Disappearance of protein supplements and their fractions in sacco

..Immal I"ecdSctem'e and I'echnoh~gy. 40 ( 1993 ) 2 8 5 - 2 ~ 3 Elsc~ ier Science Publishers B.V.. Amsterdam

285

Disappearance of protein supplements and their fractions in sacco M. Wadhwa, G.S. Makkar and J.S. lchhponani Department of ..lmmal Nutritimt anti P'oragt's. t'unlah. I ~'rtt'ultural ~"nlvt'r~ttt'. Ludhiana- 141 004. India ( Received 12 February 1992: accepted 14 September 19~2 )

ABSTRACT Wadhwa. M.. Makkar. G.S. and [chhponani, J.S.. 1993. Disappearance of protein supplement, and their fractions in saeco..Inim. I"ced&'t. 7i'chn,,I.. 40: 2S5-293. The rumcn degradahility of animal and plant protein supplements (eight of each ) ~as asscs,cd m sacco under two feeding regimens. The supplements as such and those obtained after in sacco dcgradability were fractionatcd into soluble (albumin and globulin ) and insoluble (prolamin and glutch, ) proteins. Skimmed milk powder had the highest ratio of soluble to in,a~luble fractions. I'ollos~cd b~ cotton sccd cake. deoiled mustard cake and blood meal. -l'hc casein and so.~be:m meal had a simtlar hut relatively low ratio compared with the above protein supplements. ! [owcvcr. these v,cre completely dcgr;tdcd. ('orn gluten meal had the It)v,csl ratio tit' soluble to inst)lublc fractions, which was rellccted in the lowest dry m;|lter ;Ind crude protein degrad:lbtlily. Simil-'lrly. bone meal :lnd mealcure-bone nle:tl, having low r:ttios, showed poor tlcgradatlon of t l ~ matter, crude I)rotcin and their fractions. The feeding regimens of the animals h:ld slgnil~canl { I' .- 0.115 ) inllucnce on the dcgr:ld.'tlion of some of the protein suppletllents. Further. irrespccltvc ol[hc fct'thng sy,~tcwltand the ,~ourcc of protein, albumin was dcgr:idctl the most and prol:mun the least. It was conchtdcd, thcrclbrc. Ill:it the solubility of protein suplflcmcnts is an imptirtant factor for tlcternllning the susccptd~ility or rcslr,I:lncc of prolcHI stlpplcmcnls It) rtlnlcn dcgrad;lllOn.

INTR( )DUCT[( IN

The degradability of proteins by rumen micro-organisms is directly related to their solubility (Henderickx and Martin, 1963). The rate and extent of degradation of protein supplements is determined by the ratio of soluble (albumin and globulin) to insoluble (prolamin and glutelin) fractions (Wohit et al., ! 973, ! 976; Tamminga, 1979 ). In the present study some protein (from animal and plant origin) supplements have been fractionated in order to determine their relationship with rumen degradability in buffaloes fed on two feeding regimens. Correspondence to: M. Wadhwa. D e p a r t m e n t o f Animal Nutrition a n d Forages. Pttnjab Agricultural Univcrsity. Ludhiana-141 004, India.

(O 1993 ['IsevierScience Publishers B.V. All rights reserved 0377-8401/93/$06.01)

_~86

M. WADHWJ~

ET J~L.

MATERIALS AND METHODS

The in sacco degradability of ground (2.5 mm) animal and plant protein supplements (eight samples each) was assessed by the nylon bag (7 cm × 15 cm; pore size 50/zm) technique (Mehrez and Qrskov, 1977). The bags containing 5 g sample in triplicate were incubated for 48 h in the lumen of two fistulated, adult male buffaloes (350-400 kg body weight) maintained on two feeding regimens. One animal was offered 2 kg ofconcentrate mixture ( maize 3.5, deoiled groundnut cake 30, deoiled rice bran 32, mineral mixture 2, common salt 1 (parts by weight) ), 6 kg of wheat straw and 5 kg ofgreen fodder (FI), the second animal was fed on 35 kg of green winter maize (F2) as a sole diet, to meet their nutrient requirements (Kearl, 1982). The bags were taken out after completion of the stipulated period, washed under tap water until the rinsing water became colourless, then dried in a forced air oven at 70°C. The residue of each bag was weighed and used for further analysis.

