THE INTAKE AND DIGESTIBILITY OF SILAGES MADE FROM DOLICHOS LABLAB L. ALONE AND WITH SORGHUM CV. SUGARDRIP

Transcription

1 THE INTAKE AND DIGESTIBILITY OF SILAGES MADE FROM DOLICHOS LABLAB L. ALONE AND WITH SORGHUM CV. SUGARDRIP By J. G. MORRIS* and M. S. LEVITT* Summary The digestibility was determined of silages made in experimental towers from Dolichos lablab. Dolichos was ensiled immediately on harvesting, after wilting for 2 days with and without added molasses, and after wilting for 3 days. All silages were readily eaten by sheep and showed only minor differences in the digestibility coefficients of major components. Intake and digestibility were also measured on silages made from Dolichos and Sorghum cv. Sugardrip in the following ratios: 100/O, 75/25, 50/50, 25/75, The ph decreased and the lactic acid concentration increased as the proportion of sorghum in the silage increased. The voluntary intake of the silage (g/w. ) decreased as the proportion of sorghum increased. Intake was not related to the digestibility of dry matter, organic matter or crude fibre. The intake and digestibility of a silage made in a large trench from non-wilted Dolichos were considerably lower than those recorded with silage from experimental towers. I. INTRODUCTION The tropical legume DoZichos ZabZab L. was first recorded in Queensland in 1875 by Hill, in a collection of plants growing in the Brisbane Botanic Gardens. Although it has been known locally for many years, there appear to be few, if any, reports of its use as a silage crop. This is surprising because of the low nitrogen content of most summer growing crops, in particular the sorghums which have been extensively used for silage production. This paper describes the production and evaluation of silage from D. Zablab alone and in combination with Sorghum cv. Sugardrip. II. MATERIALS (a) Silage Production Experiment A A crop of D. Zablab cv. Rongai (C.P.I ) was grown at the Husbandry Research Farm, Brisbane on a heavy clay loam soil. The seed was treated with a commercial Rhizobium inoculum and sown on August 11, 1964 in 0.9 m rows at the rate of 16.8 kg/ha. Superphosphate containing 0.03 % molybdenum was applied at 250 kg/ha. One third of the crop was harvested in the green state 169 days after planting with a flail-chopper type forage harvester and ensiled in experimental concrete towers of 1.2 m diameter which contained approximately 900 kg green material. The remaining two thirds of the crop was cut on the same day with a mower and allowed to wilt either two or three days in the field. It was then harvested with a flail-chopper forage harvester, and well tramped into the silos. For the *Animal Research Institute, Department of Primary Industries, Yeerongpilly, Brisbane. 78

2 molasses treatments, 0.81 kg of molasses was sprinkled over each 22.7 kg addition of chopped Dolichos to the silo. A description of the silos and the method of effluent collection have been given by Levitt, Taylor and Hegarty (1962). Experiment B The same area which produced the crop of Dolichos for Experiment A was planted on December 30, 1965 to Dolichos and Sorghum cv. Sugardrip. The planting details for the Dolichos were the same as in the previous year. Sorghum was planted at the rate of 5.6 kg/ha in the same row spacings as the Dolichos, but received a dressing of sulphate of ammonia at 180 kg/ha. Both sorghum and Dolichos were harvested 78 days after planting with a flail-chopper forage harvester and ensiled in the experimental towers used in Experiment A. Experiment C Dolichos was planted on November 25, 1965, into a heavy alluvial clay loam using the same seeding rate, row spacings and fertilizer treatments as for Experiment A. Harvesting was interrupted by rain, and accomplished in two stages: days and days after planting. A total of 145 metric tons was ensiled in a large concrete hillside trench silo (Radel 1961) and covered with black polyethylene film (0.15 mm) and wood shavings. It was opened 237 days later for feeding to steers and sheep. (b) Experimental A nima;ls The following animals were used to evaluate the silage:- Experiment A-Six Merino wethers of approximately 35 kg body-weight. Experiment B-Ten Merino x Border Leicester wethers of a mean (t S.E.) bodyweight of kg. Experiment C-Six adult steers of a mean body-weight of 530 f- 35 kg and the same 10 sheep as used in Experiment B. III. METHODS (a) Feeding Schedule In Experiment A, the green Dolichos and silages were fed below ad libitum intake in order to minimise refusals. In Experiments B and C, the animals were presented once daily with 20% more silage than the net wet intake of the previous day. The quantity presented to any animal was not reduced if the intake on a single day was considerably below the mean intake. A 14-day preliminary and a 14-day collection period were employed for each silage in Experiment A. In Experiment B, because of the limited quantity of silage available, only five-day collection and three-day preliminary periods between silages were used. For Experiment C, a 28-day preliminary and duplicate loday collection periods were employed. In experiments where more than one silage type was fed, these were allocated to the animals in a random sequence. (b) Analytical Methods Representative samples of feed, faeces and residues were analysed by methods of the Association of Official Agricultural Chemists ( 1960). Dry matter 79

