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The effects of different sources of nitrogen supplementation on the digestion of fibre components in the rumen of steers
Animal Feed Science and Technology, 17 (1987) 65-73
65
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
The Effects of Different Sources of Nitrogen Supplementation on the Digestion of Fibre Components in the Rumen of Steers A.B. McALLAN ~and E.S. GRIFFITH 1
National Institute for Research in Dairying, Shinfield, Reading RG2 9 A T (Gt. Britain) (Received 20 January 1986; accepted for publication 11 September 1986)
ABSTRACT McAllan, A.B. and Griffith, E.S., 1987. The effects of different sources of nitrogen supplementation on the digestion of fibre components in the rumen of steers. Anim. Feed Sci. Technol., 17: 65-73. Four protozoa-free steers were given diets consisting of approximately equal proportions of a concentrate mixture of rolled barley plus tapioca and ground and pelleted alkali-treated straw. The diets were supplemented with urea and casein ( UC ), soya bean meal (SBM), 'normal' whitefish meal (FMN) or white-fish meal designated as being of 'low' rumen degradability (FML). The diets were iso-energetic and were given in amounts calculated to provide sufficient metabolisableenergy (ME) to support a growth rate of 0.5 kg day- i.R u m e n degradable nitrogen (R D N ) : M E values (g M J - ~) were estimated to be greater than 1.40 for alldiets.The diets were given in a 4 × 4 Latin square design. Polyethylene glycoland chromic oxide were given as flow markers and flows (g 24 h-i) at the abomasum of structural carbohydrate fractions were calculated. Carbehydrate fractions were defined by detergent extraction procedures. Digestibilitycoefficientsfor the ash-free N D F - A D F (hemicellulose) fractions were 0.72, 0.80, 0.85 and 0.83 for diets UC, S B M , F M N and FML, respectively.Values obtained with fishmealcontaining diets were significantly different (P < 0.05) from those with U C diets. Digestibility coefficientsof the ash-free ADF-lignin (cellulose) fractionswere 0.63,0.68,0.76 and 0.74 for diets UC, S B M , F M N and F M L , respectively. Significant differences were observed between U C and S B M diets (P < 0.05) and between U C and F M diets (P < 0.02 ). It was concluded that the type as well as the amount of R D N provided in ruminant diets isimportant in optimizing the digestion of dietary fibre in the rumen.
INTRODUCTION
McAllan and Smith (1976) showed that the addition of supplementary dietary N to basal diets of roughage and concentrates improved fibre (hemicel'Present address: Animal and Grassland Research Institute, Hurley, Maidenhead, Berks, SL6 5LR, Gt. Britain.
0377-8401/87/$03.50
© 1987 Elsevier Science Publishers B.V.
66 lulose and cellulose) digestion in the rumen but there were no significant differences between the different sources of N used. Similarly, to obtain maximum digestibility of diets containing alkali-treated roughage, supplementary N is also necessary (Miller et al., 1977) and different N sources were found to elicit different responses, with protein supplements being more effective than non-protein nitrogen ( N P N ) ( Saxena et al., 1971; McAllan and Smith, 1983 ). In these experiments, alkali-treated roughages were long or chopped, but often commercially-prepared alkali-treated straw is in a ground and pelleted form. On grinding, the penetration of the alkali into the fibres may be increased thus enhancing the improvement in digestibility associated with alkali treatment (Jackson, 1977; Evans, 1979) and it has been shown that grinding increased the digestibility in vitro of straw organic matter, with a further increase with NaOH treatment ( Smith et al., 1981 ). However, grinding roughages has been shown to reduce rumen digestibility (Beever et al., 1981), presumably as a result of faster rumen outflow of the smaller particles, and increased sodium intake has also been found to increase digesta flow rates from the rumen (Berget et al., 1980). If these effects are additive for ground and pelleted alkalitreated roughages then much of the potential additional benefit could be lost. Indeed, Coombe et al. (1979) have found that with steers receiving high ( 90% ) roughage diets, alkali treatment of the roughage significantly reduced rumen retention time of the particulate fraction, with further reduction when the alkali-treated roughage was pelleted. Thus the source and type of supplementary N required for maximum utilization of ground and pelleted alkali-treated straw may be quite different from that required for long or chopped alkalitreated straw. The present experiments were designed to study the effects of different sources of supplementary N added to diets containing ground and pelleted alkali-treated straw on the rumen degradability of fibrous components of the diet. MATERIALSAND METHODS Animals
The experiment was designed as a 4 x 4 Latin square. Four Friesian steers, which remained virtually protozoa free throughout the experiment, were used. The natural absence of protozoa was a direct result of the rearing environment (Smith and McAllan, 1974). At 12-16 weeks of age each steer was fitted with simple rumen and abomasal cannulas. At the beginning and end of the experiment, respectively, the animals had mean (with SE ) weights (kg) of 117 ( 3.7 ) and 163 {2.9 ) and mean (with SE ) ages ( weeks ) of 21.9 (1.14) and 33.9 (1.14).