A nalytk'al methods The defatted samples and those obtained after 48 h in sacco degradation (as such ) were fractionated on the basis of their solubility in various solvents ( Mitchel, 1948 ) as described by Pant and Tulsani ( 1969 ). Each fraction was then assayed by the method of Lowry et al. ( 1951 ) for its rclativc concentration in protein components. The samples wcrc also analysed for crude protein (Association of Official Analytical Chemists, 1975 ) and acid detergent insoluble nitrogen (ADIN)content (Robertson and Van Soest, 1981 ).

&atistical attalys& The data from the two feeding regimens were analysed statistically using the/-test (Snedecor and Cochran, ! 968 ). RESULTS AND DISCUSSION

The crude protein ofthe different plant protein supplements (Table I ) was comparable with the values reported earlier (National Research Council, 1989). The fractionation of protein supplements revealed that deoiled mustard cake (DMC) had the highest soluble fractions (240 mg g - ' ), followed by cotton seed cake (CSC), deoiled groundnut cake (DGNC) and guar meal (GM). The corn gluten meal (CGM) had the highest insoluble fraction (214 mg g - ' ), followed by soybean meal (SBM), DGNC and GM, whereas the CSC had the lowest (73 mg g- ' ) insoluble fractions. The ratio of soluble to insoluble protein fractions was the highest in CSC followed by DMC, GM,

33.3 ~-0.14 49.7_* 0.21 43.6~'0.61

G u a r meal ( G M )

36.3_~ 0.08 37.~*_0.U7

26.5,0.22 2~.0 ~_t).U 53.1___0.36

Suntlo~cr cake (SF(" I Til cake {TC) ('orn glulcn meal ( ( ' t I M )

Values arc nlcan ~ SI- o f six obscr~ at ion~.

C o t t o n seed cake ( ( ' S ( ' )

l)eoiledmusiardcakclDM(')

So)bean meal ( S B M ) I)coilcd groundnut cake ( D G N C I

CP (%)

Sample

63.7 _"0.0 43.5 : U.30 12.3 _'_ I.IO

145.0 "_ O.0 12"~.4 z 2.24

a5.7_- 2.36 43.~ ~ 0.61 ~ . U : 13.02

Albumin

5_'i.5 ~ I).20 82.8 "_ 1.26 'L4 : t).O5

94.5 -_u.u ~0.'o -- 1.02

72.u~ 1.96 51.0zO.0 87.8~ I~.t)~

Globulin

Protein fraction ( m g g - R)

Composition o f plant protein supplements ( D M basis I

TABLE I

13.4±0.0 I 1.3_, 0.24 109.6±1.22

24.5 "," 0.2~i 2 1 . 8 _+ 1.67

8.3_*0.12 5.7_+t).16 10.4_+ 1.02

Prolamin

1.31 (1. l(1

IUS.0 y_ 1.59

1.47 I).04 1.35 2.82 2.'~4 1.41

5.oq J. 0.44

2.h2 ~ 0.32

0.66 ± I).31 3.0{) ~ 0.02 O.X8 : 0.62 3.116 + IJ.(~5 2.4O ,_ IJ.31

(%)

fractions

71.3 L.L3J 85.2 L 5.35

60.7 ± 2.20 51.lJ ,_ ().86

')9.2 z 1.84 142.0 !: 21.47 127.9 ±9.31

Glutelin

AI)IN

Ratio o f soluble : insoluble

~J

sunflower cake (SFC), DGNC and til cake (TC). The CGM contained the lowest ratio of soluble to insoluble fractions and the highest ADIN content (Table l ). The dry matter and crude protein degradabilities ( D M D and CPD) were the highest in GM followed by SBM, DGNC, DMC and they were quite low in CGM (Table 2). The low rumen degradability of CGM could be a result of its high ADIN content as also reported by Clark et al. ( 1987 ). Recently, Titgemeyer et al. (1989) have reported that 86% of CGM nitrogen (N) escapes rumen degradation, about 80% of which was digested in the small intestine of steers. On the other hand, SBM-N was degraded the least in the duodenum mainly because most of the soluble fraction is degraded by rumen microbes leaving only the most refractory portion. This was indicated by significantly higher bacterial N flow to the duodenum in the case of SBM fed steers compared with those fed on CGM (Garrett et al., 1987 ). The low efficiency of bacterial N synthesis in the CGM fed steers could be attributed to a low NH~ concentration in the rumen (Satter and Slyter, 1974). On the other hand, although the D M D of SFC and TC was lower than for all other cakes, their CPD was comparable with that of DMC, which could bc because of the very high degradability of their soluble fractions (Table 2). The maximum DMD and CPD in GM could be attributed to 100% dcgradaTAIII.I- 2 1)cgrad;dulily (in sacco ) o f pl:mt protein sUpldcntcnts a n d their i)rotcin I'r:lctions (% I)M basis ) under two I'ccdmg rcgintcns SitmldC ~

