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 ^<^'X ;(^**DProceediii8S 23d Annual Meeting 
 
 ^SOCIETY FOR PROMOTION 
 
 AGRICULTURAL SCIENCE 
 
 THe Available Energy 
 
 of TimotHy Hay 
 
 By HENRY PRENTISS ARMSBY, PH. D., 
 
 and 
 
 J. AUGUST FRIES, 
 
 State College, Pennsylvania. 
 
 7/ 
 
 »«■■■« 
 
 ^ »i» 1902 1? ^ 
 

 ll^e ^Available Energy of Timoil^y Hay. 
 
 By Henry Prentiss Armsby, Ph., J)., and J. August Fries, 
 State College, Pennsylvania. 
 
 The increasing interest and importance attaching to 
 the study of the nutrition of domestic animals, as well as 
 of man, from the standpoint of the energy involved in- 
 duced the Pennsylvania Experiment Station to undertake 
 the construction of a respiration-calorimeter upon the 
 pi in devised by Atwater & Rosa, bnt enlarged and modi- 
 fied to admit of experiments upon cattle. In the con- 
 struction and operation of this expensive apparatus, 
 the Station has enjoyed the cooperation of the Bureau 
 of Animal Industry of the U. S. . Department of Ag- 
 riculture, and with the permission of its Chief, Dr. D. 
 E. Salmon, the following preliminary report of some 
 of the results is presented. Acknowlegment should also 
 be made of the skill and faithfulness of our assistants, 
 Messrs. C. W. Norris, J. B. Robb, T. M. Carpenter and N. 
 W. Buckhout, in the execution of the laborious respira- 
 tion and calorimetric experiments and of the coopera- 
 tion of the Chemical Division of the Station, under the 
 direction of Dr. Wm. Frear, in the examination of feeds 
 and excreta. Dr. C. A. Browne, Jr., having had general 
 charge of the reception and care of samples and having 
 executed the determinations of carbon and hydrogen, 
 while the determinations of heats of combustion have 
 been made by Mr. Norris. 
 
 The experiment constitutes a study of the energy-con- 
 tent of timothy hay (this material having been selected 
 because it constitutes a fairly definite farm product) and 
 
THE AVAII,ABI<E ENERGY OF TIMOTHY HAY. 97 
 
 oi the use made of this energy in the organism of cattle. 
 Although few in number, the results seem to us worthy of 
 consideration in the light of suggestions for further inves- 
 tigation, while they possess a certain interest also as being, 
 so far as we are aware, the first direct determininations 
 of the heat production of a farm animal. 
 
 At the outset, one or two definitions seem desirable. 
 The heat of combustion of a material like timothy hay 
 measures the total amount of kinetic energy which we can 
 obtain from it. This quanity is commonly spoken of as the 
 potential energy or "gross energy" of the hay. By no 
 means all of this gross energy is capable ,of being used by 
 the animal organism. A considerable proportion of it re- 
 appears as potential energy in the various excreta, solid, 
 liquid and gaseous, of the animal, and therefore escapes 
 from the body entirely unused for its purposes. By sub- 
 tracting the quantity of potential energy thus rejected by 
 the body from the total amount supplied in the food we 
 obtain the amount which is capable of conversion into 
 the kinetic form in the organism. This portion has been 
 somewhat commonly designated as "available" energy, 
 or more specifically as "gross available" energy to indi- 
 cate that it represents the maximum amount available 
 for any purpose. We shall see presently, however, that 
 there are not wanting indications that a portion of this 
 so-called available energy may in some instances be of no 
 direct use to the organism; that is, that it may neither serve 
 immediately to maintain the vital processes nor add to the 
 store of potential energy in the body, but simply increase 
 the heat production of the animal. We therefore venture 
 to propose the substitution for the term available energy, 
 oftheterm. metuboliziible energy as equivalent to energy of 
 food minus energy of excreta. Although not particularly 
 euphonious, this term has the advantage of expressing 
 the facts of the case, while avoiding any implications re- 
 garding the uses to which this energy is put in the body, 
 as well as the necessity of using the word available in t\Yo 
 senses. 
 
