Energy metabolism with particular reference to
methane production in Muzaffarnagari sheep fed
rations varying in roughage to concentrate ratio
Chandramoni
*,1, S.B. Jadhao
2, C.M. Tiwari
3, M.Y. Khan
Energy Metabolism and Respiration Calorimetry Laboratory, Animal Nutrition Division, Indian Veterinary Research Institute, Izatnagar 243 122, India
Received 28 April 1997; received in revised form 28 January 1999; accepted 11 November 1999
Abstract
Methane production in Muzaffarnagari sheep was studied using open circuit respiration calorimetry technique. Twelve rams were divided in three treatment groups of four each and were fed at about maintenance with diets having three roughage (oat hay) to concentrate ratio (R : C), i.e. 92 : 8 (group I), 50 : 50 (group II), 30 : 70 (group III). Concentrate mixture was formulated to contain 93% crushed maize grain, 3.5% wheat bran and 3.5% groundnut cake forti®ed with minerals. Whereas the digestibility of dry matter, organic matter and energy was similar, the digestibility of nitrogen was signi®cantly (p< 0.05) higher in groups II and III and of neutral detergent ®ber (NDF) was signi®cantly (p< 0.05) lower in-group III than the other groups. Nitrogen retention was improved but not beyond 50R : 50C. As a percent of gross energy intake, urinary energy losses in groups I, II and III were 3.0, 2.9 and 2.8%, and methane energy losses were 3.39, 3.34 and 2.98%, respectively. Even though, gross energy intakes (kcal/kg W0.75) were similar, methane loss (g) per 100 g digestible organic matter was signi®cantly (p< 0.05) higher in group I (2.2) than in groups II (1.84) and III (1.54), the latter did not differ in this respect. Metabolisable energy (ME) value (Mcal/kg DM) and energy balances (kcal/kg W0.75) on rations in groups II and
III were similar but on ration in group I was signi®cantly (p< 0.05) lower than that in other groups. Ef®ciency of utilisation of ME for maintenance (km) of diets in groups I, II and III calculated as per
ARC (1980) were 0.674, 0.688 and 0.693, respectively, and did not differ signi®cantly. Based on the evaluation of three R : C, it was inferred that R : C ratio of 50 : 50 in diet of Muzaffarnagari sheep is
83 (2000) 287±300
*Corresponding author. Fax:91-226361573.
E-mail address: chandramoni@hotmail.com (Chandramoni).
1Quarter 11, Road 9, Bihar Veterinary College, Patna 800 014, India.
2Central Institute of Fisheries Education, Seven Bunglows, Versova, Mumbai 400 061.
3Deptt. Animal Nutrition, Rajiv Gandhi College of Veterinary and Animal Sciences, Kurumbapeth,
Pondicherry 605 009.
optimum for economical and sustainable sheep production through reduced methane emissions. #2000 Published by Elsevier Science B.V. All rights reserved.
Keywords:Muzaffarnagari sheep; Energy metabolism; Methane production; Roughage: concentrate ratios; Nutritive value
1. Introduction
Methane production in recent years has assumed more signi®cance in animal production due to its undesired effect on environment including its contribution to global warming. There is now considerable general understanding of the contribution of ruminants to methane production (Johnson and Johnson, 1995; Mathison et al., 1998). Sustainable animal production systems henceforth require that methane produced should be less per unit output. Dietary manipulation is one of the means to reduce methane (see Review, Moss, 1994) and is practicable in India and other third World countries.