67 TABLE I Amounts of the main dietary components (kg dry matter day-~), nitrogen (N; g day -~) and metabolisable energy (ME; M J day - i) given to steersweighing 120-139 kg. Also shown are estimated rumen degradable nitrogen ( R D N ) intakes (g day- I) and calculatedR D N : M E values
Diet Component Rolled barley Alkali-treated straw (ground and pelleted) Tapioca Soya bean meal White-fish meal (normal degradability) White-fish meal (low degradability) Casein Urea N RDN1 ME2 RDN : ME
UC 0.867 0.991 0.345
SBM 0.867 0.991
FMN 0.867 0.991 0.089
FML 0.867 0.991 0.102
0.435 0.316 0.317 0.053 0.064 61.4 52.1 25.1 2.08
0.040 57.2 34.3 24.4 1.41
75.1 45.6 24.0 1.90
0.040 74.9 40.8 24.1 1.69
1Calculated from degradability values derived in these experiments using ~sS. 2Calculated from energy values for individual components (Ministry of Agriculture, Fisheries and Food, 1975). Diets The animals were given four isoenergetic diets calculated to provide sufficient metabolisable energy ( M E ) to support an average growth rate of approximately 0.5 kg d a y - 1 over the whole experimental period. All the diets contained the same amounts of ground and pelleted alkali-treated straw ( Viton; B.O.C.M. Silcock Ltd. ), and rolled barley. Diets were supplemented with urea and casein {Diet U C ) , soya bean meal (Diet S B M ) , white-fish meal designated to be of 'normal' rumen degradability (Diet F M N ) or of'low' rumen degradability ( Diet F M L ) . Some diets contained tapioca to maintain similar energy levels between diets. All diets contained sufficient rumen degradable nitrogen ( R D N ) to satisfy rumen microbial requirements according to Agricultural Research Council (1984). Supplementary vitamins and minerals were also given. Daily intakes of the main dietary components are shown in Table I. These intakes were held constant over the first two periods of the experiment (42 days ) then increased by 15% for the last two periods. Actual mean weight gain over the whole experimental period of 84 days was 46 + 3 kg. The diets were given in two equal amounts at 09.00 and 17.00 h daily.
68 T A B L E II
Neutral detergent fibre ( N D F ) , acid detergent fibre (ADF), derived NDF-ADF, lignin (g kg ~ash-free DM) and ash ( g kg- ' DM ) of the major individual feed components. Results are mean values, with their standard errors, for four samples of each component Component
Rolled barley Alkali-treated straw White-fish meal ( nor mal degradability ) White-fish meal (low degradability) Soya bean meal
NDF
ADF
NDF-ADF
Lignin
Ash
Mean
SE
Mean
SE
Mean
SE
Mean
SE
Mean
SE
175.1 755.1 74.6 94.8 83.3
5.9 6.5 1.1 28.4 0.4
62.7 580.6 15.1 9.0 63.6
0.3 8.9 1.2 1.6 0.4
112.4 174.5 59.5 85.9 19.7
6.2 15.0 0.7 28.1 0.6
19.3 217.3 nil nil 9.7
1.2 12.8 nil nil 2.2
24.2 112.8 211.0 212.4 68.3
1.6 4.2 12.3 13.2 1.8
Experimental procedures and digesta collection The work reported in this paper formed part of a larger study, the full experimental details of which have been described elsewhere (McAllan et al., 1986). The pertinent details for this part of the study are as follows. Diets were given for a period of 21 days. From Day 10 onwards, 100 ml of a solution containing 30 g polyethylene glycol (molecular weight 4000; PEG) was introduced directly into the rumen at each feed together with shredded paper impregnated with chromic oxide (containing 2.62 g Cr203 ). On Day 18, samples ( approximately 150 g) of abomasal digesta were taken immediately before the morning feed and then at 3-hourly intervals over the next 21 h. Individual samples were homogenised and sub-samples (100 g) were combined, re-homogenised and stored for subsequent analysis.
Analytical Dry matter (DM) and organic matter (OM) were determined as described by Smith et al. (1978). Chromic oxide was determined according to the procedure of Williams and Smith (1974) and PEG by the method of Smith and McAllan (1971). Acid detergent fibre (ADF) and neutral detergent fibre (NDF) were determined according to Van Soest (1973) and Van Soest and Wine (1967), respectively. Lignin (L) was estimated as the fraction of ashfree ADF insoluble in 72% sulphuric acid. Estimates of the amounts of constituents flowing past the abomasum in 24 h were calculated using the dual phase marker system described by McAllan and Smith (1983). Analysis of variance was carried out according to Cochran and Cox (1962). RESULTS
The detergent fibre fractions (NDF and ADF), lignin and ash contents of the main dietary components are presented in Table II. Intakes, daily flows at
69 Table III Daily intakes ( g day 1), abomasal flows ( g day - x) and apparent ruman digestibility (g g - ~ intake ) of dietary detergent fibre fractions (results are the mean values for four animals receiving the diets described in Table I) Fibre fraction
Neutral detergent fibre (NDF) Intake Flow at abomasum
Proportion digested in tureen
Diet I
SEM
UC
SBM
FMN
FML
968 329 0.66
1007 282 0.72
992 208 0.79
1000 230 0.77
677 271 0.60
707 240 0.66
682 191 0.72
291 81 0.72
300 60 0.80
428 158 0.63
453 145 0.68
Statisticalsignificanceof differences U C v. S B M
U C v. F M N
S B M v. F M L
47.3 23.2 0.026
NS NS NS
NS +
NS NS NS
680 190 0.72
31.7 19.3 0.030
NS +
NS * *
NS NS +
311 47 0.85
320 54 0.83
14.7 11.2 0.045
NS NS NS
NS * *
NS NS NS
433 104 0.76
430 112 0.74
21.6 13.2 0.027
NS NS *
NS ** **
NS + +
Acid detergent fibre (ADF) Intake
Flow at abomasum Proportion digested in rumen NDF-ADF Intake
Flow at abomasum Proportion digested in rumen ADF-lignin {cellulose) Intake Flow at abomasum
Proportion digested in rumen
~UC: alkali-treated straw + barley+ urea + casein; SBM: alkali-treated straw + barley + soya bean meal; FMN: alkali treated straw + barley + normal degradability fishmeal; FML: alkali treated straw + barley + low degradability fishmeal. 2NS, not significant; +P < 0.10; *P < 0.05; **P < 0.02.
