Interferência de Arbustos Nocivos no Pastejo por Bovinos - Plantas Daninhas (2024)

Prévia do material em texto

Planta Daninha 2019; v37:e019185644MARCHI, S.R. et al. Interference of noxious shrubs on grazing behavior by bovines 1151103-PD-2016 (9 páginas) PROVA GRÁFICAMARCHI, S.R.1*SILVA, H.M.1FERREIRA, C.F.1MARQUES, R.F.2MORAES, J.B.1ArticlePLANTA DANINHASOCIEDADE BRASILEIRA DACIÊNCIA DAS PLANTAS DANINHAS1 Universidade Federal de Mato Grosso, Barra do Garças-MT, Brasil; 2 Universidade Federal de Goiás, Jataí-GO, Brasil.Doi: 10.1590/S0100-83582019370100009<http://www.sbcpd.org>ISSN 0100-8358 (print) 1806-9681 (online)* Corresponding author: <sidneimarchi.ufmt@gmail.com>Received: October 6, 2017Approved: November 11, 2017Planta Daninha 2019; v37:e019185644Copyright: This is an open-accessarticle distributed under the terms of theCreative Commons Attribution License,which permits unrestricted use,distribution, and reproduction in anymedium, provided that the originalauthor and source are credited.INTERFERENCE OF NOXIOUS SHRUBS ON GRAZINGBEHAVIOR BY BOVINESInterferência de Arbustos Nocivos no Pastejo por BovinosABSTRACT - The grazing behavior practice by bovines can be positive or negativelyinfluenced by the pasture structure where the animal is inserted. Several factorsdetermine the pasture structure and the presence of weeds is considered one of themost important. This study aimed to assess the effect of species with and withoutstiff structures over the grazing behavior of bovines in pasture areas. The experimentaldesign was a split block design with four replications, in which treatments werearranged in a 4 x 3 factorial design: four weed species (Zanthoxylum rhoifolium,Cnidoscolus urens, Dasyphyllum brasiliensis, and Luehea divaricata) associatedwith three proximity strips of weeds: 0-50, 50-100, and 100-150 cm in relation to themain stem of the studied weed. Forage intake by animals was measured by determiningthe real forage offers at 0, 3, 6, 9, and 15 days after the beginning of animal grazing(DAP). The presence of noxious shrubs influenced bovine grazing behavior. Theinfluence on the intake is most evident in the presence of plants that promote animaldiscomfort. The species Z. rhoifolium, C. urens, and D. brasiliensis were the weedswith the greatest influence on feed access among the species that have stiff structures.The negative influence on grazing behavior is higher in the proximity strip closest tothe plant, i.e. 0-50 cm from the main stem of the weed.Keywords: thorny shrub, nettle, pastures utilization, animal access, weed.RESUMO - O hábito de pastejo praticado pelos bovinos pode ser positiva ounegativamente influenciado pela estrutura da pastagem onde esse animal estáinserido. Vários são os fatores que determinam a estrutura da pastagem, e apresença de plantas daninhas pode ser considerada um dos principais. O presentetrabalho teve por objetivo avaliar o efeito de espécies com e sem estruturascontundentes sobre o comportamento de pastejo de bovinos em áreas de pastagens.O experimento foi conduzido em faixa no delineamento de blocos completoscasualizados com quatro repetições, onde os tratamentos foram dispostos em faixas4 x 3: quatro espécies de plantas daninhas (Zanthoxylum rhoifolium, Cnidoscolusurens, Dasyphyllum brasiliensis e Luehea divaricata) associados a três faixas deproximidade das plantas daninhas: 0-50, 50-100 e 100-150 cm de distância emrelação ao caule principal da planta daninha estudada. O consumo de forragempelos animais foi mensurado determinando-se a oferta real de forragem aos 0, 3, 6,9 e 15 dias após o início de pastejo animal (DAP). A presença de arbustos nocivosinfluencia o comportamento de pastejo de bovinos. A influência no consumo é maisevidente quando existem plantas que promovem desconforto animal. Z. rhoifolium,C. urens e D. brasiliensis e foram as daninhas de maior influência negativa sobreo acesso ao alimento entre as espécies que possuem unidades contundentes. Ainfluência negativa no pastejo é maior na faixa mais próxima à planta, ou seja, 0-50 cm de distância do caule principal da daninha.Palavras-chave: arbusto espinhoso, urtiga, utilização da pastagem, acesso animal,planta daninha.Planta Daninha 2019; v37:e019185644MARCHI, S.R. et al. Interference of noxious shrubs on grazing behavior by bovines 2INTRODUCTIONThe pasture ecosystem is very dynamic, with mechanisms and processes