of DM intake. Nitrogen excretion was ex- to concentrate ratio of the ration.

Transcription

1 METABOLIC FECAL NITROGEN IN RUMINANTS ESTIMATED FROM DRY MATTER EXCRETION R. HIRONAKA, C. B. BAILEY and G. C. KOZUB Research Statin, Canada Department f Agriculture, Lethbridge, Alberta. Received September 10, Can. J. Anim. Sci. Dwnladed frm by n 02/06/18 Fr persnal use nly. ABSTRA.CT Relatinships between dry matter (DM) and 0.137x j 0.891, wtrere y = g N excretin nitrgen 1N) intakes and excretins'were per 100 g f fecal DM and t- = g N intake examined using digestibility data frm 45 per 100 g fecal DM. Extraplating- N excreratins fed t iheef and c;ttle. The prpr- iin t zer N intake, the pint f- interce_pt tin f ttal variatin due t regressi6n.was at y : g N per 100 g f fecal DM greater when N intake was explessed as a excretin is suggested as a measure f metaiunctin f DM excretin than is a functin blic fecal nitigen independent f the hay f DM intake. Nitrgen excretin was ex- t cncentrate rati f the ratin. pressed by the equatin y - -O.02lf * INTRODUCTION Measurement f metablic fecal nitrgen (MFN) is a prerequisite f estimates f true prtein digestibility and its bilgical value. Mukherjee and Kehar (6) used the direct methd f feeding a prtein-free diet t determine MFN. They fund that cattle excreted 0.3 g N per 100 g f fd dry matter (DM) intake n a O.O2V N ratin cmpsed f dextrinized sag, sugar, ht-alkali-treated bagasse, il, and salt. Hwever, nnnal rumen micrrganism activity wuld nt be expected with a lw N ratin, which culd influence the MFN excretin' Kehar and Mukherjee (5) later suggested that MFN is related t fecal DM excretin rather than DM intake. The MFN determined by the direct methd culd nt be applied, t ratins that differed in DM excretin. An indirect methd f determining MFN was used by Titus (7) wh pltted N excretin as a functin f N intake and extraplated t a zer prtein intake t arrive at the MFN. Using this methd, Blaxter and Mitchell (3) fund that MFN was the same fr alfalfa and grass hay, even thugh the digestibilities differed as indicated by the different regressin equatins. In pigs, fecal N excretin increased as the level f cellulse in the ratin was increased (8). This lends supprt t the suggestin f Kehar and Mukherjee (5) that MFN is related t fecal DM excretin. If MFN is related t fecal DM excretin, thse values expressed in relatin t DM intake wuld nt be applicable t ratins that differed in DM digestibility. T assess the merits f the tw methds f estimating MFN, the data frm several digestibility trials invlving a wide variatin in feed cmpsitin were examined. EXPERIMENTAL PR(rcEDURE The digestibility data frm 45 ratins (Table 1) were gathered t examine the relatinships between dry matter and N intakes and excretins in ruminants. The ratins differed widely in cmpnents and in N cntent. Five ratins were all hay and ne was all barley. Each ratin was fed t fur r five sheep, except in ne instance where each ratin was fed t 12 sheep and in tw instances t tw cattle each (prairie hay and atfalfa) (Table 1). Each ratin was fed fr 2l days at abut maintenance level, except prairie hay and pinegrass hay ratins, which were fed at fur levels. The sheep were kept in metablism crates t separate urine and feces fr the last Can. J. Anim. Sci. 50: (Apdl 1970) ))

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3 HIRONAKA ET' AL.-MET'ABOLIC FECAL N )t Can. J. Anim. Sci. Dwnladed frm by n 02/06/18 Fr persnal use nly. b I a a t{!j ( q I { q l{ l( 10 days n each ratin and ttal cllectins were made during the final 7 days. In sme cases the frmulatin f the ratin (Table 1) was the same but it differed in the starting materials frm year t year. Feed and fecal DM and N cntents were determined by drying at 135 C fr 2 hr and by the AOAC Kjeldahl methd (2). Ttal dietary N intake and fecal N excretin were calculated and expressed as a percentage f dietary DM intake r fecal DM excretin. Three methds f expressing the relatinship f N excretin t N intake were cmpared. The methd f least squares (9) was used t fit plynmials f successively increasing degree t the pairs f N intake excretin values, with an IBM cmputer. RESULTS Methd 1 When g N intake per 100 g f DM intake was used as the independent variable and g fecal N per 100 g f DM intake as the dependent variable (Fig. 1), nly higher degree plynmials (e.g., quartic) signiflcantly reduced the variatin f the dependent variable. These plynmials were nt suitable qd F EE N / loog FEED DM (c, Fig. 1. Relatinship f feed N per 100 g DM intake as the independent variable and fecal N per 100 g DM intake as the dependent variable.

