Feed Requirements of Stock

New Zealand Journal of Agriculture, Volume 60, Issue 2, 15 February 1940, Page 81

Feed Requirements of Stock

How To Assess The Nutritive Value Of Foodstuffs

I. J. CUNNINGHAM,

Chief Biochemist, Animal Research Station, Wallaceville.

T' I HE food consumed by animals is I their sole source of raw materials for fulfilment of the many and varied needs of their existence. It is the fuel which can be. burned to produce energy for all movements, such as those of walking about, of collecting and masticating food, of passing food along the digestive tract, or even of flicking a tail or an ear or blinking an eyelid. Food must supply all materials for maintenance of tissues in a healthy condition, and must provide also for the repair and replacement that must regularly go on. This .repair may be clearly evident, as in the case of healing of a surface abrasion, or it may be the unseen, but periodic replacement of aged and wornout body tissues, such as effete blood corpuscles or muscle fibres. Again, food must supply all the materials necessary for growth; thus, it must provide minerals for bone formation, proteins 1 for muscle formation, and so on.

Finally, food .is the only raw material for the production by domestic animals of the large quantities of meat, milk, wool, eggs, etc., which are regularly harvested, and which constitute the wealth of an agricultural community. This great diversity of ~ uses complicates the problem of measuring the nutritive values of different foodstuffs and reducing them to a common basis so that direct comparisons may be

made between one food and another. A direct comparison of any real value can, in fact, be made only between foods of the same class, such as, for example, between ' cereals or between hays, or between protein concentrates such as meat meals and fish meals. Even then, the value of a particular food can be properly assessed only when the other constituents of the ration are known and when the purpose for which the ration is being fed is considered. Maintenance and Production Although food must fulfil so many functions in the animal body, it is possible to divide • food requirements into two main sections, namely, food required for ' maintenance, and food required for production. By maintenance food ' or. MAINTENANCE RATION is understood the minimal amount of foodstuff that must be supplied to keep the .body of a resting

animal in equilibrium so that there is neither loss nor gain in weight, but yet so that normal functioning is not impaired. By PRODUCTION RATION is understood the food that must be provided, over and above that necessary for maintenance, for the special objective for which the animal is kept. This objective may be growth, as in the raising of young stock to maturity; it may be fattening, as in the fatten- - ing off of adult stock for the butcher; . it may be work, as in the use of horses for draught; it may be milk, as in the feeding of dairy cows; , or it may be eggs, as in the feeding of poultry, and so on. Individual foods or combinations of foods may - possess special - virtues in . the productive section of a ration. A product rich in protein, for example, would require a ration providing ample of z this material, whereas a product rich in fat is better achieved from a

ration rich in carbohydrate. This last may not at first sight be readily understandable until it is realised that the animal can convert carbohydrate into fat and store this fat in its body. Mention has been made of the dif- : ferent chemical constituents' of foodstuffs, and it may be helpful to give some general description of these different constituents. Essentially, a desirable ration is . composed of foodstuffs which provide sufficient weight and bulk and due quantities of protein, carbohydrates, fats, vitamins, minerals, and water. The art of the animal husbandman is to compound such a ration and present it to the animal in a palatable form. Importance of Weight Weight is probably one of the most important features of a ration, as this is the measure of the total raw material allowed. Obviously, unless

there is sufficient quantity, partial starvation will result no matter what the quality of the food may be. The first requisite of a , ration must therefore be that it provides sufficient weight of food. It is now generally recognised that animals require daily from between two-fifths to one-half an ounce of dryweight of food per lb. of live weight. This would correspond to about 25 to 351 b. of dry-weight of food daily per 10001 b. live-weight in cattle, and for pigs and sheep about 2 J to 3 Jib. dry-weight of food daily per 1001b-live-weight. It is important to note dry-weight of food, and to remember that a succulent pasture may contain 80 to 85 per cent, of water. Its content of dry food is therefore only 15 to 20 per cent., and a correspondingly greater weight of green food would necessarily be required to supply sufficient dry-weight of food.