3 (DM) of the silage was corrected for loss of volatile acids during drying. Total nitrogen was estimated on samples of wet silage and faeces. Volatile bases, amino acids, lactic acid and ph were determined by the methods described by Barnett ( 1954). Sugars were extracted from fresh silage with 80% ethanol and after removal of the alcohol were determined by the anthrone method of Clegg ( 1956). (c) Design In Experiment A, the effects of wilting versus non-wilting and of the addition of molasses at the rate of 35.7 kg/metric ton of material ensiled on the chemical composition and digestibility of the silage were investigated. In Experiment B, the effect of the addition of various proportions of sorghum to Dolichos on the chemical composition, intake and digestibility were studied. The comparative intake and digestibility by sheep and cattle of non-wilted Dolichos silage conserved in a trench was investigated in Experiment C. Intake was expressed in terms of DM (g) per head per day, DM/W (g DM per kg body-weight), DM/ W mt5 and digestible DM (DDM) /W.75. IV. RESULTS (a) Chemical Composition of the Silages The chemical composition of the fresh green materials used to prepare the silages in Experiments A and B and of the silages as fed to the animals in all experiments, is presented in Table 1. The Dolichos had a reasonably high level of nitrogen, but the sugar content was low being only about one fifth of that in sorghum. In Experiment A, the composition of the silages was not markedly different from that of the green Dolichos with the exception of the higher crude fibre and lower NFE components. There were also only minor differences between the chemical compositions of the mixed silages of Dolichos and sorghum in Experiment B and the parent materials. The addition of molasses to wilted and non-wilted Dolichos reduced the ph and increased the lactic acid concentration of the silage. Also, the ph decreased and the lactic acid concentration increased as the proportion of sorghum in mixed silages of Dolichos and sorghum increased. The DM losses in the silos in Experiment A were less for silages from wilted Dolichos without molasses (2 days 6.9 %, 3 days 5.9 % ) than for the nonwilted Dolichos (15.6% ). The silage made from non-wilted Dolichos with molasses had a DM loss of 10.8 % whereas silage made from Dolichos wilted for 2 days plus molasses had a loss of 8.6%. The mean DM loss in Experiment B was %) largely from effluent, with no apparent I relationship between the magnitude of the loss and the percentage sorghum in the silage. (b) Intake and Apparent Digestibility Experiment A Silage was fed on a restricted basis with a mean DM intake of 602 to 609 g per sheep per day. Although significant differences were recorded in the digestibility coefficients of the various silages, Table 2 shows that the magnitude of these differences for major components was not great. The digestibility coefficients of organic mat-

4 TABLE 1 Composition of green dolichos and sorghum before ensi1in.g (Experiments A and B) and silages used in Experiments A, B and C

5 TABLE 2

6 ter (OM) were greater for silages with added molasses, but were not increased by wilting. Nitrogen digestibility coefficients were significantly greater for green Dolichos, or silage made from green Dolichos, than for silage from wilted Dolichos. Experimenqt B The daily intake of DM per sheep and DM/W0e7 decreased as the percentage sorghum in the silage increased and showed no relationship to the apparent digestibility coefficient of DM, OM or crude fibre (Table 3). The intake of DDM/ W - was directly related to the level of Dolichos in the silage in the range of 100% to 25 % Dolichos. The apparent digestibility of nitrogen was significantly greater for silages made with 50% or more of Dolichos than those made with 75%or 100% sorghum. Experiment C e Although the same DM intakes of silage were obtained with sheep and cattle on a DM/W basis (Table 4), expression on a DM/W0-75 basis gave significantly higher DM and DDM intakes for cattle than sheep. The apparent digestibility of DM, OM and nitrogen was not significantly different between sheep and cattle. The intakes of DM/W, DM/We-75 and DDM/W0-55 for sheep were appreciably less than those recorded in Experiment B.. TABLE 3 Intake and apparent digestibility coefficients of five silages ma& from variable percentages of dolichos and sorghum in experimental concrete towers (Experiment B) 83

