The possibility of using anaerobically fermented cattle manure (biodigester effluent) as a source of protein in a straw based diet for growing indigenous (Bos indicus) bulls was studied. Eight bulls (256 ±33.1 kg liveweight and 18.5 ±3.86 months old) were randomly allocated to two experimental diets having either 0.5 kg/day mustard oil cake or biodigester effluent (from cattle manure) ad libitum, as the source of protein. Both groups of animals had an ad libitum supply of rice straw (enriched with urea 3%; molasses 15%) together with daily quantities of 1 kg wheat bran, 0.3 kg molasses, 40 g of oyster shell powder and 70 g of salt/head. Compared to the fresh cattle manure, the effluent had 81% higher total nitrogen (N) and 24% lower acid detergent fibre (ADF) content. None of the effluent-fed animals showed any symptoms of behavioral or physiological abnormalities. When the animals were fully adapted, effluent constituted 13% of the total DM intake (about 17 kg fresh material/day). Straw dry matter intake was the same (104 g/kg W0.75/d) for both groups, but effluent-fed animals had higher (P<0.05) organic matter intake and lower (P<0.05) dry matter digestibility than those fed mustard oil cake. There were no differences (P>0.05) between dietary treatments in: digestibilities of organic matter, nitrogen and ADF; in calculated microbial N yield; in N retention and growth rate. It is concluded that biodigester effluent can be fed to Bos indicus bulls but that it is probably inferior to mustard oil cake as a supplement for a straw-based diet.
The fact that the availability of the world's raw materials is diminishing as population grows exponentially, together with the real threat of global feed shortage, contributes to the increasing awareness of the need for conservation and recycling of materials which once would have been thrown away without a second thought. Anaerobic fermentation of livestock manure for production of biogas is widely used in China, India and many other South Asian countries and recently is becoming popular in Bangladesh. So far, the use of digested effluent has been limited to use as fertilizer for crops (Le Ha Chau 1998), water plants (Rodriguez and Preston 1996; Chara et al 1999) and fish production (Chan 1996). However, according to Marchaim (1992), anaerobically fermented manure (biodigester effluent) from cattle or poultry can be used safely as a feed supplement for ruminant animals, providing protein, macro- and micro-minerals and vitamins. Since feed cost usually represent 60-90% of total production costs, replacing feed by farm wastes could lead to a significant reduction in the cost of meat, milk and other animal products. At the Maya Farm in the Philippines, solid and dried effluent provided 10-15% of the feed requirements for pigs and cattle and 50% for ducks (Marchaim 1992). Alivar et al (1980) also found that dried sludge could be used in cattle feed with satisfactory weight gains and savings of 50% in the feed concentrate used. Liquid biodigester effluent was successfully fed to weaned calves supplying 14.4 g of N daily and increasing the daily N balance by 4.4 g (Ørskov, personal communication).
The present study was designed with the following objective:
Eight growing indigenous (Bos indicus) bulls (256 ±33 kg live weight and 18.5 ±3.9 months old) were randomly allocated to two treatments: Oil Cake (Control) and Effluent (see Table 1 ). They were housed individually in a stanchion barn throughout the 12 week experimental period (November 1996 to January 1997). They were fed twice daily and the feed residue was collected and weighed every morning. The effluent was introduced gradually to the animals by adding it to the concentrate mixture in increasing levels. The amount offered during the experiment was fixed at the highest level beyond which the animals refused to accept the mixture.
|Table 1: Dietary ingredients used for the oil cake and effluent- fed animals (amounts in kg/day)|
|Feed ingredients||Oil cake||Effluent|
|Enriched straw#||Ad libitum||Ad libitum|
|Mustard Oil Cake||0.50|
|Oyster shell powder||0.04||0.04|
|#Rice straw 82%, urea 3%, molasses 15%|
A fixed dome (Chinese model) biodigester (about 29 m³ liquid volume) was charged daily with 50 kg fresh cow manure mixed with 50 kg water. The fresh effluent collected from the outlet of the biodigester was used for feeding the animals.
At the end of the feeding trial, all the animals were transferred to metabolism stalls. After allowing for a one week adjustment period, the production of faeces and urine were recorded separately for five consecutive days. Feed offered daily and the residues were also measured.