(;M SlIM

I)(;N(" I)M(' (.'SC SF('

T(" ('GM

Feeding rt.'gilncn

FI I :'~ I"1 !:2 FI F2 FI 1:2 FI F2 FL I:2 FI F2 FI t:2

I )M

99.4 _~0.(14 99.5 f 0.0 87.5 ~0.04 97.4 t 0.(14 89.1 t 11.41 88.5 .~ 0.77 82.8 :_~0.77 83.1 ± 0 . 1 6 77.1 +0.73 78.1 +0.61 65.2±0.12" 69.0 ± 0 . 1 2 h 61.5+'0.04" 63.3 ±0.20 h

55.2 +-0.04" 59.6 ± 0.00 h

('1'

99.7 _~.0.04 99.2 ~-0.08 99.1 L 0 . 0 98.2±0.04 97.9*-0.49 98.11 ± 0.49 94.4+-0.53 93.4 ± 0 . 0 8 89.4±0.41 89.2 ±0.41 94.8 ± 0 . 2 4 • 96.5 1"0.16 h 93.9 ± 0 . 0 8 ~ 95.4±0.12 h 43.3 ~0.12" 44.1 _+0.12 h

I ' r o l c m fraction Albumin

(;Iobulin

Prolamm

(;lutclm

100.0 I11(I.0 84.8 81.8 95.4 94.3 95.5 95.8 67.8 88.4 96.2 96.8 91.6 96.2 64.8

100.0 100.0 92.5 96.7 96.4 95.5 98.4 97.8 92.4 96.8 97.8 97.5 97.7 98.3 34.3 64.5

100.0 100.0 44.8 47.9 53.9 55.4 13.2 53.8 57.8 51.8 58.8 48.9 48.0

1(10.0 I(10.0 97.7 93.6 83.9 86.2 85.9 89.4 43.2 74.2 88.2 94.0 71.8 83.3 0.1 0.5

F I. conccnlral¢ supplcmcnlcd whh wheal slraw and green l'oddcr; F2, only green Ibddcr. Me;ms wilh difl~:rcn! supcrscripls in a column differ significantly ( !'< 0.05 ). I.-Xbbrcvi;Itions as in Tabh: I.

IN SJ~CCODEGRAD-~BILITY ()F PROTEIN SUPPLEMENTS

2~ ~)

bility of its protein fractions. The low CPD of CSC and CGM could be a result of the poor degradability of their insoluble ( major portion ) fractions. The feeding regimens did not show any significant influence on DMD or CPD except in the case of SFC, TC and CGM. The DMD and CPD of these supplements were significantly ( P < 0.05 ) higher in the all roughage diet ( F2 ) compared with the system where a concentrate mixture was a supplement to wheat straw and green fodder ( F l ) . This could be the result of the higher degradability of the insoluble protein fractions in the all roughage diet than in the concentrate diet (Table 2 ) as reported earlier for proteins of vegetative origin (Ganev et al., 1979; Rode, 1981: Zinn and Owens, 1983). It has been attributed to the predominant cellulolytic microbial activity in an all roughage diet thereby exposing more surface area for microbial degradation (Owens and Bergen, ! 983 ). Like plant protein supplements, the CP content of animal protein supplements (Table 3) was comparable with the values reported earlier (National Research Council, 1989) except that of fish meal ( FM ) which had a low CP content (39.1%). The CP content of blood meal and liver meal (BM and LM ) was lower than that ofcasein. Bone meal (BnM ) had the lowest protein content. Fractionation of the animal protein supplements indicated that skim milk powder (SKM) had the highest proportion of total soluble fractions followed by casein and FM. The maximum amount of insoluble fractions was observed in casein ( mainly because of the glutelin fraction ), followed by FM and meat-turn-bone meal ( MCBM ). The BnM had the lowest proportions of soluble as well as of insoluble fractions. The ratio of soluble to insoluble fractions was the highest in SKM, followed by that in BM and dried inactivated yeast (DIY); MCBM, FM and LM had comparable ratios, while casein had tile lowest ratio, Casein, SKM and DIY had nearly 100% DMD and CPD (Table 4 ) because of complete degradation of their protein fractions in the rumcn, irrespective of the diet fed to the animal. Similar observations were made by Zinn et al. ( 1981 ). The DMD and CPD of LM was also very high, as indicated by more than 70% degradation of its protein fractions as well as its high ratio ofsoluble to insoluble tractions. Among the various animal protein supplements, the degradability of BnM and MCBM was minimum, as also indicated by their lower ratio of soluble to insoluble fractions. The values obtained were comparable with those reported earlier (National Research Council, 1989). The degradability of BM was the lowest, in spite of its high ratio of soluble to insoluble fractions and considerable degradation of its soluble fractions. It has been reported that 82-96% of BM-N and 43-100% of FM-N escaped tureen degradation (Loereh et al., 1983: Siddons et al., 1985; Titgemeyer ¢t al., 1989). The BriM, MCBM and FM contained relatively high proportions of collagen, which is low in lysine, high in proline and hydroxyproline, or they may be extensively cross-linked by disulphide bonds, which may prevent ac-