involved in theproduction, harvesting, and transformation of forage into animal product acting in an integratedand compensatory way. This hinders to reach positive net results from isolated actions in anycompartment of the productive system (Santos et al., 2011; Carvalho et al., 2016). In order toachieve satisfactory productive indices and enable shorter cycle livestock with economicefficiency, it is necessary that the animal feed process does not become an obstacle to theirachievement (Gléria et al., 2017).In most tropical pasture production systems, the forage harvesting task rests with the animalsthemselves, which have specific strategies to obtain their nutritional demands (Teixeira et al.,2010). It has been experimentally demonstrated that animals have a certain wisdom in thechoice of food so that the vital balance of nutrients is ensured (Shariatmadari and Forbes, 1993;Cooper et al., 1995; O’Reagain and Schwartz, 1995).Thus, the animal must search for and choose its food within the pasture, which can presentdifferent types of structure regarding the quality and abundance variable in time and space. Theassociation between all factors determines the pasture structure, which cannot be consideredonly as a description of its characteristics, but rather consider it as a management attributesince the structural characteristics are at the interface of the plant with the animal (Carvalhoet al., 2007a; Teixeira et al., 2010). In other words, just as the structure of pasture affects theamount of consumed dry mass, the animal also has a marked influence on the pasture structure.The distribution of animals in the pasture can be influenced by some factors of pasturestructure, namely relief (Ganskopp and Vavra, 1987), location of the water source (Hart et al.,1993), botanical composition and forage quality (Bailey et al., 1996), factors that favor thermalregulation such as shade and wind (Senft et al., 1985), cattle management (Skovlin, 1957), andlocation of supplements (Bailey et al., 2001). The presence of unwanted plants may also affectthe pattern of use of certain grazing sites. Some studies show that animals avoid areas withlarge quantities of plants having stiff structures such as thorns or stinging trichomes (Williams,1954; Cook, 1966; Senft et al., 1985; Owens et al., 1991; Santos et al., 2011; Carvalho et al.,2016). More recent studies conducted by Santos et al. (2011) and Carvalho et al. (2016) reportedthat Solanum sisymbriifolium causes spatial variability of Urochloa decumbens cv. Basilisk in acontinuous stocking with bovine.Thus, the aim of this study was to assess the effect of weed species with and without stiffstructures on the intake habit of bovine in the pasture of Urochloa brizantha cv. Marandu.MATERIAL AND METHODSThe experimental phase was performed in a pasture of Urochloa brizantha (Hochst. Ex A.Rich.) Stapf cv. Marandu located at the geographical coordinates of 15o29’57" S and 52o33’31" W,with climate type Aw according to Köppen classification.The entire experimental area was previously mowed with a rotary cutter aiming at eliminatingforage residues from the previous grazing and stimulating the production of new aerial biomassby the forage and weed community.The experimental area was isolated for the presence of animals immediately after the mowingoperation and the access to cattle was allowed only 40 days after mowing when the forage grassand voluntary plants had emitted a new aerial part. The same grazing system routinely used bythe farm was adopted, i.e. a continuous grazing for15 days by Nellore barrows with an averageage of 3.0 years, at an intensity equivalent to 2.4 animal units per hectare (AU ha-1), andconsidering 1.0 AU as 450 kg live weight.The experiment was conducted in a 4 x 3 factorial scheme, represented by four weed species(with and without a stiff structure) associated with three proximity strips of weeds: 0-50, 50-100,and 100-150 cm in relation to the main stem of the studied weed, in a randomized completeblock design with four replications, whose blocking criterion was the weed species. In addition,we adopted the experiment in strips due to operational reasons aiming at arranging the factorPlanta Daninha 2019; v37:e019185644MARCHI, S.R. et al. Interference of noxious shrubs on grazing behavior by bovines 3distance from the stem respectively at each level. Treatment casualization in