Bulk must also be considered along with dry-weight intake. There is a definite limit to the capacity of the stomachs of animals, and when this limit of storage is reached no further ingestion can occur until space is made by digestion of some of the food already there. With very bulky foods, or those which swell markedly after being swallowed, the limit of appetite may be reached before the needs for dry-weight of food have been satisfied. This is important in highproducing animals whose demands for food are high to meet the production requirements. A certain amount of bulk is desirable as an aid to the normal movements of the digestive tract. Need of Proteins Protein is the name applied to a special class of chemical compound which is. a characteristic component of living tissue. Not all proteins are exactly the same. . There is,. in fact, very ..great variation between proteins when their efficiency as foodstuffs is considered. Protein .is required in the diet to make good the loss of tissues, to fulfil requirements for the manufacture of many special secretions employed in the ordinary processes of metabolism within the body, and to supply the necessary units for the production of protein-containing materials, such as milk and eggs. The protein requirement for maintenance of cattle of 10001 b live-weight is approximately two-thirds of a pound of digestible food protein daily, and for other classes of stock an amount bearing approximately the same proportion to the live-weight of the animal. The need for protein increases as the production increases, and in a milking cow it is necessary to supply in addition a little over half a pound of digestible protein for each gallon of milk. . A cow producing four gallons of milk daily would then need nearly 31b. of digestible protein in its food. The significance of the term digestible will be made clear later on. Sources of Energy Carbohydrate is the main source of energy in a ration, and is also largely the source of material from which fat is formed. Adequate carbohydrate will be present if sufficient weight of ration is supplied and if the ration is composed of good materials. Fat is another source of, energy, although this is not its sole function in a ration.' It cannot, for example,

be entirely replaced by carbohydrate without ill-health developing •in stock. The necessary minimal amount is present in most foodstuffs, although. this is not readily apparent. Even pasture grass contains about 1 per cent, of fatty substances. In the fat. moreover, are dissolved some of the important vitamins, notably vitamins A and D. , Vitamins are now familiar to nearly everyone, and the effects of their deficiency are commonly discussed. For farming stock there is little need for concern while the animals are allowed natural foods. Sheep,, cattle, and pigs running freely on good pasture are unlikely to suffer from a deficiency. Trouble might be experienced under certain conditions of restricted quarters and lack of natural variety of foods as. for example, pigs kept in dark pens and fed only skim milk. Such considerations are beyond the scope of this article, and it would be confusing and unnecessary to detail the specific functions of the individual vitamins. It is desirable to stress, however, that vitamins are essential and important foods, most of which must be present in the food in minute quantity. . Minerals Minerals form a small but none the less important fraction of the food. Somewhere in the region of 5 per cent.

of the dry-weight of foods is mineral matter, and a great variety of different minerals is present. Thirteen different mineral' elements are at present known to be essential to animal life, • but the amounts necessary vary widely. Minerals such as lime and phosphorus are required in comparatively large quantity, while, ‘on the other hand, so-called trace minerals, such as cobalt, are required only in minute amount. A high percentage of the skeleton, and a relatively small percentage of the soft tissues is mineral matter, and minerals . participate in many and varied ways in the reactions that go . on in the living body. It is important that a suitable quantity and a full complement of minerals be present in the diet. Of all constituents of the living body, water is present in the greatest proportion. About 60 to 70 per cent, or more of all living animals is water and in the course of a day large volumes are used in the digestion of foods, in transmission of digested food to various points within the body, and in' the elimination of waste. products. No diet can be. complete unless due consideration is given to the water requirements. Such is a very brief and sketchy account of the requirements a ration must fulfil and what needs must be taken into account in assessing the

.'nutritive properties of a feeding stuff. It would seem that chemical analysis might be an extremely useful aid in showing the constituents present in a food and the proportions in which they occur. To a limited extent chemical analysis is useful, and the limitations will be discussed more fully later on. Another even more useful measurement of a food is its energy-content. Measurement of Energy Speaking very broadly, the energycontent of any substance is its power to do work. Everyone is familiar with the conception that petrol contains energy and that, by burning it in an engine, work can be done. Similarly, food also contains energy, for animals are able to burn up food to perform work. It may not be so familiar a fact that the energy contained in. such substances is capable of . very accurate measurement. This, however, is true, for when energy is dissipated it is converted into heat, and accurate measurement of heat is readily accomplished. Energy, then, may be stated in terms of . heat. The unit of measurement of

