exchange; all ultimately seek to measure oxygen consumption and CO2 production
per unit of time
1. OPEN CIRCUIT SYSTEM
Devices allow the animal to breath
atmospheric air of determined composition; the
exhaust air from a chamber or expired air from a
mask or cannula, is either collected or else
metered and sampled and then analysed for O2 and CO2 content. Analysis of gases has been accomplished with chemical and volumetric or manometric techniques.
2. CLOSED CIRCUIT SYSTEM
Devices require the animal to rebreathe the same air. CO2 is removed with a suitable absorbed which may be weighed before and after use to determine its rate of production. The use of
oxygen by the animal body decreases the volume of the respriratory gas mixture, and this change in volume is used as a measure of the rate of oxygen consumption. Oxygen used by the animal is then replaced by a metered supply of the pure gas. Both O2 consumption and CO2 production must be corrected for any differences in the
amounts present in the circuit air at the beginning and end of the experiment. Methane is allowed to accumulate in the circuit air, and the amount present is determined at the end of the experiment.
2) ENERGY REQUIREMENT BY FEEDING TRIALS.
In this method an attempt is made to determine the amount of feed in terms of energy which is sufficient to maintain constant weight for an extended period. The value so obtained may be expressed in terms of TDN by inclusion of a digestion trial or may be calculated from the average digestion coefficients. The inclusion of metabolic trial helps to calculate the results in terms of ME. As live weight is the sole criterion of exactness of this method, it should be noted that the weight should remain constant over an extended period for direct application into practice. If for any reason there be gain in weight or loss, necessary correction in intake should accordingly be made for such loss or gain in weight.
Correction figures are shown below:
Pounds gained x 3.53 = TDN required for gain
Pounds lost x 2.73 = TDN equivalent to loss.
Such correction are, however, only approximate since the nature of tissue gained or lost is difficult to assess, eg., if the accumalation of water, which has no feed equivalent, be responsible
for weight gain, then the use of the above correction factor form gain will be meaningless. The object, therefore, is to use these correction factors as minimum as possible for reasons as already
stated above. Another defect of this method is that constancy of weight does not necessarily mean the integrity of body tissue or in other words the weight maintenance does not mean the energy maintenance. This defect, however, can be eliminated by inclusion of slaughter test which, however, adds to the cost experiment and at the same time may not be practicible for all classes of stock.
PROTEIN REQUIREMENTS FOR MAINTENANCE:
Loss of protein continuously occurs through wear and tear of body tissue, for renewal of hairs, nails, feathers, etc., and if the losses are not completed promptly by proper amount of protein either in the form of tissue protein or NPN substance, the animal will rundown in condition and its reproducing ability of productivity will be adversely affected. The losses of body protein in the animal when kept on a protein free ration occurs through urine and faeces in negligible amount, through shedding of hairs, loss of nail, skin etc. The loss which occurs through urine is known as EUN or endogenous urinary nitrogen loss and loss which occurs through faeces is called MFN or Metabolic faecal nitrogen loss.
Urinary nitrogen:
EUN: Here the loss of nitrogen is due to the catabolism incidental to maintenance of the vital tissues of the body, which can be measured at the minimum urinary excretion on a nitrogen
free otherwise adequate (particularly energy adequacy) diet. It is so likely that the quantity of nitrogen thus lost through urine will be dependent on the body size. However, this loss like
energy loss is not directly proportional to body weight but to W0.75 where W is the body weight in kg.
Faecal nitrogen:
Faecal nitrogen consists of two parts; undigested food nitrogen and another part known as MFN which comprises residues originated from the body, eg. residues of bile digestive enzymes, epithelial cells derived from the alimentary tract and undigested bacteria.
MFN: Metabolic faecal nitrogen unlike EUN is not proportional to body weight but rather this value is dependent on the amount of feed ingested. There is also species difference.
The value will be lower with rations low in roughage and higher where roughage alone will be fed.