the abomasum and mouth to abomasum digestibility of NDF, ADF, N D F - A D F (hemicellulose) and ADF-L (cellulose) are shown in Table III. Mouth to abomasum digestibility of NDF (total fibre) was highest in FMN diets, followed in descending order by Diets FML, SBM and UC. None of the differences were significant at the 5% level. Mouth to abomasum digestibility of N D F - A D F (hemicellulose) and ADF (cellulose + lignin) followed the same dietary pattern as NDF, but the differences between FMN and UC diets were significant (P < 0.05 ) for both. Digestibility of ADF-L (cellulose) was significantly greater with diets containing soya bean meal (SBM) ( P < 0 . 0 5 ) or with either type of fishmeal (FMN and FML) ( P < 0.02 ) than with UC diets. There were no significant differences between values obtained for the two fishmeal-containing diets (FMN and FML), but the values obtained with these diets tended to be greater ( P < 0.10) than those obtained for the soya bean meal-containing diets. DISCUSSION Although ash-free ADF-L has been found to overestimate the cellulose content of certain feeds and digesta samples, the overestimation was found to be reasonably constant throughout, thus the values obtained by this method for
70 cellulose digestibility are very similar to those obtained from the analysis of cellulose (McAllan and Griffith, 1984). It is also known that values derived for hemicellulose content of alkali-treated straw and of digesta from NDF-ADF are subject to error as are the derived mouth-to-abomasum digestibility values ( McAllan and Griffith, 1984 }. However, the present experiments confirm earlier findings (Playne et al., 1972; McAllan and Griffith, 1984) that the use of NDF fractions can give nutritionally significant results in that the digestibility values obtained ranked the diets in the same order as those obtained using ADF-L, although with much greater variation and lower levels of significance of differences between diets. Mouth to abomasum digestibility values obtained for the fibre fractions of the diets used in the present work were high (0.72-0.85 for hemicellulose and 0.63-0.75 for cellulose ). These were slightly but consistently higher than those obtained for steers receiving similar diets but in which the alkali-treated straw was in a chopped form (McAllan and Smith, 1983). Rumen particulate outflow rates were not measured in the present experiments but liquid outflow rates were in the range 0.08-0.13 h -~ (McAllan et al., 1986) and of the same order as those reported for steers receiving untreated chaffed straw diets (0.07-0.16 h - 1) (A.B. McAllan, unpublished observations, 1985). Thus the expected increase in rumen outflow rates and associated decrease in fibre digestion with ground and pelleted alkali-treated straw were not observed in the present experiments. It must also be borne in mind, however, that in the present experiments the animals were receiving relatively low intakes of feed of diets containing only 50% roughage. Most other work showing changes in flow rates as a result of grinding, pelleting or alkali treatment has involved animals receiving diets high ( > 70% ) in roughage and given ad libitum. The values obtained for fibre digestion in the rumen are net results of a combination of positive and negative effects. On the one hand alkali treatment or grinding and pelleting roughages reduce rumen retention time ( Coombe et al., 1979; Berger et al., 1980; Beever et al., 1981 ) and increased water intake associated with higher sodium intakes increases liquid turnover rate (Voigt and Piatkowski, 1974). On the other hand the absence of protozoa leads to significant increases in the volume of rumen contents and numbers of cellulolytic bacteria and significantly reduces fluid outflow rates ( Orpin and Letcher, 1984), and alkali treatment and grinding increase the number of available adhesion sites for bacteria (Latham et al., 1979 ). Thus in the present experiments the positive effects, with respect to fibre digestion, appear to predominate. The significant differences observed in mouth to abomasum digestibility of dietary fibre fractions obtained with different sources of supplementary-N confirm and extend earlier findings (McAllan and Smith, 1983 ). Whilst it is known that the presence of some readily available source of energy (starch) is necessary to achieve maximum cellulolytic activity in rumen bacteria (Arias et al., 1951; Williams et al., 1984) it is also known that the addition of large
71 amounts of starch to roughage diets generally reduces rumen digestibility of hemicelluloses and cellulose {Chappell and Fontenot, 1968; Fick et al., 1973; Agergaard et al., 1984; Ben-Ghedalia and Miron, 1984). However, little effect on cellulose digestibility was observed when the starch content of the diet comprised 35% or less of the DM (Chappell and Fontenot, 1968; Coombe et al., 1985). In the present experiments starch contributed approximately 36% of the DM intake of UC diets. This contribution was reduced to approximately 27 and 22% for FM- and SBM-containing diets, respectively. Thus some of the increase in cellulose digestibility observed with the FM and SBM diets may be attributable in part to the replacement of some starch (tapioca) by the protein supplements and alleviation of the depressive effect of starch on cellulose digestion. However, the greatest improvement observed in cellulose digestion was with FM-containing diets, in which a smaller proportion of the starch had been replaced by protein than with SBM diets. Thus it appears that factors other than the starch:cellulose value in the diet were responsible for the improvement observed in fibre digestion with protein supplements. Increased dietary-N results in increased numbers of rumen bacteria, with considerably greater increases with protein- than with urea-supplemented diets (Teather et al., 1980). The greatest increases were in those species known to require branched chain VFA for optimum growth in vitro, including some predominant cellulose digesters. It is also well recognised that pre-formed amino acids are utilised by rumen bacteria ( Maeng and Baldwin, 1976) and that fibre digesting bacteria are stimulated by amino acids, peptides and branched chain VFA {Huque and Thomsen, 1984; Gorosito et al., 1985). Indeed, high molecular weight polypeptides have also been shown to support microbial growth to an even greater extent than free amino acids (Huque and Thomsen, 1984; Copper and Ling, 1985). The improvement in rumen digestibility of fibre observed in the present experiments is probably attributable to the protein supplements of the diet. Rumen degradability values of the four N supplements were approximately 0.90, 0.48, 0.33 and 0.11 for urea and casein, soya bean meal, 'normal' degradability fish meal and 'low' degradability fish meal, respectively (A.P. Williams and A.B. McAllan, unpublished observations, 1986 ) and the extent to which they supported fibre digestion in the rumen appeared to be inversely related to their degradability in the rumen. ACKNOWLEDGEMENTS The authors thank Dr. J.W. Sissons for the preparation of the animals and C. Chard for supervising their care. This work was financed through the Agricultural and Food Research Council. The work formed part of a commission from the Ministry of Agriculture, Fisheries and Food.