7 TABLE 4 Intake of apparent digestibility coefficients by sheep and cattle of non-wilted dolichos silage prepared in. a concrete hillside trench silo (Experiment C) V. DISCUSSION The low nitrogen level of conserved roughages has been a major factor limiting their use for supplementary and survival feeding of sheep and cattle in Northern Australia. Silages can be made successfully from the sweet sorghums, but intakes of these silages have frequently been low, even when supplemented with nitrogen. (Morris 1958; Skerman and Wynn 1960; Ryley 1961). This study has shown that in experimental towers, relatively high protein silages can be made from Dolichos, or mixtures of Dolichos and sorghum, and these are capable of supplying wether sheep with approximately maintenance levels of digestible OM. The voluntary intake of mixed Dolichos and sorghum silages showed no relationship to the apparent digestibility of DM or OM as proposed by Blaxter, Wainman and Wilson (1961) but was directly related to the proportion of Dolichos in the silage. The highest intake of DM/WOS~~ was recorded with the silage of the lowest OM, DM and crude fibre digestibility. The reason for the observed decline in intake of the mixed silages as the proportion of sorghum in them increased is not apparent. Although intake was positively related to,the level of nitrogen and ph, and negatively related to lactic acid concentration of the silage, it does not necessarily mean intake is controlled by any of these factors. It would appear from the sheep s requirement of nitrogen that this nutrient was not the limiting factor, for the effect was apparent with silages of a high nitrogen content. For example, there was a significantly lower DM/ W.75 intake of the silage with 25% sorghum and containing 2.6% nitrogen with an apparent digestibility of 68.8 % than the silage made from 100% Dolichos and containing 3.2% nitrogen. It is possible that lactic acid concentration may have an effect on intake. However, Moore, Thomas and Sykes (1960) were unable to demonstrate a reduction of intake following intra-ruminal infusions of lactic, acetic and propionic acids in amounts equivalent to those consumed in silages. A more tenable theory may be that the rate of digestion of sorghum is slower than that of Dolichos. The digestibility of the OM in green Dolichos and silages made in towers from Dolichos alone and mixed with sorghum was comparable to the upper values 84

8 (mean 53.1 f- 1.4 and a range of 42.5 to 57.6) found by Minson and Milford (1966) for Phasleolus atkpurpureus and greater than the single value of 44% reported by Graham (1967) for Desmodium uncinatum. In comparison with grasses, the, DM digestibility of green Dolichos and Dolichos silage was higher than the general range of 40 to 50% quoted by Milford (1960) as typical for subtropical grasses. However, these grasses may have digestibility coefficients considerably higher than this range as was shown by Minson and Milford (1966) who reported values for DM digestibility ranging from 40.7 to 69.8 (mean 57.7 t- 2.1) for Digitaria decumbens and 35.6 to 67.8 (mean 51.8 A 1.6) for Sorghum almum. Voluntary intake and apparent digestibility coefficients of DM and GM for a silage made fro& green Dolichos alone in a large trench were not comparable with these of similar silages made in small towers. The high ph and low lactic acid concentration of the trench silage, coupled with rapid deterioration when exposed to air, indicates the need for the addition of fermentable carbohydrate to Dolichos when ensiled in trenches. Although this can be achieved by adding molasses, a more practical solution would appear to be a mixed Dolichos and sorghum silage. VI. ACKNOWLEDGMENTS The authors acknowledge Miss Patricia M. Pepper for statistical analyses, Miss Jane M. Dalby for technical assistance and thank Mr. M.J. Radel for the aspects associated with the growing and harvesting of the crops.. VII. REFERENCES A SSOCIATION OF OFFICIAL A GRICULTURAL CHEMISTS ( 1960). Official Methods of Analysis. 9th Ed. (Ass. Off. Agric. Chemists: Washington.) B ARNETT, A. J. G. (1954). Silage Fermentation. (Butterworths: London.) BAXTER, K. L., W AINMAN, F. W., and W ILSON, R. S. ( 1961). Anim. Prod. 3: 5 1. C LEGG, K. M. (1956). J. Sci. Fd Agric. 7: 40. G RAHAM, N. McC. (1967). Aust. J. agric. Res. 18: 137. H ILL, W. (1875). Catalogue of the plants in the Queensland Botanic Gardens. (Govt- Printer: Brisbane.) LEVITT, M. S. TAYLOR, V. IT., and HEGARTY, A. ( 1962). Qd. J. agric. Sci. 19: 153. MILFCIRD, R. (1960). Aust. J. agric. Res. 11: 121. MINSON, D. J., and MILFORD, R. (1966). Aust. J. agric. Res. 17: 411. M OORE, L. A., T HOMAS, J: W., and S YKES, J. F. ( 1960). Proc. 8th int. Grassld Congr., Reading, p MORRIS, J. G. (1958). Qd. J. agric. Sci. 15: 181. RADEL, M. J. ( 196 1). Qd. agric. J. 87: RYLEY, 3. W. ( 1961). Qd. J. agric. Sci. 18: 409. S KERMAN, P. J., and W YNN, B. C. (1960). Proc. Aust. Soc. Anim. Prod. 3: