CARDOSO, F. F.

GENRO, T. C. M.

PRATES, E. R.

SAN'THIAGO, L. R. L.

English

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Diet selection in a pasture of Panicum maximum cv. Mombaça with different swardheightsT.C.M. Genro", Ê.R. Prates/, F.F. Cardoso I and L.R.L. San'Thiag03'Embrapa Pecuária Sul. Postal box 242. 96401-970. Bagé, R5. Bra::iI. Email: cristinaiiccppsul.emhrapa.hr,!UFRG5. Av. Bento Gonçalves. 7712 Postal box 15.100. 91501-970. Porto Alegre. RS - Brazil. JEmbrapa Gadode Corte. Postal box 154. 79002-970. Campo Grande. MS. BrazilKeywords: leaf blade, n-alkanes, non-negative least squares, stern and sheathIntroduction The n-alkane method allows to measure dry matter (OM) intake and to determine the proportionof grass and legume ingested by ruminants grazing mixed pastures. Dove & Mayes ( 1996) pointed out that usingthis methcd, beyond estirnating intake of individual plant species. it may also be possible to determine intake ofanatomical components of the plant. The aim of this work was to use the non-ncgative least squares proccdure toestimate diet selection based on plant alkanes and animal faeces.Materiais and methods The experiment was conductcd at the Embrapa Beef Caule Ccntre, Campo Grande. MSto study intensive bcef production based on tropical grasses under rotational grazing throughout lhe ycar. Thegrazing system included 16 paddocks. a 2-day grazing pcriod followed by a 30-day resting period. In this study.samples of stern+sheath and leaf blade were collcctcd in 20 em strati fied Ia' rs of a pasture of PUllicUIIImaximum cv. Mornbaça during three pcriods of the year: in lhe rniddlc of lhe dry season tPeriod I), at thebeginning (Period 2) and at lhe end of the ofthe wet season (Period 3). Beforc grazing, three rcprescntative arcasof the paddock were selected for sarnpling. Six Nelore steers dosed during 12 days. twice a day. with alkane (,:were used to estimare OM intake (OM I). The determination of n-alkanes within lhe range of C-chain betwcen 27and 35 was pcrformcd according to Mayes et al. (1986). N-alkane profilcs were corrected by faccal rccovcricsusing rncan valucs found in litcraturc (Dovc & Mayes. 1996). The diet sclcction was calculatcd by thc "Eatwhat"program dcscribcd by Deve & Moere ( 1995). using thc non-ncgative lcast squarcs algorithrn.Results The pcrccntage of dict sclcctcd within the strata of Mornbaça grass pasturc and lhe OMI cxpresscd aspereent 01' live wcight for the thrcc pcriods studicd are given in Tablc I. In thc first pcriod, the prograrncstimatcd that OMI was dividcd among thrce strata: stcm+sheath 0-20 em. lcaf bladc 0-20 em above groundlevel, and leaf blade 40-60 em. In lhe other two pcriods. lhe stratum preferred was stcm+shcath > 20 em.According 10 these rcsults, the steers ingcstcd 0\'Cr 60 % from this laycr, in stcad 01' the lcaves frorn higher strata.These data. however, are not supportcd by lhe litcraturc, whcre it was cstablishcd that bovinos prcfer catinglcaves frorn the top of the pasture. This may bc duc 10 problcms in the alkanes dctcrmination. or pcrhaps, anothcrpossibility is that lhe prograrnme was designcd to work with diet selcction betwccn diffcrent plant specics. butnot within parts ofthe sarne plant, particularly oftall tropical plants such as Panicum spp ..Table I Dict sclcctcd (%) within thc strata 01' Mornbaça pasture and the dry mattcr intakc (0\11. o o LW)Period Stratum height (em)Siem 0-20 Stern >20 LeafO-20 Leaf 20-40 Leaf-W-60 Leal' 60-80 Leaf>80 OMI (°0)Diet selected, % of intakeI 35.6 O 30.6 O 33.8 NE* :\E 2.262 O 60.5 NE O 39.5 O l\E 2.723 O 84.0 O O .5 4.3 11.2 1.93*NE= Stratum not existentConclusions The use of non-negative least squares proeedure to determine diet cornposition based on the plantalkanes does not seern to adequately estimare plant part selection within the plant profile.ReferencesDove, H. & R.W. Mayes, (1996). Plant wax components: a new approach to estimating intake and dietcomposition in herbivores. American Journal of Nutrition, 126. 13-26.Oove, H & A.O. Moere, (1995). Using a least-squares optirnisation proeedure to estimare diet cornposition basedon the alkanes of plant cuticular wax. Australian Journal ofAgricultural Research, 46. 1535-1544.Mayes, R.W., C.S Larnb.. & P.M Colgrove,. (1986). The use' of dosed and herbage »-alkanes as markers for thedeterrnination of herbage intake. Journal of Agricultura! Science, 107, 161-170.Offered papers 505

Diet selection in a pasture of Panicum maximum cv. Mombaça with different sward heights.

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Diet selection in a pasture of Panicum maximum cv. Mombaça with different sward heights.

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