1. ESTIMATION OF PEOTEIN REQUIREMENT FOR MAINTENANCE FROM ENDOGENOUS URINARY METABOLIC FAECAL NITROGEN (THE FACTORIAL METHOD)
From the above discussion it is evident that the minimum protein requirement of an adult for maintenance must be met by supplying digestible protein required to compensate losses through EUN and MFN plus losses for adult growth in an otherwise adequate diet. In
practice, however, a larger amount is given to afford a margin of safety for variation of requirement from animal to animal arising out of variable wastage in metabolism like loss of nitrogen in hair etc., which being very negligible can also be omitted for all practical purposes or an account may be taken from an estimate of 0.02 W0.73gm nitrogen loss per day in cattle.
2. NITROGEN BALANCE METHOD AS MEASURE OF PROTEIN MAINTENANCE:
The protein requirement as determined by nitrogen balance studies is a satisfactory and reliable measure. In this method, rations containing different levels of protein but adequate in all other respects are fed to the animals and the minimum protein intake capable of enforcing nitrogen equilibrium in well-nourished animal is said to be the maintenance requirement of protein it is important that animals chosen for such determination must be in a
good state of protein nutrition at the start. Minimum intake capable of maintaining nitrogen equilibrium is also very important.
3. FEEDING TRIAL TO DETERMINE MAINTENANCE REQUIREMENT OF PROTEIN:
Rations containing different levels of protein but otherwise adequate in energy and other nutrients are fed to determine the amount of intake capable of maintaining an audit non-producing animal in sufficiently good condition for an extended period without loss of weight or otherwise. Data obtained from slaughter tests (although very difficult to perform in adult cattle) are very helpful to determine the integrity of the nitrogenous tissues.
NUTRIENT REQUIREMENT FOR GROWTH
Growth is defined as increase in weight and size of the body of animal.
Subject to individual variability there is a characteristic rate of growth for each species.
The maximum size and development are fixed by heredity.
Nutrition is key factor to determine whether this maximum weight is achieved.
An optimum nutritional fulfilment is one, which enables an animal to take full advantage of heredity, but maximum size fixed by heredity cannot be exceeded by nutrition.
True growth involves an increase in structured constituents such as bones, muscles and
organs and not by deposition of fat.
The growth is measured by increase in weight as growth/day. The relative measures which record the increase percent can also be used for measuring the growth. Along with this we can have dimensional measures such as increase in height, length and girth. A combination of both are more useful measure of growth.
The rate of growth in an animal is influenced by level of nutrition that the animal gets.
ENERGY REQUIREMENT FOR GROWTH:
Energy requirement for growth can be determined from feeding trials or by factorial method.
From feeding trials ———–
Here the experimental animals in different groups throughout the growth period are fed at different levels of energy intake so as to determine the optimum level most suited to normal growth and development without being unnecessarily high. The energy so found may be expressed in terms of any desired measure of energy. TDN data are most common in such studies by inclusion of digestion trial or by use of average coefficients of digestibility.
By the factorial method
The principle of energy requirement for growth is that the energy of the tissue formed is determined first and the value of basal metabolism increased by an activity factor is added to it.
Thus the requirement of energy is determined at any given period by the expected rate of gain and the average body weight during the period in question.
Data from the slaughter experiment in respect of the fat and protein provides the figure for computing the calories for expected rate of gain while the body weight data provide the basis for arriving at the required energy for basal metabolism.
An activity increment over the energy required for basal metabolism has to be considered.
The data of basal metabolism and activity factor is to cover the maintenance requirement.
Thus the sum of calories of basal metabolism + activity increment factor + growth tissue formed is the estimated energy requirement expressed as net energy which in turn can be converted to ME or DE or TDN by the appropriate conversion factors: 70% DE = NE, 80% DE = ME, 1 Kg TDN = 4.4. M.Cal. DE
PROTEIN REQUIREMENT FOR GROWTH:
Protein plays a vital role in growth as well as in production and reproduction. Young calves require relatively larger proportion of protein for rapid growth. As the animals grow older, the amount of protein requirement is proportionately lower. This is primarily due to growth in the beginning of life being protein in nature followed by growth of tissue of less protein and more fat.
