011de1 .. ~tepoo1t Journal of rete1i11ary Science rind cl11illlol L11rlitslry, i·ofll?ne 131 .V11mber 1, hil.1;, 1.939.
l'ri11t0d in thlo' l'nion ol' Soulli Al'rit:a IJy till' GovPr11n1(•11t Printer, Pretoria.
The Endogenous Nitrogen Metabolism of Young Sheep w ith Reference to the Estim a tion of
th e Maintena n ce Requirem e nt of Sheep.
By
D. B. S'JIU'l'S, and .J. i:l. C. MARAJS, Section of Xutrition, 01tderstepoort.
'l'iiat tlw mai11len:mce n·quin·ment of 11itl'oge11 of an anirnnl L"nn be measured liy the total ni1 rogen t>:>;<·J'e1ion in the urine after i.lll' e1doge1wus ll·Ycl i,; :1tl;1i11ed, is no11· ge11L01all.1· ;u·ct·ptefl. 011 tlii,.; h;1,;is, tliP eudogenou:> 11i.trog·l'11 exci-dio11 of rnatu1·(· sheep 11·as lltP:isurPd (Smuts :ind .Jlarnis HJ:38) and the rl'sulls 111lnprel1•<l in
rp\;\tion lo lite m;1i11!e11;111ce req11ire111enl of prnlein. H(i1n·Yer, it is e1·i<le11! from thP literature that the i·elationship hl·I 11·ee11 the ondop:t•1111us nitrog·pn and hn,.;:il llll'laholi:>m e,;l'ablishecl lff Srnub (UH.)) for 111alurP anirnal~ may ulw hold gon<l fol' ym111g 'aniu1<tl:;.
Du Hoi, (l!J\fi) 11·illt liu111<1n heings, Dt·ip:hlo11 (1~J:l4) 11ith pigs, .JlitC'hPll (llJ:!(i) \1·ilh rnb, anc1 Hilzma11 ;md Derll'llil't (l~J:30) 11·ith :sht•t•p. li:i1·e .-d1mn1 lhal the basal 11tetaholism of i1111l!alun· ;111illl:il,;
i~ i111·;ll'i;ihl.1· liigl11-'r than tha1 of m;i111re animals of Liu' sarne :species. (Jn lht· olhPr hand, frl>rn daia of TPrrniue (lG:n ) 11·itli rat,;, it ;1ppear,.;
lliat 1\it· l'ndog·eno11,; nitrogen lllt>laliolisn1 rp;1ds in l'he ,;;rnie. 11·u.\·
a11d fo!I011·,; the sanw µ-erwrnl trend as tl1e b:1,;a] rnebiholi,;rn.
Conseq11<·11tly it folio\\·;; that the t•1Hlop;enou:-: nitrogPn lllt>Liholi,;lll.
;111,\ thl'rdon· the maintP11anl·t· J'el[UiremPnt of proh·in for i.mrn;1ture
~ilPl-'P 11·i\I Lt> gTenler tli:1n tli:1t aln·;1<l,\· e~labli~hc·d li.\· u~ for rn;ilure .~lit•t•p.
111 !hi,; stucll· ;Ill pffort \1·as rnacle lo mc·a:sure tl1t' l'ndug·P!1ou~
nllrogPn melahol°is111 of young· sh<'op with a vie1Y io e,;1ahli~liiug thPir 111;iintPn<11we rt•quirement.
XinP ,\'Ouup: :Jlnino 11·etlwrs npproxirnately four months of ;1g·e, nn<l \Ycighing frorn 17 lo 28 Kgms., ll'ere utilizerl. These shPep wpn· rut for :j 1n•Pks 011 ;1 :slan<lanl rntion cn11tnini11g J.+ per c·c·1it.
lucerue prntPin. After lhe termination of this prPlilllinrtr,\' perinfl, tlwv ,1.NP rPrnoYPd t·o thf' nwtabolisrn ragea and vut on rt nitrng·eu- low rntion, the compo,;ilion of "·hi('h is the snme ::is preYiou~J.,·
·desnihrd b,v 8rnu1,; anrl ~i:nais (1 ~):18). It 11·as, ho1YPYl'r. found
ENDOGENOUS NITROGEN METABOLISM OF YOUJ'\G SHEEr.
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~ c ::,, ~ Cl
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necessary to include 10 per cent. of wheat straw and to reduce the agar to 15 per cent. in order to ensure a high enough food intake to cover the energy requirements. By this methocl it was possible to stu<ly the complete curve of nitrogen excretion.
ExrERIMEJ'\TAL HES'GLTS.
Curves representing the total nitrogen excretion in the urine of the 9 sheep or:. a nitrogen lovv ration are given in graphs 1 ancl 2.
In comparison with matnre shePp kept under the same standard
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· Aep Jad N ·sw>!)