 Rubner's well-known experiments^ with dogs and 
 
 'Zeit. f. Biol., 19, 312. 
 
98 THE AVAILABLE ENERGY OF TIMOTHY HAY. 
 
 other animals showed that, at or below the maintenance 
 requirement, nearly pure nutrients could be substituted 
 4n the metabolism of the animal for the ingredients of 
 body tissue, and that they were valuable for this purpose 
 approximately in proportion to their metabolizable energy 
 as above defined. For example, Rubner found that when 
 neark pure proteids were given to a fasting dog, the 
 amount of proteids destroyed in the body was largely 
 increased, but that a correspondingly smaller amount of 
 fat was oxidized, and further that the proteids replaced 
 fat in inverse proportion to their content of metabolizable 
 energy. Under these conditions there was, of course, no 
 increase in the total amount of heat produced in the body 
 but simply a substitution of one kind of fuel for another. 
 Rubner experimented with fats and carbohydrates as 
 well as with proteids and found the same law to hold, 
 while in a single experiment he also substituted carbo- 
 hydrates for fats in the food in a corresponding ratio. 
 This law of the substitution of nutrients in the manner 
 just indicated is called by Rubner the law of isodynamic 
 replacement and the relative values of the nutrients as 
 deduced from it, isodynamic values. Rubner experiment- 
 ed chiefly with carnivora, but his law has been generally 
 assumed to apply to all animals. Thus Kellner^, in his 
 extensive investigations upon cattle, regards the results 
 which he obtained for the metabolizable energy of various 
 materials as representing their value as part of the 
 maintenance ration and speaks of them as replacement 
 Yalues (Vertretungswerte). 
 
 It has been well established by the investigations of 
 Zuntz and others that there is a not inconsiderable ex- 
 penditure of energy in the digestion and assimilation of 
 the food. This energy must ultimately assume the form 
 of heat in the body, the amount of heat produced depend- 
 ing on the kind and amount of food consumed. This 
 would seem to imply an increase in the heat production 
 with increasing quantities of food, and therefore 
 to contradict the law of isodynamic replacement. 
 Rubner explains this apparent discrepancy by the 
 
 ^ Landw. Vers. Stat., 53, 440. 
 
THE AVAILABLE ENERGY OF TIMOTHY HAY. 99 
 
 hypothesis that the heat into which the energy expended 
 in digestion and assimilation is ultimately converted is 
 substituted in the body for an equivalent amount of heat 
 which would otherwise be produced by oxidation of body 
 substance, so that there is no increase in the total heat 
 production. 
 
 Kubner's conclusions have exerted a profound influence 
 upon the science of nutrition, but at the same time their 
 value lies more largely in the point of view which they 
 opened up than in their exact numerical accuracy. As 
 just stated, isodynamic replacement implies that there is 
 no increase in heat production with an increasing amount 
 of food. As a matter of fact, however, the great majority 
 of Rubner's experiments do show more or less increase in 
 the heat production, the only exceptions being a single ex- 
 periment with fat, and three or four upon cane sugar, 
 some of which Rubner himself considers of doubtful value. 
 From theoretical considerations the writer has been led 
 to question the entire applicability of Rubner's law to 
 herbivorous animals, and especially to ruminants with 
 their large expenditure of energy in digestive work, and 
 the experiment here reported was planned to test the 
 equivalence of the metabolizable energy of hay and that 
 of body tissue. 
 
 Four different amounts of timothy hay, with the ad- 
 dition of a small uniform amount (400 grms.) of linseed 
 meal, were fed to the same steer, weighing about 400 
 Kgs. Each ration was fed for two weeks, during the second 
 of which the visible excreta were collected quantitatively 
 and during which the animal passed 48 hours in the 
 respiration-calorimeter at the uniform temperature of 
 18.2° C. for the determination of gaseous excreta and heat 
 production. 
 