4 )d CANADIAN JOURNAL OF ANIMAL SCIENCE Can. J. Anim. Sci. Dwnladed frm by n 02/06/18 Fr persnal use nly. EI \ 2a q-- {\() l{ \ 2.O b s t -l \ $ l{l r.s \.^ FEED N / loog FEcAL M (c) Fig.2. Relatinship f feed N per 100 g fecal DM as the independent variable and fecal N per 100 g fecal DM as the dependent variable. Methd 2 With g N intake per 100 g fecal DM as the independent variable and g fecal N per 1OO g f fecal DM as the dependent variable, a secnd degree plynmial curve was the best fit and had the equatin y : -O.O2Ix" * O.I37x (Fig. 2). The 95V cnfidence limits f the y intercept were 0.70 t The quadratic regressin described the line f best flt adequately, as shwn by the cefficient f determinatin f 48.38V (P < 0.01). There was n further imprvement in regressin sums f squares when higher degree plynmials were used. Methd 3 When g N intake per 100 g DM intake was used as the independent variable and g fecal N per 100 g f fecal DM as the dependent variable, a linear relatinship with equatiny : O.255x * was btained. The cefficient f determinatin was II.1V. N further imprvement in estimatin f regressin was btained frm regressin by higher degree plynmials. Variability due t deviatin abut the regressin was less when N intake and excretin were expressed as a functin f fecal DM excretin rdther than as a Q-

5 HIRONAKA ET AL.-METABOLIC FECAL N 59 functin f DM intake. The variability was intermediate between the abve tw when N intake was expressed as a functin f DM intake and N excretin was expressed as a functin f fecal DM. Can. J. Anim. Sci. Dwnladed frm by n 02/06/18 Fr persnal use nly. DISCUSSION Fecal N excretin was mre clsely related t fecal DM excretin than DM intake' By extraplatin f g N intake per 100 g fecal DM excreted t zer, the g fecal N p.r 1b0 g fecal ivt f 0.S9t g n in N-free diet is estimated. The value derived -uy-u" used as an estimatj f MFN; it agreed clsely_with the values f 0.95 and ci.z g N per 100 g fecal DM that Mukherjee andl Kehar (6) btained using an N-free-ratin. The-variatin abut the regressin was_small, even with u *idu variatin in type f feeds. Therefre, the estimate f MFN appears t be applicable t a wide variety f feeds rather than t a single feed r type f feed. Althugh Blaxter and Mitchell (3) fund a linear regressin between fecal N per 100 g f DM intake and dietary N per 100 g f intake, they _DM fund a different regressin fr alfalfa hay and grass hay. The extraplatin f their regressins tizer N intake per 100 g f DM intake resulted in a cmmn intercept 6n the rdinate. The feial DM wuld be expected t be related t DM intake. Therefre, within each frage, the linear relatinship (3) cnfirms the relatinship that we fund by expressing N intake and excretin per 100 g f fecal DM. Since sme differenie in digestibility can be expected between alfalfa and pasture grass, a difference in DM excretin can be expected: This difierence in DM excreiin culd accunt fr the difierent regressins fund by Blaxter and Mitchell (3). The N intake required fr N balance may be estimated frrn ur equatin' Fr example, a 25Gkg steer wuld require abut 8665 kcal f DE fr maintenance (4). Asiuming a feed with 2090 kcal DE, per kg DM and 5OV digesnble DM, 4I4O g f feed DM wuld be cnsumed. Fecal excretin f DM wuld be 2O7O g. The MFN wuld be (27a x 0.891)/rcO g. An estimate f endgjnus urinary N f 6.92 g (1) added t the MFN gives a ttal f 25.3 g N that must be absrbed t maintain N balance. If the apparent digestibility f the N f the ratin is 7a7, the ratin must cntain (25.3 x IOO') /70 : 36 g f N, r 225 gf. prtein (36 x 6.25). Therefre, a ratin with (225 x IOO)/4140 : 5.4Vi prten in the dry matter wuld be required t maintain the N balance and ffset nrmal MFN lsses. REFERENCES 1. AGRICULTURAL RESEARCH COUNCIL The nutrient requirements f farm livestck. N. 2. Ruminants. Lndn. 2. ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS OffiCiAI ME' thds f analysis. 10th ed' Washingtn, D.C. p. 16' 3. BLAXTER, K. L. and MITCHELL, H. H The factrizatin f the prtein requirements f ruminants and f the prtein values f feeds, with particular reference t tire significance f the metablic fecal nitrgen. J. Anim. Sci.7: GARRETT, W. N., MEYER, J. H. and LFGREEN, G. P The cmparative energy requirementi f sheep and cattle fr maintenance and gain. J. Anim' Sci. 18: KEHAR, N. D. and MUKHERJEE, R Studies n prtein metablism. IV. Influence f certain factrs n the metablic faecal nitrgen f cattle and rats. Indian J. Vet. Sci. Anim. Husb. 19: ll3-124.

6 Can. J. Anim. Sci. Dwnladed frm by n 02/06/18 Fr persnal use nly CANADIAN JOURNAL OF ANIMAL SCIENCE MUKHERIEE, R. and KEHAR, N. D Studies n prtein metablism. III. An imprved technique fr estimating the metablic faecal nitrgen f cattle. Indian J. Vet. Sci. Anim. Husb. 18: 99-lll. TITUS, H. W The nitrgen metablism f steers n ratins cntaining alfalfa as the sle surce f nitrgen. J. Agr. Res. 34: WHITING, F. and BEZEAU, L. M The metablic fecal nitrgen excretin f the pig as influenced by the amunt f fiber in the ratin and by bdy weight. Can. J. Anim. Sci. 37: WILLIAMS, E. J Regressin analysis. Jhn Wiley and Sns Inc., New Yrk, N,Y.