Protein requirement for growth can be determined by factorial method or by nitrogen balance method or by feeding trials.
Factorial method:
The amount of protein required for maintenance is determined first. The value thus obtained is added to the amount of protein required for growth (or say gain in weight) plus losses in metabolism.
The maintenance needs can be determined directly on the basis of endogenous urinary nitrogen or calculated from the basal energy metabolism and later corrected for metabolic faecal nitrogen losses. The amount required for the growth tissue formed can be estimated from the slaughter data as shown below:
Example: A calf weight 70 kg and consumes 2 kg dry matter per day. Its EUN and MFN would be approximately 3.5g and 7.0g respectively. The slaughter tests reveal that the amount of nitrogen deposited in the tissue will be 16 g per day for a calf gaining at the rate of 0.5 kg per day.
Theoretically, the sum of nitrogen excreted as EUN and MFN plus the amount of nitrogen deposited in the body as growth tissue should be supplied in the diet for proper protein nutrition. Thus 3.5 + 7.0 + 16.0 = 26.5 g nitrogen x 6.25 = 166 g protein should be supplied in the diet. The biological values of protein for body building activity in growing animals is taken for only 65% as against 70% in adults in consideration of rumen function which is not fully
developed in a growing animal and that there is greater loss of feed nitrogen in urine. Thus the amount of true digestible protein will be 100/65 x 166 = 255 g. As the feeding standards Table
show the requirement of protein in terms of apparent digestible protein say, DCP, the value of MFN in terms of protein should be deducted from the figure of true digestible protein.
Therefore, 255 – (6.25 x 7) = 211 g or 0.21 kg is the minimum requirement of DCP for calf weighing 70kg and growing @ 0.5 kg. per day.
Nitrogen balance method for estimation of protein for growth:
The protein requirement may also be determined by nitrogen balance studies and is said to be exact measure of actual requirement of protein. In this method, calves are raised on equal amounts of dry matter and on isocaloric rations which contain different levels of protein and the minimum intake of protein which provides maximum retention is taken as the estimate of requirement. However, in such studies, the animals must be making satisfactory rate of growth during the study.
Feeding trials for estimating protein need for growth:
In this method, the rations containing different levels of protein are fed to determine the minimum level required to give the maximum rate of growth. The nature of growth thus obtained may be further tested by slaughter tests for assessing the integrity of the nitrogenous tissues.
NUTRIENT REQUIREMENT FOR REPRODUCTION
The reproductive cycle may be considered to consist of three phases:
The first phase, which is important to both the sexes, comprises the production of ova and spermatozoa.
The second phase of the cycle is pregnancy
and the third phase is lactation.
Nutrient requirements for the first phase in mammals are small compared with the egg production in birds. The quantities of nutrients required in excess of those needed for maintenance are moderate for the second and large for the third phase.
Consequently, nutrient requirements fluctuate considerably during the reproductive cycle, especially when there is an interval between weaning and the next conception.
Effect of nutrition on the initiation and maintenance of reproductive ability Puberty in cattle is markedly influenced by the level of nutrition at which animals have been reared. In general terms, the faster an animal grows, the earlier will it reach sexual maturity. In cattle, puberty occurs at a particular live weight or body size rather than at a fixed age.
In practice, the factor which decides when an animal is to be first used for breeding is body size, and at puberty animals are usually considered to be too small for breeding. Thus although heifers of the larger dairy breeds may be capable of conceiving at 7 months of age, they are not normally mated until they are at least 15 months old. The tendency today is for cattle, sheep and goats of both sexes to be mated when relatively young, which means that in the female the nutrient demands of pregnancy are added to those of growth. Inadequate nutrition during pregnancy is liable to retard foetal growth and to delay the attainment of mature size by the
mother. Incomplete skeletal development is particularly dangerous because it may lead to difficulties of parturition.
Rapid growth and the earlier attainment of a size appropriate to breeding has the economic advantage of reducing the non-productive part of the animal’s life. But there are also some disadvantages of rapid growth in breeding stock, especially if there is excessive fat deposition. Over fat animals do not mate as rapidly as normal animals and during pregnancy may suffer more embryonic mortality.