 Passing over the details of the experiments, only the 
 final results as regards energy are presented here, as fol- 
 lows: — 
 
roo 
 
 tHK AVAIXABI.E ENERGY OTF TIMOTHY HAY". 
 
 %7\ 
 
 
 
 
 h- 
 
 
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 t- 
 
 t-(M Oi >0 
 
 -^ 
 
 CM Cq 00 "^1 
 
 'X> 
 
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 a 
 
 tH --< 
 
 'M 
 
 
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 CO 5^ 
 
 lO 
 
 00 L^ 
 
 LC 
 
 1—1 ^ 
 
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 rH --I 
 
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 tH 
 
 tH 
 
 1) 
 
 S '^ 
 pig 
 
 DC 
 
 O 
 
 00 
 
 cq 
 
 t- lO T^ -^1 
 
 CM 
 (M 
 
 cq 
 
 O -^ 
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 1) 
 
 O CO 
 
 so 
 
 O 
 
 CM 
 
 O 
 
 >0 Oi (M "* 
 QO rH :5i 
 
 00 ^ 
 
 o 
 
 CM 
 
 o 
 
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 CM 
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 tH OOOi ^ 
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 0!D 
 
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 -1^ 
 
 CO 
 
 ^ 
 
 
 
 -■vj 
 
 Oi 
 
 
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 <D as 
 
 OJ O) eg 
 
 Comparing the four periods, we note at once that with 
 increasing amounts of feed the heat production also 
 shows a material increase, which should not be the case if 
 isodynamic replacement took place in accordance with 
 Rubner's theory. 
 
 Proceeding now to consider the results quantitatively, 
 we may for simplicity set aside the energy of the excreta 
 and compare directly the amount of metabolizable energy 
 
103 
 
 ve 
 to 
 ce 
 id 
 he 
 he 
 
 in 
 3d 
 
 >y 
 
 ae 
 
 o- 
 le 
 
 IS 
 
 )d 
 
 le 
 t*e 
 a- 
 le 
 il 
 
 '.y 
 
ro 
 
 12000 Cals. l:MOO Cals. 
 rZABLE ENERGY. 
 
 
 , "^ 
 
 « 
 
 
 ly 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 h- -^i 
 
 L ^ 
 
 y^. : 
 
 ^ 
 
 
 
 
 
 
 
 
 
 
 ^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 : :±_:_:::: 
 
 j 
 
"THE AVAII^ABLE ENERGY OF TIMOTHY HAY. 
 
 103 
 
 furnished the animal in each period with the nutritive 
 effect produced. This effect is measured by the extent to 
 which loss of tissue was prevented below the maintenance 
 ration, or by the increased gain above maintenance, and 
 may be compared in the different periods by re^^arding the 
 ration of Period A as a basal ration and subtracting the 
 results for that period from those of the other three. 
 
 Thus, comparing- Periods A and B, we find that in 
 Period B 2864 Cals. of metabolizable energy were added 
 to the basal ration and diminished the loss of tissue by 
 1725 Cals., or in other words that 60.24 percent, of the 
 additional metabolizable energy supplied was used for 
 maintenance, while 39.76 per cent, gave rise to the pro- 
 duction of heat which was in excess of the needs of the 
 animal, so far as maintaining the body temperature was 
 concerned, since the normal temperature was maintained 
 on the lesser supply of metabolizable energy. 
 
 The results of similar comparisons for each of the 
 three periods are contained in the following table, and are 
 also represented graphically by the full Hue in the accom- 
 panying diagram, in wnich the abscissae represent the 
 quantities of metabolizable energy supplied to the animal 
 ^-i^and the ordinates the resulting gain or loss of energy by 
 the body. The points show the results for each period 
 and the line the average result: 
 
 
 Metabolizable 
 Energy. 
 Cals. 
 
 Gain of 
 
 Tissue. 
 
 Cals. 
 