the plots wasperformed according to the recommendation of Barbosa and Maldonado Jr. (2015).The weed species were Dasyphyllum brasiliensis (Spreng.) Cabrera, with an average heightof 1.55 m, average dry mass of 493.9 g m-2, and 251 thorns m-1 of stem with an average size of1.97 cm; Cnidoscolus urens (L.) Arthur, with an average height of 1.73 m, average dry mass of371.0 g m-2, and stinging trichomes in the leaf blade and petiole; Zanthoxylum rhoifolium Lam.,with an average height of 1.75 m, average dry mass of 280.1 g m-2, and 460 thorns m-1 of stemwith an average size of 0.84 cm; and Luehea divaricata Mart., with an average height of 1.77 m,average dry mass of 383.1 g m-2, and no stiff structure that would cause discomfort to animals,being considered as the control.The forage plants were assessed at 15 days after the beginning of animal grazing (DAP), atwhich time the samples were collected by cutting the forage 10 cm above the soil in an areadelimited by a 1.0 x 1.0 m metallic square randomly chosen in the experimental unit.The collected samples were immediately taken to the laboratory and fractionated into greenleaf, green stem, and dead material. The eventually present inflorescences were considered asthe green stem. The samples were then packed in paper bags and maintained in a forced airventilation oven at 65 oC for three days, at which time the weight of each forage fraction wasmeasured in a scale with an accuracy of 0.01 g.From the data of the weight of each fraction, we determined the amount of green leaf drymass (GLDM), green stem dry mass (GSDM), dead material dry mass (DMDM), and the total drymass (TDM), all of them expressed in grams per square meter (g m-2). The leaf weight to stemweight ratio (L:S) was calculated as the following equation:L: S GLDMGSDM where L:S is the relationship between leaf and stem, GLDM is the green leaf dry mass (g), andGSDM is the green stem dry mass (g).The evolution of height and real forage offer (RFO) for each species and distance was assessedduring the period of animal grazing. Readings and collection of samples were carried out at eachsub-grazing period, namely 0, 3, 6, 9, 12, and 15 DAP. The relative RFO was calculated by thequotient of the arithmetic mean of the initial and final forage mass of each grazing sub-periodand the number of days of that sub-period plus the corresponding accumulation rate. Theavailability was divided by the average animal load of the sub-period (in kg ha-1 of animal liveweight) and the obtained value was multiplied by 100 to express the offer in relation to the liveweight (Mezzalira et al., 2011):RFO MFi FMf2n ARAL∗ 100 where RFO is the real forage offer (kg DM 100 kg-1 LW), FMi is the initial forage mass (kg ha-1DM), FMf is the final forage mass of the sub-period (kg haŠ1 DM), n is the number of days in theperiod, AR is the daily forage accumulation rate (kg ha-1 DM), and AL is the animal load (kg ha-1LW). The rate of daily forage accumulation was determined by the grazing exclusion cagetechnique, as proposed by Klingman et al. (1943), a methodology that was adapted to eliminatepossible competition effects of weeds on forage.The results of dry mass from fractions and total produced by the forage and the leaf to stemratio obtained in this experiment were submitted to analysis of variance by the F test and themeans were compared by the Tukey’s test (p≤0.05) using the statistical software AgroEstat(Barbosa and Maldonado Jr., 2015). Height evolution was submitted to regression analysis (p≤0.05)and the real forage offer was adjusted according to the Boltzmann’s sigmoidal model, as proposedby Kuva et al. (2001).Planta Daninha 2019; v37:e019185644MARCHI, S.R. et al. Interference of noxious shrubs on grazing behavior by bovines 4RESULTS AND DISCUSSIONThe evolution of the canopy height of forages during the 15 day period of grazing reveals thebovine behavior in the presence or absence of stiff structures in spontaneous plant species(Figure 1). The animals avoided areas located in the strip between 0 and 50 cm from species thatpresented discomfort to the animal, regardless of the size and quantity of thorns in the stem orstinging structure (Figure 1A, B, and C). Thus, the absence of animal grazing allowed linearincreases in the average plant height after 15 days from the beginning of animal grazing in thedistance strip closest to the stem.The reduction in height in the forage species was noticed at the beginning of animal grazingin the strip of 0-50 cm from the species that does not have any structure that causes animaldiscomfort (LUEDI, Luehea divaricata) (Figure 1D), demonstrating that the animals were presentand grazed the forage in this area.The average forage height decreased considerably over the animal grazing period in thestrips of 50-100 and 100-150 cm, regardless of the spontaneous species. The reductions wereexponential for the species ZANRO (Zanthoxylum rhoifolium), DASBR (Dasyphyllum brasiliensis),and LUEDI and linear for the species IATUR (Cnidoscolus urens) (Figure 1A, B, C, and D).In addition, these reductions in height were proportional to an increase in distance to thestem of the undesired plant since the average forage heights obtained during the animal grazingpresented the order 0-50 > 50-100 > 100-150 cm (Figure 1). However, a similarity was observedin the average forage height before the beginning of animal grazing (0 DAP).** Significant at 1% probability; * significant at 5% probability.Figure 1 - Evolution of the average height of pasture as a function of the proximity to the weeds (A) ZANRO (Zanthoxylumrhoifolium), (B) DASBR (Dasyphyllum brasiliensis), (C) IATUR (Cnidoscolus urens), and (D) LUEDI (Luehea divaricata).0 3 6 9 12 1520304050Height (cm)Days after grazing 0-50 cm Y** = 43.81 (X - 0.18)R2 = 0.6494 50-100 cm Y** = 45.43 - 3.76X + 0.14 X2R2 = 0.6560 100-150 cm Y** = 44.57 - 4.11X + 0.14X2R2 = 0.84790 3 6 9 12 1510152025303540Height (cm)Days after grazing 0-50 cm Y** = 0.26 (X - 74.02)R2 = 0.8154 50-100 cm Y** = 33.39 - 2.32X + 0.04X2R2 = 0.8894 100-150 cm Y** = 35.96 - 3.31X + 0.11X2R2 = 0.76090 3 6 9 12 1510203040506070Height (cm)Days after grazing 0-50 cm Y** = 0.27 (X - 233.75)R2 = 0.8667 50-100 cm Y** = -3.2 (X - 20.00)R2 = 0.9415 100-150 cm Y** = -0.347 (X - 17.79)R2 = 0.83270 3 6 9 12 1581624324048566472Height (cm)Days after grazing0-50 cm Y** = 67.11 - 5.18X + 0.16X2R2 = 0.860550-100 cm Y** = 69.21 - 8.14X + 0.35X2R2 = 0.7804100-150 cm Y* = 69.32 - 9.89X + 0.43X2R2 = 0.6885LUEDI(A) (B)(C) (D)Planta Daninha 2019; v37:e019185644MARCHI, S.R. et al. Interference of noxious shrubs on grazing behavior by bovines 5Rajcan and Swanton (2001) observed that the competition between forage and weed by water,nutrients, space, and light causes changes in the structural characteristics of the pasturebecause the forage modifies its growth pattern and hence its morphology in response to thedifferentiated microclimate that is established near the weed.The highest forage heights obtained in the strip of 0-50 cm from the stem occur because thespontaneous species are competing for light with the Marandu grass. One of the responses ofthe forage plant in a shaded environment is the elongation of its internodes, which results in ahigher plant height. This pattern of response is in line with that observed by Gobbi et al. (2009),who verified an increase in plant height of U. decumbens cv. Basilisk when the shading levelincreased from 0 to 70%, indicating an adaptive morphological response (phenotypic plasticity)of this species. Santos et al. (2011) reported that the presence of the weed Solanum sisymbriifoliumconditioned an increase in tiller height of U. decumbens cv. Basilisk, especially in the striplocated within a radius of 0.50 cm from the stem.The lowest height of the Marandu grass in the strips farther from weeds is due to a higherintensity of defoliation related to animal grazing. Thus, probably, many tillers had their apicalmeristems eliminated due to animal grazing and, consequently, tiller development wasinterrupted. In fact, the elimination of the pseudo-stem apex can determine tiller death (Cecatoet al., 2008), preventing the forage canopy to reach a higher height.The analysis of variance showed a significance for the sources of variation weed speciesand distance in relation to weed stem and for the interaction between both factors, indicatingthat the variables GLDM, GSDM, DMDM, TDM, and L:S were differently affected. In addition, noeffect was observed for the source of variation weed species only on the variable L:S (Table 1).Table 1 - Summary of the analysis of variance for green leaf dry mass (GLDM), green stem dry mass (GSDM), dead material drymass (DMDM), total dry mass (TDM), and leaf to stem ratio (L:S)Source of variation F values GLDM(1) GSDM(2) DMDM(3) TDM(4) L:S(5) Species (S) 250.00** 117.60** 94.77** 356.64** 0.95NS Distance (D) 505.09** 444.35** 44.12** 404.57** 8.42* S x D 57.29** 34.80** 22.29** 38.13** 3.18* CV Residual S (%) 5.68 9.65 7.19 3.99 12.32 CV Residual D (%) 5.42 7.03 7.02 4.84 6.47 CV Residual S x D (%) 6.78 11.21 7.52 6.04 13.42 NS Not significant. ** Significant at 1% probability. * Significant at 5% probability.The dry mass of the various fractions of U. brizantha assessed at 15 DAP can also be used tounderstand animal grazing behavior. The green leaf (GLDM), green stem (GSDM), and total (TDM)dry masses obtained in the strip of 0-50 cm from the LUEDI stem were statistically lower whencompared to the other species. Considering only the species with stiff structures, GLDM, GSDM,and TDM obtained in the strip between 0 and 50 cm from the IATUR species were significantlyhigher when compared to those obtained in the same strip from the ZANRO and DASBR species(Table 2).The variables GLDM and TDM were also statistically lower in the strip between 50 and 100 cmfrom the LUEDI stem when compared to the species ZANRO, DASBR, and IATUR. The fractionsobtained in the same proximity strip of IATUR were also statistically higher when compared tothose of ZANRO and DASBR (Table 2).The amount of dead material dry mass (DMDM) was statistically higher in the strips of 0-50 cmand 50-100 cm from the stem of ZANRO. However, a higher amount of DMDM in the strip of100-150 cm was obtained for the IATUR species (Table 2).Similar to that observed in relation to plant height evolution and analyzing GLDM, GSDM,DMDM, and TDM only as a function of weed, we observed that the respective amounts of drymass decreased as the distance from plant stem of ZANRO, DASBR, and IATUR increased. InPlanta Daninha 2019; v37:e019185644MARCHI, S.R. et al. Interference of noxious shrubs on grazing behavior by bovines 6Table 2 - Pasture dry mass obtained at 15 DAP as a function of distance and weed speciesSpecies(5) GLDM(1) (g m-2) GSDM(2) (g m-2) DMDM(3) (g m-2) TDM(4) (g m-2) 0-50 50-100 100-150 0-50 50-100 100-150 0-50 50-100 100-150 0-50 50-100 100-150 IATUR 265.7 aA 142.3 aB 122.2 aC 256.7 aA 114.9 aB 102.8 aB 184.0 bA 146.9 bB 202.5 aA 706.5 aA 404.2 aB 427.5 aB DASBR 179.8 bA 117.7 bB 82.4 bC 148.7 bA 84.4 bB 76.7 bB 147.3 cA 134.1 bAB 125.2 cB 475.8 cA 336.2 bB 284.4 cC ZANRO 160.3 cA 108.9 bB 96.2 bB 161.1 bA 92.5 bB 75.2 bB 263.9 aA 181.7 aB 160.6 bC 585.3 bA 383.1 aB 332.0 bC LUEDI 93.0 dA 101.1 cA 93.4 bA 71.1 cA 88.4 bA 73.7 bA 141.2 cA 128.1 bA 137.7 cA 305.4 dA 315.3 bA 304.8 bcA Means followed by the same lowercase letter in the column and uppercase letter in the row do not differ statistically from each other by theTukey’s test at 5% probability. (1) GLDM – green leaf dry mass; (2) GSDM – green stem dry mass; (3) DMDM – dead material dry mass; (4) TDM– total dry mass; (5) Species: ZANRO (Zanthoxylum rhoifolium), IATUR (Cnidoscolus urens), DASBR (Dasyphyllum brasiliensis), andLUEDI (Luehea divaricata).addition, the dry mass of the various fractions obtained within the different strips from the stemof the LUEDI species was significantly similar after the 15 day grazing period (Table 2). Theseresults are in accordance with Mezzalira et al. (2011), who observed that the herd behavior in apasture can cause unevenness in grazing, which has many negative implications, such as thereduction in forage plant stand and soil coverage in certain areas, with a consequent increasein the risk of erosion and weed infestation, poor fecal distribution in pasture and impairment ofnutrient cycling, and a reduced productivity in the system.In fact, Hein and Miller (1992), working on native grasses infested with weeds containingthorns, found that for every 10% increase in weed infestation led to an 8.7% reduction in theuse of the pasture forage. Thus, some tillers of U. brizantha close to the weeds have probablydeveloped up to the reproductive stage, a situation in which stem elongation is common (Cecatoet al., 2008), which results in a higher plant height and lower density of morphological components,as observed in our study.Deleterious effects on the forage structure due to weed presence were also observed byseveral authors (Williams, 1954; Cook, 1966; Senft et al., 1985; Owens et al., 1991). Santos et al.