heat is the calorie, which represents the amount of heat that is required to raise one gram of water through'one degree centigrade. The unit applied to the measurement of energy of a feeding stuff is the therm, which is, one million calories. The therm was adopted for simplicity in recording, as it is much easier to record a few figures than a large number. Two conceptions of a food have now been developed. First, that it is a mixture of chemical substances, and second, that it is a store of energy. We know that chemical transformations occur in the food during its metabolism by an animal, for we feed one substance, for example, grass, and collect an entirely different product, for example, milk. It is possible to follow the transformation and to learn how much milk is yielded from so much food. Equally so is it possible to follow the transformation of energy and with great accuracy and precision. The energy-content of a food is a very convenient measure of its value, because it expresses the total value as one figure instead of in a series of

figures, as is the case in a , chemical analysis. The two methods are both necessary, however, because energy does not differentiate between the different constituents, all of which, as was explained earlier, have their specific functions to fulfil. The energycontent, however, enables a rapid comparison to be made between foods. Limitations of Animal So far we have been dealing. witn the food alone and have not considered the limitations of the animal in dealing with the foodstuff. The nutritive value of any material is governed entirely by the ability of the animal to convert that material to its own needs. After ingestion a foodstuff must be subjected to complicated processes of digestion, absorption, and transformation before it is in a state suitable for use by the body cells. Certain losses occur during these processes, and the nutrient value of a foodstuff to the animal is unavoidably reduced by the exact extent of these losses. The total loss varies for different feeding stuffs and for the same feeding stuff when

metabolised by different species of animals. ■The causes of loss always are three: —■ (1) Part of the food is not digested. (2) During digestion and during metabolism part of the food is trans- ' formed into materials which cannot be utilised by the animal and which are excreted. (3) All foods, to a different degree, stimulate vital processes. This stimulation is not observed by the eye, but nevertheless it results in the dissipation of energy in the same way as does muscular movement. These three points require a little elaboration to make clear just why each constitutes a loss to the animal. Process of Digestion The term “digestibility” is used in animal nutrition in a special sense to mean the percentage of feed which is extracted during its passage through the alimentary tract. It should be realised that the ingestion of a food does not mean that is is then all utilised by the animal. While food is in the alimentary tract it is merely conveniently placed for action by digestive processes. Only the part which is digested and absorbed is utilised by the animal. The undigested’ portion is passed on and eliminated in the faeces, and is a total loss so far as metabolism is concerned. 'The undigested residue can readily be measured by collecting the faeces under suitably controlled conditions. The practice in the determination of digestibility is to feed the same weight of food daily over a long period and to collect the faeces for this period. The difference between the food intake and the faecal outgo is considered as the digested portion. The digestible portion can be expressed as a percentage of the total food intake. It is apparent, also, that by chemical analyses of food and of faeces the percentage digestibility of any of the food constituents, such as proteins, carbohydrates. fats, etc.,* can be measured. , Digestibility It was stated earlier that digestibility varies for different foodstuffs and for the same foodstuff fed to different species of animal. A sheep, for example, can digest 55 per cent, of the total dry-matter of hay, but can digest nearly 90 per cent, of the total drymatter of maize. A fowl can digest only about 30 per cent, of clover, but digests about 80 per cent, of wheat.

A sheep will digest more than 40 per cent, of wheat -chaff, whereas a pig will digest, only approximately 20 per cent, of this same substance. A knowledge of digestibility of a foodstuff is obviously of first importance in assessing its nutritive properties. Attempts have been made to use the percentage digestibility or, as variously expressed, the DIGESTIBLE NUTRIENTS* or the GROSS DIGESTIBLE ENERGY as a measure of nutritive property of foods. Such a procedure neglects the two remaining causes of loss which were indicated earlier. During digestion, especially by cattle, a gas known as methane ,is formed as an inevitable consequence of the processes of fermentation. Methane contains energy which was present in the original food, but which cannot be utilised by the animal. The loss of methane, therefore, is a direct loss from the food. When some foods are fed to cattle and sheep this loss reaches or exceeds 10 per cent, of the total food energy, although it is usually 8 per cent, or less. In horses the loss is usually less than 2 per cent., • and in pigs less than. 1 per cent. In addition to the loss due to gas formation,. further loss occurs due to the fact that there are excreted in the urine certain substances which are incompletely oxidised. The loss by way of the urine is frequently in the region of 5 per cent, of the total food energy. The GROSS DIGESTIBLE ENERGY, therefore, does not represent the nutritive value of a food, because the losses which have just been described must be subtracted before the nutrients available 'to the animal can be computed. Metabolisable Energy The nutrient value of a food after subtraction of the undigested matter and the losses due to gas formation and excretion in the urine is defined as METABOLISABLE ENERGY of- the food. ' This metabolisable energy is the fraction which is finally left for the use of the animal. But not yet all the metabolisable energy is available to the animal for production purposes or for the provision of maintenance requirements, because the third cause of loss has yet to be allowed for. This loss is due to the stimulating effect of the food on the body cells. Energy is used by this stimulation, and must be debited to the food which causes the stimulation.

