Short communication
Comparison of diet and faecal collection methods for
assessment of seasonal variation in dry matter intake
by sheep maintained on a
Cenchrus ciliaris
pasture
S.K. Sankhyan
*, A.K. Shinde, R. Bhatta, S.A. Karim
Central Sheep and Wool Research Institute, Avikanagar 304 501, Rajasthan, India
Received 14 August 1997; received in revised form 28 April 1998; accepted 24 August 1999
Abstract
Four diet collection methods: clipping(C), mouth grab (MG), plucking (P) and oesophageal extrusa (OE) and two faecal output estimation methods: faecal bag (FB) and Cr2O3marker (I) were
compared to assess seasonal changes in nutrient composition of diet and dry matter intake of sheep
onCenchrus ciliarispasture. Crude protein (CP) and lignin contents of OE were higher than C, MG
and P during all the seasons. Fiber fractions were lowest in MG, highest in C and intermediate in OE and P methods. Pooled CP contents of diet samples declined (P< 0.01) from 12.7% in monsoon to 9.3 and 7.9% in winter and summer while ADF, cellulose and lignin increased from monsoon to summer. Clipped samples had lower NDF, ADF, cellulose, hemicellulose and gross energy digestibility compared to P, MG and OE methods in all the seasons. Nutrient digestibility declined from monsoon to winter and summer in all the diet samples collected by the four techniques. CP digestibility showed marked depression from 63.1% in monsoon to 44.1 and 14.4% in winter and summer. Faecal collection bag and Cr2O3marker methods estimated similar faecal outputs in all the
seasons. The OE method estimated a lower DM intake of the animals (mean 960 g/day) compared to C, P and MG methods (mean 1381 g/day). Animals consumed more dry matter during winter (mean 1706 g/day) than during monsoon and summer (mean 1030 g/day) seasons.
It is concluded that diet sampling method and season had an influence on the estimated diet composition and DMI of sheep on semi-arid pastures. Both methods of faecal collection, however, estimated similar daily faecal output in sheep.#1999 Elsevier Science B.V. All rights reserved.
Keywords: Sheep; Grazing; Pasture; Diet sampling; Faecal sampling; Seasonal changes; Nutrient utilization 82 (1999) 261±269
*Corresponding author. Fax:91-1437-28163
E-mail address: sankhyan@cswri.raj.nic.in (S.K. Sankhyan)
1. Introduction
Sheep in the semi-arid region of India mainly depend on rangeland to meet their nutritional requirement, the seasonal change in forage yield is reflected in their production performances (Shinde and Singh, 1995). Assessment of dietary nutrient content of forage and dry matter intake by sheep on such grazing resources is necessary to formulate suitable range management strategies to identify the seasonal factors that limit animal production. Basic prerequisite in determining dry matter intake of sheep on pasture is to collect representative samples of forage consumed by the animals accurately and precisely. Oesophageal cannula is widely used for collecting diet sample of grazing animal (Goddard and Fraser, 1994). Various other methods viz. hand plucking, clipping and mouth grab sampling are also used to collect diet samples of animal. Similarly the accurate estimation of total faecal output is essential to determine the nutrient digestibility and intake of grazing animals. Faecal bag or Cr2O3 marker is commonly used methods for estimation of total faecal output in grazing studies (Holechek et al., 1982). However, each of these diet and faecal collection method has its own advantages and disadvantages. In view of inconsistencies in using these collection methods, an experiment was planned to investigate the effect of seasons and sampling techniques on the diet composition and dry matter intake of sheep on cenchrus pasture.
2. Materials and methods
2.1. Site
The study was conducted at the Central Sheep and Wool Research Institute, Avikanagar, India located at 728280E latitude and 26
8170N longitude, 320 m above mean
sea level. Climate of the region is typical semi-arid with yearly mean minimum and maximum temperature of 8 and 418C and 257 mm of annual precipitation of which 93% is distributed between June and September and remaining 7% in form of short showers from January to March.
2.2. Season
The animals were introduced in the pasture in the month of August, 1995 and continued till July, 1996. Three digestion trials on four rams, one in each season of monsoon (August), winter (December) and summer (June) were conducted.