Optimum roughage to concentrate is one of the dietary means, which has potential to reduce methane production. Number of studies concerning supplementation of concentrate to straw or poor quality roughages has been done which has demonstrated reduced methane production (Sundstol, 1982; Birkelo et al., 1986; Wainman and Dewey, 1987; Silva and érskov, 1988). However, few studies on supplementation to good quality hay-based diets near maintenance level has been done. The effects of supplementation of concentrate to good quality roughages are unclear (Moss, 1994). Blaxter and Wainman (1964) showed greater production of methane for hay than maize grain and that methane production with mixtures of these feeds was not additive and was invariably greater than could be predicted from composition of the rations. In contrast, the ME content and the ef®ciency of utilisation of metabolisable energy (ME) for maintenance and fattening increased from 71 to 79 and 29 to 61%, respectively. Hence, it is likely that methane production per unit of animal product would decline with increasing maize in ration. On the other hand, Webster (1987) observed reduce energy loss as methane with increasing the ratio of cereal to forage, which decreases the ratio of acetic to propionic acid. Low cereal inclusion rate to grass silage-based diets enhances milk yield and increase milk fat content (Rae et al., 1986) when compared with silage fed alone. Methane produced per unit animal product in this situation seems to be decreased. High propionate fermentations (indicative of reduced methane) are common in hay-based diet containing high proportion of concentrate (Thomas and Chamberlain, 1982).
Therefore, it was thought to investigate methane production on good quality oat hay-based rations with different roughage to concentrate ratio. As such the combined effect (associate effect) of starchy feeds (alone or with little quantity of oil cake and bran) supplementation to good quality roughage like oat hay is little studied. Similarly, the literature on energy balance studies in Muzaffarnagari sheep (sturdy and meat type breed) which is important animal resource in this area, is lacking. Keeping in view the above facts, the present study was speci®cally designed to study energy metabolism of Muzaffarnagari sheep with special reference to methane production on diets varying in roughage and concentrate ratio.
2. Materials and methods
2.1. Selection of animals
Fifteen healthy male uncastrated, Muzaffarnagari sheep, ca. 6±8 months of age, were procured in October, 1993 from Central Institute for Research on Goats, Makhdoom. The animals were dewormed before start of the experiment and good managerial practices were followed in the sheds. The animals were fed on a balanced ration for about a month before the start of experimental feeding.
2.2. Housing and management
The animals were housed in a well-ventilated shed having cemented ¯oor with individual feeding and watering arrangement throughout the experimental period. Concentrate mixture was offered to individual animals between 9.00 and 10.00 a.m. and oat hay was offered in after noon at 3.00 a.m. in the same manger. Fresh water was provided ad libitum daily at 2.30 p.m.
2.3. Experimental plan
Twelve sheep were randomly allocated on the basis of liveweight to three groups comprising each of four animals, following complete randomized design. Rations were given to meet the maintenance requirement of sheep as per NRC (1985). Group I was offered oat hay plus minimal concentrate mixture (ca. 100 g of concentrate mixture I) to meet CP requirement. Group II was offered 50% concentrate mixture and 50% oat hay, whereas group III animals were offered 70% concentrate mixture and 30% oat hay only. Concentrate mixture (11.7% CP and 4.37 Mcal GE/kg DM) contained 93% crushed maize grain, 3.5% deoiled groundnut cake, and 3.5% wheat bran. To every 100 kg concentrate mixture 2 kg of mineral mixture (contained moisture maximum 5%, Calcium minimum 28%, Phosphorus minimum. 12%, Iodine as KI 0.026±0.130%, Copper 0.077± 0.130%, ¯uorine maximum 0.04%) and 1 kg of common salt were added.
Metabolism trial was conducted after 60 days of feeding (with three days of adaptation) in metabolic cages for seven days. All the animals were weighed before and after the trial. Representative samples of feed offered and residue left were taken daily for dry matter estimation and analysis. The total amount of faeces voided by each animal was collected quantitatively at 9 a.m. daily. It was weighed and representative sample of each animal was drawn in sample bottles after crushing and mixing all the pellets and was brought to the laboratory for analysis. Urine excreted daily by individual animal was collected separately in bucket with dilute sulphuric acid for 24 h and was measured with the help of measuring cylinder. Representative samples from individual animals were brought to the laboratory in properly marked, well-stoppered sample bottles.