72 REFERENCES Agergaard, N., Boisen, S., Neergaard, L., Andersen, P.E. and Ternrud, I.E., 1984. Influence of sodium hydroxide treated straw on the metabolism of carbohydrates, nitrogen and minerals in sheep. National Institute of Animal Science, Denmark. Report No. 574, pp. 33-67. Agricultural Research Council, 1984. The Nutrient Requirements of Ruminant Livestock. Supplement No. 1. Slough: Commonwealth Agricultural Bureaux, p.12. Arias, C., Burroughs, W., Gerlaugh, P. and Bethke, R.M., 1951. The influence of different amounts and sources of energy upon in vitro urea utilisation by rumen micro organisms. J. Anita. Sci., 10: 683-692. Ben-Ghedalia, D. and Miron, J., 1984. The digestion of total and cell wall monosaccharides of alfalfa by sheep. J. Nutr., 114: 880-887. Bsever, D.E., Osbourn, D.F., Cammeli, S.B. and Terry, R.A., 1981. The effect of grinding and pelleting on the digestion of Italian ryegrass and timothy by sheep. Br. J. Nutr., 46: 357-370. Berger, L.L., Klopfenstein, T.J. and Britton, R.A., 1980. Effect of sodium hydroxide treatment on rate of passage and rate of ruminal fibre digestion. J. Anita. Sci., 50: 745-749. Chappell, G.L.M. and Fontenot, J.P., 1968. Effect of level of readily available carbohydrates in purified sheep rations on cellulose digestibility and nitrogen utilisation. J. Anim. Sci., 27: 1709-1715. Cochran, W.G. and Cox, G.M., 1962. Experimental Designs, 2nd edn., Wiley, New York, p. 50. Coombe, J.B., Dinius, D.A., Goering, H.K. and Oltjen, R.R., 1979. Wheat straw-urea diets for beef steers:Alkalitreatment and supplementation with protein, monensin and a feed intake stimulant. J. Anita. Sci.,48: 1223-1233. Coombe, J.B.,Mulholland, J.G. and Forrester,R.I.,1985. Effect of treatment with sodium hydroxide on the feeding value of oat and rape straw for sheep. Aust. J. Agric. Res., 36: 623-636. Copper, P.B. and Ling, J.R., 1985. The uptake of peptides and amino acids by rumen bacteria. Proc. Nutr. Soc., 44: 144A. Evans, P.J., 1979. Chemical and physical aspects of the interaction of sodium hydroxide with the cellwall components of straw. In: E. Grossbard (Editor), Straw Decay and its Effect on Disposal and Utilization.Wiley, Chichester, pp. 187-197. Fick, K.R., Ammerman, C.B., McGowan; C.H., Loggins, P.E. and Cornell, J.A., 1973. Influence of supplemental energy and biuret nitrogen on the utilizationof low quality roughage by sheep. J. Anita. Sci.,36: 137-143. Gorosito, A.R., Russell,J.B. and Van Soest, P.J., 1985. Effect of carbon-4 and carbon-5 volatile fatty acids on digestion of plant cellwalls in vitro.J. Dairy Sci.,68: 840-847. Huque, Q.E. and Thomsen, K.V., 1984. Source of nitrogen for rumen microbes. Acta Agric. Scand., 34: 26-32. Jackson, M.G., 1977. The alkali treatment of straws. Anim. Feed Sci. Technol., 2: 105-130. Latham, M.J., Hobbs, D.G. and Harris, P.J., 1979. Adhesion of rumen bacteria to alkali-treated plant stems. Ann. Rech. Vet., 10: 244-245. McAllan, A.B. and Griffith, E.S., 1984. Evaluation of detergent extraction procedures for characterising carbohydrate components in ruminant feeds and digesta. J. Sci. Food Agric., 35: 869-877. McAllan, A.B. and Smith, R.H., 1976. Effect of dietary nitrogen source on carbohydrate metabolism in the rumen of the young steer. Br. J. Nutr., 36: 511-522. McAUan, A.B. and Smith, R.H., 1983. Factors influencing the digestion of dietary carbohydrates between the mouth and abomasum of steers. Br. J. Nutr., 50: 445-454. McAllan, A.B., Williams, A.P., Cockburn, J.E., Griffith, E.S., Lewis, P.E. and Smith, R.H., 1986. The effects of different sources of nitrogen supplementation on the post ruminal flows of organic matter and different nitrogenous constituents in steers. Arch. Tierernaehr., 36: 409-418. Maeng, W.G. and Baldwin, R.L., 1976. Factors influencing rumen microbial growth rates and
73 yields:Effects of amino acid additions to a purified diet with nitrogen from urea. J. Dairy Sci., 59: 648-655. Miller, E.L., Johnson, F.L., Briggs, M.C.E. and Kempsey, R.G., 1977. The effects of alkali and urea on ground and pelleted all-straw diets for sheep. Proc. Nutr. Soc., 36: 129A. Ministry of Agriculture, Fisheries and Food, 1975. Technical Bulletin No. 33. H.M.S.O., London, pp. 26-43. Orpin, C.G. and Letcher, A.J., 1984. Effect of absence of ciliate protozoa on rumen fluid volume, flow rate and bacterial populations in sheep. Anita. Feed Sci. Technol., 10: 145-153. Playne, M.J., McLeod, M.N. and Dekker, R.F.H., 1972. Digestion of dry matter, nitrogen, phosphorus, sulphur, calcium and detergent-fibre fractions of the seed and pod of Stylosanthes humilis contained in terylene bags in the bovine rumen. J. Sci. Food Agric., 23: 925-932. Saxena, S.K., Otterby, D.E., Donker, J.D. and Good, A.L., 1971. Effects of feeding alkali-treated oat straw supplemented with soybean meal or non protein nitrogen on growth of lambs and on certain blood and rumen liquor parameters. J. Anita. Sci., 33: 485-490. Smith, R.H. and McAllan, A.B., 1971. Nucleic acid metabolism in the ruminant. 