(2011) observed that the volumetric density of green leaf and total dry mass produced by Urochloadecumbens cv. Basilisk was statistically lower in plants located within a radius of 0.50 cm fromthe weed Solanum sisymbriifolium when compared to plants located at longer distances.Another important parameter used in the study of forage grass morphogenesis is the leaf tostem ratio, in which the highest values were obtained near the species LUEDI and ZANRO (1.31and 1.21, respectively) in the strip of 0-50 cm from the stem. In addition, the leaf to stem ratioobserved in this proximity strip of LUEDI was statistically higher when compared to the ratiosobtained in the same strip from the stems of IATUR and DASBR (Table 3). However, the leaf tostem ratio also tended to increase in the strips farther from the stems of IATUR, DASBR, andZANRO, while the values of this ratio remained statistically similar in the three strips from thestem of LUEDI (Table 3).All the parameters mentioned above are susceptible to a direct interference by weeds sincethe forage and the other four species are dividing the same space in the environment. Thiscommon survival can favor the establishment of the biological relationship between individualscalled competition in which each plant species will exert some degree of interference on theTable 3 - Leaf dry mass to stalk dry mass ratio (leaf:stem) obtained at 15 DAP as a function of distance and weed speciesSpecies(1) Leaf:stem 0-50 50-100 100-150 IATUR 0.99 bB 1.18 bAB 1.29 aA DASBR 1.04 bB 1.27 bA 1.22 aAB ZANRO 1.21 abAB 1.39 aA 1.07 aB LUEDI 1.31 aA 1.14bA 1.26 aA Means followed by the same lowercase letter in the column and uppercase letter in the row do not differ statistically from each other by theTukey’s test at 5% probability. (1) Species: ZANRO (Zanthoxylum rhoifolium), IATUR (Cnidoscolus urens), DASBR (Dasyphyllum brasiliensis),and LUEDI (Luehea divaricata).Planta Daninha 2019; v37:e019185644MARCHI, S.R. et al. Interference of noxious shrubs on grazing behavior by bovines 7neighboring species. This interference will influence the horizontal growth and the biomassaccumulation capacity of the individuals. Furthermore, each of the spontaneous species hasdifferent adaptation levels to the local environmental conditions and will probably provide differentdegrees of interference in the behavior of the exotic species U. brizantha.The real pasture offer is an important parameter that relates the availability of forage drymass proportional to each of spontaneous species and resulting from the animal grazing activity.Thus, we can isolate the differences of possible competitive pressures exerted by the spontaneousspecies during the experimental period. The RFO were pratically the same in the assessmentperformed immediately before the beginning of animal grazing (0 DAP), indicating that the weedsdid not compete with the forage grass during the period of conducting the experiment (Figures 2,3, and 4).0 3 6 9 12 15 1870140210280RFO (kg DM 100 kg-1 LW)Days after grazingY* = DASBRIATUR Y* = 45.1 1 + (x/7.69)3.1+ 187.4 R = 99.50 101.6 1 + (x/7.59)6.3+ 129.8 R = 99.41 Y* = ZANRO51.8 1 + (x/7.26)9.5+ 164.1 R = 99.67 Y* = LUEDI188.4 1 + (x/6.56)3.4+ 43.8 R = 99.21 * Significant at 5% probability. ZANRO (Zanthoxylum rhoifolium), DASBR (Dasyphyllum brasiliensis), IATUR (Cnidoscolus urens), andLUEDI (Luehea divaricata).Figure 2 - Evolution of the real forage offer (RFO) obtained in the strip of 0-50 cm from the stem of the spontaneous plantspecies throughout the animal grazing period.The variable RFO remained practically unchanged in the strip of 0 50 cm from the stem ofthe species IATUT, DASBR, and ZANRO up to 6 DAP. Expressive reductions in RFO in the samedistance strip from the stem of LUEDI occurred at the beginning of the grazing period (3 DAP),while the reductions were more evident only from 6 DAP in this distance strip for the speciesDASBR and ZANRO and only from 9 DAP for the species IATUR (Figure 2).Curiously, the RFO obtained in the same distance strip from the species that have structuresthat cause animal discomfort did not reduce from 9 DAP and remained constant until the end ofthe grazing period, indicating that the animals avoided the species IATUR, DASBR, and ZANROin this strip (Figure 2).The evolution of the RFO relative to the species observed in the other two distance stripsfrom the stem presented alterations regarding the closest distance strip, and an increase in thedistance gave higher reductions in RFO values. The availability of RFO obtained in the strip of50-100 cm from the stem of the species DASBR and ZANRO decreased considerably from 3 DAPPlanta Daninha 2019; v37:e019185644MARCHI, S.R. et al. Interference of noxious shrubs on grazing behavior by bovines 8* Significant at 5% probability. ZANRO (Zanthoxylum rhoifolium), DASBR (Dasyphyllum brasiliensis), IATUR (Cnidoscolus urens), andLUEDI (Luehea divaricata).Figure 3 - Evolution of the real forage offer (RFO) obtained in the strip of 50-100 cm from the stem of the spontaneous plantspecies throughout the animal grazing period.