2.4. Aliquoting of faeces and urine
determination. Similar aliquots were dried in another hot air oven maintained at 408C. The dried aliquots of all the seven days were pooled and kept for analysis of proximate principles, except nitrogen, gross energy and other constituents. For the analysis of crude protein (N6.25) another aliquot equal to 1/40th of the total faeces voided by each animal were preserved with dilute sulphuric acid (1 : 4) in wide mouth air tight stoppered weighed bottles. The aliquots of seven days were composited for each animal in separate bottles. At the end of collection period, the bottles were weighed. The composited weighed samples were mixed thoroughly and suitable aliquots were taken for nitrogen estimation. Duplicate aliquots equal to 1/100th of the total urine excreted daily was taken in 500-ml Kjeldahl's ¯ask containing 30 ml of concentrated sulphuric acid for nitrogen determination. Another aliquot equal to 1/100th of total urine excreted daily was pooled in the brown coloured bottles for seven days. The bottle was air tightened and preserved in a refrigerator for the estimation of energy.
2.5. Respiration calorimetry
Complete energy balance trials were conducted on individual sheep one after the other, in an open circuit respiration chamber for small animals. Fasting heat production was determined after withholding feed for 72 h, but water made available throughout.
2.6. Respiration calorimetry equipment
Respiration calorimetry study was conducted in a simple type of open circuit calorimeter developed and described by Khan and Joshi (1983) for sheep and goat which consisted of a wooden chamber with internal dimensions (in metres) 1.50.91.75 (height). The chamber was maintained at 20±258C with relative humidity of ca. 65%. Difference in oxygen concentrations of incoming and outgoing air was recorded in a dual type paramagnetic oxygen analyser (Servmex Taylor, model OAT 184). Carbon dioxide measurement was conducted by a modi®ed Sonden apparatus with a 100-ml burette. Measurement of methane was done by an infra-red gas analyser (Analytical Development, Hoddesdon, England, Model 300). Representative samples of the incoming and outgoing air from the respiration chamber were collected separately into two Douglas bags with the help of two sampling air pumps (Charles Austen Pumps, Survey, UK) with ¯ow rate of 3 l per minute and provided with a bypass arrangement to reduce their ¯ow rate.
2.7. Prechamber handling of animals
The selected animal was weighed in the morning prior to feeding and watering and kept in a pre-respiration chamber room. After that the animal shifted to respiration chamber for adaptation followed by recording the respiration calorimetry data for two consecutive days.
2.8. Feeding
The animals were maintained on the prescribed nutritional regime. Weighed quantities oat hay and concentrate mixtures were given in the manger attached in the metabolic
crate kept inside the chamber. Animal inside the chamber was provided with suf®cient amount of water through water trough kept inside the chamber.
2.9. Measurement of respiratory exchange
After keeping the feeds inside, the chamber was made airtight by closing the door and blower was started along with the ventilation system of the chamber. The equipment was run for an hour in order to stabilize the recorder. Observations on gaseous exchange were recorded for two consecutive days on each animal after adaptation period of three days in metabolic crate and two days in the respiration chamber. Recording the temperature of dry and weight bulb, ¯ow rate, volume, atmospheric pressure was done manually. The sample of outgoing and incoming air from the respiration chamber were collected in Douglas bag separately with continuous sampling device at 12 hourly intervals. The chamber was opened after 24 h; the residues of feeds, faeces voided and urine excreted were collected and measured. Representative samples of feed offered, residue left, faeces and urine were drawn and preserved for nitrogen and energy estimation. Heat production was calculated as per Brouwer's (Brouwer, 1965) equation. Samples of feeds, residue and faeces were ground and analysed for proximate principles as per AOAC (1980) method. NDF and ADF in feeds and faeces were estimated by using method of Goering and Van Soest (1970). Estimation of Gross energy of samples was done by Gallenkamp automatic adiabatic bomb calorimeter (CBA 301 series) as per the procedure of Gallenkamp manual. The data were subjected to test of signi®cance (Snedecor and Cochran, 1967) using the analysis of variance.
3. Results and discussion
It is important to mention that under present situations high concentrate feeding to ruminants is not possible in India for economical reasons. So, the effects of limitedly varying roughage and concentrate ratio (R : C) in rations on methane production in Muzaffarnagari sheep were studied. Small amount of concentrate (100 g) was given for balancing the ration in respect of protein and energy and as such the ratio of R : C was 92 : 8 instead of 100 : 0 in group I. Groups II and III were containing R : C ratio of 50 : 50 and 30 : 70, respectively. Chemical composition of oat hay and concentrate mixture is given in Table 1.