At the beginning of the trial, the animals were weighed for three consecutive days and the mean was taken as the initial live weight. Subsequently, the animals were weighed at fortnightly intervals. Growth rate was calculated as the slope of the linear regression of liveweight over time.
Samples of feeds, residues and faeces were analyzed for dry matter, organic matter, and nitrogen (N) and urine was analysed for N according to the methods of AOAC (1984). Acid detergent fibre (ADF) was determined according to Goering and Van Soest (1970). Urinary purine derivatives (allantoin) were measured using the technique of Chen and Gomes (1992). Microbial N yield in the rumen was quantified from the purine derivatives (allantoin + 15% correction for the uric acid contained in the urine) according to Chen and Gomes (1992).
The data were analyzed by ANOVA (Snedecor and Cochran 1967) for a completely randomized design. The linear regressions for estimating liveweight gain were of the form y = a + bx.
The chemical composition of the feed ingredients (Table 2) show that the effluent contained (in dry matter) 97.6% organic matter, 2.94% N and 26.7% ADF. The corresponding data for fresh faeces (taken from the animals in the present experiment) were 80.6, 1.62 and 33%, respectively. The effluent had 81% more total N and 24% less ADF.
|Table 2: Chemical composition of feed ingredients|
|Dry matter||Organic matter#||Nitrogen#||ADF#|
|Mustard oil cake||93.5||80.5||4.95||26.7|
|#In g/100 g dry matter|
Marchaim (1992) suggested that most of the increase in the N content of biodigester effluent is due to an increase in the non-ammonia fraction. He calculated that the increase in N, assuming the increase to be all of microbial origin, was of the order of 230% compared with the amino acids in fresh cow manure. The residual fibre in the effluent is likely to be of low digestibility and therefore of little value as a source of energy. Thus it is apparent that anaerobic fermentation of cow manure produces an effluent which is a good source of microbial amino acids but a poor source of energy.
Both oil cake and effluent-fed animals were healthy throughout the experimental period, except for one animal in the oil cake group which suffered from Epimeral Fever (or Three Days Sickness), a viral fever causing very high temperature (41.1 - 41.7 ºC), but recovered within a week. None of the effluent-fed animals showed any symptoms of behavioral or physiological abnormalities. This is similar to the observation by Smith and Wheeler (1979) that biodigester effluent could be fed to livestock with some nutritional benefit and with little adverse effect on animal health . This is due to the fact that most of the pathogenic organisms and parasitic eggs die under the prolonged mesophyllic (35 ºC) and anaerobic conditions prevailing in the biodigester.
The animals were gradually introduced to the fresh effluent by mixing it with the other concentrates (wheat bran, molasses and minerals) to form a broth or soup which was consumed as a drink. Effluent intake increased almost linearly with time (Figure 1 ). Starting from about 2 kg/head, the mean daily effluent intake reached slightly over 7 kg (0.5 kg DM) in the 5th week, and over 17 kg (1.2 kg DM) by the l2th week. Intake was very similar in all four experimental animals up to the 5th week of the trial, but showed large variation among individuals from the 6th week onwards when the quantity of effluent was increased. Occasionally some of the animals completely refused to drink the effluent-concentrate mixture, for no apparent reason, but returned to normal consumption within a week. It was observed that intake of the mixture was less on a cold and wet day than on a hot and dry day. At the highest level of intake (in the l2th week), the effluent constituted over 13% of the total DM intake which is similar to the observation of Marchaim (1992) who reported intakes of solid and dried effluent equivalent to 10-15% of the feed requirements for pigs and cattle.