* Significant at 5% probability. ZANRO (Zanthoxylum rhoifolium), DASBR (Dasyphyllum brasiliensis), IATUR (Cnidoscolus urens), andLUEDI (Luehea divaricata).Figure 4 - Evolution of the real forage offer (RFO) obtained in the strip of 100-150 cm from the stem of the spontaneous plantspecies throughout the animal grazing period.0 3 6 9 12 15 1870140210280RFO (kg DM 100 kg-1 LW)Y* = DASBRIATUR Y* = 224.3 1 + (x/7.67)5.5+ 46.3 R = 99.19 240.4 1 + (x/6.31)3.1+ 20.7 R = 99.44 Y* = ZANRO204.7 1 + (x/6.43)4.1+ 49.3 R = 99.73 Y* = LUEDI227.7 1 + (x/7.15)2.3+ 0.7 R = 99.24 Days after grazing0 3 6 9 12 15 1870140210280RFO (kg DM 100 kg-1 LW)Y* = DASBRIATUR Y* = 199.0 1 + (x/6.61)4.1+ 69.1 R = 99.67 224.4 1 + (x/6.09)4.0+ 36.9 R = 99.33 Y* = ZANRO196.7 1 + (x/6.34)3.9+ 47.7 R = 99.49 Y* = LUEDI238.8 1 + (x/6.33)2.4+ 5.4 R = 99.67 Days after grazingPlanta Daninha 2019; v37:e019185644MARCHI, S.R. et al. Interference of noxious shrubs on grazing behavior by bovines 9and was relatively similar to the reduction obtained in the same distance strip from the stem ofthe species LUEDI (Figure 3). The RFO relative to the species IATUR also decreased in thisdistance strip, but the reduction was relatively higher only from 6 DAP (Figure 3). This probablyoccurred because the species IATUR have stinging bristles, which bovine identifies as a higherdiscomfort at the time of approach to obtain the food since the animals develop an ingestivememory based on mechanisms by which they search, select, defoliate, and ingest forage in thepasture (Carvalho et al., 2013).The evolution of RFO values relative to the species in the strip of 100-150 cm from the stemwas considerable and similar from 3 DAP, regardless of the spontaneous species (Figure 4).In addition, although the RFO relative to the species is practically the same at the beginningof animal grazing, the relative values of RFO from 3 DAP obtained near IATUR were alwayshigher when compared to the others species regardless of the studied strip (Figures 2, 3, and 4).Although forage offer describes the amount of feed made available to the animal, it does notgive any information about the way the forage is presented to it. This form of spatial distributionof plant shoot, which is called pasture structure, considerably affects the intake and selection ofdiets of grazing animals (Carvalho et al., 2007b).According to Mezzalira et al. (2011), animals transmit signals on the pasture structure,through ingestive behavior, regarding the abundance and quality of its pastoral environment.The reduction in food availability obtained in this experiment practically forced the animals toget closer to the plants with stiff structures at 15 DAP, especially in the distance of 50-100 cm.However, even with offer reductions, bovine showed an ability to choose the food according to thepasture structure since the areas between 0 and 50 cm from the stem of the species IATURwere not practically grazed by the animals.The influence on the animal intake is evident in the presence of plants containing structuresthat promote animal discomfort, as in the case of Zanthoxylum rhoifolium, Cnidoscolus urens, andDasyphyllum brasiliensis. Cnidoscolus urens was the species that had the highest negativeinfluence on food access among the species that have stiff structures. The negative influenceon food access is higher in the strip closest to the plant, i.e. 0-50 cm away from the main stem.REFERENCESBailey DW, Gross JE, Laca EA, Rittenhouse LR, Coughenour MB, Swift DM, et al. Mechanisms that result in large herbivoregrazing distribution patterns. J Range Manage. 