 Gain in 
 
 per cent, of 
 
 Metabolizable 
 
 Period B 
 
 " A 
 
 9482 
 6618 
 
 — 724 
 -2449 
 
 
 Difference 
 
 2864 
 
 1725 
 
 60.24 
 
 Period C 
 " A 
 
 11222 
 6618 
 
 + 616 
 -2449 
 
 
 Difference 
 
 4604 
 
 3065 
 
 66.57 
 
 Period D 
 
 " A 
 
 12255 
 
 6618 
 
 -fl072 
 —2449 
 
 
 Difference 
 
 5637 
 
 3521 
 
 62.46 
 
 Average 
 
 
 
 63.09 
 
:::::::::::::::: t:: :::::: :::::::■ 
 
 
 
 
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 ^^ 
 
 
 
 
 
 
 
 
 
 
 
 
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 :: : ":::_::.:;:".. .:±-:: 
 
 
 
 
 7000 Cnls SOOO Hals 9000 Cala. 10008 Gala. 11000 Cala. 12000 CalH 1:1000 Cala 
 
 metabolizabIjE energy. 
 
iq4 THE AVAItABI^E ENERGY OF TIMOTHY HAY. 
 
 It is obvious that in each case a considerable propor- 
 tion of the inetabolizable energy of the added food was 
 used for other purposes than the maintenance of body 
 tissue, the amount thus expended ranging, in round num- 
 bers, from 33% to 40%, and averaging 37%. In other 
 words, the metabolizable energy of the hay had only 
 about 63% of the nutritive value which the theory of iso- 
 dynamic replacement would ascribe to it. The same fact 
 is, of course, indicated in the graphic representation by 
 the fact that the line representing the average results 
 make an angle of more than 45 degrees with the vertical. 
 
 The facts that the external conditions, particularly 
 temperature and relative humidity, were almost absolute- 
 ly identical in the four periods, and that the smallest 
 amount >:f heat produced was sufficient to prevent any 
 material fall of body temperature for two weeks, seem . to 
 negative the supposition that the additional heat evolved 
 in the later periods was a mere production of heat for its 
 own sake. 
 
 There was no noticeable difference in the several 
 periods as regards the muscular activity of the animal, 
 with the exception of differences in the amount of time 
 passed respectivnly in the standing and lying posture.^ 
 This difference, however, was not inconsiderable, the 
 number of minutes per 24 hours passed in the standing 
 position ranging, during the eight days of the respiration 
 trials, from 675 to 1026. The muscular exertion neces- 
 sary to maintain the standing posture is an important 
 source of heat. In this experiment the amount of heat 
 given off from the animal by radiation and conduction 
 and brought out of the calorimeter in the water current 
 has been computed separately for the periods when the 
 animal was standing or lying, omitting from the compu- 
 tation all periods of less than three hours. The ratio of 
 heat given off while lying to that given off while standing 
 was as follows: 
 
 Period A 1 
 
 Period B 1 
 
 Period C 1 
 
 Period D 1 
 
 1.321 
 1.332 
 1.296 
 1,286 
 
 We have no means of comparing in a similar way the 
 
THE AVAILABIvK ENERGY OF TIMOTHY HAY. 
 
 105 
 
 heat given off by the animal as latent heat of water 
 vapor. If, however, we make the not improbable assump- 
 tion that this amount was proportional to that given 
 off by radiation and conduction, we may computf> the 
 total amount of heat produced respectively in the lying 
 and the standing position per minute or per 24 hours 
 with the following results: 
 
 Period A 
 B 
 
 " C 
 D 
 
 Heat Production (per 24 hours) 
 
 Observed. 
 Cals. 
 
 9067 
 10206 
 10606 
 11183 
 
 Computed 
 Lying. 
 Cals. 
 
 7664 
 8325 
 9086 
 9512 
 
 Computed 
 Standing. 
 Cals. 
 
 10125 
 11088 
 11772 
 12232 
 
 Comparing these computed amounts ot heat, we can 
 also compute the gain or loss of tissue and its relation to 
 the metabolizable energy supplied, in the same manner as 
 before, with the results contained in the following tables 
 and represented by the broken lines in the diagram: 
 
 I 
 
 
 Metabolizable 
 
 Energy. 
 