3. Amounts of nucleic acids and total and ammonia nitrogen in digesta from the rumen, duodenum and ileum of calves. Br. J. Nutr., 25: 181-190. Smith, R.H. and McAllan, A.B., 1974. Some factors influencing the chemical composition of mixed rumen bacteria. Br. J. Nutr., 31: 27-34. Smith, R.H., McAllan, A.B., Hewitt, D. and Lewis, P.E., 1978. Estimation of the amounts of microbial and dietary nitrogen compounds entering the duodenum of cattle. J. Agric. Sci. (Camb.), 90: 557-568. Smith, T., Broster, W.H., Broster, V.J. and Siviter, J.W., 1981. The effects of grinding either with or without sodium hydroxide treatment on the utilisation of straw by yearling dairy cattle. J. Agric. Sci. (Camb.), 96: 159-165. Teather, R.M., Erfle, J.D., Boila, R.J. and Sauer, F.D., 1980. Effect of dietary nitrogen on the rumen microbial population in lactating dairy cattle. J. Appl. Bacteriol., 49: 231-238. Van Soest, P.J., 1973. Collaborative study of acid detergent fibre and lignin. J. Assoc. Off. Agric. Chem., 56: 781-784. Van Soest, P.J. and Wine, R.H., 1967. Use of detergents in the analysis of fibrous feeds. IV. Determination of plant cell wall constituents. J. Assoc. Off. Agric. Chem., 50: 50-55. Voigt, J. and Piatkowski, B., 1974. Studies on the chemical degradation of cereal straw. 5. The effect of sodium in NaOH treated straw on the excretion of various compounds. Arch. Tierernaehr., 24: 589-599. Williams, A.P. and Smith, R.H., 1974. Concentrations of amino acids and urea in the plasma of the ruminating calf and the estimation of the amino acid requirements. Br. J. Nutr., 32: 421-433. Williams, P.E.V., Innes, G.M. and Moor, P.J., 1984. Supplementation of a diet of straw or fishmeal:Effects on the degradability and rate of outflow of straw from the rumen. Anim. Prod., 38: 551.
65
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
The Effects of Different Sources of Nitrogen Supplementation on the Digestion of Fibre Components in the Rumen of Steers A.B. McALLAN ~and E.S. GRIFFITH 1
National Institute for Research in Dairying, Shinfield, Reading RG2 9 A T (Gt. Britain) (Received 20 January 1986; accepted for publication 11 September 1986)
ABSTRACT McAllan, A.B. and Griffith, E.S., 1987. The effects of different sources of nitrogen supplementation on the digestion of fibre components in the rumen of steers. Anim. Feed Sci. Technol., 17: 65-73. Four protozoa-free steers were given diets consisting of approximately equal proportions of a concentrate mixture of rolled barley plus tapioca and ground and pelleted alkali-treated straw. The diets were supplemented with urea and casein ( UC ), soya bean meal (SBM), 'normal' whitefish meal (FMN) or white-fish meal designated as being of 'low' rumen degradability (FML). The diets were iso-energetic and were given in amounts calculated to provide sufficient metabolisableenergy (ME) to support a growth rate of 0.5 kg day- i.R u m e n degradable nitrogen (R D N ) : M E values (g M J - ~) were estimated to be greater than 1.40 for alldiets.The diets were given in a 4 × 4 Latin square design. Polyethylene glycoland chromic oxide were given as flow markers and flows (g 24 h-i) at the abomasum of structural carbohydrate fractions were calculated. Carbehydrate fractions were defined by detergent extraction procedures. Digestibilitycoefficientsfor the ash-free N D F - A D F (hemicellulose) fractions were 0.72, 0.80, 0.85 and 0.83 for diets UC, S B M , F M N and FML, respectively.Values obtained with fishmealcontaining diets were significantly different (P < 0.05) from those with U C diets. Digestibility coefficientsof the ash-free ADF-lignin (cellulose) fractionswere 0.63,0.68,0.76 and 0.74 for diets UC, S B M , F M N and F M L , respectively. Significant differences were observed between U C and S B M diets (P < 0.05) and between U C and F M diets (P < 0.02 ). It was concluded that the type as well as the amount of R D N provided in ruminant diets isimportant in optimizing the digestion of dietary fibre in the rumen.
