Improving the nutritive value of low quality forages.

Abstract

10 IMPROVING THE NUTRITIVE VALUE OF LOW QUALITY FORAGES R.C. KELLAWAY* Summary .,The availability of, and nutrient deficiencies in, low quality 'forages in Australia are discussed. Effects of NaOH, KOH, Ca(OH)2, Na2C.03 and NH40H on the digestibility and .edibility of forages are reviewed, together with the techniques used in application of alkalis. ,It is concluded that substantial increases in the nutritive value of low quality forages can be effected by spraying solutions of, alkali and supplementary nutrients onto forages, using batch or continuous-flow processes suitable for use on farms. I. INTRODUCTION Low quality forages are characterised primarily by their low edibility and low content of available energy. These deficiencies ' frequently are compounded by low contents of nitrogen and certain minerals. The edibility and available energy content of forages can be increased by chemical, physical and enzymic processes. Commercial adoption of such processes is being determined by the cost of measured improvements iti nutritive value in relation to,the cost of alternative feedstuffs. AVAILABLE FORAGES II. Cereal straws represent the most readily accessible source of low quality forages. Approximately 12 million hectares of cereals grown in Australia produce about 30 million tonnes straw annually. Much of this is burnt, a practice which is becoming increasingly unacceptable because of air pollution, and much of it is. grazed by sheep and cattle. Grazing may.assist straw dispersal, but the animals are unable to maintain bodyweight on cereal straw residueswhich are free of weeds (Mulholland et a l . 1976). The composition of cereal straws varies considerably as.shown in Table 1. Comparisons of mean values for'components,ofstraws with dietary concentrations recommended for the maintenance of 200 kg steers, ' indicates that these cereal strawsare deficient in available energy as measured by digestible organic matter in the dry matter (DOMD), as well 'as nitrogen and phosphorus. , Certain straws would also be deficient in calcium, sodium and potassium. In order.to maintain a nitrogen (N) to sulphur (S) ratio of 10 : 1 in the diet a sulphur concentration of 1.36 g S/kg DM would be required. Sulphur levels of 0.8-2.1 g S/kg DM have been recorded in wheat straw in South Australia (Schultz and French 1976). DOMD values in Table 1 rank the cereals in the order barley > oats > wheat, with considerable overlap between species. DM digestibility was found to be. negatively related to the length of the growing season . within the range 22-36 % DMD and 8.0-3.5 months growing season (Dr. D.B. Purser - personal communication). * Department .of Animal Husbandry, University of Sydney, Camden, N.S.W. 2570. I 11. Chemical composition and digestible organic matter in the dry I TABLE 1 matter (DOMD) of cereal straws collected from seven locations in Victoria(l) and dietary concentrations recommended for the maintenance of 20.0 kg steers(2) Mature pasture grasses, native and improved, constitute an even greater reservoir than cereal straws of low quality forages which are potentially useful to ruminants. Difficulties in harvesting native pastures from uncultivated land may be well worth overcoming, if promising improvements in nutritive value effected by alkali treatments (Siebert 1974) are confirmed by further study. III. ALKXGIS USED TO INCREASE FORAGE DIGESTIBILITY.AND EDIBILITY The alkalis NaOH, KOH, Ca(OH)2, Na2C03 and NH&OH have all been shown to improve the nutritive value of loti quality forages. The mode, of action is to disrupt cell walls by dissolving hemicellulose, lignin and silica, by hydrolysing uranic and acetic acid esters and by causing cellulose fibres to swell (Jackson 1977). (a) NaOH NaOH has been used to upgrade low quality forages for over 80 years, much longer than other chemicals. For this reason a considerable amount of inforrnation'has accumulated concerning its use (see review by Jackson 1977). Recently, information ,was recorded on the kinetics of digestion of untreated and NaOHitreated forages (Table 2). These observations showed that NaOH treatment increased the,proportion of potentially digestible cell'walls and increased clearancerates of cell walls from . the rumen, both by digestion and onward passage of undigested materials. The distribution of particle sizes in the rumen indicates that the clearance of particles small enough to pass through the reticula-omasal ..orifice (< 1 mm) was more rapid'with NaOH-treated than with untreated . forages.. A consequence of this was that the ratio of cell walls digested in the rumen : cell walls digested in the caecum was reduced by NaOH treatment (Redman, R.G. and Kellaway,'R.C., unpublished data). This re'sulted in a small l&s of microbial protein synthesised in th,e. . . caecun, but was more than'compensated for by greater quantities of microbial protein synthesised in the rumen (loci cit.). Intakes of dry -matter (DM) and digestible DM were'increased greatly by NaOH treatment . 