21.6_+ 0.07 46.6_* 0.63 39. I ± 2.39 66.1 -*0.0 73.9_*0.02 49.2 *_0.07 76.6*_0.22 33.2 ~ 0.0

Bone meal ( B n M ) Meat-cure-bone meal ( M C B M ) Fish meal ( F M ) LiYer meal ( L M ) Blood meal iBM ) Dried inactivated yeast ( DIY ) Casein Ski,n milk pounder ( SKM )

Values are mean ± SE o f six observations.

C P [%)

Sample

Con)position o f animal prolcin s u p p l e m e n t s 11)M basis )

TABLE 3

9.3 '" 0.04 68.0 ~_6.61 85.8 -* 6.85 38.0,- 1.75 5 7 . 6 - 0.85 63.0 -* 0.24 63.8 -* 1.51 281.3 _.z4.16

Albumin 3.5 *- 0.1)8 23.9 ± 4.45 34.1 _* 3.96 17.0-_0.73 20.9*_ 2.41 IU.6 ± O. 16 56.8 ± 2.U8 37.2 + 1.43

Globulin

Protein fraction ( m g g - ' )

1.2 *_0.08 10.8 ± 1.06 10.8 _ 2.08 IO.6± 1.14 5.5 _+0.16 4.4 + 0.04 49.9 _ I. I1) 4.2 ± 0.12

Prolamin

22.2 105.4 140.7 66.3 24.6 55.5 330.7 48.8

± I).37 ± 9.43 +- 6.45 +_ 1.43 ±O. IO ± 2.6 I _+7.96 +-O. 16

Glut¢lin

0.55 O.79 0.79 I).72 2.61 1.23 0.32 6.OI

Ratio of soluble: insolubl¢ fractions

..r

IJ q~

IN Y,ACCO DEGRADABILITY OF PROTEIN SUPPLEMENTS

29 [

TABLE 4 Dcgradability ( in sacco ) of animal protein supplements and their protein fractions {% DM basis ) under tv, o feeding regimens Sample ~

BnM

MCBM FM LM BM

DIY Casein NKM

Feeding regimen

FI F2 FI F2 FI F2 FI F2 FI F2 FI F2 FI F2 FI F2

DM

31.7±0.61" 25.6_+0.73 t" 32.2 -+0.86" 34.3± 1.0C' 71.7 ±0.77" 68.9_+0.73 ~' 69.1 _+0.94 68.2±0.77 50.3_+0.37 48.3_*0.49 99.8-+0.04 99.9 -+0.04 99.6_*0.04 99.4 _+0.04 99.5±0.04 99.6-+0.32

CP

38.7+2.98 40.8_+0.82 43.4-+ 1.88 • 48.7-+ 1.51 b 91.9+ 1.06 9 0 . 8 ± 1.06 80.6 -+0.57" 93.1 +0.32 h 21.4_+0.61 a 13.1 + 0 . 7 7 h 100.0±0.0 100.0 +_0.0 98.9±0.49 I (}0.0 _~0.0 100.0 +-0.0 IO().O_+0.O