INTRODUCTION
McAllan and Smith (1976) showed that the addition of supplementary dietary N to basal diets of roughage and concentrates improved fibre (hemicel'Present address: Animal and Grassland Research Institute, Hurley, Maidenhead, Berks, SL6 5LR, Gt. Britain.
0377-8401/87/$03.50
© 1987 Elsevier Science Publishers B.V.
66 lulose and cellulose) digestion in the rumen but there were no significant differences between the different sources of N used. Similarly, to obtain maximum digestibility of diets containing alkali-treated roughage, supplementary N is also necessary (Miller et al., 1977) and different N sources were found to elicit different responses, with protein supplements being more effective than non-protein nitrogen ( N P N ) ( Saxena et al., 1971; McAllan and Smith, 1983 ). In these experiments, alkali-treated roughages were long or chopped, but often commercially-prepared alkali-treated straw is in a ground and pelleted form. On grinding, the penetration of the alkali into the fibres may be increased thus enhancing the improvement in digestibility associated with alkali treatment (Jackson, 1977; Evans, 1979) and it has been shown that grinding increased the digestibility in vitro of straw organic matter, with a further increase with NaOH treatment ( Smith et al., 1981 ). However, grinding roughages has been shown to reduce rumen digestibility (Beever et al., 1981), presumably as a result of faster rumen outflow of the smaller particles, and increased sodium intake has also been found to increase digesta flow rates from the rumen (Berget et al., 1980). If these effects are additive for ground and pelleted alkalitreated roughages then much of the potential additional benefit could be lost. Indeed, Coombe et al. (1979) have found that with steers receiving high ( 90% ) roughage diets, alkali treatment of the roughage significantly reduced rumen retention time of the particulate fraction, with further reduction when the alkali-treated roughage was pelleted. Thus the source and type of supplementary N required for maximum utilization of ground and pelleted alkali-treated straw may be quite different from that required for long or chopped alkalitreated straw. The present experiments were designed to study the effects of different sources of supplementary N added to diets containing ground and pelleted alkali-treated straw on the rumen degradability of fibrous components of the diet. MATERIALSAND METHODS Animals
The experiment was designed as a 4 x 4 Latin square. Four Friesian steers, which remained virtually protozoa free throughout the experiment, were used. The natural absence of protozoa was a direct result of the rearing environment (Smith and McAllan, 1974). At 12-16 weeks of age each steer was fitted with simple rumen and abomasal cannulas. At the beginning and end of the experiment, respectively, the animals had mean (with SE ) weights (kg) of 117 ( 3.7 ) and 163 {2.9 ) and mean (with SE ) ages ( weeks ) of 21.9 (1.14) and 33.9 (1.14).
67 TABLE I Amounts of the main dietary components (kg dry matter day-~), nitrogen (N; g day -~) and metabolisable energy (ME; M J day - i) given to steersweighing 120-139 kg. Also shown are estimated rumen degradable nitrogen ( R D N ) intakes (g day- I) and calculatedR D N : M E values
Diet Component Rolled barley Alkali-treated straw (ground and pelleted) Tapioca Soya bean meal White-fish meal (normal degradability) White-fish meal (low degradability) Casein Urea N RDN1 ME2 RDN : ME
UC 0.867 0.991 0.345
SBM 0.867 0.991
FMN 0.867 0.991 0.089
FML 0.867 0.991 0.102
0.435 0.316 0.317 0.053 0.064 61.4 52.1 25.1 2.08
0.040 57.2 34.3 24.4 1.41
75.1 45.6 24.0 1.90
0.040 74.9 40.8 24.1 1.69
1Calculated from degradability values derived in these experiments using ~sS. 2Calculated from energy values for individual components (Ministry of Agriculture, Fisheries and Food, 1975). Diets The animals were given four isoenergetic diets calculated to provide sufficient metabolisable energy ( M E ) to support an average growth rate of approximately 0.5 kg d a y - 1 over the whole experimental period. All the diets contained the same amounts of ground and pelleted alkali-treated straw ( Viton; B.O.C.M. Silcock Ltd. ), and rolled barley. Diets were supplemented with urea and casein {Diet U C ) , soya bean meal (Diet S B M ) , white-fish meal designated to be of 'normal' rumen degradability (Diet F M N ) or of'low' rumen degradability ( Diet F M L ) . Some diets contained tapioca to maintain similar energy levels between diets. All diets contained sufficient rumen degradable nitrogen ( R D N ) to satisfy rumen microbial requirements according to Agricultural Research Council (1984). Supplementary vitamins and minerals were also given. Daily intakes of the main dietary components are shown in Table I. These intakes were held constant over the first two periods of the experiment (42 days ) then increased by 15% for the last two periods. Actual mean weight gain over the whole experimental period of 84 days was 46 + 3 kg. The diets were given in two equal amounts at 09.00 and 17.00 h daily.