Nutrient requirement of breeding male animals:
In male the spermatozoa and the secretions associated with it represents only avery small quantity of matter. The average ejaculate of the bull, for example, contains 0.5g of dry matter.
Therefore the nutrient requirements for the production of spermatozoa is small (inappreciable) compared with the requirements for maintenance and for processes such as growth and lactation.
Then adult male animals kept only for semen production would require no more than a maintenance ration appropriate to their species and size, but in practice such animals are given food well in excess of that required for maintenance in female of the same weight. There is no reliable evidence that high planes of nutrition are beneficial for male fertility, though it is
recognized that underfeeding has deleterious effects. Males, however, do have a higher fasting metabolism and therefore a higher energy requirement for maintenance than females and castrates.
Effects of prolonged under or overfeeding of breeding animals:
Animals given a sub-maintenance ration eventually show some reduction in fertility. In males this may be brought about by a decreased output of spermatozoa or by a smaller output of the accessory secretions. In females continued underfeeding leads to a cessation of ovarian function; the farm animals most likely to suffer in this way are heifers kept on inadequate rations during the winter feeding period.
Overfeeding can also bring about impaired reproductive ability Very fat animals frequently are sterile. Over-fat animals may continue to produce ova while failing to show signs of oestrus; it has been suggested that the oestrogens intended to be responsible for the exhibiting heat symptoms are absorbed in the fat depots.
Effects of specific nutrient deficiencies on the production of ova and spermantozoa:
Protein deficiency leads to reproductive failure. The effects of protein deficiency on reproduction appear to be much more severe in growing than in mature animals.
When deficiencies of minerals or vitamins occur in breeding animals, the general signs of deficiency described usually appear before reproductive ability is seriously affected. The effect of Vitamin A deficiency illustrates this point, for although such a deficiency ultimately causes complete failure of reproduction, animals blinded by the deficiency may still be capable either of producing semen or of conceiving. Prolonged deficiency leads eventually in males to degeneration of the testis and in females to keratinisation of the vagina.
Deficiency of Vitamin E has a profound effect on reproduction in rats, but the evidence suggests that deficiency of the vitamin does not play any appreciable role as a cause infertility in cattle and sheep.
Of the mineral elements, both calcium and phosphorus are important in reproduction, although of the two it is phosphorus whose deficiency is more commonly associated with reproductive failure. Phosphorus deficiency arises most commonly in ruminants grazing on herbage deficient in the element and in such circumstances the failure of reproduction occurs in conjunction with the general signs of phosphorus deficiency. In male animals, zinc deficiency may impair the production of spermatozoa.
NUTRIENT REQUIREMENT FOR PREGNANCY
During pregnancy nutrients are required for
1. Foetal growth
2. Uterus growth
3. Placental growth
4. Mammary gland development
5. Pregnancy anabolism
The growth of the foetus is accompanied by the formation of the membranes associated with it, and also by considerable enlargement of the uterus.
In the early stage of pregnancy the amounts of nutrients deposited in the uterus and mammary gland are small, and it is only in the last third of pregnancy (from the sixth month onwards in cattle) that it becomes large.
Mammary gland development takes place throughout pregnancy, but it is only in the later stages that it proceeds rapidly.
In a pregnant animal is given a constant daily allowance of food, its heat production will rise towards the end of gestation. The increase is due mainly to the additional energy required by the foetus for both maintenance and growth. It has been found that
metabolisable energy taken in by the mother in addition to her own maintenance requirement is utilised by the foetus with comparatively low efficiency.
The live weight gains made by pregnant animals are often considerably greater than can be accounted for by the products of conception alone. The mother herself, deposits 3 – 4 times as much protein and 5 times as much calcium as is deposited in the products on conception. This pregnancy anabolism, as it is sometimes called, is obviously necessary in immature animals which are still growing, but it occurs also in older animals. Frequently much of the weight gained during pregnancy is lost in the ensuing lactation.
