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Intake and digestibility of sorghum silage by goats
Animal Feed Science and Technology, 41 ( 1993 ) 17 I - 179
171
Elsevier Science Publishers B.V., Amsterdam
Intake and digestibility of sorghum silage by goats M. Tjandraatmadjaa, I.C. M a c R a e b a n d
B.W. N o r t o n a
aDepartment of Agriculture, The University of Queensland, Brisbane, Qld. 4072, Australia bDepartment of Microbiology, The University of Queensland, Brisbane, Qld. 4072, Australia (Received l0 April 1992; accepted 24 November 1992)
ABSTRACT Tjandraatmadja, M., MacRae, I.C. and Norton, B.W., 1993. Intake and digestibility of sorghum silage by goats. Anim. Feed Sci. Technol., 41: 171-179. This study investigated the effects of extraction of juice from forage sorghum on the final silage quality and nutritive value for goats. Sorghum forage was prepared for ensiling in mini-silos either by chopping (UCR) or by crushing and extraction of juice (C0), or by adding back 50% (C50) or 100% (C100) of juice to the extracted residue. Sorghum forage was harvested at two different times (Periods 1 and 2) and ensiled for 6 months and 4 months, respectively, prior to feeding. Treatment silages were fed ad libitum to Australian cashmere goats for 17 days during which intakes and digestibilities were determined. The dry matter (DM) content of the silage was low (UCR, 19.8%), and increased with juice removal (CO, 22.6%). There were no significant effects of pre-ensiling extraction of juice on water-soluble carbohydrate (WSC, 31 g kg - t DM), total N (TN, 4.9 g kg -~ DM), lactic acid (66.3 g kg - t DM, 71% total acids) and acetic acid (20.6 g kg - t DM) contents of silage. All silages were of high quality (pH < 3.75, ammonia N less than 6% TN). There were no significant (P < 0.05 ) differences between silages in nutritive value for goats. Mean values (n = 16 ) for voluntary feed intake were: 22.5+ 1.90 g DM kg - l live weight (W) day - l or 44.9_+4.17 g DM W -°-75 day -t. Mean values for digestibilities (%) were: DM 65.9 + 1.08, organic matter 67.4_+ 1.05, neutral detergent fibre 62.0_+ 1.94, nitrogen 43.0_+ 2.40. It was concluded that whilst all silages were acceptable and of high nutritive value, the low N contents may have partly limited their utilisation by goats.
INTRODUCTION
Among tropical cereal crops, maize and sorghum are the most widely used for silage because they produce high yields of dry matter, and have the low buffering capacity and high contents of water-soluble carbohydrates (WSC) necessary to produce high quality silages (Stuart, 1984). Tjandraatmadja et al. ( 1991 ) recently reported the effects of environmental temperature, anaerobicity and WSC contents on the quality of sorghum silage. In their study high environmental temperatures (30-40°C) and aerobic conditions Correspondence to: M. Tjandraatmadja, Department of Agriculture, The University of Queensland, Brisbane, Qld. 4072, Australia.
© 1993 Elsevier Science Publishers B.V. All rights reserved 0377-8401/93/$06.00
172
M. TJANDRAATMADJA ET AL.
decreased silage quality, but the extraction and removal of WSC from the forage had no significant effect on final silage quality. Mena et al. ( 1981, 1982 ) showed that sugar cane juice (75 kg total sugars t-t fresh cane) may be used as an alternative to sorghum grain in the diets of growing pigs. These workers were unable to effectively ensile the extracted sugar cane residue (R. Elliott, personal communication, 1986 ). Our studies suggest that up to 25 kg WSC t - ~of forage sorghum DM may be extracted for a similar use, without affecting the quality (pH, lactic acid content ) of the silage subsequently made from the residue. The nutritive value of silages made from temperate and tropical forages for cattle and sheep has been extensively reported, but there have been few reports of silage feeding to goats in the tropics (Adebowale, 1983 ). The following study investigated the effects of juice extraction from forage sorghum on the nutritive value of these silages for goats. MATERIALS AND METHODS
Silage preparation Two crops of forage sorghum (Sorghum bicolor cultivar 'Sugardrip') were grown and harvested at the early milk stage on 16 April (Period 1 ) and 9 June (Period 2 ) 1984. WSC of the forages was varied by either chopping the whole plant ( 1 cm) in a chaff cutter (UCR) or by crushing through a sugar cane press and chopping the residue (C0). The juice collected by crushing ( 10% fresh weight) was added back at rates of 100% (C100) or 50% (C50) to CO to generate the four silage types. Ensiling was carried out in 200-1 steel drums lined with two plastic bags. The forages were consolidated by trampling, and prior to heat sealing, air was evacuated from the bags with a vacuum pump. The drums were opened after approximately 4 (Period 2) and 6 (Period 1 ) months ofensiling; the contents were mixed thoroughly, weighed and distributed into small polyethylene bags in 2 to 2.5-kg amounts. The air inside the bags was evacuated using a vacuum pump and the bags were subsequently sealed. A number of small bags from the different treatments sufficient to provide a 1 day ration for the animals were then placed in a large polyethylene bag which was vacuum sealed and stored at 4 ° C until feeding.
Animal management and experimental design The experiment was a completely randomised factorial design with four treatment diets, two periods of ensiling and two animal replications. Sixteen young female Australian cashmere goats ( 13.8-18.0 kg ) were held in individual metabolism cages and offered Pangola grass (Digitaria decumbens) hay. Intakes measured during the last 8 days of this 14 day period were used as
INTAKE AND DIGESTIBILITYOF SORGHUM SILAGEBY GOATS
173
covariates to minimise variations between individual animals in subsequent comparisons. The animals were then allocated randomly to the dietary treatments for 17 days consisting of a 10 day preliminary and a 7 day collection period. The goats were weighed before feeding the hay, and again before and after feeding the silage. The silages were offered ad libitum daily ( 15% in excess of previous day's consumption). Refusals were collected before the morning feed, weighed and dried immediately. Faeces were sampled ( 10% total excretion) daily during the collection period, frozen and bulked, and sub-sampled at the end of the period for chemical analyses.