3.1. Nutrient intake and digestibility
Table 1
Chemical composition of oat hay and concentrate mixture (CM) on DM basis
Oat hay CM
Daily intake of feeds by sheep fed on different roughage and concentrate ratios (R : C) and nutritive value of rations during metabolic trial (DM basis)
Attribute Treatmentsa SEMb
92R : 8C 50R : 50C 30R : 70C
Liveweight (kg) 37.1 38.0 39.1 1.78
Metabolic weight (kg) 15.0 15.3 15.6 0.58
Concentrate mixture intake (g DM/day) 91.6 687.2 870.5
Oat hay intake (g DM/day)** 1004.1 c 615.5 b 382.9 a 29.8 Total intake (g DM/day)** 1095.7 a 1302.3 b 1253.4 b 29.82 DM intake (g /kg W0.75/day)* 73.9 a 85.2 b 81.0 b 1.80
DM digestibility (%) 58.0 60.0 62.4 0.70
Organic matter intake (g/kg W0.75/day)* 68 a 79.2 b 75.6 b 1.92
Digestibility (%) 62.0 64.5 66.6 0.75
Crude protein intake (g/kg W0.75/day)* 7.3 a 9.1 b 8.86 b 0.22
Digestibility (%)* 57.5 a 60.5 b 61.5 b 0.49
NDFcintake (g /kg W0.75/day)** 34.5 b 30.3 b 25.4 a 0.83
Digestibility (%)* 62.0 b 60.0 b 55.5 a 0.61
ADFdintake (g/kg W0.75/day)** 28.0 c 18.7 b 12.2 a 0.67
Digestibility (%) 52.3 51.5 49.8 0.53
Cellulose intake (g/kg W0.75/day) 24.0 c 16.2 b 10.6 b 0.58
Digestibility (%)* 60.2 b 58.8 ab 56.9 a 0.58
Hemicellulose intake (g/kg W0.75/day)** 6.5 a 11.6 b 13.2 c 0.26
Digestibility (%)** 98.2 b 73.5 a 60.6 a 3.32
Nutritive value
DCP (%)** 5.73 a 6.46 b 6.73 c 0.05
TDN (%)** 58.8 a 62.1 b 65.5 c 0.44
DE (Mcal/kg DM)* 2.29 a 2.45 b 2.54 b 0.03
MEe(Mcal/kg DM)* 2.0 a 2.29 b 2.30 b 0.03
aMean with different letters differ signi®cantly. bStandard error of means.
cNeutral detergent ®ber. dAcid detergent ®ber.
eME estimated from calorimetric trial (Table 3). *p< 0.05, **p< 0.01.
(Egan, 1980). The basic urge to consume the feed is the tendency of animal to realise the genetically determined maximum capacity for growth/production. This genetic capacity corresponds to the maximum rate at which tissues can utilise the nutrients (Ketelaars and Tolkamp, 1992). Ali et al. (1979) in Muzaffarnagari sheep observed signi®cantly (p< 0.01) higher total intake on high concentrate diet. In their studies, DM intake on all roughage, 25R : 75C, 50R : 50C and 25R : 75C diets were 79, 72, 76 and 73 g/kg W0.75/ day, respectively. The observed higher DM intake on diets II and III than in diet I is also in agreement with the ®ndings of Sekine et al. (1986); Ketelaars and Tolkamp (1992) and Santra (1995). The digestibility of DM, OM was similar on all R : C ration but the digestibility in group I was signi®cantly (p< 0.05) lower than other two groups. However, although nonsigni®cant, two to four percent improvement in digestibility of diets with 50 and 70% concentrate diets is in agreement with Slabbert et al. (1992) who reported that DM digestibility was not in¯uenced by the plane of nutrition but linearly reduced as proportion of roughage in the diet increased from 30 to 80%. Ali et al. (1979) also found increased digestibility of dry matter with increasing the proportion of concentrate in the diet of Muzaffarnagari sheep. The digestibility of DM depends on quality of roughage in question, which in turn depends on the content of protein and energy together with minerals and vitamins. The oat hay used in present experiment showed better OM digestibility than 57% reported by Weston (1967) for sheep given wheaten hay with 4.4% protein. Crude protein digestibility was signi®cantly (p< 0.05) increased with inclusion of higher proportion of concentrate in diet. Digestibility of protein depends primarily on protein content of the diet and intake (Sahlu et al., 1993). Ali et al. (1979) reported nonsigni®cant differences in CP digestibility in same breed of sheep fed different roughage to concentrate ratio, which may be due to ad libitum feeding regime. The increase in N digestibility with higher consumption of concentrate in sheep in groups II and III is supported by similar reports of Weston (1967); Sekine et al. (1986) and Slabbert et al. (1992).