2.3. Pasture
Field research was conducted on 5.0 ha plot of pasture dominated by perennial grass (Cenchrus ciliaris), native grasses and forbes (Commelina forskalaei,Eleusine aegypticae
3.24 and 1.89 ton DM/ha, respectively. Pasture vegetation was lush green and dense in the monsoon, long and stalky in the winter and dry and patchily distributed in summer. Animal diets constituted of perennial grasses, forbes and few browse species during the digestion trials. The contribution of fodder trees and tall shrubs was negligible in the diet of the animals, as these species were lopped and fed to the grazing sheep only after completion of digestion trials in each season.
2.4. Animals
Twenty adult Malpura rams (3±4 years old) with average body weight of 37.0 kg were adopted from the Institute flock. They were solely maintained on cenchrus pasture under continuous grazing system at a stocking density of four sheep per hectare. The animals were allowed 9 h of grazing extending from 08:00±17:00 h under supervision of a shepherd. Two rams were fitted with oesophageal cannulas following the technique of Karim et al. (1997) and maintained on stall-feeding with ad lib.Cenchrus hay and 300 g concentrate mixture per day individually. The fistulated animals were taken to pasture 21 days before the digestion trials in each season to make them acclimatized to prevailing pasture conditions and during this period they were not offered other feeds.
2.5. Pasture and diet sampling
Diet samples of grazing sheep were collected during 5 consecutive days of the digestion trial in each season by four methods:
1. clipping: ten 1 m2quadrate of grazing area (two quadrate per hectare) were clipped 2± 3 cm above the ground level for estimation of pasture yield and collection of diet samples (C);
2. mouth grab: daily 30±35 bites from the mouth of 20 sheep were snatched before swallowing by a operator and the samples with excessive salivary contamination were discarded immediately (MG);
3. plucking: daily 25±30 samples of forage species were collected by the same operator, simulating the animal's dietary preference from a flock of 20 animals (P) and; 4. oesophageal extrusa: extrusa samples were collected from two fistulated animals
during first 3 h of active grazing. Samples were squeezed in muslin cloth to remove saliva (OE).
Diet samples collected by the four methods were dried at 608C for 48 h in an oven. The representative samples of diets were drawn for chemical analysis by pooling the daily samples of 5 days collection.
2.6. Faeces sampling
twice daily at 08:00 and 17:00 h. Out of 10 days, the initial 5 days were allotted to acclimatization of animals for harness and uniform chromic oxide excretion and the later 5 days were used for collection of diet and faeces samples. Faecal bags were emptied in the morning (08:00 h) and evening (17:00 h) to estimate daily faecal output (FB) and at the same time faecal pellets from rectum were also collected for indicator method (I). Representative samples (10%) of faeces collected by the two techniques (Faecal bag and Cr2O3 marker) were pooled separately for 5 days collection period and representative samples were dried in oven at 608C for 48 h.
2.7. Laboratory analysis
Dried forage, diet, and faeces samples were ground to pass through 1 mm sieve in a Wiley mill and stored in polyethylene bags for further analysis. Diet and faeces samples were then analyzed for dry matter (DM), crude protein (CP) and ash (Association of Analytical Chemists, 1984) and acid detergent fiber (ADF), neutral detergent fiber (NDF) and lignin (Van soest et al., 1991). Gross energy (GE) content was determined by Ballistic Bomb Calorimeter (Gallenkamp). Dry matter intake and digestibility in sheep were estimated individually from four diet and two faecal sampling methods by the lignin ratio technique (Wallace and Van Dyne, 1970).
2.8. Statistical analysis
The data were analyzed according to a factorial split plot design with animal as a main plot and sampling methods as subplots. Animal variations were removed by arranging animals and seasons in factorial design and seasonal effects were tested against the error source of animal X season interaction, while sampling methods and their interactions were tested against the residual variance using following model with four replications.