 Cal. 
 
 Gain, 
 
 Lying. 
 
 Cal. 
 
 Gain in 
 
 per cent, of 
 
 Metabolizable 
 
 Period B 
 A 
 Difference 
 
 Period C 
 " A 
 Difference 
 
 Period D 
 " A 
 Difference 
 Average 
 
 9482 
 6618 
 2864 
 
 11222 
 6618 
 4604 
 
 12255 
 6618 
 5637 
 
 +1157 
 
 -1046 
 
 2203 
 
 +2136 
 
 -1046 
 
 3182 
 
 +2743 
 
 -1046 
 
 3789 
 
 76.92 
 69.12 
 
 67.22 
 71.09 
 
io6 
 
 THE AVAILABLE ENERGY OF TIMOTHY HAY. 
 
 
 Metabolizable 
 
 Energy. 
 
 Cal. 
 
 Grain, 
 
 Standing. 
 
 Cal. 
 
 Gain in 
 
 per cent, of 
 
 Metabolizable 
 
 Period B 
 A 
 
 Difference 
 
 9482 
 6618 
 2864 
 
 —1606 
 
 -3507 
 
 1901 
 
 66.51 
 
 Period C 
 A 
 Difference 
 
 11222 
 6618 
 4604 
 
 - 550 
 
 -8511 
 
 2961 
 
 63.31 
 
 Period D 
 A 
 Difference 
 Average 
 
 12255 
 6618 
 5637 
 
 + 23 
 
 —3511 
 
 3534 
 
 62.70 
 64.51 
 
 According to these figures, if our animal had passed 
 all his time in the recumbent posture he would have 
 gained upon each ration except the first one, while, on the 
 other hand, if he had spent all his time standing, he would 
 have lost upon everj ration except the heaviest. It is 
 scarcely necessary to do more than call attention to 
 the practical importance attaching to this large difference 
 between the metabolism of the animal in the two posi- 
 tions. Its bearing upon the differences observed in the 
 productive power of different animals, as well as 
 upon questions of practical management, is obvious. 
 
 But while the absolute results thus computed differ 
 materially from each other and from those actually ob- 
 served, the elimination in this way of the influence of 
 varying amounts of muscular exertion does not material- 
 ly affect the main result. There is still a large percentage 
 of the metabolizable energy which is not used for con- 
 structive purposes, although the proportion appears to 
 be somewhat less when lying than when standing. The 
 most natural supposition is that this energy is expended 
 in the digestion and assimilation of the food. Apparent- 
 ly the amount of heat thus produced, even on the loweist 
 ration, was so large a? to reach or pass the limit of 
 possible substitution for heat which would otherwise be 
 produced by the oxidation of tissue. As food was added 
 
THE AVAII.ABLE ENERGY OF TIMOTHY HAY. 107 
 
 above this amount, tlie heat resulting from its digestion 
 and assimilation was necessarily in excess of the needs of 
 the organism under the conditions of the experiment and 
 became simply an excretum. 
 
 If this interpretation of the results is correct, it has 
 important theoretical bearings. It becomes evident, in 
 the first place, that the maintenance requirement of cattle 
 is a question of tissue replacement rather than of heat 
 production, and, therefore, that the ^alue of a given feed- 
 ing stuff for maintenance depends upon the availability of 
 its energy. We may, for instance, regard it as at least 
 very probable that the work of digestion and assimilation 
 in the case of a material like corn meal would be material- 
 ly less than in the case of hay; or, in other words, that a 
 larger percentage of its energy would be availab e for the 
 maintenance of tissue. It would follow from this that in 
 case of a ration consisting largely of grain a less amount 
 of material or of metabolizable energy would be required 
 for maintenance than in the case of a ration consisting 
 exclusively of coarse fodder. In other words, the main- 
 tenance raticm is a variable rather than a constant, de- 
 pending upon the kind of food used. It may be noted 
 that this conclusion has already been indicated by the 
 experiments upon the maintenance ration of cattle made 
 at this Station in 1896-7.^ 
 
 Furthermore, if the heat production upon the 
 maintenance ration is in excess of the requirements of 
 the animal, it seems unlikely that small variations in 
 the stable temperature to which the animal is exposed 
 will have the effect upon the maintenance requirement 
 which is ordinarily attributed to them. Still less is this 
 likely to be the case with fattening cattle, where the 
 amount of food and the consequent heat production are 
 largely in excess of the maintenance ration. 
 