3.2. Nutritive value
Nutritive value in terms of DCP and TDN increased (p< 0.05) with inclusion of concentrate in the diet. Improvement of 1% in DCP and 7% in TDN was observed on 30R : 70C over 8C : 92R group. Mean DCP intake (kg W0.75/day) was signi®cantly higher in diet II (5.5) and III (5.45) than in diet I (5.45). TDN intake (kg W0.75/day) was also higher on diet II (52.9) and III (52.9) than in diet I (42.9). The range of intake is similar to that found by Graham, (1967) for adult sheep and is higher than that found by Ranjhan (1977).
3.3. Nitrogen intake and outgo
Data on N metabolism on different roughage concentrate ratio is presented in Table 3. N intake in groups II and III followed similar trend as DM intake and was signi®cantly (p< 0.01) higher than in group I. Faecal and urinary energy loss was not different. Total N balance increased with the increase of concentrate in diet, but not beyond 50% concentrate in diet. Nitrogen retention depends on its content in the diet, intake and the availability of fermentable energy in the rumen. On high concentrate diet, the availability of fermentable energy is more which helps rumen microbes to capture N leading to its increased utilisation.
3.4. Distribution of energy
Total GE (3594, 4467, 4328 in I, II and III, SEM 124.6), DE (2005, 2644, 2646 in I, II and III, SEM 64.8), ME (1755, 2366, 2397 in I, II and III, SEM 60.1) intakes in groups II and III were signi®cantly (p< 0.05) higher than in group I. However, former two groups did not differ in this respect. Energy evaluation of different R : C ratio-based diets are described in Table 4. Intake and losses were expressed relative to metabolic body weight and on this basis except methane energy (signi®cantly less in group III than other two), neither energy losses nor respective intakes differ signi®cantly. The GE intake is the
Table 3
Nitrogen (N) metabolism in sheep fed on rations with different roughage and concentrate ratios
Particulars Treatmentsa SEMb
92R : 8C 50R : 50C 30R : 70C
N intake (g/day)** 17.5 a 22.2 b 21.9 b 0.53
Faecal N (g/day) 7.4 8.7 8.4 0.29
Urinary N (g/day) 8.6 10.8 9.43 0.30
N balance (g/day)* 1.46 a 2.71 b 3.04 b 0.11
N balance (mg/kg W0.75/day)* 100 a 182 b 198 b 5.62
N retained as % of intake* 8.3 a 12.3 b 13.9 b 0.25
N retained as % of N absorbed* 14.5 a 20.5 b 22.6 b 0.27
aMeans bearing different letters in a row differ signi®cantly. bStandard error of means.
*p< 0.05, **p< 0.01.
function of level of energy and energy density of ration besides the function for which it is used (ARC, 1980).