Analytical methods Silage from each treatment was sub-sampled and analysed for pH and the contents of dry matter (DM), ash, volatile fatty acids, lactic acid, WSC, total nitrogen (TN), ammonia nitrogen (NH3-N), neutral detergent fibre (NDF), acid detergent fibre (ADF) and lignin by the methods described by Tjandraatmadja et al. ( 1991 ). Refusals and faecal samples were oven dried at 60°C for 48 h, ground to TABLE 1
Chemical composition of Pangola grass and the effects of juice extraction and period of preparation on the chemical composition of forage sorghum prior to ensiling Component (g kg- ~dry matter)
Pangola Treatment ~ grass UCR CI00
Dry matter (g kg-~ ) 898 Neutral detergent fibre 746 Acid detergent fibre 405 Hemicellulose 341 Cellulose 364 Lignin 41 Ash 83 Water-soluble carbohydrates nd Total nitrogen (TN) 15.0 NH3-N (gkg - l TN) nd pH nd Lactic acid nd Acetic acid nd
236 570 361 209 321 40 48 165 9.6 3.2 4.1 2.3 7.1
229 580 376 204 323 53 48 170 8.8 13.4 4.2 2.7 5.5
SEM 2
Period
SEM 2
C50
CO
1
2
250 562 359 202 318 41 45 109 9.0 10.8 4.4 4.2 12.3
258 11.4 603 4.7* 377 3.4* 226 6.6 332 1.3" 45 4.2 45 2.4 90 18.8" 8.7 0.65 8.0 3.21 4.3 0.17 3.0 0.63 4.2 3.17
249 593 393 199 333 60 46 170 7.9 12.9 4.4 4.2 11.6
243 8.0 565 3.4* 343 2.4* 222 4.6* 313 0.9* 29 2.9* 47 1.7 97 13.3" 10.1 0.46* 4.8 2.68 4.2 0.12 1.9 0.45* 2.9 2.24
~UCR, uncrushed; CI00, crushed plus 100% juice; C50, crushed plus 50% juice; CO, crushed without juice. /Standard error of mean. *Significant difference between treatments ( P < 0.05 ).
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M. TJANDRAATMADJA ET AL.
TABLE2 Chemical composition of experimental silages fed to goats
Component
SEM 2 P
Treatment
Period
SEM 2 P
(g kg - t dry matter)
Dry matter (g kg- ~) Neutraldetergent fibre Acid detergent fibre Hemicellulose Cellulose Lignin
Ash
UCR
C100
C50
CO
198 655 401 254 357 43 55
206 637 392 244 349 43 54
204 684 428 256 383 45 55
226 636 399 238 356 43 53
3.8 6.5 5.7 3.1 4.7 1.2 1.3
* *** ** ** *** NS NS
1
2
216 645 404 241 355 50 50
200 661 406 256 368 38 58
2.7 4.6 4.1 2.2 3.3 0.9 0.9
** * NS ** * ** ** ** ** NS NS NS
Water-soluble
carbohydrates Total nitrogen (TN) NH3-N (gkg - l TN) pH Lacticacid Lactic acid (% total acids) Acetic acid Propionicacid iso-Butyricacid n-Butyric acid Valericacid Caproicacid
27.4 9.3 43.6 3.60 70.2
33.9 9.9 59.1 3.75 72.1
24.2 8.7 40.1 3.50 66.6
38.6 8.7 54.3 3.55 56.4
3.76 0.34 4.51 0.024 5.70
NS NS * *** NS
37.3 6.9 47.8 3.62 63.7
24.8 11.4 50.8 3.58 69.0
2.66 0.24 3.19 0.017 4.03
71.8 17.6 1.3 3.3 1.90 0.08 2.62
73.5 20.5 5.0 1.1 0.08 0.00 0.28
73.4 19.1 1.4 3.3 0.00 0.00 0.00
65.3 25.5 0.5 4.2 0.45 0.82 0.00
3.00 1.80 0.68 0.55 0.932 0.214 0.692
NS NS ** ** NS * NS
63.7 25.7 3.2 4.2 1.22 0.45 0.80
78.2 15.6 0.9 1.8 0.00
2.12 1.28 0.48 0.39 0.659
** ** ** ** NS 0.00 0.152 NS 0.65 0.489 NS
tUCR, uncrushed; CI00, crushed plus 100% juice; C50, crushed plus 50% juice; CO, crushed without juice. 2Standard error of mean. *P< 0.05; **P< 0.01 ; ***P< 0.001 ; NS, not significant.
pass a 1 mm screen and stored at ambient temperature until analysed. These samples were also analysed for TN, NDF, ADF and lignin.
Statistical analysis The significance of the differences in chemical composition of the silages due to treatments or period of ensiling were measured by analysis of variance while those relating to intake and digestibility were determined by analysis of covariance (Snedecor and Cochran, 1967). RESULTS
Silagefermentation and composition The chemical composition of the Pangola grass used for pre-feeding and of the sorghum forage treatments prior to ensiling is shown in Table 1. The
INTAKE AND DIGESTIBILITYOF SORGHUM SILAGE BY GOATS
175
TABLE 3 Mean values for intake and digestibility of forage sorghum silages by goats as influenced by treatments prior to ensiling and cutting dates Measurement
Treatment ~
SEM 2
UCR
C100
C50
CO
22.8 45.5
22.5 45.1
20.6 41.3
24.2 47.5
1.90 4.17
67.0 68.6 63.8 61.7 66.60 67.0 41.1
65.1 66.7 59.6 56.2 61.6 64.7 46.7
63.9 65.3 60.9 59.0 64.2 64.1 41.3
67.5 69.0 63.6 61.1 66.1 67.7 43.0
1.08 1.05 1.94 2.03 2.01 2.15 2.40
P
Period
SEM 2
P
1
2
NS NS
22.4 44.3
22.7 45.3
1.34 2.95
NS NS
NS NS NS NS NS NS NS
65.7 67.1 60.9 58.7 63.7 64.6 29.3
66.0 67.7 63.0 60.3 65.5 67.1 56.7
0.76 0.74 1.37 1.44 1.42 1.52 1.70
NS NS NS NS NS NS ***
Silage dry matter intake g W -J day -~ gW-°75day-I
Silage digestibility (%) Dry matter Organic matter Neutral detergent fibre Acid detergent fibre Cellulose Hemicellulose Nitrogen
~UCR, uncrushed; C100, crushed plus 100% juice; C50, crushed plus 50% juice; CO, crushed without juice. ZStandard error of mean. *P< 0.05; **P< 0.01 ; ***P< 0.001 ; NS, not significant.
