GRAZING ECOLOGY RESEARCH IN SOUTH BRAZIL: TOWARDS A COMPREHENSION OF THE UNDERLYING

PROCESSES*

PAULO CESAR DE FACCIO CARVALHO, CESAR HENRIQUE ESPIRITO CANDAL POLl, JoAo RICARDO DITTRICH, ANIBAL DE MORAES AND

CARLOS N ABINGER

Faculdade de Agronomia - Universidade Federal do Rio Grande do SuI (UFRGS) Porto Alegre-RS / Brasil. E-mail: paulocfc@vortex .ufrgs.br

Grazing Ecology Research Group

Coordinador: Paulo Cesar de Faccio Carvalho - Associate Professor (UFRGS - Rio Gran· de do Su\)

Investigadores: Andre B. Soares - PhD student (UFRGS - Rio Grande do SuI) ; Ana LuiSI Palhares - PhD student (UFPR - Parana) ; Anibal de Moraes - Associate Professor (UFPR· Parana) ; Carlos Nabinger - Associate Professor (UFRGS - Rio Grande do Su\) ; Cesar H. E

C. Poli - Researcher (FEPAGRO - Rio Grande do Su\); Christian R. C. de Castro - MSc student (UFRGS - Rio Grande do Su\); Emanuel O. da Silveira - MSc student (UFRGS - Ril Grande do Su\); Gerzy E. Maraschin - Associate Professor (UFRGS - Rio Grande do Su\); Guilherme K. Mar~al - graduate student (UFRGS - Rio Grande do Su\); Henrique M. N. Ribeiro Filho - Assistant Professor (UDESC - Santa Catarina); Joao Ricardo Dittrich -

Associate Professor (UFPR - Parana); Julio K. da Trindade - graduate student (UFRGS -Rio Grande do Su\); Laise S. Pontes - MSc student (UFRGS - Rio Grande do Su\) ; Luis M.

G. Rosa - Associate Professor (UFRGS - Rio Grande do Su\)o

Our research activities are trying to answer a simple question: What domesti herbivores eat and why? There are no simple answers to this question. Since 199: we have been working mainly at the plant and patch scales, and in two environment with different levels of heterogeneity, high (natural pastures) and low (cultivate I pastures). Productive responses (e.g., animal performance and pasture production have been measured at community and landscape levels . In our conceptual model grazing is the main driving force that determines vegetation dynamics, tissue flow and animal performance because in our systems there are few environmentallimi tations to forage production (in general) and because our flora has a low grazinl history in the presence of large herbivores . Therefore, we believe that grazing in tensity is the key variable concerning ecosystem function and trends.

We have recently added a more ecological approach to our agronomically ori ented studies (Carvalho 1997). We are trying to understand the basic processe: underlying our complex grazing system and not only measure its final output. II this more global approach, we have tried to evaluate the impact of different graz ing intensities, mainly by manipulating herbage allowance or sward height as cen

• We have been supported by grants from FAPERGS, CNPq, CAPES and Agropecuaria Cern Coroado.

tral variables (Carvalho et al. 2001b; Pontes et al. 2001). The effect of fertilization as a way to increase nutrient flow in our grazing system, has also been considered (N abinger et al. 2000). In a more analytical approach we have studied grazing pro­cess, trying to identify the importance of sward structure on animal behavior and performance (Carvalho et al. 1999a, Carvalho et al. 2001c) . Visual and low cost methodologies have been used to address grazing animal behavior (Carvalho et al. 2001d; Dittrich et al . 1999) . Recently, more sophisticated equipment was acquired but it has not been used yet. Labeling vegetative units has allowed the estimation of defoliation patterns and daily intake (Carvalho et al. 2001c; Dittrich et al. 1999). Intake rate has been measured with the double-weight technique (Carvalho et ai. 2001c) and diet selection was estimated with oesophageal-fistulated animals (Poli et al. 2001b). Time scale differs from minutes to days in behavior oriented studies, and months to years in production oriented ones. Our group has been working with large domestic herbivores, such as cattle, sheep and horses.