As percentage of GE, DE (55.9, 59.3, 61.2 for groups I, II and III, SEM 0.85)) was not different. Percent metabolisability (ME/GE) was higher (p< 0.05) in group III (55.2) than in group I (48.9), but metabolisability of ration in Group II (55.0) did not vary from either of these two groups (SEM 0.82). High proportion of oat hay in the diet was conspicuously re¯ected by signi®cant depression in the ME value obtained in-group I (Table 2). With increase in the energy intake, there was no signi®cant increase in faecal energy output. As the level of feeding of ruminants increases the proportional loss of energy in faeces increases and apparent digestibility declines (ARC, 1980). In the present experiment sheep were fed at maintenance level, that is why faecal loss may not be different. Blaxter and Wainman (1964) found increased faecal energy loss with increasing proportion of ¯aked maize in the diet. However, this loss declined markedly when the diet of sheep fed above maintenance level contained beyond 60±80% of ¯aked maize. Similar observation was made by Krishna et al. (1969). Wagner and Loosli (1967) also noted slightly increased values of TDN at maintenance level of feeding with increased percentage of concentrate in diet.
Urinary energy (UE) loss as a proportion of GE intake on 92R : 8C, 50R : 50C and 30R : 70C was 3.0, 2.9 and 2.8% (SEM 0.008) and is in agreement with earlier reports (Blaxter and Graham, 1955, 1956; Blaxter and Wainman, 1961). These ®gures were signi®cantly (p< 0.05) different from each other. It has been found that UE loss was never more than 5% of GE intake in sheep and cattle (Blaxter and Wainman, 1964). As the total ME intakes were signi®cantly higher on concentrate containing diet, UE loss as percent of GE intake was decreased. Kishan et al. (1987) also found that the UE loss as a percentage of GE intakes decreased on high level of ME intake.
Table 4
Energy metabolism (kcal/kg W0.75/day) of Muzaffarnagari sheep fed diets with varying roughage to concentrate
(R : C) ratio
Attribute Treatmentsa SEMb
92R : 8C 50R : 50C 30R : 70C
Gross energy intake 242.2 274.2 256.5 7.45
Faecal energy 106.6 116.6 97.2 3.29
Energy balance* 23.5 a 44.8 b 47.8 b 3.27
kmc 0.674 0.688 0.693 0.003
kmgd 0.655 0.672 0.720 0.001
aMean with different letters in a row differ signi®cantly (p< 0.05). bStandard error of means.
ck
mis ef®ciency of utilisation of ME for maintenance (calculated as per ARC, 1980). dk
Methane production data are presented in Table 5. Total methane (g/day) was not signi®cantly different between groups. Moss (1994) recommended that units used for expressing methane production from ruminants should be extended beyond the traditional expression of methane energy as proportion of GE intake to methane production per kg of OM digested or per kg of animal product. Thus, the methane loss (per 100 g digestible OM or CHO) was signi®cantly higher on 92R : 8C than either 50R : 50C or 30R : 70C ratios, which did not differed in this respect. As the level of digested organic matter or carbohydrate was increased in the diet, methane production decreased signi®cantly (p< 0.05). Type of the roughage and also concentrate (starchy or oil cake) can substantially in¯uence on methane production (Moss and Givens, 1993). In their experiment, they offered isoenergetic forage (grass silage): concentrate (rolled barley or soyabean meal) diets of 1.0, 0.75, 0.50 and 0.25 (DM basis ) level in wether sheep at maintenance level. It was found that the methane production (l kgÿ1
FOM) increase signi®cantly and linearly with decreasing forage concentrate for rolled Barley diet but was nonlinear for soyabean meal diets with low levels at forage concentrate ratio of 0.76 and 0.51.