1 2 (Table 2). r NaOH effects linear increases in DM digestibility of straw in vitro corresponding,to about 4.5 digestibility units for each 10 g increment 'in NaOH over the range O-100 g NaOH/kg forage dry matter (Chandra and Jackson 1971; Rohb.1976). Above 80 g NaOH/kg forage,.DOMD in vitro was : found to fall,. due to the diminishing response in digestibility and the increasing dilution effect of forage dry matter with NaOH (Robb 1976). When NaOH-treated forages are fed to ruminants, organic matter (OM) digestibility increases by about 3.6 units per 10 g increment in NaOH. over the range O-45 g NaOH/kg forage dry matter (Rexen and Thomsen 1976). . Above 45-50 g NaOH/kg forage OM digestibility does not increase when the forage contributes over 70 % of the diet (Rexen and Thomsen 1976; Singh and Jackson 1971). This suggests that high pH or higher' intakes of Na could be interfering with rumen function.. However, this is not supp.orted by observations that digestibilities of wheat straw treated with 30 and 60 *g NaOH/kg DM were similar when the wheat straw contributed only about 30 % of DM intake (Holzer, Levy and Folman 1978). Also, neutralization of excess NaOH does not appear to change the NaOH.level (45-50 g NaOH/kg forage), above which digestibility in vivo is not increased (Jayasuriyaand Owen 1975; Holzer, Levy andTo= 19.78). A possible reason for this is that with high,$evels of NaOH treatment, i'ncremental increa'ses in passage rates of fibre from the rumen are, greater than incremental increases in digestion rates of fibre. NaOH treatment of low quality forages generally increases their edibility'by up to 100 %'(Table 2,) but as-with digestibility, responses only occur up to about'&50, g NaOH/kg forage (Singh and Jackson 1971; Ho1ze.r) Levy and'Fol.man 1978): 13 '. (b) KOH Ruminants are well adapted to high intakes of potassium. It is of interest that steers given a free choice of NaOH or KOH-treated forages showed a strong preference for the latter (Siebert 1974). Without free choice, the edibility of KOH-treated forage was shown to be higher than that of NaOH-treated forage (Petchey and Mbatya 1977). KOH increases digestibility to about the same extent as NaOH (Rounds et al. 1976; Wilkinson and Santillana 1978), but its use is likely toberestricted because it costs about three times more than equi-molar amounts of NaOH. In contrast to KOH, Ca(OH)2 is about a quarter of the cost of NaOH on an equi-molar basis. However, it is much less. soluble'than NaOH and as a consequence it reacts more slowly. When forage is kept moist for long periods, as with ensilage, Ca(OH)2 has proved to be almost as effective as NaOH (Wilkinson and Santillana 1978). Combinations of NaOH and Ca(OH)2 may prove to.be more effective than either alkali alone (Waller and Klopfenstein 1975). (d) Na2C03 Na2C03, like.Ca(OH)2, is a much safer Evidence on its efficacy is conflicting; it to be much less effective than NaOH, found that DM digestibility of oat straw to 84'% in l-3 days by NaOH and from 47 (e) NH40H Recently, considerable interest has been shown in the use of anhy.drous ammonia, NH3, and aqueous ammonia, NHbOH, for treating low quality forages. Anhydrous NH3 is cheaper than aqueous ammonia but it can only act as an alkali when it dissolves in water to form NH40H. Comparisons between .NaOH and NH40H are given in Table 3. Anhydrous NH3 is more costly than NaOH, but because the optimum level bf application is lower (Jackson 1977; Sundstdl, Said and Arnason 1979) the cost of the chemicals per tonne forage treated is similar. About 26 %'of the nitrogen in NH40H is retained in the forage after treatment (Table 3) so that 1 ess urea is,require,d to overcome deficiencies'of nitrogen in NHbOH-treated forages. I Comparisons of NaOH and NHhOH-treated forages indicate that, + increases in digestibility in vitro. effected by'NH40H are about 64 % (Hartley and Jonesl978) to79 % (Bales, Kellogg and Miller 1979) of those effected by NaOH. In vivo, 3 % NH3 was foundto increase DM digestibility .of cereal s??axorn 42 to 57 56 and DM intake by sheep from 257 to 457 g/day (Lawlor and.O%hea 1979). More comparative information on the efficacy of NaOH and NH40H.is required. . The reaction times for low quality forages treated with 35 g NH4'0H/* ' kg forage are 4-8 weeks at 545OC, l-4 weeks at 1%30�C and less than 1 week above 30�C (Sundstdl, Coxworth and Mowat 1978). In contrast, NaOHo reactions with forage fibre appear to be complete in about 2 days at 20 c .(Kellaway et al. 1978) and 20 seconds under conditions of high pressure -m chemical to use than NaOH. Chandra and Jackson (1971) found whereas Coombe and Dove (1978) in vitro was increased from 47 to7%in 7 days by Na2C03. 14 TABLE 3 Comparisons between NaOH and NH40H as alternative alkalis for upgrading the nutritive vaiue of forages and temperature.