Our current results allow us to present management guidelines in terms of herbage allowance or sward height (Carvalhoet al. 2001b), to optimize the efficiency of pasture utilization (Pontes et al . 2001) . These results also increased our knowl­edge on underlying processes on our grazing systems. Tissue fluxes at tiller level have allowed us to comprehend plant responses to environment by morphogenetic traits, as well as, the response to defoliation patterns in terms of tissues removal, plant growth and senescence, and intake. Leaf elongation rate increases and dura­tion of elongation decreases with the increase of sward height. Leaf lifespan and phyllochron are not affected by sward height. Italian ryegrass utilization is opti­mized in sward heights of 10 or 15 cm if the objective is high grazing efficiency or high animal production, respectively (Carvalho et al. 2001b). As the sward height decreases, animals tend to increase grazing time (Carvalho et al. 2001b). In the same way, the grazing processes at feeding station level (searching + handling) increase as the same time as the sward height increase. The more abundant the forage source is, the more the animals respond with decreasing meal and grazing times, and in­creasing the number of meals, while decreasing bite rate . Analytical studies on bite depth revealed the consistency of the constant proportionality concept in relation to herbage removal, being this removal around 50% of the extended tiller height in different pastures (C4, C3, tall, prostrate) used by different animal species (cattle, sheep, horses) (Carvalho et al. 1998a; 1999b, Dittrich et al . 1999; Lesamaet al. 1999). At sward heights greater than what is normally used in this kind of studies (e.g., sheep pasture taller than 50 cm), intake rate can be depressed when leaf mass is dispersed, even with high herbage allowances in the grazing strata (Carvalhoetai. 2001c). Time per bite can be increased up to 40% as a consequence of increasing time for bite formation (Carvalho et al. 2001a). Intake rate decreases despite the quadratic response of bite mass to sward height. Ewe lambs exhibit some sort of «spaghetti grazing style» when forced to graze leaf laminas greater than 50 cm on a one per one basis. In defining the grazing efficiency not only the vertical struc­ture of the vegetation is important (Poli et al. 2001a), but the horizontal structure is important as well (Carvalho et al. 1997; Carrere et al. 2001). Horses prefer tall patches rather than short ones, and the horizontal distribution of grazing items affects diet selection (Dittrich et al. 1999). Horses select a mix diet of grasses and legumes, the former being partially preferred. White clover is better identified and consumed by ewes and horses when presented in strips. It was observed, using marked tillers, that taller grasses and legumes in a vegetative stage are preferred

---

(Carvalho et al. 1999b). The average height of labeled consumed plants are always greater than that of non consumed ones, and these differences can only be some millimeters, showing that grazing animals are able to identify differences in a very small grain (Carvalho et al . 1998b, 2000). In addition, this shows the importance of visual cues to domestic herbivores.

Carcass evaluation has helped us to evaluate the responses up to the final prod­uct (Oliveiraet al. 2001), including variables related to the quality of the meat that arrives to the consumers, and it can also be a variable indicative of the production system traceability. We have learnt that the responses verified in animal performance are also observed in commercial cuts, and that there are substances which allow us to make inferences about system production quality. The grazing ecosystem responds to different intensification levels, particularly fertilization . It has changed all the earlier concepts of our natural resources potential, bringing support to policies which intend to promote a better use of this important resource (Lemaire et al. 2000; Maraschin 2001).

PUBLICATIONS

Carrere, P. , F. Louault, P.C.F. Carvalho, M. Lafarge & J.F. Soussana. 2001. How does the ver· tical and horizontal structure of a grass clover sward influence grazing? Grass and Forage Science. Reading, v.56, n.2 .

Carvalho, P.C.F. 1997. A estrutura da pastagem e 0 comportamento Ingestivo de ruminantes em pastejo. En: Simp6sio sobre avaliac;ao de pastagens com animais. Ed.Maringa-PR : Universidade Estadual de Maringa, p.25·52 .

Carvalho, P.C.F., C.H.E.C. Poli & C. Nabinger. 2000. Comportamento ingestivo de bovinos em pastejo e sua relac;ao com a estrutura da pastagem. En: Pecuaria 2000: A pecuaria dE corte no III Milenio. Ed.Pirassununga: USP. CD·ROM.

Carvalho, P.C.F. , S. Prache & J .C. Damasceno. 1999a. a processo de pastejo: desafios da pro· cura e apreensao da forragem pelo herbivoro. En: Reuniao Anual da Sociedade Brasileira de Zootecnia, Anais 36,Porto Alegre·RS. p. 253·268.

Carvalho, P. C. F., H .M.N. Ribeiro Filho, C.H .E.C. Poli, A. Moraes & R. Delagarde . 2001c Importiincia da estrutura da pastagem na ingestao e selec;ao de dietas pelo animal em pastejo. In : Anais da XXXVIII Reuniao Anual da Sociedade Brasileira de Zootecnia Ed.Piracicaba: FEALQ. p. 853·871.