The energy used up is converted to heat, and is eliminated from the body' in this form. The fraction. of the energy lost by this heat formation is a direct loss to the body for production, although the heat can be employed in maintaining the body temperature. Losses of from 17 per cent, to nearly 40 per cent, of the total energy of the foodstuff may occur as a result of this stimulation. Net Energy What is left to the animal after the three losses have been deducted is the proportion of the food available for maintenance or. for production purposes. It is defined as the NET ENERGY of the food. For ruminants the net energy of roughages may vary from 5 per cent, of the total energy for wheat straw to 24 per cent, for clover hay; for concentrates it may vary from 30 per cent, for wheat bran to 50 per cent, for molasses. The net energy of a food can be measured only by actual experiment on animals. The methods employed are highly technical, and a description of these is beyond the scope of this article. It will suffice to say that in the measurement all the losses which occur during metabolism of a foodstuff and which were described earlier are properly allowed for. The net energy, then, is ' the net value of the foodstuff to the animal. The unit for stating net energy is the therm, and the practice is to give the number of therms of net energy per 1001 b. of foodstuff. Thus, for ruminants the net energy of wheat straw is 7 therms per 1001 b. and of hay is 40 therms per 1001 b. Starch Equivalent ‘ The therm has not yet been adopted universally as a means of expressing net energy, mainly because of the difficulty sometimes experienced in applying an ■ abstract conception like a therm to the rationing of stock. An older measure of net energy will, therefore, often be encountered. This measure is the STARCH EQUIVALENT. The starch equivalent is the number of pounds of starch which yield the same net energy to the animal as do 1001 b. of the food. The reason for selecting starch as the standard of reference was that it was a familiar substance, and therefore easily visualised. The net energy of pure -starch for cattle was found by

, ■experiment to be 107.1 therms per 1001 b. •or 1.071 therms per lb. Starch equivalent for cattle may, therefore, be converted to therms per 1001 b. by multiplying by 1.071, and, conversely, therms . per 1001 b. may be converted to starch equivalent by dividing by 1.071. The two methods of expressing net energy bear a simple relation to each other. In a small table at the end of this article figures are quoted from a publication issued by the Ministry of Agriculture of Great Britain and entitled “Rations for Livestock.” Starch equivalent is used in this publication, and the significance to be attached to the figures for starch equivalent is that described above for net energy. Basis for Relative Costs - It must be repeated that the value for 'net energy is a summation of the nutritive values of all the constituents of the foodstuffs. It does not differentiate between the protein, or the carbohydrate, or the fat, etc. Neither does it indicate in any way the payability of the food to different classes of stock, nor the particular value that some foodstuffs have been shown by experience to possess for the nutrition of certain species of animal. In spite of this, however, net energy values provide the animal husbandman with a logical basis for comparison of relative costs of purchased foodstuffs when these foodstuffs are of the same, class. For instance, all cereal grains have much the same chemical composition; they are rich in carbohydrates and contain similar percentages of protein. In other words, they are carbo- , hydrate concentrates, and are more or less interchangeable in a ration. The question might well arise as to whether it is cheaper to buy barley or oats. For example, say barley is quoted at 4s 6d per bushel (501 b. and oats at 4s per bushel (401 b. The cost per 1001 b. is then 9s for barley and 10s for oats. The net energy is 71.41 b. starch equivalent for barley, and 59.51 b. starch equivalent for oats. The cost per lib. of starch equivalent as barley is 1.51 d, and for lib of starch equivalent as oats is 2.03 d. It would, therefore, be cheaper to buy barley, even though the price paid per bushed is higher. In the great majority of cases food will be purchased because there is not sufficient food on. the farm to meet the