The main component affecting methane production is the type of carbohydrate and relative rate of fermentation. Kreuzer et al. (1986) found signi®cantly lower methane loss (total as well as % of GE) on rations with native starch than rations with cellulose. Johnson et al. (1993) showed that there was decreased methane production with increased energy intake, when expressed as percent of GE. Methane production do fall from a level of 6±7% of energy intake when forages are fed at maintenance to as low as 2±3% when high grain concentrates are fed at near ad libitum intake levels (Johnson and Johnson, 1995). Although fed approximately at maintenance during experimental study, the intakes were found to be exceeded far towards achieving positive balance. Van Soest (1994) indicated that a high grain diet and or the little addition of soluble carbohydrate with resulting shift in the fermentation pattern in the rumen are associated with a more hostile environment for methanogenic bacteria in which a passage rates are increased, ruminal pH is lowered and certain population of protozoa, ruminal ciliates and methanogenic Table 5
Methane production in sheep fed on rations with varying roughage and concentrate (R : C) ratios
Methane production Treatmentsa SEMb
92R : 8C 50R : 50C 30R : 70C
As % of gross energy* 3.93 b 3.34 ab 2.98 a 0.12
As % of digestible energy* 7.02 b 5.62 a 4.87 a 0.18
l/day 14.8 15.7 13.6 0.52
g/day 10.6 11.2 9.7 0.37
g/100 g digestible DM* 2.10 b 1.76 a 1.46 a 0.06
g/100 g digestible OM* 2.20 b 1.84 a 1.54 a 0.06
g/100 g digestible CHO* 2.65 b 1.88 a 1.62 a 0.08
aMeans bearing different letters in a row differ signi®cantly. bStandard error of means.
*p< 0.05.
bacteria may be eliminated or inhibited. In present study also total energy intake was signi®cantly higher in groups II and III than in I.
The methane losses in this study were lower than some of the earlier reports (Blaxter and Clapperton, 1965; Moe and Tyrrell, 1980; Khan et al., 1988; Prakash, 1990). Neergaard (1974) observed 3% methane energy loss as percent of GE in some calves in his experiment fed on a concentrate diet. Methane energy loss as percent of GE ranged from 2.5 to 13% in sheep fed on different diets (FEU, 1978). The low values of methane as compared to others can be attributed to numerous reasons, one of that is breed. Blaxter and Wainman (1964) studied methane production of a Cheviot, a Suffolk cross weather and black face weather. When fed on different ratio of oat hay and maize at maintenance or twice the maintenance level, Cheviot produced higher (p< 0.01) methane with all ratios of roughage to concentrate than the other two breeds, and this discrepancy was more marked with concentrate diet. This is indicative of the fact that it is the genetics of the animal (besides diet) which may be controlling the rumen size and its complex ecosystem, which can have great impact on methane production. In studies of Blaxter and Wainman (1964), methane production was found to be reduced from 6.76 to 3.65% of GE intake. High propionate fermentation (indicative of reduced methane production) are apparent in hay based diet containing high proportion of concentrate (Thomas and Chamberlain, 1982) which may be a one more factor in reducing methane loss in such dietary combination. In studies of Blaxter and Wainman (1964), range examined was from 100 to 5% hay: 95 ¯aked corn maize. To verify the results obtained in other sheep, it is necessary to evaluate C : R beyond 70 : 30 in Muzaffarnagari sheep.
As such there is less information to show comparative methane production from different animal species/breeds. Report from this laboratory indicated that there is variation in methane production by different breeds. Murarilal et al. (1987) showed higher methane loss as a percent of GE intake for Holstein-Friesian (HF)Hariana cross than HF cattle or buffaloes. Recently, we (Chandramoni et al., 1998) reported higher methane production in crossbred sheep than Muzaffarnagari sheep, when fed same rations. Galbraith et al. (1998) reported methane losses of 6.6, 5.2 and 3.3% of GE intake for bison, waipiti and white tailed deer, respectively, when the animals were fed lucern pellets.
Unadjusted (Table 4) and energy retention (kcal/kg W0.75) adjusted for similar ME intake (data not shown) was signi®cantly (p< 0.05) higher on groups II and III than in group I. Ef®ciency of utilisation of ME (km) was calculated using equation of ARC (1980) which relates kmto metabolisability (qm). Assuming thatqqm, the calculated
4. Conclusion
Based on the evaluation of three roughage concentrate ratio (R : C), this study concluded that as dry matter intake and digestibility, N retention, reduction in methane loss (g/100 g digestible OM or CHO) and ME value does not improve and on contrary NDF digestibility reduces signi®cantly (p< 0.05) beyond 50R : 50C, ratio of 50 : 50 in diet of Muzaffarnagari sheep is optimum for economical and sustainable sheep production through reduced methane emissions.
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