The effects of the spatial dispersion of ryegrass (Lolium perenne L) and clover (Trifolium repens L), at the feeding station scale, on diet composition and feeding behaviour were studied for sheep. There were no significant changes in diet composition with changes in the spatial dispersion of sward components. Bite size, bite rate and intake rate did increase as the species became more aggregated

Gordon, I J

Illius, A W

English

University of Kentucky

University of Kentucky UKnowledge IGC Proceedings (1997-2023) XVIII IGC (1997) Manitoba & Saskatchewan Intake and Diet Selection by Sheep Grazing Grass/Clover Patches I J. Gordon Macaulay Land Use Research Institute, UK A W. Illius University of Edinburgh Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, and the Weed Science Commons This document is available at https://uknowledge.uky.edu/igc/1997/session5/7 <>Grasslands 2000</> This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in IGC Proceedings (1997-2023) by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu. Session 5 - Foraging Strategy 5-11ABSTRACTThe effects of the spatial dispersion of ryegrass (Lolium perenne L)and clover (Trifolium repens L), at the feeding station scale, on dietcomposition and feeding behaviour were studied for sheep. Therewere no significant changes in diet composition with changes in thespatial dispersion of sward components. Bite size, bite rate and intakerate did increase as the species became more aggregated.KEYWORDSSheep, grass, clover, intake, diet composition, feeding stationINTRODUCTIONForaging herbivores make decisions about where to forage, what toforage on and how to forage at a range of scales, from leaves tolandscapes (Senft et al., 1987; Gordon & Illius, 1993). Thesedecisions determine the intake rate of forage and the composition ofthe diet. The ability of animals to exploit the heterogeneity in theenvironment is primarily determined by the spatial dispersion of thefood plants which affects the rates at which the herbivore can consumefood because of the process of searching and selecting componentsfrom the vegetation on offer.Whilst there have been several studies of the effects of the spatialdispersion of resources on diet composition there have been noneshowing the response of herbivores to the dispersion of food itemsat the level of the feeding station (i.e. the area covered by theherbivore’s search without moving its feet, Senft et al., 1987). Theaim of this research was to determine the effect of the distribution ofplant species on diet selection and intake rate in sheep within a foodpatch.MATERIALS AND METHODSPlastic seed trays were filled with 3l of a mixture of peat-basedcompost and vermiculite to provide a firm rooting medium. The seedtrays measured 320 x 120 x 45mm, giving a sown area of 0.029m2,with 32 pull-out cellular modules each 30mm x 30mm in size. 400trays were sown with white clover and 400 trays were sown withperennial ryegrass at a rate of 10 seeds/module. The trays were housedin a greenhouse allowing control over temperature, fertiliser, wateringand cutting regimes during germination, establishment and growth.After sward establishment, the trays were cut to 3 cm above the peatsurface every week for 3 months. One week prior to the experimentall the ryegrass swards were trimmed to 5cm. Immediately beforethe experiment the modules were removed from the trays, pairs oftrays were placed side by side, and the modules rearranged to create4 patterns of distribution of ryegrass and clover (Fig. 1). The pairedtrays give a grazed area of 0.058m2, with equal area coverage of thetwo plant species.Six mature wether oesophageal fistulated Scottish Blackface sheep,which had been trained in the procedures used in the trials, werepresented with test swards (pairs of trays) under controlled conditions.A total of 288 trials were conducted; each sheep received each swardpattern/bite number (see below) combination twice. Before each trialthe fistula plug was removed and a plastic collection bag attached tothe animal’s neck. The animal was allowed to take 10, 20, 30, 40, 50or 60 bites from the sward and then that trial was terminated. Theextrusa samples were removed from the collection bag and stored inplastic zip top bags at -20oC.The occurrence and timing of each bite within a trial was recordedmanually on a hand-held portable computer. These data were analysedin order to summarise the total number of bites taken, the rate ofbiting, and the number and length of biting bouts within each trial.On occasion an animal paused during a trial and stopped chewing;since