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D. Jl. SMUTS AJS"D J. S. C. )[AHAlS.
conditions of feeding, namely 14 per cent. lucerne protein, there exists a disti11ct difference in the nitrogen elimination, when placec1
Ull a nitrogen low ration. vVith mature sheep, it n-as noticed that after the initial sharp drop in nitrogen excretiou on the first .. fay, there was a further prominent deerease up to the eighth clay.
Thereafter the decrease was more gradual, mid such that the
Aep J<td N SW.JO
<O
E:\JJOGENOt;S NlTlWGicl'i METAilOLISJ\1 CH' YOUl'iG SHEEP.
endogenous level was only reaehed round about the 14th day. vVith young sheep, as will be seen from the grnphs, the position is very different. There is in each case the eharacteristic sharp drop in the nitrogen excretion the first clay, with a very gradual reduction up to the 5th or Gth day, when in nearly eve1y case the endogenous level is attained. From there 011wards the curve representing the daily uriuary nitrogen almost assumes a straight line representing a very conslallt output. 'rhus there appears to be a rlistinct
<lifferenee in the amount of nitrogen stored by the actively growing sheep and the non-growing or mature sheep. Such a <lifference may be expected on the basis that the growing animal needs in addition to its maintenance requirement, a substantial portion of the available nitrogen for tissue synthesis, leaving thus a mur h smaller fraction of the total nibogen intake for reservation. 'rhis statement is endorsed by the fad that matme sheep on an 8 per cent. lueerne protein rntion for 3 months, attain their endogenous level after G days 011 a niirog1,•n low ratiou, in cmnparison with 14 days after a 14 per cent. luc;erne protein ration. This indicates, that at the higher level of protein feeding almost twice as much nitrogen was available for storage as at the lower level.
The ell'dogeuous nitrogen per unit weight in accordance with the general view, is higher for young sheep than for mature ones. The average figure recorded by us for mature sheep is · 041 grms. per Ko' weio·ht while for immature sheep the averao·e fio·ure obtaiued in'"' .tl1is ~tu~ly is · 051 gnns. per Kg. Expressed on ° the basis of utifomble protein these figures per 100 lb. 1reight become 11 · G gnns. and 14 ·4 grms. protein.
111 trying· to find a general method for estimating the protein n·qnirernents for rnaintPnance, it was stated in an earlier paper I S111uts and Marais (1D38)
l
that the formula adopted by Smuts (1935) for the predic;tion of the protein requirements of mature animals of rlifferent species could be applied to sheep. However, after assembling all the data thus far obtained on the ell'Jogenous nitrogen excretion of sheep, it was found that the percentage cleviation from the determined values by the application of the above formula could be decreased 1~onsiderahly by the intmduction of a different constant. In Table l the data perbining to the endogenous nitrog·en determinations are tabulated. From these figures a value for ~- in the formuila P = PiV · 73'' has been establishecl. As will he seen, the same value for k was obtained for mature and young sheer>. 'rl1is value was then introduced into the formula anll the utilizable protein pn•dicted, as shown in column 6. In column 7 the percentage deviation has been determined. For mature sheep this<leYia ti on is on:Iy ± 2 · 5 per cent., and with young sheep± 5 · 4 per cent. The rnagnitu<le of these deviations is considered exceptionally small and much lP:;s than the deviation when the general formula
P-~ ·88 \V·134 for different species iR applied. Con,:e1uently the 11e1Y formula P= ·74 vV ·734 appears to be better applicable for the e8timation of the protein requinnnents for maintenance of mature m: 1Yell as :voung sheep. J11 this formula P equals utilizable prntein and \\' wPig-ht in Kg-m.
D. U. SMUTS .AKfJ .J. S. C. ~UR.US.
TAULE 1.
Fornwlrz for Predicting the Endogenoils Nitrogen (Protein) of Sheep.
Animal
~o.
2
;3 4
;)
7 8
()
10
LA 2A aA 4A ii A GA SA VA lOA
Weight End. N. as in Kgm. Dotormined.
44·5 2·03
40·0 1·81
37·7 l · 72 42·0 l ·84
:rn·O 1. 72
40·0 1·76
44·0 1·79
f\(). 0 2·01
40·0 1·75
AYcra.ge ..
17 ·907
20 1·02
22 I ·00
JS ·930
23 l·:W
22 1·23
:W 1·34
:!i\ 1·33
28 I ·40
Average ...
End. N.
Expressed as Protein.
12·69 11·34 10·75 ] l ·50 10·75 11 ·00 l l · 19 12·56 10·9.5
YOT-NC:
5·67 6·38 6·25 5·81 7·48 7·69 8·38 3.;34 8·75
Average of Total.
Percentage Valuo kin End Protein Dm-iation P = kW·734 P= ·74 vV·734 from
Value.