removal of juice significantly ( P < 0.05 ) increased fibre content of the forage and significantly ( P < 0.05 ) decreased the content of water-soluble carbohydrates. There was also a significant ( P < 0.05 ) difference between periods in the chemical composition of the forages prepared for ensiling. The effects of the different treatments and cutting dates on the chemical composition of silages are shown in Table 2. Crushing and/or chopping the fresh forage resulted in small but, in some cases, significant differences in chemical composition and other fermentation characteristics of the silages. DM increased significantly ( P < 0.05 ) as the level of the juice added back to the crushed and chopped materials was reduced. Moisture content was the highest with the uncrushed forages (UCR). The contents of fibrous fractions and some fermentation acids (propionic, iso-butyric and valeric acids) in the DM of the different treatments were also significantly ( P < 0.05 ) different. Cutting dates significantly (P< 0.05-0.001 ) affected the contents of the proximate components and some of the fermentation products. The contents of TN, NDF, hemicellulose, cellulose and ash were significantly (P<0.05) higher in silages from Period 2 than from Period 1. Silages in Period 1 contained significantly (P<0.01) higher DM, WSC, acetic, propionic and isobutyric acids than silages in Period 2. Lactic acid contents of the silages made in the two periods, however, were not significantly different. As a result, the proportion of lactic acid in the total was significantly higher ( P < 0.001 ) in
176
M. TJANDRAATMADJA ET AL.
silages made in Period 2 than in silages made in Period l; the pH of the silages in Period 2 was slightly lower than that in Period l, but this was not significantly different.
Intake and digestibility of silages There were no significant ( P > 0.05 ) differences between treatment groups in their pre-experimental intakes of Pangola grass hay (49.9 g DM kg -°75 d a y - l ) . Table 3 shows mean values for the main effects of treatment and cutting date (period) on silage DM intakes and digestibilities of the various feed components. There were no significant differences between treatments or cutting dates in DM intake and digestibilities of DM and its fibrous components. The intake of N of silages in Period 2 was significantly higher (P < 0.01 ) than that of Period 1 (0.31 vs. 0.54 g W -°75 day- 1) which was associated with differences in N contents of both silages. Consequently, the apparent digestibility of N was significantly higher ( P < 0.001 ) in Period 2 than in Period 1. DISCUSSION
Silage fermentation The silages made in 200-1 drums in this experiment were well preserved as indicated by low pH ( < 3.8 ), high content of lactic acid ( 56-72% total acids ), and low content of butyrate ( 1.2-5.2 g kg-~ DM) and NH3-N (40-59 g kg-1 TN). These silage characteristics compare favourably with those of laboratory silages made in oxygen-impermeable bags reported in an earlier study (Tjandraatmadja et al., 1991 ). The WSC contents of the silages in the present experiment (24-39 g kg-1 DM) were lower than those of the laboratory silages (98 g kg-1 DM), presumably due to the longer incubation time of the drum silages (approximately 6 months and 4 months for Period l and Period 2, respectively). However, these lower WSC contents did not appear to adversely affect the quality of the silages produced.
Intake and digestibility of silages In terms of nutritive value for goats, the silages used in the present experiment were characterised by high digestibility and low voluntary feed intake. The apparent digestibility of silage DM (64-68%) was similar to that for maize silages (65-70%) fed to sheep (Johnson and McClure, 1968 ) but higher than that (60%) of sheep fed silages made from Dekalb FS24 forage sorghum cut at milk stage (Black et al., 1980). The present value was also higher than the predicted digestible dry matter for sorghum silages by sheep (48.8 +_7.2%)
INTAKE AND DIGESTIBILITYOF SORGHUM SILAGE BY GOATS
17 7
(Trigg and Moran, 1984 ). Similarly, the present digestibility values for NDF, ADF and cellulose (62%, 59% and 65%, respectively) were higher than the corresponding figures (57%, 49% and 57%) for the sorghum silages reported by Black et al. (1980). Adebowale ( 1983 ) found that the DM digestibility of maize silages by goats (56%) was higher than by sheep (50%). There is evidence that goats may digest fibrous feeds more efficiently than sheep as indicated by longer rumen retention times in goats (Doyle and Egan, 1980; Watson and Norton, 1982; Alam et al., 1983 ). Despite the comparatively high digestibility of the DM and its components average DM intakes for goats in the present experiment (45 g W -°-75 day- 1) were lower than that reported by Johnson et al. ( 1971 ) for sheep given silages made from AKS 614 bird-resistant grain sorghum cut at milk stage (73 g W -°75 day- ~). However, the silage DM intakes for the goats were similar to the voluntary intakes of Angora goats (49.5 g organic matter kg -°Ts day-~ ) fed high-quality Pangola grass (Watson and Norton, 1982), suggesting that goats may have a lower potential for voluntary consumption than sheep. Unlike fresh and dried forages and hays, the intake of silages by sheep and cattle is not closely related to its digestibility (Balch and Campling 1962; Wilkins et al., 1971 ). This may be partly attributed to the poor fermentation quality often found with ensiling immature forages of low DM which are otherwise high in digestibility. However, this cannot explain the low intake of the present silages, since the fermentation characteristics of all the silages were satisfactory. Wilkins et al. ( 1971 ) have suggested that voluntary silage intake by sheep was positively correlated with the DM contents. Silage DM (19.822.6%) in the present experiment was lower than that (26%) reported by Johnson et al. ( 1971 ), and may have contributed to the lower intakes by goats observed in the present study. The silages produced in the present experiment contained less than 8% crude protein (CP), and comparable low values (6-14% CP ) have been reported by others for sorghum silage (Browning and Lusk, 1967; Johnson et al., 1971; Black et al., 1980). Thomas et al., (1975) have concluded that silages containing less than 9% CP do not provide sufficient nitrogen for effective microbial fermentation in the rumen, and are therefore of low nutritive value. It would seem therefore that the low voluntary feed consumption by the goats in our study may be related to the low CP contents of these silages. The present results show that extracting the juice prior to ensiling forage sorghum did not adversely affect the fermentation quality of the resulting silages; presumably the level of WSC of the forages following extraction was still within the minimum value (90 g kg- l DM ) required to produce an effective lactic acid fermentation. The juice extracted from the sorghum forage prior to ensiling contained similar concentrations of sugars (200 g kg-l juice) to juice from sugar cane ( 150 g kg- 1 juice) (Mena et al., 1981 ). Juice extracted from sorghum forage may be used as a principal dietary energy source for