Consequences of malnutrition in pregnancy
Malnutrition – meaning both inadequate and excessive intakes of nutrients – may affect pregnancy in several ways. The fertilized egg may die at an early stage (i.e. embryo loss) or later in pregnancy the foetus may develop incorrectly and die; it may then be resorbed in uterine, expelled before full – term (abortion) or carried to full term (still birth). Less severe mal nutrition may reduce the birth weight of young and the viability of small offspring may be diminished by their lack of strength or by their inadequate reserves (eg. of fat).
Effect on the young:
o Death of embryo
o Abortion
o Deformities in foetus
o Still birth
o Weak young one
Deficiencies of individual nutrients on pregnancy must be severe to cause the death of fetuses; proteins and vitamin-A are the nutrients most likely to be implicated, although deaths through iodine, calcium, riboflavin and pantothenic acid deficiencies have also been observed congenital deformities of nutritious origin often arise from
o vitamin-A deficiency, which causes eye and bone malformations in particular.
o Iodine deficiency causes goitre in the unborn, and pigs has been observed to result in a complete lack of hair in the young.
o Hairlessness can also be caused by an inadequate supply of riboflavin during pregnancy.
o Copper deficiency in the pregnancy eve leads to the condition of sway back in the lamb.
Young animals should be born with reserves of mineral elements, particularly iron and copper and of vitamin-A, D and E, because the milk, which may be the sole item of diet for a time after birth, is frequently poorly supplied with the nutrients. With regard to iron, it appears that if the mother is herself adequately supplied and is not anaemic, the administration of extra iron will have no influence on the iron reserves of the new born. The copper and fat soluble vitamin reserves of the newborn are more susceptible to improve through the nutrition of the mother.
Effects on the mother:
The high priority of the foetus for nutrients mean that the mother is the more severally affected by directly deficiencies. The foetus has a high requirement for
carbohydrate and by virtue of its priority is able to maintain the sugar connection of its own blood at a level higher than that of the mother. If the glucose supply of the mother is sufficient
her blood glucose may fall considerably, to levels at which nerve tissues (which rely on carbohydrate for energy) are affected. This occurs is sheep in the condition known as pregnancy toxaemia, which is prevalent in ewes in the last month of pregnancy. Affected
animals will become dull and lethargic, lose their appetite and show nervous signs such as trembling and holding the head at an unusual angle, in animals showing these signs the mortality
rate may be as high as 90%. The disease occurs most frequently in ewes with more than one
foetus – where its alternative name of ‘twin lamb disease’ – and is most prevalent in times of food shortage and when the ewes are subjected to stress in the form of inclement weather or transportation. Blood samples from affected animals usually show, in addition to hyperglycaemia, a marked rise in ketone content and an increase in plasma free fatty acids. In the later stages of the disease the animal may suffer metabolic acidosis and renal failure.
NUTRIENT REQUIREMENT FOR THE LACTATING COW
The nutrient requirement of the dairy cow for milk production depends upon the amount of milk being produced and upon its composition.
Energy requirement for lactation
The energy standard for lactation may be derived either by using formulate or by factorial method.
The formula is based on the statistical interrelationships between milk constituents to calculate the gross energy content from the percentage of single constituent since as fat (F) i.e. kcal per kg milk = 304.8 + 114.1 Х F
Assuming fat content of a sample of milk 4.5%, the gross energy content of 1 kg of milk will thus be equivalent to 304.8 + (114.1 Х 4.5) = 818.25 kcal.
Apart from formula, energy liberated per kg of milk may also be derived by two other methods.
• The gross energy determined either by bomb calorimetry
• or by a detailed chemical analysis; the amounts of protein, fat and carbohydrate which are then multiplied by their individual calorific values.
The efficiency of conversion of feed ME into energy content of milk is 70%; so that for providing sufficient energy the calorific value of milk is multiplied by 100÷70 = 1.43.
Protein requirement for lactation
Extensive studies have been made to determine the amount of protein requirement for milk production. Milk is rich in protein.
It is obviously, therefore, that the animal must be provided with sufficient quantity, in addition to maintenance requirement, in order to able to cope with the continuous drain of protein from its body. It has been shown that the lactating animals can efficiency convert food protein into milk protein.