Yijkl uAlSi ASliDjFk SDij DFjk SFik SDFijk
ADSijkleijkl
Where A: Animals; S: Seasons; D: Diet sampling methods; and F: Faecal collection methods.
i1;2;3; j1;2;3;4; k1;2; 11;2;3;4;
Significance was declared where P< 0.05. No statistical analysis was performed on data of chemical composition of diet samples collected by four methods as pooled samples were used for chemical analysis.
3. Result and discussion
3.1. Diet composition
in extrusa samples over plucked and clipped samples in sheep by 3.6 and 4.8% units have been reported by Forbes and Beattieg (1987). Salivary contamination has contributed to higher value of CP in OE compared to MG samples (Bhatta et al., 1996). In spite of this fact, lower value of CP in OE compared to MG in monsoon season is a consequence of collection of tender portion of forage containing higher CP value while snatching from the mouth of the animals. Such effect was not observed in winter and summer because of the age and maturity of forage. Thus, lower estimate of CP value in MG compared to OE method was recorded. Higher lignin content of extrusa samples compared to other three methods (MG, P and C) indicated that maceration of plant cell by animal in extrusa samples might have caused an increase release of tannin which have elevated lignin value as result of tannin±protein reactions (Osbourn et al., 1971). Papachristou and Nastis (1994) also reported higher value of lignin in extrusa sample when compared to hand plucked sample. Higher NDF, ADF, cellulose and hemicellulose content estimated by C over OE and MG methods was obvious, as clipping method of diet sampling represented the pasture forage at offer without considering forage selection by the animals while MG, P and OE method represented the diet sample of preferred forage. Progress in age and maturity of pasture forage was reflected in decline of CP content from 12.7% in monsoon to 9.3 and 7.9% in winter and summer and increase of ADF, cellulose and lignin content of diet. NDF content was highest in monsoon (67.1%), lowest in winter (57.4%) and inter-mediate in summer (62.4%) season. Moreover, the hemicellulose and gross energy content of diet also showed declining trend from monsoon to winter and summer (Table 1).
3.2. Faecal output
Faecal output of animals assessed by two methods (faecal bag versus indicator) were almost similar in three seasons indicating that both the methods were equally effective in estimating the faecal output of grazing sheep. This observation confirm the finding of Buntinx et al. (1990) who also reported similar estimation of faecal output in sheep by faecal bag and chromic oxide release device (CRD) methods.
3.3. Digestibility
related to maturity and lignification of pasture grasses. Such seasonal trend in nutrient digestibility in sheep on cenchrus pasture in semi arid region was also reported by Shinde et al. (1998). Faecal bag or indicator method of total faecal collection in combination with either of the four diet sampling methods (C, P, MG and OE) estimated similar digestibility of DM, ADF, hemicellulose, CP and GE except NDF and cellulose.
Table 1
Chemical composition (on % DM basis) and gross energy (MJ/kg) of diet collected by different methods Clipping Mouth grab Plucking Oesophageal extrusa Dry matter
Monsoon 20.10 16.47 17.90 a
Winter 65.65 38.49 53.00 a
Summer 87.38 82.36 83.36 a
Crude protein
Monsoon 10.18 13.96 14.48 12.15
Winter 6.38 10.17 7.22 13.58
Summer 4.37 8.05 6.30 13.12
Neutral detergent fibre
Monsoon 68.63 62.76 69.18 68.00 Winter 68.97 49.67 57.52 53.62 Summer 72.70 53.50 60.92 62.45 Acid detergent fibre
Monsoon 39.30 34.09 36.24 39.10 Winter 42.42 35.90 39.97 40.30 Summer 64.80 46.26 52.16 49.73 Cellulose
Monsoon 31.21 27.99 30.16 30.76 Winter 34.44 27.75 31.93 29.02 Summer 41.16 31.08 35.94 30.30 Hemicellulose
Monsoon 29.33 28.67 32.94 28.70 Winter 26.55 13.77 17.55 13.32
Summer 7.90 7.24 8.76 12.72
Lignin
Monsoon 3.75 5.60 4.33 7.13
Winter 5.91 6.05 6.30 9.13
Summer 22.06 12.36 15.13 17.97 Gross energy
Monsoon 18.58 18.24 17.40 17.26 Winter 17.36 17.40 17.44 17.90 Summer 16.94 17.32 17.36 17.90 Total ash
Monsoon 13.63 11.21 11.18 12.95
Winter 8.01 10.39 10.10 15.80
Summer 8.51 14.60 9.72 15.35
3.4. Intake
Oesophageal extrusa sampling estimated lower (P< 0.01) dry matter intake (DMI) of animals compared to P, MG and C methods and the trend remained similar on its expression in terms of unit body weight or metabolic body size (Table 3) reflecting under estimation of digestibility when estimated from extrusa samples, probably due to elevated value of lignin as a result of tannin±protein reaction. Average DMI of animals was higher in winter (mean 1706 g/day) than in monsoon and summer (mean 1030 g/day) seasons.