[ 78
M. T J A N D R A A T M A D J A ET AL.
fattening or growing pigs as in the case of sugar cane juice (Mena et al., 1981, 1982 ), and the residue would still be a useful substrate for silage production. However, animal production resulting from feeding juice extracted sorghum silages as a sole ration is likely to be poor due to low voluntary intakes of silage. The effects of including legume forages in such silages to overcome this deficiency have been examined in subsequent studies (Tjandraatmadja et al., 1993a,b). ACKNOWLEDGEMENTS
This study was funded in part by the Mayne Bequest Fund, University of Queensland. Muljana Tjandraatmadja was the recipient of a scholarship under the Columbo Plan of the Australian and Indonesian governments. The skilled assistance of the staff of the University farm at Mr. Cotton during this study is gratefully acknowledged.
REFERENCES Adebowale, E.A., 1983. The performance of West African Dwarf goats and sheep fed silage and silage plus concentrate. WId Rev. Anim. Prod., 19:15-20. Alam, M.R., Poppi, D.P. and Sykes, A.R., 1983. Intake, digestibility and retention time of 12 forages by kids and lambs. Proc. NZ Soc. Anita. Prod., 43:119-121. Balch, C.C. and Campling, R.C., 1962. Regulation of voluntary feed intake in ruminants. Nutr. Abst. Rev., 32: 669-686. Black, J.R., Ely, L.O., McCullough, M.E. and Sudweeks, E.M., 1980. Effects of stage of maturity and silage additives upon the yield of gross and digestible energy in sorghum silage. J. Anita. Sci., 50:617-624. Browning, C.B. and Lusk, J.W., 1967. Effect of stage of maturity at harvest on nutritive value of combine-type grain sorghum silage. J. Dairy Sci., 50:81-85. Doyle, P.T. and Egan, J.K., 1980. Intake and digestion of herbage diets by Angora goats and Merino sheep. Proc. Aust. Soc. Anita. Prod., 13:521. Johnson, R.R. and McClure, K.E., 1968. Corn plant maturity. IV. Effects on digestibility of corn silage in sheep. J. Anim. Sci., 27: 535-540. Johnson, R.R., De Varia, V.P. and McClure, K.E., 1971. Effects of maturity on chemical composition and digestibility of bird resistant sorghum plants when fed to sheep as silages. J. Anim. Sci., 33:1102-1109. Mena, A., Elliott, R. and Preston, T.R., 1981. Sugarcane juice as an energy source for fattening pigs. Trop. Anim. Prod., 6: 338-344. Mena, A., Elliott, R. and Preston, T.R., 1982. The substitution of grain sorghum by sugarcane juice in diets for growing pigs. Trop. Anim. Prod., 7: 226-231. Snedecor, G.S. and Cochran, W.G., 1967. Statistical Methods. Sixth Edition. Iowa State University Press, Ames. Stuart, P., 1984. Summer forage crops for silage. In: T.J. Kempton, A.G. Kaiser and T.E. Trigg (Editors), Silage in the 80's. University of New England Press, Armidale, pp. 58-62. Tjandraatmadja, M., Norton, B.W. and MacRae, I.C., 1991. Fermentation patterns of forage sorghum ensiled under different environmental conditions. Wld. J. Micro. Biotech., 7: 206218.
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Tjandraatmadja, M., MacRae, I.C. and Norton, B.W., 1993a. The effect of inclusion of tropical tree legumes, gliricidia and leucaena, on the nutritive value of silages prepared from tropical grasses. J. Agric. Sci., in press. Tjandraatmadja, M., MacRae, I.C. and Norton, B.W., 1993b. The digestion and utilisation of tropical grass/legumes silages for sheep. J. Agric. Sci., in press. Thomas, C., Wilkinson, J.M. and Tayler, J.C., 1975. The utilization of maize silage for intensive beef production. I. The effect of level and source of supplementary nitrogen on the utilization of maize silage by cattle of different ages. J. Agric. Sci., 84: 353-364. Trigg, T.E. and Moran, J.B., 1984. The role of fodder crop silages in the Australian dairy industry. In: T.J. Kempton, A.G. Kaiser and T.E. Trigg (Editors), Silage in the 80's. New England Press, Armidale, pp. 352-364. Watson, C. and Norton, B.W., 1982. The utilization of pangola grass hay by sheep and Angora goats. Proc. Aust. Soc. Anim. Prod., 14: 467-470. Wilkins, R.J., Hutchinson, K.J., Wilson, R.F. and Harris, C.E., 1971. The voluntary intake of silage by sheep. I. Interrelationships between silage composition and intake. J. Agric. Sci., 77: 531-537.