Straw dry matter intake (Table 3) was very similar for the animals in both the effluent and the oil cake treatments (104g/ LW0.75/d). This value is much higher than the commonly observed DM intake of 60-80 g/kg LW0.75/d with rice straw (Chowdhury 1997) or 80-90 g/LW0.75/d with urea-molasses straw (Chowdhury and Huque 1996) in growing Bos indicus bulls observed previously in our laboratory. Total organic matter intake was higher (P<0.05) in the animals fed effluent than in those fed oil cake. This was due to a higher organic matter content in the effluent than in the oil cake. The difference in rate of liveweight gain (38% higher for the oil cake-fed animals) was not significant which implies a high degree of variation for this parameter and because of this the need for a greater number of animals.
|Table 3: Mean dry matter (DMI) and organic matter (OMI) intakes, and liveweight gain, for the animals fed oil cake and effluent|
|Total DMI (kg/d)||9.48||8.91||0.245||NS|
|Straw DMI (kg/d)||7.21||7.34||0.267||NS|
|Effluent DMI (kg/d)||1.16|
|Oil cake DMI (kg/d)||0.47|
|Straw DMI (g/LW0.75/d)||104||104||7.1||NS|
|Total OMI (kg/d)||8.38||7.72||0.201||<0.05|
|Liveweight gain, g/d||257||354||53||NS|
|NS = Not significant at P<0.05|
The apparent digestibility coefficents were significantly (P<0.05) higher in the oil cake than the effluent-fed animals for dry matter and tended to be higher for organic matter, N and ADF although the differences were not significant.
|Table 4: Apparent digestibility (%) of different nutrients in the oil cake and effluent-fed animals|
|NS = Not significant at (P<0.05).|
Nitrogen intake and urinary N excretion were almost the same in both groups of animals (Table 5). However, there were tendencies for faecal N excretion to be higher and N retention lower for animals fed effluent than for those fed oil cake.
|Table 5: Nitrogen utilization by the effluent and oil cake of animals|
|N as mg/LW0.75/d|
|Estimates of rumen microbial yield|
|Purine excretion, mmol/d||55.3||51.2||24||NS|
|Purine absorption#, mmol/d||28.6||24.0||6.4||NS|
|Microbial yield##, g/d||20.8||17.4||4.54||NS|
|#Calculated from Y = (X - 0.385*LW0.75)/0.85
where X = purine excretion and Y = purine absorption in mmol/day
## Microbial yield (g/day) = 0.727*X where X = purine absorption (mmol/day) (according to Chen and Gomes 1992)
Faecal N comprises undigested feed N and metabolic faecal N (MFN). Microscopic observations and microbial marker studies have revealed that MFN is virtually all undigested microbial N (Ørskov 1982). Thus higher faecal N excretion in the effluent-fed animals may have been due to a combination of larger quantities of undigested dietary N and/or higher microbial N yield in the rumen. In fact, digestibility of N tended to be lower (Table 4) and microbial N production to be higher (Table 5) in the effluent-fed animals. When the N retention of the individual animals was regressed against the respective N intake, the resultant equations for the effluent and the oil cake treatments were as follows :
Y = 1.64X - 2543; R² = 0.79; P = 0.21) ............... Effluent
Y = 2.06X - 3147; R² = 0.86; P = 0.14) ............... Oil cake
The animals fed effluent tended to have higher excretion of purine derivatives than the oil cake fed animals (Table 5) which gave estimates of rumen microbial yield which were also slightly, but not significantly higher, than for the animals fed oil cake. Despite this apparent difference in favour of the animals fed effluent, all other criteria (eg: N retention and growth rate) indicated that the nitrogen in the effluent was used less efficiently than the nitrogen in the oil cake.
Effluent from a biodigester charged with cattle manure is consumed by growing Bos indicus bulls, without harmful effects, provided there is an extended period of adaptation (at least 10-12 weeks) and it is mixed with other supplements such as wheat bran (1 kg/day) and molasses (0.3 kg/day).
In view of the small numbers of animals on each dietary treatment and the apparently high variation in most of the measured criteria (only the differences for organic matter intake and dry matter digestibility reached the 5% significance level), firm conclusions cannot be drawn as to the merit of the effluent compared with mustard oil cake, as a supplement for a straw-based diet. Furthermore, intake was variable and some animals refused at certain times to drink the effluent mixture. The indications are that effluent is inferior to the oil cake which would be expected on the basis of the known rumen bypass (or escape) characteristics of a proportion of the protein in oilseed cakes, and the known effect of bypass protein in stimulating animal performance on straw-based diets (Preston and Leng 1984).
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