. 78 11 ·99 ;)·5
. 75 ll ·09 2· 2
·75 10·62 l · 2
·74 11 ·50 O·O
·73 !0·89 -1- I · :3
·73 11 ·09 0·8
·70 11 ·90
+
6·4·72 13·07
+
4·06·n 11 ·09 .J... 1·3
·74 ± 2·5
SH r:F:P.
·71 5·92 + 4·4
·70 6·67 + 4·5
. 6i\ 7·15 + 14·4
·70 6· 17 + 6·2
·75 7·3() l ·2
·80 7·15 7·0
·77 8·09 3 ·:)
·79 7·86 5·4
·76 8·54 2·4
·74 ± 5·4
·74 .J... 4·4
In 'l.'able 2 the utilizable protPin, cligestible protein, and the
m1rnrn um energy requirements (basal metabolism), ha Ye been pre<li<.:tecl. 'l'he utiliza ble protein is directly calculated by means of the above equation, while the digestible protein is calculated from
TA"BLE 2.
Prediction of Maintenance Requ£rement for Prote£n for Sheep.
Weight inKgm.
15 20 30 H5 40 45
!\O
Weight in tb.
33 44 66 77 88 100 llO
Ctilizable l'rotein (P = 74W·734 }
5·40 6·67 8·94 10·06 11 ·09 12· 10 13·07
Digestible Protein.
10·80 13·34 17·88 20·12 22·18 24·20 26· 14
Basal l\Ietabolism.
Cal/day.
432 534 7li\
805 887 968 l,046
Basal
i\!Ietaboli~m
Cal/per Kgm.
:W 27 24 2:3 22 22 21
ENUUGEXOl·s .'\lTlWGE." 1LJ~TABOLIS:}I OF YOU!iG SHEEP.
the utilizable protein by :1ssuming a biologiral value of 50. The luttel' assumption naturally proYides for a fair margin of safety, since al rnaintenanee leYel 11·e haYe not experienced a biological value as low as 50.
The. basal inetabolism is cale11lated by assuming that the relationship of 2 mgm. endogenous nitrogen or 12·5 mgm. protein is equiYalent to one Calorie of bn;,al heat. ·
lt is interesting lo note that the digestible prntein require111eut as pre<lided by the general equatioll of P= ·88 \\'·"" for a 100 lb.
drnep is 29 grams, by the 11ew equation 24 grallls, aud al·c·onling to ATrnsby (lDli) 27 grarns. Xaturally .\rmsby':s figure hol<ls good for
<Ill} rntiou, whilP the figure obtained in this study will lw greatp1· or
tilll;dler depending 011 tl1e biologil:al Yalue of the feed.
The hasal metabolism in column 5 a1Hl e.s:presse<l per Kg.
"·eight i u eoluulll G is interesting iu Yie11· of the fact that i.t a llO\rn for an e;isy rneans of predidillg the minimum pnergy requiTerneut.
A 100 lb. slieep acconling to our cnkulatiow; \l'OUl<l lrnYe a basal metabolism of '.22 Calol'ies per Kg. 11·eight. This figure l:oi11cides
\\"ith the awn1ge Yalue of the \V-\Y wethers. ,,- 2-5, vV2--H, vV 2-12 and \V 2-G of Lines and Pierce (1931). Their average value for the four sheep \\·eighing from 41 to 52 Kgmi:;. is 22 calories per Kgm. Ilitzman and Beneclict (J.930) obtaineJ. an average value of 27 calories per Kg. which is slightly higher than our figure. These sheep, howeYer, \\·ere rneaslued for their basal metaboliRm 18 to 37 hourn after 11·ithdra11al of food and may probably not have reached the post ahsorpfrrn condition. Armshy (1917) on the other haud, basiug his calculations on the \rnrk of Henneberg and Kellner, arrived at a Yah1e of lG calories per Kg.
For the EE lamhs of G months of ag·e, Lines and Pie1Te (]9'.-Jl) obtainerl an average Yaiue of 36 calories pel' Kg. rrhis vnlue is higher than onr predicted value of 29 calories. However, it appears from the work of the above authors that the 1111tritional leYel of the animal or the seasonal changes in pasture may effect i he basal metabolism. The seasonal effect is ('laimed to lie Llue to the change in prntei n ('on tent. These for-tori; may therefore partly be responsible for our lo1n•r endogeuous nitrogen a1Hl consequently a lower pl'erlictPrl fi,u·ure fol' the hasnl metabolism, sirn·e onr sheep were kept on n low lr\·el of protein for a cm1sidPrahle tirnr.