Protein fraction Albumin

Globulin

Prolamin

Glutelin

85.4 88.0 94.3 94.1 96.6 96.5 77.6 92.2 88.2 9_'3.6 100.0 100.0 100.0 100.0 100.0 10(}.O

83.3 88.0 93.7 87.0 05.9 93.3 55.0 86.9 64.2 85.1 IOO.O I (}(}.0 IO0.() I {)().0 100.0 IOO.(}

3.7 62.6 39.0 82.3 64.4 100.0 100.0 100.(} 100.0 100.0 IOO.0

73.3 76.6 60.3 56.4 83.2 86.3 51.,'; 72.2 44.2 100.0 101).0 10{I.(I 100.0 I00.0 I00.{)

FI. ¢on~3.'r|trat¢ supplemented with wheat Mraw ;.Izzdgreen fodder; F2, only green folklcr. ,'~t¢:HIF,with dilK-rcnt SUl)Crscrzpts in a column differ significantly ( I'< {).05 ). 'Abbreviations as m T;dfl¢ 3.

cessibility to protcolytic enzymes resulting in decreased rumcn degradation (Nugcnt and Mangan, 1978 ). Moreover, processing conditions may render these protein fractions undcgradablc ( Miller, 1982 ). Mahadcvan et al. (198() ) reported that structural characteristics of protein supplements also play an important role in their degradation. This was quite clear in the case of casein which, in spite of having a low ratio of soluble to insoluble fractions, was degraded completely, The feeding regimens significantly ( P < 0 . 0 5 ) affected the D M D of BnM, MCBM and FM and the CPD of MCBM and BM. However, these protein supplements did not show any consistent trend. The protein tractions, irrespective of the protein source, showed the highest concentration of glutelin, followed by albumins, globulins and prolamins (Table 5). The degradability pattern indicated that albumin and globulin fractions were degraded to a significantly higher extent than were prolamin and glutelin, irrespective of the protein source and dietary regimens. Prolamin was observed to be the least degradable fraction. The results discussed conclusively revealed that solubility of proteins is an important factor in determining the protein's susceptibility or resistance to rumen degradation. Therefore, feeding protein supplements such as CGM,

2q2

M. W-~DHW.~ ET ~L.

TABLE 5

Protein fractions and their degradability ( DM basis ) Protein supplement

Albumin

Globulin

Prolamin

Glutelin

77.6 _+45.3 83.4 4- 83. I

67.5 4- 28.2 25.5 4- 16.9

25.6 ± 34.5 12.2 _+15.6

92.8 4- 31.9 99.3 4- I 01.7

89.9 _+ 10.9 94.3 4"6.6

91.0 + 17.3 89.6 4" 13.2

56.5 "L-_22.4 77.4 ± 32.2

74.5 ± 32. I 80.3 _+ 10.9

Content (rag g - =)

Plant protein Animal protein Dcgradahdtty (%)

Plant prolein Animal protein

MCBM and LM, which escape rumen degradation but are digested considerably in the postrumen gastrointestinal tract, could be used efficiently in the rations of livestock.

REFERENCES

Association o1"OfficialAnalytical Chemists, 1975. Ollicial Methods of'Analysis...~soci;.|lh)llof ()11~cialAnalytical Chemists. I ISDA, Washington. De. Clark. J.lI..Murphy, M.R. and Crooker. II.A., 1987. Supplying the prol¢in needs ol'dah'y c;fllle fron| by-product feeds. J. Dairy Sci., 7(): I{}92-I I09. ( L|ncv. (;..{)rskov, I'.R.,v|d Smart, R., 1979. The el'l~.'ct of roughage or conccnlral¢ l~'cdh|g:rod run|on retention tin|c on tot:ildegr:id:itk|nof protein in the runlen. J. Agric. Sci.,93:651 656. (;arrett.J.E., Goodrich. R.D.. Meiske, J.('.and Stern, M.I)., 1087. Influence of supplemcntzd N st|urceon digestion of nitrogen, dry mailer, org;mic nl;ltterzlnd on in vivo rate of t'umin;.tl prt|teindcgradz|tion.J. Anita. Sci.,64:1801 - 1812. llendcrickx, II. and Martin, J., 1963. In-vitn| study of the nitrogen mct.'tbolism in the run|on. C. R. Rcch. IRSIA, 31: 7. Kcarl, L.C., 1982. Nutrient requirements of rumin:mts in the developing countries. Intcrn.'|tion:|lFeedstuffs Institute.Utah Agriculture Experiment Station. Utah St;lieUniversity, Logzm, UT. Locrch, S.C., Bcrger, L.L., Plegge, S.D. and Fahey, Jr., G.C., 1983. Digestibilityand rumen escape of soybean meal, blood meal, meal and bone meal and dehydrated alfa-al1~.tnitrogen. J. Anita. Sci., 57: 1037. Lowry, O.II., Roscbrougb. N.J., Farr, A.L. and Randall, R.J.. 195 I. Prutcixanacasurcmcnt with folin-pbenol reagent. J. Biol. Chem., 193: 265-290. Mahadevan, S., Erlle.J.D. and Sauer, F.D., 1980. Degradation of soluble and insoluble proteins by Bactcroich.sam)'lophihts protease and by runten microorganisms. J. Anita. Sci., 5(]:723728. Mchrez, A.Z. and Orskov, E.R., 1977. A study of the artilicialfibre bag technique for determining the digestibilityof feeds in the rumcn. J. Agric. Sci..88: 645-650. Miller, E.L. 1982. Methods of assessing proteins for ruminants including labor.|torymethods. In: E.L. Miller, I.H. Pike and AJ.II. Van Es (Editors), Protein Contribution of Foodstuffs for Ruminants. Butterworths, London, pp. 18-35.