171
Elsevier Science Publishers B.V., Amsterdam
Intake and digestibility of sorghum silage by goats M. Tjandraatmadjaa, I.C. M a c R a e b a n d
B.W. N o r t o n a
aDepartment of Agriculture, The University of Queensland, Brisbane, Qld. 4072, Australia bDepartment of Microbiology, The University of Queensland, Brisbane, Qld. 4072, Australia (Received l0 April 1992; accepted 24 November 1992)
ABSTRACT Tjandraatmadja, M., MacRae, I.C. and Norton, B.W., 1993. Intake and digestibility of sorghum silage by goats. Anim. Feed Sci. Technol., 41: 171-179. This study investigated the effects of extraction of juice from forage sorghum on the final silage quality and nutritive value for goats. Sorghum forage was prepared for ensiling in mini-silos either by chopping (UCR) or by crushing and extraction of juice (C0), or by adding back 50% (C50) or 100% (C100) of juice to the extracted residue. Sorghum forage was harvested at two different times (Periods 1 and 2) and ensiled for 6 months and 4 months, respectively, prior to feeding. Treatment silages were fed ad libitum to Australian cashmere goats for 17 days during which intakes and digestibilities were determined. The dry matter (DM) content of the silage was low (UCR, 19.8%), and increased with juice removal (CO, 22.6%). There were no significant effects of pre-ensiling extraction of juice on water-soluble carbohydrate (WSC, 31 g kg - t DM), total N (TN, 4.9 g kg -~ DM), lactic acid (66.3 g kg - t DM, 71% total acids) and acetic acid (20.6 g kg - t DM) contents of silage. All silages were of high quality (pH < 3.75, ammonia N less than 6% TN). There were no significant (P < 0.05 ) differences between silages in nutritive value for goats. Mean values (n = 16 ) for voluntary feed intake were: 22.5+ 1.90 g DM kg - l live weight (W) day - l or 44.9_+4.17 g DM W -°-75 day -t. Mean values for digestibilities (%) were: DM 65.9 + 1.08, organic matter 67.4_+ 1.05, neutral detergent fibre 62.0_+ 1.94, nitrogen 43.0_+ 2.40. It was concluded that whilst all silages were acceptable and of high nutritive value, the low N contents may have partly limited their utilisation by goats.
INTRODUCTION
Among tropical cereal crops, maize and sorghum are the most widely used for silage because they produce high yields of dry matter, and have the low buffering capacity and high contents of water-soluble carbohydrates (WSC) necessary to produce high quality silages (Stuart, 1984). Tjandraatmadja et al. ( 1991 ) recently reported the effects of environmental temperature, anaerobicity and WSC contents on the quality of sorghum silage. In their study high environmental temperatures (30-40°C) and aerobic conditions Correspondence to: M. Tjandraatmadja, Department of Agriculture, The University of Queensland, Brisbane, Qld. 4072, Australia.
© 1993 Elsevier Science Publishers B.V. All rights reserved 0377-8401/93/$06.00
172
M. TJANDRAATMADJA ET AL.
decreased silage quality, but the extraction and removal of WSC from the forage had no significant effect on final silage quality. Mena et al. ( 1981, 1982 ) showed that sugar cane juice (75 kg total sugars t-t fresh cane) may be used as an alternative to sorghum grain in the diets of growing pigs. These workers were unable to effectively ensile the extracted sugar cane residue (R. Elliott, personal communication, 1986 ). Our studies suggest that up to 25 kg WSC t - ~of forage sorghum DM may be extracted for a similar use, without affecting the quality (pH, lactic acid content ) of the silage subsequently made from the residue. The nutritive value of silages made from temperate and tropical forages for cattle and sheep has been extensively reported, but there have been few reports of silage feeding to goats in the tropics (Adebowale, 1983 ). The following study investigated the effects of juice extraction from forage sorghum on the nutritive value of these silages for goats. MATERIALS AND METHODS
Silage preparation Two crops of forage sorghum (Sorghum bicolor cultivar 'Sugardrip') were grown and harvested at the early milk stage on 16 April (Period 1 ) and 9 June (Period 2 ) 1984. WSC of the forages was varied by either chopping the whole plant ( 1 cm) in a chaff cutter (UCR) or by crushing through a sugar cane press and chopping the residue (C0). The juice collected by crushing ( 10% fresh weight) was added back at rates of 100% (C100) or 50% (C50) to CO to generate the four silage types. Ensiling was carried out in 200-1 steel drums lined with two plastic bags. The forages were consolidated by trampling, and prior to heat sealing, air was evacuated from the bags with a vacuum pump. The drums were opened after approximately 4 (Period 2) and 6 (Period 1 ) months ofensiling; the contents were mixed thoroughly, weighed and distributed into small polyethylene bags in 2 to 2.5-kg amounts. The air inside the bags was evacuated using a vacuum pump and the bags were subsequently sealed. A number of small bags from the different treatments sufficient to provide a 1 day ration for the animals were then placed in a large polyethylene bag which was vacuum sealed and stored at 4 ° C until feeding.
Animal management and experimental design The experiment was a completely randomised factorial design with four treatment diets, two periods of ensiling and two animal replications. Sixteen young female Australian cashmere goats ( 13.8-18.0 kg ) were held in individual metabolism cages and offered Pangola grass (Digitaria decumbens) hay. Intakes measured during the last 8 days of this 14 day period were used as
INTAKE AND DIGESTIBILITYOF SORGHUM SILAGEBY GOATS
173
covariates to minimise variations between individual animals in subsequent comparisons. The animals were then allocated randomly to the dietary treatments for 17 days consisting of a 10 day preliminary and a 7 day collection period. The goats were weighed before feeding the hay, and again before and after feeding the silage. The silages were offered ad libitum daily ( 15% in excess of previous day's consumption). Refusals were collected before the morning feed, weighed and dried immediately. Faeces were sampled ( 10% total excretion) daily during the collection period, frozen and bulked, and sub-sampled at the end of the period for chemical analyses.