From the basal mebholism fignres of Lillf's and Pierce (1901), and Hitznrnn ancl Benedid (1930), and our calculated values from
tlH, (~ndogenou~ nitrogen, it appearn thut a V('J y definite relatimudtip exi»Ls betw<>en the b<t,,al rn eta bolism anrl the endog'euons 11i trogen 111et:tbolism in sheep. S11ch n rrlationship 'rnulrl in fottin' Le of (;Onsiderahle 1·alue in nssessing the ya]m' of either of i hrsr e11tities onee 1 he irn1gniturle of one is kno1Yn.
su~H[ARY AND CoKCLUSIONS.
T n a strnly on the en clogenous nitrogen excretion of i.mmaturc sheep, it 1Yas founJ that young· sheep reach their endogenous level on the Gib clay, after kn·inp: been on a standard rntion of 14 per u·nt. lucPrne protein. The enclogP11nus nitrogen excretion was founll
]). II. S)fl"TS .H,,-ll .J. S. l" . . \IAlL\lS.
1u be higher than in rnalure sheep, the average 1·,tlue for .f rnunths old welhen; lwing- · 051 grms. per Kg. A formula for estimating the mainlPna11<:e requirenH··nt of sheep wns d<·Yisetl and its applica- tion teste(l. H "·ns nlso .-;ho1,·n that the basal rneiaholisrn of sheep can be predicted from 1 he <·ndogenous K, an1l tl1:1 t t IH! figures arriYr<l nt <lp-ree Yrry \1·ell "·ith the ,-;dues reporterl i11 Hw liternbt1P.
l,fTl<:H,\TORF.
AHM~llY. 11. I'. (l~JI/). Tl"• llutrition of f::1r1n :111imals. p. :1:26. ~''" Yllrk.
IH:rGll'l"O\". T. (Ul:l-t1. _.\ stulh· of Ll1" f:isti11g nwt:ilioli.sm of ,.,,,.ious hr<"t'ds 111 ling. l. _.\gc, 11· .. iµ:ht ;111d 1 .. 11gtl1 J:1t:1 ./. Ar,1·i1· . . ~~ciencr. \'ol. 24.
pp. :l26-:J:l-l.
llli llOIS. I~. 1:. (i~llG). Tl1<· rt•spirntio11 calurillletl'l" Ill clinit·al n1.-di<·i1Je,
.1111 . . / . . \/f'rl. Sci .. \-ol. 1-51. pp. /81-l!J9 .
. \LITC'l-fl<:LL. J-1. Fl. and ('.-\TI:\U\". G. G. (l\J::'fi\ l·:ffpd of .. xc<»si,.,, ;111101111ts of ,·itnmin K on tlil' ltnsal 111daholisi11 of rnb of dift<c'r<'nl :1µ:cs, rl1111·r . . /. l'l.ysio/ .. \"ol. 16. pp. :lP.-)-:1~JI.
Lf.\"1':S. E. \\". and P[JillC'I•:. A. \\". (19:1]). Tl1e hasal (stamlardl metabolism of A11<rralian :\[eri110 Sl1eep. ('1)111. 11./ .-l11strn/io. l'rJ1111C. S1·i. 011,/ Ind.
ltes1•11rch. RLill. No. 55. p. 33.
R['rZ:\1.-\:\, E. G. n11cl l!l<:Sl·~DICT, I•'. G. (l~J:!ll). slwcp. ('11ir. uf X1•1c. J/0111pshire. 7':.rp. 8f ..
The energy rnPt:t hnl is111 of 13ull. 43. p. :.!:'l.
S.\l l'TS. D. 11. (10:\.)). The 1cb tio11 hL•t\\"!'en the linsal nwbbolism and the
"1Ldog1•11u11s nitrog1•11 rnet<1l1olis111. witl1 particular n1i'Pn•ne1.:' to the .\"11fritir,11. \'ol. 9, pp. 403-433.
:-;\!{'TS. D. B. and :\J.-\R.-\TS. :J. S. C'. (10:\8). Tltc• enduµ:e11011s 11itroµ:<'n 111ctal1olism of shl'<'Jl 11·ith spe('ial l'l'ft•re11cP to tiw maintenance requ1re- 111ents of protr·in. 1!11d1·1·sfe1){/o,./ ./011.r. f'cl. Sri. n11J .111. 711(/ .. Yol. J.l, .\o. 1. pp. J'.Jl-1.J.O.
'J'l<:KHOI :\I•:. I·:. F .. BOY. G .. C'H :\:\I PAGNE. M.
repariitio11 dr·s rcpre1;1·ntn11ts Jiri11nires <lu signification ph~-siologique JI. La depl•nse 111inic11ra du (·oms (Ip l'1 Croissanc<> . .Jiu/. Soc.
)lO!"HAT. G. (l!J:J:J). La meL:1iiolisme Azot6 et a Azotceendogpne speci fiqu«
ChPm. lliol. '/' .. Fi. p. 42.