requirements of the stock. In these circumstances the requirement in the purchased food is primarily its energycontent, and the cost of different foods should then be assessed by calculating the cost per lb. of starch equivalent as shown above. In other cases there may be ample energy-containing foods produced on the farm, but a lack of a special food constituent may occur. ' This food constituent may be. for example, protein, or even vitamins A and D. In such circumstances the value of the food to be purchased could not be assessed from its content of net energy, but only by its content of the desired constituent. In the particular . case

where protein was to be purchased the cost per lb. of digestible food protein would be the unit selected for comparison of costs of different foods. In the case of vitamins A and D the unit for comparison would be the content of these vitamins guaranteed by the makers to be contained in the material (cod-liver oil) offered for sale. These are special circumstances, however, and it should be realised that net energy as starch equivalent is the best basis for comparison. For interest, the contents of digestible proteins are given together with the starch equivalents of the foodstuffs shown below.

Feeding of Bron to Dairy Stock

AT one of the meetings of the National Council of Primary Production, Mr. W. E. Hale, Chairman of the New Zealand Dairy Board, asked for information concerning the feeding of bran to dairy stock. The following brief report is based on information supplied by the Livestock Division, Department of Agriculture. Bran, a bulky food, is rich in protein and phosphorus and by virtue of its helpful action on the bowels is frequently given to newly-calved and sick cows. Scottish reports state that bran has a corrective influence on the unduly laxative tendency of young grass. Bran would be fed dry to obtain such a result. Three 'local town-supply dairymen using bran for feeding dairy cows report very favourably on it for maintaining both production and health. Rate of feeding varied from 2 lbs. per

day to 6 lbs. along with other concentrates. Such feeding, however, could only be adopted where the higherpriced market milk is being produced. In the Waikato several reports from farmers indicate that bran is being fed in small amounts for three or four weeks after calving with apparently much less of the general after-calving troubles. Other Waikato reports indicate that small quantities of bran, fed with crushed oats and moose-nuts, bring yearling heifers through the winter in improved condition. The cost of this feeding is about 6s per head. The cost of feeding bran at the rate of 3 lbs. a day for 28 days with bran at £6 per ton would be about 4s 6d per cow. It is doubtful whether the immediate increased production would be very appreciable, but there seems no doubt that there would be an improvement in health and, in consequence, a longer flush of production.

•J»II—IIH— Illi—Illi——•Illi—-Illi——Illi——till—— Illi—llli—llli——ll®}* 1 Net energy values provide the ? 1 animal husbandmen with the 1 ! logical basis for a comparison ! I of the relative costs of pur- | 1 chased foodstuffs when _■ the I | foodstuffs are of the same class. | j This article provides a guide to j t the farmer who intends buying j = supplementary feed for his = 1 stock. 1 f 1 1 •Jon— 1111-^—llli——llli—llli——llli—llli—llli—-Illi—mi—mi—iicy

Feeding Stuff Dry Matter Per Cent. Content of Digestible Crude Protein Per Cent. Content of Net ' Energy as Starch Equivalent. Bran . . . . . . 87.0 10.9 42.6 Pollard . . . . 86.0 11.6 56.5 Barley . . 85.1 7.6 71.4 Wheat . . . 86.6 10.2 71.6 Oats . . .. 86.7 8.0 59.5 Maize . . . . • .. . 87.0 7.9 77.6 Molasses . . . . ■ . . 74.2 1.1 50.6 Meat-meal . . . .’ 89.2 67.2 91.0 Linseed cake 74.5 J Linseed cake . . . . 89.0 89.0 27.8 27.8 74.5 Lucerne hay (before flowering) 84.5 12.1 32 Very good quality hay . . 84.0 9.2 48

NUTRITIVE VALUES OF FEEDING STUFFS (QUOTED FROM “RATIONS FOR LIVESTOCK.”)