 Another important point indicated by our results is 
 that the availability of the metabolizable energy of the 
 food for tissue building is approximately constant within 
 the range of the experiment, or, in other words, that the 
 gain is a linear function of the amount of metabolizable 
 
 ^Bulletin 42, p 159. 
 
Io8 THE AVAILABLE ENERGY OF TIMOTHY HAY. 
 
 energy supplied. While this is not exactly true, the varia- 
 tions from it, as shown by thedingrara, are comparatively 
 small, and probably within the limits of experimental 
 error. We should anticipate that the inuscala.r work of 
 digestion would be approximately proportional to the 
 total diy matter supplied. As the figures show, the pro- 
 portion of the total energy of the hay which was found to 
 be metabolizable diminished as the amount was increased, 
 the difference arising chiefly from differences in digestibil- 
 ity. Since, nevei'lheless, the total expenditure of energy 
 indigestion and assimilation appearstobe approximately 
 proportional to the metabolizable energy, it seems 
 evident that a large share of this expenditure must be for 
 the work of assimilation. Probably a very large factor 
 in it is the loss of energy in the methane fermentation. 
 
 Still another indication afforded by our results is that 
 the availibility of the metabolizable energy w^as stibstant- 
 ially the same above and below the maintenance require- 
 ment. This is indicated both by a comparison of the 
 actual results in Periods C and D, dnd also b'-^ a compari- 
 son of the computed results lying and standing. We 
 might anticipate that the conversion of the as-imilated 
 food into tissue would require a still further expenditure 
 of energy, and that consequently the availability above 
 the maintenance requirement would be less than that 
 below it. Our experiments, as noted, afford no clear 
 indication of such a difference; indeed the availability 
 above the maintenance requirement, as computed from 
 from the results while lying down, is greater than that 
 below the maintenance requirement as computed from the 
 results while standing, In view, however, of the 
 assumptions involved in the computation, too much 
 weight should not be laid upon this point, and we present 
 it rather as a suggestion for future research than as a 
 eonclusion. It may be noted also in this connection that 
 Kellner's experiments in which meadow hay was added to 
 a basal ration showed a utilization of the metabolizable 
 energy for fattening of less than 42 per cent, as compared 
 with the 63 per cent, of availability found in our experi- 
 ments. 
 
 The results of our work, then, may be briefly sum- 
 
THE AVAII,ABr<E ENERGY OF TIMOTHY HAY. IO9 
 
 marized as follows, it being understood that they are 
 presented tentatively, and that they apply primarily to 
 the conditions of this experiment, namely, a rather high 
 stall temperature and comparatively light rations con- 
 sisting chiefly of coarse fodder: 
 
 1. The nutritive value of timothy hay, either for 
 maintenance or production, was not measured by its 
 metabolizable energy, but was in every case materially 
 less. In other words the digestible nutrients of the hay 
 did not replace body tissue in isodynamic proportions. 
 
 2. The work of digestion and assimilation in the case 
 of timothy hay appears to be so great that at, or even 
 below, the maintenance requirement, the heat production 
 of the animal is in excess of the amount needed for the 
 maintenance of body temperature. 
 
 3. The availability of the metabolizable energy of 
 timothy hay, within the range of these experiments, ap- 
 pears to be a linear function of its amount. 
 
 4. The experiments afford no clear indication that 
 the availability is less above than below the maintenance 
 requirement. 
 
» 
 
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