Analytical methods Silage from each treatment was sub-sampled and analysed for pH and the contents of dry matter (DM), ash, volatile fatty acids, lactic acid, WSC, total nitrogen (TN), ammonia nitrogen (NH3-N), neutral detergent fibre (NDF), acid detergent fibre (ADF) and lignin by the methods described by Tjandraatmadja et al. ( 1991 ). Refusals and faecal samples were oven dried at 60°C for 48 h, ground to TABLE 1
Chemical composition of Pangola grass and the effects of juice extraction and period of preparation on the chemical composition of forage sorghum prior to ensiling Component (g kg- ~dry matter)
Pangola Treatment ~ grass UCR CI00
Dry matter (g kg-~ ) 898 Neutral detergent fibre 746 Acid detergent fibre 405 Hemicellulose 341 Cellulose 364 Lignin 41 Ash 83 Water-soluble carbohydrates nd Total nitrogen (TN) 15.0 NH3-N (gkg - l TN) nd pH nd Lactic acid nd Acetic acid nd
236 570 361 209 321 40 48 165 9.6 3.2 4.1 2.3 7.1
229 580 376 204 323 53 48 170 8.8 13.4 4.2 2.7 5.5
SEM 2
Period
SEM 2
C50
CO
1
2
250 562 359 202 318 41 45 109 9.0 10.8 4.4 4.2 12.3
258 11.4 603 4.7* 377 3.4* 226 6.6 332 1.3" 45 4.2 45 2.4 90 18.8" 8.7 0.65 8.0 3.21 4.3 0.17 3.0 0.63 4.2 3.17
249 593 393 199 333 60 46 170 7.9 12.9 4.4 4.2 11.6
243 8.0 565 3.4* 343 2.4* 222 4.6* 313 0.9* 29 2.9* 47 1.7 97 13.3" 10.1 0.46* 4.8 2.68 4.2 0.12 1.9 0.45* 2.9 2.24
~UCR, uncrushed; CI00, crushed plus 100% juice; C50, crushed plus 50% juice; CO, crushed without juice. /Standard error of mean. *Significant difference between treatments ( P < 0.05 ).
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M. TJANDRAATMADJA ET AL.
TABLE2 Chemical composition of experimental silages fed to goats
Component
SEM 2 P
Treatment
Period
SEM 2 P
(g kg - t dry matter)
Dry matter (g kg- ~) Neutraldetergent fibre Acid detergent fibre Hemicellulose Cellulose Lignin
Ash
UCR
C100
C50
CO
198 655 401 254 357 43 55
206 637 392 244 349 43 54
204 684 428 256 383 45 55
226 636 399 238 356 43 53
3.8 6.5 5.7 3.1 4.7 1.2 1.3
* *** ** ** *** NS NS
1
2
216 645 404 241 355 50 50
200 661 406 256 368 38 58
2.7 4.6 4.1 2.2 3.3 0.9 0.9
** * NS ** * ** ** ** ** NS NS NS
Water-soluble
carbohydrates Total nitrogen (TN) NH3-N (gkg - l TN) pH Lacticacid Lactic acid (% total acids) Acetic acid Propionicacid iso-Butyricacid n-Butyric acid Valericacid Caproicacid
27.4 9.3 43.6 3.60 70.2
33.9 9.9 59.1 3.75 72.1
24.2 8.7 40.1 3.50 66.6
38.6 8.7 54.3 3.55 56.4
3.76 0.34 4.51 0.024 5.70
NS NS * *** NS
37.3 6.9 47.8 3.62 63.7
24.8 11.4 50.8 3.58 69.0
2.66 0.24 3.19 0.017 4.03
71.8 17.6 1.3 3.3 1.90 0.08 2.62
73.5 20.5 5.0 1.1 0.08 0.00 0.28
73.4 19.1 1.4 3.3 0.00 0.00 0.00
65.3 25.5 0.5 4.2 0.45 0.82 0.00
3.00 1.80 0.68 0.55 0.932 0.214 0.692
NS NS ** ** NS * NS
63.7 25.7 3.2 4.2 1.22 0.45 0.80
78.2 15.6 0.9 1.8 0.00
2.12 1.28 0.48 0.39 0.659
** ** ** ** NS 0.00 0.152 NS 0.65 0.489 NS
tUCR, uncrushed; CI00, crushed plus 100% juice; C50, crushed plus 50% juice; CO, crushed without juice. 2Standard error of mean. *P< 0.05; **P< 0.01 ; ***P< 0.001 ; NS, not significant.
pass a 1 mm screen and stored at ambient temperature until analysed. These samples were also analysed for TN, NDF, ADF and lignin.
Statistical analysis The significance of the differences in chemical composition of the silages due to treatments or period of ensiling were measured by analysis of variance while those relating to intake and digestibility were determined by analysis of covariance (Snedecor and Cochran, 1967). RESULTS
Silagefermentation and composition The chemical composition of the Pangola grass used for pre-feeding and of the sorghum forage treatments prior to ensiling is shown in Table 1. The
INTAKE AND DIGESTIBILITYOF SORGHUM SILAGE BY GOATS
175
TABLE 3 Mean values for intake and digestibility of forage sorghum silages by goats as influenced by treatments prior to ensiling and cutting dates Measurement
Treatment ~
SEM 2
UCR
C100
C50
CO
22.8 45.5
22.5 45.1
20.6 41.3
24.2 47.5
1.90 4.17
67.0 68.6 63.8 61.7 66.60 67.0 41.1
65.1 66.7 59.6 56.2 61.6 64.7 46.7
63.9 65.3 60.9 59.0 64.2 64.1 41.3
67.5 69.0 63.6 61.1 66.1 67.7 43.0
1.08 1.05 1.94 2.03 2.01 2.15 2.40
P
Period
SEM 2
P
1
2
NS NS
22.4 44.3
22.7 45.3
1.34 2.95
NS NS
NS NS NS NS NS NS NS
65.7 67.1 60.9 58.7 63.7 64.6 29.3
66.0 67.7 63.0 60.3 65.5 67.1 56.7
0.76 0.74 1.37 1.44 1.42 1.52 1.70
NS NS NS NS NS NS ***
Silage dry matter intake g W -J day -~ gW-°75day-I
Silage digestibility (%) Dry matter Organic matter Neutral detergent fibre Acid detergent fibre Cellulose Hemicellulose Nitrogen
~UCR, uncrushed; C100, crushed plus 100% juice; C50, crushed plus 50% juice; CO, crushed without juice. ZStandard error of mean. *P< 0.05; **P< 0.01 ; ***P< 0.001 ; NS, not significant.