1996;49(5):386-400.Bailey DW Welling GR, Miller ET. Cattle use of foothills rangeland near dehydrated molasses supplement,. J Range Manage.2001;54:338-47.Barbosa JC, Maldonado Jr W. Experimentação agronômica & AgroEstat: Sistemas para análises estatísticas e ensaios agronômicos.Jaboticabal: Gráfica Multipress; 2015.Carvalho PCF, Kozloski GV, Ribeiro Filho HMN, Reffatti MV, Genro TCM, Euclides VPB. Avanços metodológicos nadeterminação do consumo de ruminantes em pastejo. Rev Bras Zootec. 2007a;36:151-70.Carvalho PCF, Santos DT, Neves FP. Oferta de forragem como condicionadora da estrutura do pasto e do desempenho animal. In:Dall’AgnolM, Santana DM, Samtos RJ, organizadores. Sustentabilidade Produtiva do Bioma Pampa. Porto Alegre: Metrópole;2007b. p. 23-60.Carvalho PCF, Trindade JK, Bremm C, Mezzalira JC, Fonseca L. Comportamento ingestivo de animais em pastejo. In: Reis RA,Bernardes TF, Siqueira GR, organizadores. Forragicultura: ciência, tecnologia e gestão dos recursos forrageiros. Jaboticabal: M. L.Brandel-ME; 2013. p.525-41.Carvalho RM, Pimentel RM, Carvalho RM, Fonseca DM, Santos MER. Caracterização de perfilhos em relação à planta daninhano pasto de capim-braquiária. B Ind Animal. 2016;73:103-10.Cecato U, Skrobot VD, Fakir GR, Branco FA, Galbeiro S, Gomes JAN. Perfilhamento e características estruturais do capim-Mombaça, adubado com fontes de fósforo, em pastejo. Acta Sci. 2008;30:1-7.Planta Daninha 2019; v37:e019185644MARCHI, S.R. et al. Interference of noxious shrubs on grazing behavior by bovines 10Cook CW. Factors affecting utilization of mountain slopes by cattle. J Range Manage. 1966;19:200-4.Cooper SDB, Kyrizakis I, Nolan JV. Diet selection in sheep: the role of the rumen environment in the selection of a diet from twofeeds that differ in their energy density. Br J Nutr. 1995;74:39-54.Ganskopp D, Vavra M. Slope use by cattle, feral horses, deer, and bighorn sheep. Northwest Sci. 1987;61:74-81.Gléria AA, Silva RM, Santos APP, Santos KJG, Paim TG. Produção de bovinos de corte em sistemas de integração lavourapecuária. Arch Zootec. 2017;66(253):141-50.Gobbi KF, Garcia R, Garcez Neto AF, Pereira OG, Ventrella MC, Rocha GC. Características morfológicas, estruturais eprodutividade do capim-braquiária e do amendoim forrageiro submetidos ao sombreamento. Rev Bras Zootec. 2009;38:1645-54.Hart RH, Bissio J, Samuel MJ, Waggoner Jr JW. Grazing systems, pasture size, and cattle grazing behavior and gains. J RangeManage. 1993;46:81-7.Hein DG, Miller SD. Influence of leafy spurge on forage utilization by cattle. J Range Manage. 1992;45:405-7.Klingman DL, Miles SR, Mott GO. The cage method for determining consumption and yield of pasture herbage. J Am Soc Agron.1943;35:739-46.Kuva MA, Gravena R, Pitelli RA, Christoffoleti PJ, Alves PLCA. Períodos de interferência das plantas daninhas na cultura dacana-de-açúcar. II – Capim-braquiária (Brachiaria decumbens). Planta Daninha. 2001;19(1):323-30.Mezzalira JC, Carvalho PCF, Fonseca L, Bremm C, Reffatti MV, Poli CHEC, et al. Aspectos metodológicos do comportamentoingestivo de bovino sem pastejo. Rev Bras Zootec. 2011;40(5):1114-20.Owens MK, Launchbaugh KL, Holloway JW. Pasture characteristics affecting spatial distribution of utilization by cattle in mixedbrushes. J Range Manage. 1991;44(2):118-123.Rajcan I, Swamton CJ. Understanding maize-weed competition: resource competition, light quality and the whole. Field CropsRes. 2001;71(2):139-50.Santos MER, Fonseca DM, Gomes VM, Pimentel RM, Silva GP, Albino RL. Estrutura do capim-braquiária em relação à plantadaninha. Acta Sci. 2011;33(3):233-9.Senft RL, Rittenhouse LR, Woodmansee RG. Factors influencing patterns of cattle grazing behavior on shortgrass steppe. J RangeManage. 1985;38(1):82-87.Shariatmadari F, Forbes JM. Growth and food intake responses to diets of different protein contents and a choice between dietscontaining two levels of protein in broiler and layer strains of chickens. Br Poult Sci. 1993;34(5):959-70.Skovlin JM. Range riding - the key to range management. J Range Manage. 1957;10:269-71.Teixeira FA, Marques JA, Silva FF, Pires AJV. Comportamento ingestivo e padrão de deslocamento de bovinos em pastagenstropicais. Arch Zootec. 2010; 59:57-70.Williams RE. Modern methods of getting uniform using of range. J Range Manage. 1954;7:77-81.O’Reagain PJ, Schwartz J. Dietary selection and foraging strategies of animals on rangeland. Coping with spatial and temporalvariability. In: Proceedings of the 4th. International Symposium on the Nutrition of Herbivores. Clermont-Ferrand; 1995.Clermont-Ferrand: 1995. p.419-24.