(Rexen and Thomsen 1976). During the reaction period the + forage has to be kept a3 about 150-250 g H2O/kg forage. In Europe, the tioisture content of straw at harvest ,is normally about 150 g/kg forage, whereas in Australia, moisture levels of 70-80 g/kg are common. Thus, straw in Europe can be treated with anhydrous NH3 without addition of water (Suns%&, Coxworth and Mowat lg78), a.distlnct advantage over NaOH 'treatment, which requires the use of sufficient water to distribute the . alkali evenly over the forage. It is 'possible that this advantage of NH3 treatment may be lost in Australia if it .proves necessary to apply additional water to the forage. . I *When the initial moisture content of NaOH-treated forage is 200-250 g/kg, compression of the forage, in bales ;'pits or stacks is normally sufficient to maintain adequate moisture levels for the duration of the ,reaction. In'contrast, NHbOH-treated forage has to be kept under gastight conditions. The most inexpensive method of retaining NH3 is probably a polythene cover, the cost of which is $20.2/t forage. Thus, the cost of chemicals plus a polythene cover for NHbH treatment is $35.9,/ t forage compared with $20.8/t forage for the chemicals used in,NaOH treatment. Forage treated with 45 g NaOH/kg contains 26 g Na/kg forage which is greatly in excess of dietary requirements (Table 1). Excess Na is excreted in the urine, which is,facilitated .by anincrease in water con%umption of about 50 ml/g Na (Pirie and Greenhalgh 1978) or' 1.3 l/kg .treated forage. .These increases in waterconsumption and urine output can cause difficulties in animal management. Also, Na in the urine may adversely affect soil structure and the quality of stream water. 15 IV. TECHNIQUES FOR APPLYING ALKALIS TO FORAGES A ,technique .for applying anhydrous NH3 to forage is describ.ed in detail by .Sundst&, Coxworth and.Mowat (1978). Techniques for applying NaOH to forages may be classified as soaking or spraying. Soaking methods entail immersing forage in NaOH solution for 18-20 hours, washing it free of.excess NaOH, and drying it .(Beckmann : 1921 cited by Jackson 1977): Spraying techniques entail applying a spray of concentrated solution of NaOH with no subsequent washing or drying (Wilson and Pigden 1964). Spraying techniques require much less water, produce a lighter product and do not wash out soluble nutrients. (a) Industrial spraying techniques . Spraying techniques developed for industrial use in Europe, involve grinding the forage, spraying it with NaOH solution and pe,lleting under conditions of high temperature and pressure (Rexen and Thomsen 1976.; Wilson and Brigstocke 1977). The product is incorporated into commercial concentrate mixtures at 5-20 % of the mixtures, although there does not appear to be any information on the nutritive value of treated straw utilised'in this way (Jackson 1977). It is known that untreated cereal straws which are ground and pelleted with concentrates can supply up to ,20% of the mixture without affecting growth or feed conver.sion ratios (Lamming, Swan and Clarke 1966). It is unlikely that similar commercial methods will be developed in Australia because the cost of the product is likely to be too high in relation to that of cereal grain, which has a much superior nutritive value. '(b) F arm spraying techniques -- When alkali-treated forages can be consumed on the farms where the forages are grown, there is considerable merit in carrying out the treat.ment process on the farm. At the present time there are two alternative methods:(i) Mixer trailer (Greenhalgh 1976). The forage is passed through a hammer-mill (4 cm screen) into a mixer trailer. NaOH solution is sprayed ontothe forage whilst mixing and the treated forage is transferred into sacks. Urea and mineral . I solutions also can be sprayed onto the forage in the trailer. The results of a feeding trial with cattle (Table 4) can'be used to calcul'ate the value of untreated and NaOH-treated barley'straw. If the cost of rolled barley and soya-bean meal are assumed to be $154 and $400/t respectively, the calculated values of untreated and NaOH-treated straws in this experiment were - $31 and + $21/t respectively. On this basis, both types of straw would be.uneconomic alternatives to barley grain. However, if the inclusion level of soya&bean meal had been 29 kg/t in all three diets and the nitrogen deficits in diets. AS40 and WS4C had been supplied by urea, it may be calculated that the value of untreated and NaOHtreated straws would have been $7 and $61/t respectively (assumingthat feed conversion ratios had stayed the same). There is 'evidence that cattle eating alkali-treated straw utilise urea very efficiently and may . not need a protein supplement. Coombe et al. (1979) fed St eersuntreated and NaOH-treated wheat straw together wxh%trogen supplements containing urea (U) and soya-bean meal (SBM) supplying nitrogen in the ratios 16 Cmqarisons between a concentrate diet (C) and diets in which TABLE & 40 % of the diet was replaced with NaOH-treated (ASbO) or water-treated (WS40).barley straw which was coarsely milled (4 mm screen) and sprayed in a mixer trailer. 