removal of juice significantly ( P < 0.05 ) increased fibre content of the forage and significantly ( P < 0.05 ) decreased the content of water-soluble carbohydrates. There was also a significant ( P < 0.05 ) difference between periods in the chemical composition of the forages prepared for ensiling. The effects of the different treatments and cutting dates on the chemical composition of silages are shown in Table 2. Crushing and/or chopping the fresh forage resulted in small but, in some cases, significant differences in chemical composition and other fermentation characteristics of the silages. DM increased significantly ( P < 0.05 ) as the level of the juice added back to the crushed and chopped materials was reduced. Moisture content was the highest with the uncrushed forages (UCR). The contents of fibrous fractions and some fermentation acids (propionic, iso-butyric and valeric acids) in the DM of the different treatments were also significantly ( P < 0.05 ) different. Cutting dates significantly (P< 0.05-0.001 ) affected the contents of the proximate components and some of the fermentation products. The contents of TN, NDF, hemicellulose, cellulose and ash were significantly (P<0.05) higher in silages from Period 2 than from Period 1. Silages in Period 1 contained significantly (P<0.01) higher DM, WSC, acetic, propionic and isobutyric acids than silages in Period 2. Lactic acid contents of the silages made in the two periods, however, were not significantly different. As a result, the proportion of lactic acid in the total was significantly higher ( P < 0.001 ) in
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M. TJANDRAATMADJA ET AL.
silages made in Period 2 than in silages made in Period l; the pH of the silages in Period 2 was slightly lower than that in Period l, but this was not significantly different.
Intake and digestibility of silages There were no significant ( P > 0.05 ) differences between treatment groups in their pre-experimental intakes of Pangola grass hay (49.9 g DM kg -°75 d a y - l ) . Table 3 shows mean values for the main effects of treatment and cutting date (period) on silage DM intakes and digestibilities of the various feed components. There were no significant differences between treatments or cutting dates in DM intake and digestibilities of DM and its fibrous components. The intake of N of silages in Period 2 was significantly higher (P < 0.01 ) than that of Period 1 (0.31 vs. 0.54 g W -°75 day- 1) which was associated with differences in N contents of both silages. Consequently, the apparent digestibility of N was significantly higher ( P < 0.001 ) in Period 2 than in Period 1. DISCUSSION
Silage fermentation The silages made in 200-1 drums in this experiment were well preserved as indicated by low pH ( < 3.8 ), high content of lactic acid ( 56-72% total acids ), and low content of butyrate ( 1.2-5.2 g kg-~ DM) and NH3-N (40-59 g kg-1 TN). These silage characteristics compare favourably with those of laboratory silages made in oxygen-impermeable bags reported in an earlier study (Tjandraatmadja et al., 1991 ). The WSC contents of the silages in the present experiment (24-39 g kg-1 DM) were lower than those of the laboratory silages (98 g kg-1 DM), presumably due to the longer incubation time of the drum silages (approximately 6 months and 4 months for Period l and Period 2, respectively). However, these lower WSC contents did not appear to adversely affect the quality of the silages produced.
Intake and digestibility of silages In terms of nutritive value for goats, the silages used in the present experiment were characterised by high digestibility and low voluntary feed intake. The apparent digestibility of silage DM (64-68%) was similar to that for maize silages (65-70%) fed to sheep (Johnson and McClure, 1968 ) but higher than that (60%) of sheep fed silages made from Dekalb FS24 forage sorghum cut at milk stage (Black et al., 1980). The present value was also higher than the predicted digestible dry matter for sorghum silages by sheep (48.8 +_7.2%)
INTAKE AND DIGESTIBILITYOF SORGHUM SILAGE BY GOATS
17 7
(Trigg and Moran, 1984 ). Similarly, the present digestibility values for NDF, ADF and cellulose (62%, 59% and 65%, respectively) were higher than the corresponding figures (57%, 49% and 57%) for the sorghum silages reported by Black et al. (1980). Adebowale ( 1983 ) found that the DM digestibility of maize silages by goats (56%) was higher than by sheep (50%). There is evidence that goats may digest fibrous feeds more efficiently than sheep as indicated by longer rumen retention times in goats (Doyle and Egan, 1980; Watson and Norton, 1982; Alam et al., 1983 ). Despite the comparatively high digestibility of the DM and its components average DM intakes for goats in the present experiment (45 g W -°-75 day- 1) were lower than that reported by Johnson et al. ( 1971 ) for sheep given silages made from AKS 614 bird-resistant grain sorghum cut at milk stage (73 g W -°75 day- ~). However, the silage DM intakes for the goats were similar to the voluntary intakes of Angora goats (49.5 g organic matter kg -°Ts day-~ ) fed high-quality Pangola grass (Watson and Norton, 1982), suggesting that goats may have a lower potential for voluntary consumption than sheep. Unlike fresh and dried forages and hays, the intake of silages by sheep and cattle is not closely related to its digestibility (Balch and Campling 1962; Wilkins et al., 1971 ). This may be partly attributed to the poor fermentation quality often found with ensiling immature forages of low DM which are otherwise high in digestibility. However, this cannot explain the low intake of the present silages, since the fermentation characteristics of all the silages were satisfactory. Wilkins et al. ( 1971 ) have suggested that voluntary silage intake by sheep was positively correlated with the DM contents. Silage DM (19.822.6%) in the present experiment was lower than that (26%) reported by Johnson et al. ( 1971 ), and may have contributed to the lower intakes by goats observed in the present study. The silages produced in the present experiment contained less than 8% crude protein (CP), and comparable low values (6-14% CP ) have been reported by others for sorghum silage (Browning and Lusk, 1967; Johnson et al., 1971; Black et al., 1980). Thomas et al., (1975) have concluded that silages containing less than 9% CP do not provide sufficient nitrogen for effective microbial fermentation in the rumen, and are therefore of low nutritive value. It would seem therefore that the low voluntary feed consumption by the goats in our study may be related to the low CP contents of these silages. The present results show that extracting the juice prior to ensiling forage sorghum did not adversely affect the fermentation quality of the resulting silages; presumably the level of WSC of the forages following extraction was still within the minimum value (90 g kg- l DM ) required to produce an effective lactic acid fermentation. The juice extracted from the sorghum forage prior to ensiling contained similar concentrations of sugars (200 g kg-l juice) to juice from sugar cane ( 150 g kg- 1 juice) (Mena et al., 1981 ). Juice extracted from sorghum forage may be used as a principal dietary energy source for
