Roux, C.Z.

Scholtz, M.M.

English

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:;, Ali, J, Anim. Sc'i. 10, 23J 23.J (1q80)THE ESTIMATION OF PREWEANING ENERGY INTAKE FROM LITTER MASS IN RATS"Recetpr o l  M S 09- 06- 1 980M.M.  Scho l tz  and C.Z .  RouxAnimal and Dairy' Scienct Research Institute,Private Bag X2,lrene 1675, Republic ol 'South Afica(Key words: Rat, Ssreweaning energy intake)(Sleutelwoonde: Rot, r,oorspeense energie-inname )O6OMMI N(; I ) I I .  B I  R A M I N G  V A N  V O O R S P I  - N S I ,  l N I R ( ; I I  I N N A M I  V A N A I ]  W I , R P S F L M A S S A  B Y  R O T T I'n  Bc ran r rng  van  d i c  hoevee lhe td  e  ne rg ie  l ngcnccnr  deur  wer t r r s r ' l r  t o l  op  \p r ' rn .  I n  te rn rL ' van  p rcna la le  ve rb ru i k  en  d i c  n re l kp roduks ie  vand ic  rnoedc r r .  uo rd  d rku ,e l s  benod ig  rn  d ie  bes tuder rng  van  do r l t r r t ' l cndherd  van  s roe l .  D ikwe ls  t s  d r t  eg te r  n i c  moon t l i k  om h ie rd recnerg ie - inname d i rek  l c  l nec ' l  n ie .  ' n  Mc todc  t r  dus  onnr i kkc l  r r ' aa rvo lgens  d ie  wc rpse ln lassa  gcb ru i k  word  on r  d ie  kunru la t i euc  cnc rg i c -i n n a r n e  d e u r  r o t t c ' t o t  o p  s p c e n  l s  b c r a a m . ' n  V e r g e l y k t n g  t s  o o k  o n t w l k k e l  o m  h t e r d i c  k u m u l a b c w t ' c n e r g i r ' - r n n a n l c  v a n ' n  w e r p w l  l u s s c ndrc  tnd iv idue  van  d i c  wc rnse l  t c  ve rdcc l .SUMMA R Y.A t l  r ' \ t rn la t t '  o f  t hc  t ( ) ta l  rne rg ) ,  t n take  o l ' l t t t e rs  un t i l  wcunrng .  rnc lud ing  bo th  enc rgy  ob ta ined  ln -u te ro  and  tha t  de r i vcd  pos t -na ta l l yl rom rrr i lk  consumed. rs t r t ' ten re 'quircd in r ' rprcr iment\  on growth el ' t icrcncy.  [ r requenl ly  i t  is ,  however,  impossib le to measure th is energydr rcc t l i .  ( ' onsequcn t l y .  a  rne thod  uas  deve loped  us ing  l i t t e  r  rnass  to  es t ima te  the  cumu la t i ve  cnergy  in take  by  ra ts  to  wcanmg.  Ane( lua t ron  was  l l so  devc lopc 'd  to  d i v rdc  th i s  cun ru la t l ve  cnc rgy  ln take  o f  a  l i t t e r  be tween  the  u rd i v rdua ls  o l ' t he  l i t t e r .l n  t he  ana l yses  o f  expe r i n )en t s  i nvo l v i ng  t he  quan t i -l l ca t ion o f  an imal  growth and ef f ic iency of  feed ut i l -i z a t i < r n  (  P a r k s  l q 7 0  .  1 9 1 2 .  1 9 7 . 1 :  l c ) 7 5 a  &  1 9 7 5 b :Me issne r .  Roux  &  Ho f i ney  r .  1915 ;  Roux  , 1916 ,  Me i ssne r ,l 9 l 1  ,  Kemnr ,  1979 )  t he  cumu la t i ve  f o rn r  o f  ene rgyin take is  requi red.  s ince the in i t ia l  body mass needs to  bere la ted to  an in i t ia l  cumulat ive in take.  Th is  cumulat iveenergy in take (p) ,  whether  i t  is  in  the form of  mi lk  orfood.  u t i l i zed by an an imal  before the beginn ing of  anexper imenta l  phase is  f requent ly  not  ava i lab le .  andrne thods  o f  es t i n ra t i ne  r t  wou ld  be  use l l l .Rats  are o f ten weaned at  I  I  days o f  age,  so that  themass of  t l re  ra ts  a t  th is  s tage is  a  lunct ion o f  the mi lkproduct ion o f  the dam and the prenata l  energyconsump-t ion o f  the fe tus.  I t  is ,  however ,  very  d i f f icu l t  to  deter -rn ine the prenata l  energy consumpt ion and f requent lyi n rp rac t i cab le  t o  de te rm ine  t he  m i l k  p roduc t i on  i f  manyda rns  a re  i nvo l vcd .Material and methodsFenra les o f  the outbred Wistar  l ine were kept  underconvent iona l  condi t ions,  w i th  a  roonr  te lnperature o fI  I  t  l " ( ' .  a  re la t ive humid i ty  o f  35 5O/ ,  and a l ight -i ng  reg lme  w i t h  l 2  houn  o f  s imu la ted  day  and  I  I  hou rso l '  darkness.  The rn i lk  product ion o f  8  females wasde te rm ined  acco rd ing  t o  t he  n rc thod  desc r i bed  by  Reddy .D o n k e r  &  L i n n e r u d  ( 1 9 6 4 ) ,  R e d d y  &  D o n k e r  ( 1 9 6 5 ) .Kumaresan. Anderson & Turner (1967) and Morag(1970).  In th is method, pups are separated from theirdams for a certain per iod (secret ion interval)  Pr iorto being returned to the dzun their body n'rass i measured,whereafter they are allowed to suckle for a given period(suckling time). The body mass is then measured onceagain. The increase in l ive mass of the l itter duringsuckling time serves as an estimate of the amount ofmilk secreted during the secretion interval. Litter sizewas standardized at  l2 pups, wi th a secret ion interval  of6 hours and a suckl ing t ime of  60 minutes.  