IN ~.~('(¢ ) DE(;R4.D,~.BILITY ()F PROTEIN SUPPLEMENTS

2~3

Mitchel. C.A.. 1948. Allen's Commercial Organic Analysis. Vol. 8. Churchill. London. National Research Council. 1989. Nutrient Requirements of Dairs. Cattle. 6th revised edn. National Academy of Sciences. Washington. DC. Nugent. J.H.A. and Mangan. J.L., 1978. Rumen proteobsis of traction I. Leaf protein, casein and bovine serum albumin. Proc. Nutr. Soc.. 37: 29A. Ogens. F.N. and Bergen. W.G.. 1983. Nitrogen metabolism of ruminant animals: historical perspective, current understanding and future implications. J. Anita. Sci.. 57 (Suppl. 2 ): 498-518. Pant. R. and Tulsani. D.R.. 1969. Solubility. amino acid composition and biological value of protein isolated from leguminous seeds. J. Agric. Food Chem.. 17:361-366. Robcnson. J.B. and van Soest. P.J.. 1981. The detergent system of analysis and its application to human tbod. In: P.T. James and O. Thcander (Editors). The analysis of Dictars. Fibre in Food. Marcel Decker. New York. pp. 128-1:58. Rode. UM.. 1981. Factors affecting the measurement of microbial protein synthesis in-vitro. MSc. Thesis. University of Washington. Madison. Sattcr. UD. and Slytcr, L.L.. 1974. Effect of ammonia concentration on the rumen microbial production in-vitro. Br. J. Nutr., 32: 199-208. Siddons. R.C.. Paradinc. J.. Gale. D.L. and Evans. R.L.. 1985. Estimation of degradability of dietary protein in the sheep rumen by in-vivo and in-vitro procedures. Br. J. Nutr.. 54: 545561. Snedecor. G.W. and Cochran. W.G.. 1968. Statistical Methods. ()xford and Ills Publishing. New Delhi. Tamming:l. S.. 1971L Protein degradation in the t'~)rcslomachs of ruminants. J. Anita. Sci.. 4L~: 1615-1630. Tilgcme~,er. I.-.C.. Merehcn. N.R. and i|crger. L.I... 1~)8~. Evaluation of soybean meal. corn gh, tcn meal. blood meal, and lish meal as sources of nitrogen :rod amino acids dlsappcariflg ('ron| the small intestine ot'steers. J. Anita. Sci.. 67: 2¢,5-275. Wohlt, J.l:... Snit'l~'n. ('.J. :rod I Ioover. W.I I.. 1~73. Measurcmcn| of protein solubility in common I~'edsttffl's. J. l)airy Sci.. 56: 1052-1057. Wohll. J.E., Snifl'cn. ('.J., I Io~ver. w . I i.. Johnson. 1..1,. and Walker. ('.K.. I IJ76. N~trogen mct:d+olism in wethers :Lsafl'ccted by di¢tar.~,'prt~t¢in solubility and amino acid prol]l¢. J...~nim. Sci., 42:1280-128~. Zina, R.A. and ()wens, F.N.. 1983. Site of protein digestion in steers: predictabilil~. J. Anita. Sci.. 56:707-716. Zi,m, R.A.. Ilull. I..S. and I lenken, R.W., 1981. i.)egradalion of suPl~lenlent:d proteills in the fume,1. J. Anita. Sci.. 52: 857-867.