Table 2
Digestibility coefficients assessed by different diet and faecal collection methods during three seasons and their interactions*
Digestibility coefficients
Diet sampling methods Faecal sampling methods Clipping Mouth *Unlike superscripts (a,b,c) in a row differ significantly (P< 0.05); Unlike superscripts (A,B,C) in a column
Higher moisture content of vegetation (Minson, 1982) and gut fill limitation of animals (Yoelao et al., 1970) would have contributed to the lower DMI in monsoon season. However, the lower DMI in summer compared to winter season was reflection of prevailing hot environmental conditions (Baile and Forbes, 1974) and depletion in quality and quantity of pasture forage (Mali et al., 1984). Faecal bag or Cr2O3 marker in combination with the four diet sampling methods estimated similar DMI for all the three seasons.
In clipping method higher value DMI and lower value of CP of the diet contributed to lower DCP and higher DE intake of the animals. Whereas OE method, which was true reflection of diet selection by the animals showed higher DCP and lower DE intakes. DCP intake of sheep progressively declined (P< 0.05) from monsoon (82.6 g/day) to winter (71.0 g/day) and summer (16.4 g/day), while DE intake was highest in winter (18.94 MJ/day) followed by monsoon (13.31 MJ/day) and summer (7.57 MJ/day). Such changes are associated with seasonal variation in pasture forage availability, its quality and preference by the animals.
4. Conclusions
Season had a great influence on diet composition and intake of grazing sheep maintained on semi arid Cenchrus pasture. Estimates of intake were also influenced by different methods of diet collection. Faecal bag and Cr2O3marker methods estimated similar faecal output, hence, either of the method can be used in digestion trial of grazing animals.
Table 3
Intake assessed by different diet and faecal collection methods during three seasons and their interactions*
Intake Diet sampling methods Faecal sampling methods Clipping Mouth
grab
Plucking Oesophageal extrusa
SEM Indicator Faecal bag
SEM
Dry matter g/day/kgW0.75
Monsoon 74.2dB 49.6bA 64.2cA 39.2aA 5.31 56.8A 53.6A 3.75
Winter 98.8bC 96.5bC 92.5bB 76.5aC 5.31 88.0B 94.2B 3.75
Summer 43.3aA 78.3dB 65.8cA 53.2bB 5.31 62.9A 57.3A 3.75
Digestible crude protein g/day/kgW0.75
Monsoon 49.9bC 44.5bB 68.2cC 22.6aA 2.54 49.2C 43.4B 1.80
Winter 20.9aB 56.0cB 24.8aB 44.4bB 2.54 33.6B 39.5B 1.80
Summer 0.0A 0.5aA 0.0A 22.4bA 2.54 9.0A 9.6A 1.80
Digestible energy MJ/day/kgW0.75
Monsoon 0.94dB 0.60bA 0.82cB 0.38aA 0.07 0.70B 0.67B 0.05 Winter 1.16cC 1.12bB 1.05bC 0.59aB 0.07 0.98C 0.98C 0.05 Summer 0.13aA 0.74dA 0.52cA 0.53bA 0.07 0.46A 0.41A 0.05
*Unlike superscripts (a,b,c) in a row differ significantly (P< 0.05); Unlike superscripts (A,B,C) in a column
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