This methodwas used to determine the milk prulduction on days3 . 6 , 9 ,  1 2 , 1 5 , l 8  a n d  2 l  o f  l a c t a t i o n .As there appears to be no study on the description ofthe  lac ta t ion  curve  o f  the  ra t ,  an  equat ion ,  y :  g*Qg9* ,used by Wood (1969) to descr ibe the lactat ion cunr le ofcows, was used. l f  i r  and p are larger than zero,  theequat ion is l inear ized by t ransformat ion to the logar i th-nr ic scale.  Therefore.  the equat ionl n y  : :  I n  a  +  b  l n  x  +  c x  . . .  . ( l )is  l inear in ln y,  Inx and x where y is mi lk product ionon day  x .Par t  o f  M .S .  (Ag r i c )  t hes i s  o f  t her r r i t t ed  t o  t he  Un i ve rs i t v  o f  t hesenior author,  sub-Oranqe Free State- J JTable IValues for a, b ond c plus standard enorsValue 0 26eo 1 ,7362 - 0,0833Std. error o,5620 0,7033 0,0626ResultsEstimates of A, b and c- for equation I were obtained bymultiple regression analysis for each rat. The values ofq, ! and q with standard elrors are given in Table I .It was then possible to estimate the milk production ofrats on the different days by using equation (l). Theestimated and determined values for every third daycould be compared by calculating 12 , a measure of thegoodness of f it of a regression l ine. The calculated value of12 was 098, which indicates that equation (l) is a fairdescription of the milk production of a rat. These valueswere plotted against each other, and compared to aregression line with slope one and intercept zero (Fig. I )to determine if there was any bias in the estimates. It isevident from fig. I that there was no significant bias, sothat equation (l ) seems to be a useful equation to predict4 8 1 2Estimated milk production (g)Plot of observed volues against estimntedvalues, and regression line with slope oneand intercept zqomilk production of rats. The average total estimatedmilk production of the dams from 3 to 2l days was822,16 g.The energy content of 8 three day-old pups from 4litters was determined and found to be 388 I 0,09KUg live mass. Kielanowski (1965) reported that earlypostnatal efficiency was 85 percent. This value wastherefore multipLied UV -tP to estimate the cumulative'  8 5energy intake (prenatal and early postnatal) by a three-day-old pup. Six rats were used to obtain milk for thedetermination of the energy content of rat milk. Therats were anaesthetized and milked by hand every thirdday from day 3 to day 21. A total  of  25,6 g of  mi lk wasobtained. The energy content of rat milk was found tobe 7,84 KJ/g fluid milk. This corresponds closely withthe value of 8,1 I KJ/g fluid milk obtained by Romero,Canas & Baldwin (1975). Daily milk production can thusbe estimated (equation (1) ) and expressed in terms ofenergy units. By adding the cumulative energy intake ofthree-day-old pups to the cumulative milk produced bydams from 3 to 2l days post partum (in KJ), it is possibleto derive an estimation of the cumulative energy intake(p) of  a 2l  day old l i t ter .h'quatittnsAs litter nras is the only variable that can be measuredeasily, it is desirable to estimate p from this variable.The well known allometric equation, which expressesefficiency of growth (Roux, 1976), was used to estimatelt from litter mass. The logarithmic transformation ofthe allometric equation, y -- g xb, leads to a straightl ine.  thus:l n v  :  l n  a  +  b  l n x ( 2 )i n t ake  and  x  :  l r t t e r  mass .where,  y  :  cumulat ive energyThe mass of the 8 l itters involved in the experiment wasmeasured every third day from day 3 to 2l , and cumula-tive energy intake can be calculated from (1). With y andx known, it is possible to estimate values of g and bfrom regression analysis. The average values of slope (!)and intercept (ln A) were respectively 0,6289 + 0,0606and 2 .4440 t  0 .2583.However.  pups suckle as a l i t ter  and not as indiv iduals.Therefore,  a method of  d iv id ing g of  a l i t ter  betweenthe indiv iduals of  the l i t ter  had to be developed. Withdifferentiation the allometric equation becomes(y i  -  t ) ,results in4.  H.n. .  