68 T A B L E II
Neutral detergent fibre ( N D F ) , acid detergent fibre (ADF), derived NDF-ADF, lignin (g kg ~ash-free DM) and ash ( g kg- ' DM ) of the major individual feed components. Results are mean values, with their standard errors, for four samples of each component Component
Rolled barley Alkali-treated straw White-fish meal ( nor mal degradability ) White-fish meal (low degradability) Soya bean meal
NDF
ADF
NDF-ADF
Lignin
Ash
Mean
SE
Mean
SE
Mean
SE
Mean
SE
Mean
SE
175.1 755.1 74.6 94.8 83.3
5.9 6.5 1.1 28.4 0.4
62.7 580.6 15.1 9.0 63.6
0.3 8.9 1.2 1.6 0.4
112.4 174.5 59.5 85.9 19.7
6.2 15.0 0.7 28.1 0.6
19.3 217.3 nil nil 9.7
1.2 12.8 nil nil 2.2
24.2 112.8 211.0 212.4 68.3
1.6 4.2 12.3 13.2 1.8
Experimental procedures and digesta collection The work reported in this paper formed part of a larger study, the full experimental details of which have been described elsewhere (McAllan et al., 1986). The pertinent details for this part of the study are as follows. Diets were given for a period of 21 days. From Day 10 onwards, 100 ml of a solution containing 30 g polyethylene glycol (molecular weight 4000; PEG) was introduced directly into the rumen at each feed together with shredded paper impregnated with chromic oxide (containing 2.62 g Cr203 ). On Day 18, samples ( approximately 150 g) of abomasal digesta were taken immediately before the morning feed and then at 3-hourly intervals over the next 21 h. Individual samples were homogenised and sub-samples (100 g) were combined, re-homogenised and stored for subsequent analysis.
Analytical Dry matter (DM) and organic matter (OM) were determined as described by Smith et al. (1978). Chromic oxide was determined according to the procedure of Williams and Smith (1974) and PEG by the method of Smith and McAllan (1971). Acid detergent fibre (ADF) and neutral detergent fibre (NDF) were determined according to Van Soest (1973) and Van Soest and Wine (1967), respectively. Lignin (L) was estimated as the fraction of ashfree ADF insoluble in 72% sulphuric acid. Estimates of the amounts of constituents flowing past the abomasum in 24 h were calculated using the dual phase marker system described by McAllan and Smith (1983). Analysis of variance was carried out according to Cochran and Cox (1962). RESULTS
The detergent fibre fractions (NDF and ADF), lignin and ash contents of the main dietary components are presented in Table II. Intakes, daily flows at
69 Table III Daily intakes ( g day 1), abomasal flows ( g day - x) and apparent ruman digestibility (g g - ~ intake ) of dietary detergent fibre fractions (results are the mean values for four animals receiving the diets described in Table I) Fibre fraction
Neutral detergent fibre (NDF) Intake Flow at abomasum
Proportion digested in tureen
Diet I
SEM
UC
SBM
FMN
FML
968 329 0.66
1007 282 0.72
992 208 0.79
1000 230 0.77
677 271 0.60
707 240 0.66
682 191 0.72
291 81 0.72
300 60 0.80
428 158 0.63
453 145 0.68
Statisticalsignificanceof differences U C v. S B M
U C v. F M N
S B M v. F M L
47.3 23.2 0.026
NS NS NS
NS +
NS NS NS
680 190 0.72
31.7 19.3 0.030
NS +
NS * *
NS NS +
311 47 0.85
320 54 0.83
14.7 11.2 0.045
NS NS NS
NS * *
NS NS NS
433 104 0.76
430 112 0.74
21.6 13.2 0.027
NS NS *
NS ** **
NS + +
Acid detergent fibre (ADF) Intake
Flow at abomasum Proportion digested in rumen NDF-ADF Intake
Flow at abomasum Proportion digested in rumen ADF-lignin {cellulose) Intake Flow at abomasum
Proportion digested in rumen
~UC: alkali-treated straw + barley+ urea + casein; SBM: alkali-treated straw + barley + soya bean meal; FMN: alkali treated straw + barley + normal degradability fishmeal; FML: alkali treated straw + barley + low degradability fishmeal. 2NS, not significant; +P < 0.10; *P < 0.05; **P < 0.02.