100 u : 0 SBM and 90 U : 10 SBM (Table 5). This experiment showed that replacement of urea with soya-bean meal did not increase feed intake or liveweight gain. It also showed that fine grinding and pelleting greatly increased feed intake and growth rate with untreated straw, and had smaller effects with NaOH-treated straw. In a survey on the effects of grinding and pelleting roughages, .Greenhalgh and Wainman (1972) concluded that pelleting and grinding generally increase intake by up to 30 %, with smaller responses from more-digestible materiali In the mixer trailer technique discussed the amounts of water applied were '360 (Greenhalgh 1976) and 400 (Coombe et al. 1979) kg/t air dry straw. An application rate of 200 kg/t is almost as'effective (Kellaway et al. 1978) and has the advantages. of requiring less water - 17 . and producing a stable product which can be stored indefinitely without mould development. In conclusion, the mixer trailer technique of alkali treatment is suitable for batch treatment of forage which has bee.n baled, Machines capable of holding 500 kg forage cost about $8,000. (iii) 'Alkalage** technique This technique has been developed in the Department of Animal Husbandry at the University of Sydney during the past three years. It is a continuous-flow process in which forages are treated before being packaged for transport or storage. This eliminates the double handling of forage, required in all other systems and this results in a considerable reduction in costs. Forages are,collected by a forage harvester fitted with spray jets inthe chute, through which chemicals are ,applied to the 'continuous stream of forage. Turbulent air movement in the chute provides very effective conditions for achieving uniform coverage of forage vith the chemical solutions. Two separate spray systems are used,,one for NaOH- solution `(21.6 % w/w), applied at the rate of 190 l/t forage, 'and the other for an acid solution containing urea, sulphuric acid and phosphoric acid, which supplies 11.5 g N, 1.2 g S and 1.6 g R/kg forage. The acids neutY;alize 16.5 % of the NaOH, leaving 40 g NaOH/t forage. Treated forage should be kept moist for about 2 days (Kellaway et al. wR% This is done by compressing the forage in bales, stacks or bulk; storage containers. Conventional bales are made by directing the forage harvester chute into a baler fitted with a hopper above the pickup drum. For bulk storage, the forage harvester chute is directed into a tipping trailer in which the forage is transported to a pit or tower silo. B o t h these systems require two men and two tractors during the harvesting operation. A simpler system which uses one man and one tractor hasbeen `developed for use with the 'Stak Hand' harvesting machine. This machine consists of a forage harvester joined to a forage compression box. A spray trailer has been designed for towing behind a forage harvester or alongside a 'Stak Hand' machine. The capacity of the spraytrailer currently used is 3400 1, which is sufficient to treat 13 t forage. When wheat Straw was treated by the *Alkalage' technique, DOm increased from 38 to 51 % and the growth rates of heifers fed the forages were412 and +23 g/day on the respective treatments (Kellaway et al. 1978). When oat straw was treated by the same technique DOMD increased from 47 to 58 % and'the growth. rates of heifers fed the forages were 143 and 564 g/day on the respective treatments (op. cit.). In both these experiments the straw was baled. In a subsequent experiment (Table 6) the straw was stored in pits and in 'Stak Hand' stacks. DOMD 'and nitrogen values on treated straws ,indicate that the straw in pits was more effectively treated than that in ,stacks. Approximately 30 %.of urea nitrogen was lost. It is believed that much of this loss occurred before spraying : because in this experiment the urea solution was mixe.d in the same tank as the NaOH solution and evolution of NH3 was apparent. Urea and alkali solutions are now kept in separate tanks. Despite these technical difficulties, animal responses were'very large, indicating that the technique upgraded the nutritive value of the straw sufficiently to convert it from a sub-maintenance diet into a diet on which modest growth was made. Rumen . VFA concentrations were higher and mania concentrationslower in * Registered as a trade.name by the University of Sydney 18 Comparisons between wheat straw sprayed by the 'Alkalage' TABLE 6 technique with urea + minerals (U) and NaOH + urea + minerals (A), stored in pits (P) and in 'Stak Hand' stacks (S), fed to Hereford steers (15 per treatment) cattle eating NaOH-treated straw than in cattle eating untreated straw which indicates that microbial fermentation was more active in animals -eating the NaOH-treated straw. In studies on the flow of microbial protein to the intestines in cattle fed NaOH-treated wheat straw, we have determined that the optimum level of urea is about 25 g/kg forage (Leibholz, J.M.L, and Kellaway, R.C.; unpublished data). In relation to 'Alkalage' utilisation we are currently investigating responses to protein supplements and efficiencies of mineral absorption. 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