[ 78
M. T J A N D R A A T M A D J A ET AL.
fattening or growing pigs as in the case of sugar cane juice (Mena et al., 1981, 1982 ), and the residue would still be a useful substrate for silage production. However, animal production resulting from feeding juice extracted sorghum silages as a sole ration is likely to be poor due to low voluntary intakes of silage. The effects of including legume forages in such silages to overcome this deficiency have been examined in subsequent studies (Tjandraatmadja et al., 1993a,b). ACKNOWLEDGEMENTS
This study was funded in part by the Mayne Bequest Fund, University of Queensland. Muljana Tjandraatmadja was the recipient of a scholarship under the Columbo Plan of the Australian and Indonesian governments. The skilled assistance of the staff of the University farm at Mr. Cotton during this study is gratefully acknowledged.
REFERENCES Adebowale, E.A., 1983. The performance of West African Dwarf goats and sheep fed silage and silage plus concentrate. WId Rev. Anim. Prod., 19:15-20. Alam, M.R., Poppi, D.P. and Sykes, A.R., 1983. Intake, digestibility and retention time of 12 forages by kids and lambs. Proc. NZ Soc. Anita. Prod., 43:119-121. Balch, C.C. and Campling, R.C., 1962. Regulation of voluntary feed intake in ruminants. Nutr. Abst. Rev., 32: 669-686. Black, J.R., Ely, L.O., McCullough, M.E. and Sudweeks, E.M., 1980. Effects of stage of maturity and silage additives upon the yield of gross and digestible energy in sorghum silage. J. Anita. Sci., 50:617-624. Browning, C.B. and Lusk, J.W., 1967. Effect of stage of maturity at harvest on nutritive value of combine-type grain sorghum silage. J. Dairy Sci., 50:81-85. Doyle, P.T. and Egan, J.K., 1980. Intake and digestion of herbage diets by Angora goats and Merino sheep. Proc. Aust. Soc. Anita. Prod., 13:521. Johnson, R.R. and McClure, K.E., 1968. Corn plant maturity. IV. Effects on digestibility of corn silage in sheep. J. Anim. Sci., 27: 535-540. Johnson, R.R., De Varia, V.P. and McClure, K.E., 1971. Effects of maturity on chemical composition and digestibility of bird resistant sorghum plants when fed to sheep as silages. J. Anim. Sci., 33:1102-1109. Mena, A., Elliott, R. and Preston, T.R., 1981. Sugarcane juice as an energy source for fattening pigs. Trop. Anim. Prod., 6: 338-344. Mena, A., Elliott, R. and Preston, T.R., 1982. The substitution of grain sorghum by sugarcane juice in diets for growing pigs. Trop. Anim. Prod., 7: 226-231. Snedecor, G.S. and Cochran, W.G., 1967. Statistical Methods. Sixth Edition. Iowa State University Press, Ames. Stuart, P., 1984. Summer forage crops for silage. In: T.J. Kempton, A.G. Kaiser and T.E. Trigg (Editors), Silage in the 80's. University of New England Press, Armidale, pp. 58-62. Tjandraatmadja, M., Norton, B.W. and MacRae, I.C., 1991. Fermentation patterns of forage sorghum ensiled under different environmental conditions. Wld. J. Micro. Biotech., 7: 206218.
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Tjandraatmadja, M., MacRae, I.C. and Norton, B.W., 1993a. The effect of inclusion of tropical tree legumes, gliricidia and leucaena, on the nutritive value of silages prepared from tropical grasses. J. Agric. Sci., in press. Tjandraatmadja, M., MacRae, I.C. and Norton, B.W., 1993b. The digestion and utilisation of tropical grass/legumes silages for sheep. J. Agric. Sci., in press. Thomas, C., Wilkinson, J.M. and Tayler, J.C., 1975. The utilization of maize silage for intensive beef production. I. The effect of level and source of supplementary nitrogen on the utilization of maize silage by cattle of different ages. J. Agric. Sci., 84: 353-364. Trigg, T.E. and Moran, J.B., 1984. The role of fodder crop silages in the Australian dairy industry. In: T.J. Kempton, A.G. Kaiser and T.E. Trigg (Editors), Silage in the 80's. New England Press, Armidale, pp. 352-364. Watson, C. and Norton, B.W., 1982. The utilization of pangola grass hay by sheep and Angora goats. Proc. Aust. Soc. Anim. Prod., 14: 467-470. Wilkins, R.J., Hutchinson, K.J., Wilson, R.F. and Harris, C.E., 1971. The voluntary intake of silage by sheep. I. Interrelationships between silage composition and intake. J. Agric. Sci., 77: 531-537.