the abomasum and mouth to abomasum digestibility of NDF, ADF, N D F - A D F (hemicellulose) and ADF-L (cellulose) are shown in Table III. Mouth to abomasum digestibility of NDF (total fibre) was highest in FMN diets, followed in descending order by Diets FML, SBM and UC. None of the differences were significant at the 5% level. Mouth to abomasum digestibility of N D F - A D F (hemicellulose) and ADF (cellulose + lignin) followed the same dietary pattern as NDF, but the differences between FMN and UC diets were significant (P < 0.05 ) for both. Digestibility of ADF-L (cellulose) was significantly greater with diets containing soya bean meal (SBM) ( P < 0 . 0 5 ) or with either type of fishmeal (FMN and FML) ( P < 0.02 ) than with UC diets. There were no significant differences between values obtained for the two fishmeal-containing diets (FMN and FML), but the values obtained with these diets tended to be greater ( P < 0.10) than those obtained for the soya bean meal-containing diets. DISCUSSION Although ash-free ADF-L has been found to overestimate the cellulose content of certain feeds and digesta samples, the overestimation was found to be reasonably constant throughout, thus the values obtained by this method for
70 cellulose digestibility are very similar to those obtained from the analysis of cellulose (McAllan and Griffith, 1984). It is also known that values derived for hemicellulose content of alkali-treated straw and of digesta from NDF-ADF are subject to error as are the derived mouth-to-abomasum digestibility values ( McAllan and Griffith, 1984 }. However, the present experiments confirm earlier findings (Playne et al., 1972; McAllan and Griffith, 1984) that the use of NDF fractions can give nutritionally significant results in that the digestibility values obtained ranked the diets in the same order as those obtained using ADF-L, although with much greater variation and lower levels of significance of differences between diets. Mouth to abomasum digestibility values obtained for the fibre fractions of the diets used in the present work were high (0.72-0.85 for hemicellulose and 0.63-0.75 for cellulose ). These were slightly but consistently higher than those obtained for steers receiving similar diets but in which the alkali-treated straw was in a chopped form (McAllan and Smith, 1983). Rumen particulate outflow rates were not measured in the present experiments but liquid outflow rates were in the range 0.08-0.13 h -~ (McAllan et al., 1986) and of the same order as those reported for steers receiving untreated chaffed straw diets (0.07-0.16 h - 1) (A.B. McAllan, unpublished observations, 1985). Thus the expected increase in rumen outflow rates and associated decrease in fibre digestion with ground and pelleted alkali-treated straw were not observed in the present experiments. It must also be borne in mind, however, that in the present experiments the animals were receiving relatively low intakes of feed of diets containing only 50% roughage. Most other work showing changes in flow rates as a result of grinding, pelleting or alkali treatment has involved animals receiving diets high ( > 70% ) in roughage and given ad libitum. The values obtained for fibre digestion in the rumen are net results of a combination of positive and negative effects. On the one hand alkali treatment or grinding and pelleting roughages reduce rumen retention time ( Coombe et al., 1979; Berger et al., 1980; Beever et al., 1981 ) and increased water intake associated with higher sodium intakes increases liquid turnover rate (Voigt and Piatkowski, 1974). On the other hand the absence of protozoa leads to significant increases in the volume of rumen contents and numbers of cellulolytic bacteria and significantly reduces fluid outflow rates ( Orpin and Letcher, 1984), and alkali treatment and grinding increase the number of available adhesion sites for bacteria (Latham et al., 1979 ). Thus in the present experiments the positive effects, with respect to fibre digestion, appear to predominate. The significant differences observed in mouth to abomasum digestibility of dietary fibre fractions obtained with different sources of supplementary-N confirm and extend earlier findings (McAllan and Smith, 1983 ). Whilst it is known that the presence of some readily available source of energy (starch) is necessary to achieve maximum cellulolytic activity in rumen bacteria (Arias et al., 1951; Williams et al., 1984) it is also known that the addition of large
71 amounts of starch to roughage diets generally reduces rumen digestibility of hemicelluloses and cellulose {Chappell and Fontenot, 1968; Fick et al., 1973; Agergaard et al., 1984; Ben-Ghedalia and Miron, 1984). However, little effect on cellulose digestibility was observed when the starch content of the diet comprised 35% or less of the DM (Chappell and Fontenot, 1968; Coombe et al., 1985). In the present experiments starch contributed approximately 36% of the DM intake of UC diets. This contribution was reduced to approximately 27 and 22% for FM- and SBM-containing diets, respectively. Thus some of the increase in cellulose digestibility observed with the FM and SBM diets may be attributable in part to the replacement of some starch (tapioca) by the protein supplements and alleviation of the depressive effect of starch on cellulose digestion. However, the greatest improvement observed in cellulose digestion was with FM-containing diets, in which a smaller proportion of the starch had been replaced by protein than with SBM diets. Thus it appears that factors other than the starch:cellulose value in the diet were responsible for the improvement observed in fibre digestion with protein supplements. Increased dietary-N results in increased numbers of rumen bacteria, with considerably greater increases with protein- than with urea-supplemented diets (Teather et al., 1980). The greatest increases were in those species known to require branched chain VFA for optimum growth in vitro, including some predominant cellulose digesters. It is also well recognised that pre-formed amino acids are utilised by rumen bacteria ( Maeng and Baldwin, 1976) and that fibre digesting bacteria are stimulated by amino acids, peptides and branched chain VFA {Huque and Thomsen, 1984; Gorosito et al., 1985). Indeed, high molecular weight polypeptides have also been shown to support microbial growth to an even greater extent than free amino acids (Huque and Thomsen, 1984; Copper and Ling, 1985). The improvement in rumen digestibility of fibre observed in the present experiments is probably attributable to the protein supplements of the diet. Rumen degradability values of the four N supplements were approximately 0.90, 0.48, 0.33 and 0.11 for urea and casein, soya bean meal, 'normal' degradability fish meal and 'low' degradability fish meal, respectively (A.P. Williams and A.B. McAllan, unpublished observations, 1986 ) and the extent to which they supported fibre digestion in the rumen appeared to be inversely related to their degradability in the rumen. ACKNOWLEDGEMENTS The authors thank Dr. J.W. Sissons for the preparation of the animals and C. Chard for supervising their care. This work was financed through the Agricultural and Food Research Council. The work formed part of a commission from the Ministry of Agriculture, Fisheries and Food.
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