on replacing dx by (x i  -  x) ,  dy byy by y and x by x the di f ferent ia l  equat iont 6oo3 1 4JlE 8Pc)(hl 64r_bv-I"-ig. I234y i  =where hereandDiscussionSince equation ( I ) seems to describe the milk productionof rats fairly well (r2 : 098). it may be useful inestimating the milk production of rats when values forg,b and c are available. The relationship between estimatedand detennined values is a straight l ine with a slope ofone and a  in te rcept  o1 'zeroSince the cumulative energy intake of l i tters at thebeginning of an experimental phase is very seldomknown, equat ion (2) can be used to est imate th is com-ponent when the l itter mass is known and values for I n aand b are avai lable.  Our est imates depend on the f i rod.the environmental and experimental conditions and thestrain used. For similar circumstances the above valuesshould be adequate. for different circumstances, newvalues for the constants hould be estimated dependingon the degree of accuracy required.lndividual body mas values are, for example, needed inselection experiments where individual or within familyselection is practised. Equation (3) provides a method bywhich the p for a litter can be divided between theindividuals of the l itter.Equations (l), (2) and (3) are based on small numbersand may not be very accurate, but appear adequate forthe purposes mentioned. lt is unrealistic to allocate acumulative energy intake of zero to a rat at the beginningof an experimental phase. A nonzero estimate, even if i tis not very accurate, is to be preferred because thecontribution of p to the cumulative nergy intake during,say a groMh experiment, decreases rapidly with time.The error in y due to pr thus soon becomes relativelysmall and unimportant.vXr -  x  + xb_ , _  : . . . ( 3 )Iu:  p  o f  r a t i_ average pr of the l itter- average mass of the [tter_ mass of rat i:  s lope (0,6289)viv.xxibReferencesKEMM, 8.H., 1979. The influence of dietary energy consentration on the growth efficiency of ad l ibitum fed pigs.Proc. 8th L.nerg1, Symp., Cambridge 1979 (in press).KIELANOWSKI, J., 1965. Estimates of the energy cost of protein deposition in growing animals. I 'roc. 3rd EnergyMetab., Troon I 964. fubl. Eur. Assoc. Anim. Prod. I I ,l 3.KUMARESAN, P., ANDERSON, R.R. & TURNER, C.W., 1961 . Effect of l i tter size upon milk yield and litter weightgains in rats. hoc. Soc. Exp. Biol. Med. 126,41 .MEISSNER, H.H., 1977 . An evaluation of the Roux mathematical model for the functional description of growth.Ph. D. thesis, University of Port Elizabeth, Republic of South Africa.MEISSNER, H.H.,  ROTIX ,  C Z. & HOFMEYR, H.S..  1975 . Voluntary feed intake, body composi t ion and ef f ic iency inthe sheep: Breed and sex differences.Agroonimalio 7, 105.MORAG, M.,  1970. Est imat ion of  mi lk y ie ld in the rat .  Lab Anim. 4,259 .PARKS, J.R.,  1970. Growth curves and the physiology of  growth. l  Animals.  Amer J.  Ph.vsictL 2l9,833.PARKS, J.R., 1972. The physiology of growth. Animals as input-output divices. Proc. of the Internotional SummerSchool on the Computer and Rel in Nutr. and Vet. Med, 37 - 51, Denmark: Elsinore.PARKS, J.R., 1973. A stochastic model of animal growth. J. Theor, Biol. 42, 505.PARKS, J.R.,  1975a. The animal growth phase plane.J.  Theor.  Biol .  55,371.PARKS, J.R., 197 5b. A theory of animal weight response to controlled feeding. J. Theor, Biol. 55, 381 .REDDY, R.R. & DONKER, J.D., I 965. Lactation studies. Vl Effects of different intervals between nursing and durationof suckling on rate of milk production in Sprague-Dowley ratsin the first lactation.J. Dairy ̂ Sci 48,978.REDDY, R.R.,  DONKER, J.D. & LINNERUD, A.D.,  1964. Lactat ion studies.  IV Rates of  mi lk secret ion dur ing betweennursing intervals of  3,  6,  9 and l2 hours using Sprague-Dowley rats.  - / .  Dairv Sci .  41 ,554.ROMERO, JJ. ,  CANAS, R & BALDMN, R.L. ,  1975. A technique for est imat ing mi lk product ion in rats.  J.  Nutr .1 0 5 , 4 1 3 .ROUX ,  C .2.  A model for  the descr ipt ion and regulat ion of  growth and product ion.  Agroanimal ie 8,83.WOOD,  P.DP. .  1969.  Fac tors  a f fec t ing  the  shape o f  t l i e  lac ta t ion  curve  in  ca t t le  .  An in .  I ' rod .  1 ,307.13 -5

The estimation of preweaning energy intake from litter mass in rats

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The estimation of preweaning energy intake from litter mass in rats

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