the inclusion of these pauses would cause underestimation ofthe maximum biting rate achieved, a pause of longer than 4 secondswas taken to be a non-grazing interval and excluded from the data.The weight of herbage removed during the trial were measured byweighing the sward to the nearest 0.1g before and after each trial.Evaporative weight loss for each trial was estimated by concurrentlyweighing representative ungrazed swards at the start and end of eachtrial. Weight losses from grazed swards were subsequently correctedfor evaporative weight loss. Bite weight (BW, mgDM) was estimatedfrom the dry weight of plant material removed and the total numberof bites taken by an animal during the trial. The instantaneous intakerate was calculated from the product of the rate of biting and the dryweight of the bite.The proportion of grass and clover in the extrusa and herbage wasdetermined using the n-alkane method on the herbage and extrusasamples following a modified version of the procedure outlined inMayes, Lamb and Colgrove (1986) (R.W. Mayes, pers. comm.).Mean and standard error of difference values of diet composition,bite size, bite rate and intake were estimated using analysis of varianceusing the Genstat 5.2 programme (Genstat 5 Committee, 1993). Theanimal was used as the blocking factor in the analysis in order toovercome the problem of pseudoreplication.RESULTS AND DISCUSSIONFor all analyses there was no significant interaction between the swardpattern and bite number treatments. Therefore, the means for thesward pattern treatments, across bite numbers are given here.The sheep consumed approximately equal proportions of grass andclover across all sward pattern treatments (Table 1; F3,5 =0.382; NS).It, therefore, appeared as though the sheep were not demonstrating astrong preference for or against either one of the two components ofthe sward (see Illius et al., 1992; Newman et al., 1992). There was asignificant change in bite size (Table 1; F3,5=4.04; P<0.01) and biterate (Table 1; F3,5=2.98; P<0.05) as the grass and clover became moreaggregated (sward pattern treatments P1 - P4). This resulted in asignificant increase in intake rate (Table 1; F3,5=5.94; P<0.001) asthe aggregation of grass and clover increased.These results suggest that the sheep maintained their diet compositionwith changes in the spatial dispersion of grass and clover, and theyincreased their rate of intake as grass and clover were clumped intolarger patches.The work was funded by the Scottish Office Agriculture, Environmentand Fisheries Department.ID NO. 23INTAKE AND DIET SELECTION BY SHEEP GRAZING GRASS/CLOVER PATCHESI J Gordon1 and A W Illius21Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, AB15 8QH, UK.2Institute of Cell, Animal and Population Biology, Ashworth Buildings, University of Edinburgh, West Mains Road, EdinburghEH9 3JT, UK.Session 5 - Foraging Strategy 5-12REFERENCESGenstat 5 Committee 1993. Genstat 5 Release 3 Reference Manual.Clarendon Press, Oxford.Gordon, I.J. and A.W. Illius. 1992. Foraging strategy: frommonoculture to mosaic. Pages 153-170 in A.W. Speedy, ed. Progressin sheep and goat research C.A.B. International, Wallingford, pp.153-170.Illius, A.W., D.A. Clark, and J. Hodgson. 1992. Discriminationand patch choice by sheep grazing grass-clover swards. J. Anim.Ecol. 61: 183-194.Mayes, R.W., C.S. Lamb, and P.M. Colgrove. 1986. The use ofdosed and herbage n-alkanes as markers for the determination ofherbage intake. J. Agric. Sci., Cambs. 107: 161-170.Newman, J.A., A.J. Parsons, and A. Harvey. 1992. Not all sheepprefer clover: diet selection revisited. J. Agric. Sci., Cambs. 119:275-283.Senft, R.L., M.B. Coughenour, D.W. Bailey, L.R. Rittenhouse,O.E. Sala, and D.M. Swift. 1987. Large herbivore foraging andecological hierarchies. Biosci. 37: 789-799.Figure 1Dispersion of grass and clover in artificial swards offered to sheepTable 1Changes in the proportion of grass in the diet, bite size, bite rate andintake rate under treatments which comprised differences in thedispersion of clover and grass in the sward (see Fig. 1)Sward patternP1 P2 P3 P4 sedxProp. grass in diet 0.431 0.403 0.443 0.470 0.0383Bite size (gDM) 0.056 0.053 0.059 0.067 0.0043Bite rate (Bites.s-1) 0.894 0.913 0.988 0.948 0.0337Intake rate (gDM.s-1) 0.051 0.049 0.059 0.064 0.0040x Standard error of difference of means

Intake and Diet Selection by Sheep Grazing Grass/Clover Patches

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Intake and Diet Selection by Sheep Grazing Grass/Clover Patches

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