Results of various studies have shown that provision 1.25 times as much protein as secreted in the milk will be sufficient for milk production. This allowance should be given in addition to maintenance requirement. This extra provision of protein for milk production will, therefore, depends on the amount of milk produced.
NUTRIENT REQUIREMENTS FOR WOOL PRODUCTION
The weight of wool produced by sheep varies considerably from one breed to another, and an average value is useful only for guidance. For eg: a Merino weighing 50 kg produces annually of 4 kg fleece. Such a fleece would contain about 3 kg of actual wool fibre, the remaining 1 kg being wool wax, suint, dirt and water. Wool wax is produced by the sabaceous glands, and consists mainly of esters of cholesterol and other alcohols.
The wool fibre consists almost entirely of the protein, wool keratin. To grow in one year, a fleece containing 3 kg protein the sheep would need to deposit a daily average of about 8 g
protein or 1.3 g nitrogen. If this latter figure is compared with the 6.6 g nitrogen which a sheep of 50kg might lose daily as endogenous nitrogen, it seems that in proportion to its requirement for maintenance, the sheep’s nitrogen requirement for wool growth is small.
These figures however do not tell the whole story, since the efficiency with which absorbed amino acids are used for wool synthesis is likely to be much less than that with which they are used for maintenance.
Keratin is characterised by its high content of the sulphur-containing amino acid, cystine, which although not an indispensable amino acid is synthesised from another indispensable amino acid, methionine.
The efficiency with which food protein can be converted into wool is therefore likely to depend on their respective proportions of cystine and methionine. Keratin contains 100 – 200 g/kg of these acids, compared with the 20 – 30 g/kg found in plant protein and in microbial proteins synthesised in the rumen and so the biological value of food protein for wool growth is likely to be not greater than 0.3.
Wool growth reflects the general level of nutrition of the sheep. At sub-maintenance levels, when the sheep is losing weight, its wool continuous to grow, although slowly. As the
plane of nutrition improves and the sheep gains in weight, so wool growth too increases. There appears to be a maximum rate of growth for wool, varying from sheep to sheep within range as great as 5 to 40 g/day. Wool quality is influenced by the nutrition of the sheep. High levels of nutrition increase the diameter of the fibres and it is significant that the finer wools come from the nutritionally less favourable areas of land. Periods of starvation may cause an abrupt reduction in wool growth; this leaves a week point in each fibre and is responsible for the fault in fleeces with the self-
explanatory name of ‘break’. An early sign of copper deficiency in sheep is a loss of ‘crimp’ or waviness in wool; this is accompanied by a general deterioration in quality, the wool losing its elasticity and its affinity for dyes.
NUTRIENT REQUIREMENT FOR WORK
Increased muscular activity results in nutrients being oxidised in the system. All the organic constituents of feed are capable of being oxidised and utilised as energy sources. As long as supply is adequate, the working animal is to draw sources of carbohydrates and fat to meet the energy need. If the supply is inadequate, body fat will be drawn upon first and in the last stage, the protein tissues may be broken down to furnish energy for work as it is now
accepted that the protein is not the normal fuel of muscular work and that no protein catabolism or extra wear and tear of tissues occurs during work. Therefore, theoretically no extra protein is
required to be supplied as long as the ration provides sufficient carbohydrate and fat for extra energy required for work. From the stand point of an efficient ration for work, however, other
considerations appear more important than the question as to whether the protein requirement is actually increased during work or not. During hard work, the need for energy may be almost
doubled and unless the protein content of the ration is simultaneously increased, nutritive ratio becomes wide. As a result efficiency of energy utilization will be poorer since digestibility will be depressed by wide ratio and metabolic heat losses will also be increased. Naturally, therefore an efficient ration in all respects will demand inclusion of additional protein along with energy for maintaining the proper nutritive ratio (as in lactating animals having different fat content mentioned earlier) for increased muscular activity although the additional protein may not be specifically required for muscular activity.
TO BE CONTINUED ON PART-3