Lemaire, G., J. Hodgson , A. Moraes , P.C.F. Carvalho & C. Nabinger (eds). 2000. Grassland Ecophysiology and Grazing Ecology. Wallingford-axon: CAB International, 422 pp.

Maraschin, G. E. 2001. Production potential of South America grasslands. In: International Grassland Congress, 19, Piracicaba, Brasil. pg. 5·18.

Nabinger, C., A. Moraes & G.E. Maraschin . 2000. Campos in Southern Brazil. En: Grassland Ecophysiology and Grazing Ecology.1 ed. Wallingford-axon: CAB International, v.l. p .355-376.

ABSTRACTS

Carvalho, P.C.F., F. Louault & M. Lafarge. 1997. Effect of species horizontal distribution on defoliation of ryegrass-cJover swards grazed by sheep In: International Grassland Congress, XVIII, Winnipeg, Canada. CD-ROM.

Carvalho, P.C.F., A. . Moraes y S. Prache. 1998a. Profundidade do bocado de ovinos em pastagens de Dactilis e Festuca. En' Reuniao Anual da Sociedade Brasileira de Zootecnia, xxxv, B a - P. ANAl . .21 - 217.

Carvalho, P.C.F., L.R.A. Rodrigues, F. Louault & M. Lafarge. 1998b. Sele~ao de dietas por ovinos em pastejo: efeito da altura das plantas na desfolha~ao de uma pastagem consorciada. En: Reuniiio Anual da Sociedade Brasileira de Zootecnia, XXXV, Botucatu -SP' ANAlS., p.46- 48.

Carvalho, P.C.F., G.K. Mar~al, H.M.N. Ribeiro Filho, C.H .E.C. Poli, J .K. Trindade, J.O.R. Oliveira & C. N abinger. 2001a. Pastagens altas podem limitar 0 consumo dos animais. En: Reunido Anual da Sociedade Brasileira de Zootecnia, 200 1, Piracicaba-SP' Anais da XXXVIII Reunido Anual da Sociedade Brasileira de Zootecnia. Piracicaba-SP: FEALQ, v.38. p.265-266.

Carvalho, P.C.F., L.S. Pontes, E.O. Silveira, C.H.E.C. Poli, C. Nabinger, O.A. Pereira Neto & G.E. Maraschin. 2001b. Sheep performance in Italian ryegrass swards at contrasting sward heights. En: International Grassland Congress, Siio Pedro. Proceedings of the XIX International Grassland Congress. Piracicaba: FEALQ, p.845 - 846.

Carvalho, P.C.F. , S. Prache, C. Roguet & F. Louault. 1999b. Defoliation process by ewes of reproductive compared to vegetative swards. En: International Symposium on the Nutrition of Herbivores, 5, San Antonio, USA .. CD-ROM.

Carvalho, P.C.F., E .O. Silveira, L.S. Pontes, C.H .E .C. Poli, A.B. Soares & H .M.N. Ribeiro Filho. 2001d. The effect of sward surface height on sheep grazing activities. En: International Grassland Congress, Sao Pedro . Proceedings of the XIX International Grassland Congress. Piracicaba: FEALQ, p.299 - 300.

Dittrich, J.R., P.C.F. Carvalho, A. Moraes, S. Prache, S.B.C. Lustosa & E.O. Silveira. 1999. Preferencia e profundidade do bocado de equinos em diferentes gramineas do genero Cynodon. En: Reuniiio Anual da Sociedade Brasileira de Zootecnia, Porto Alegre. CD-ROM.

Lesama, M. F, P.C.F. Carvalho , A. Moraes & L. Hazard . 1999. Estrutura da pastagem e profundidade do bocado de vacas leiteiras: Efeito da especie forrageira e da aplica~ao de nitrogenio . En: Reuniao Anual da Sociedade Brasileira de Zootecnia, 1999, Porto Ale· gre. Anais da XXXVI R euniiio Anual da Sociedade Brasileira de Zootecnia. CD·ROM.

Oliveira, J . O. R., P.C.F. Carvalho, L.S. Pontes, E.O. Silveira, G.E . Maraschin, O.A. Pereira Neto, J .M. Rubensam & A.B. Soares. 2001. Caracteristicas da carca~a de cordeiros em pastagens de azevem (Lolium multiflorum Lam) manejadas em diferentes alturas. En: Reuniiio Anual da Sociedade Brasileira de Zootecnia, 2001 , Piracicaba. Anais da XXXVIII Reuniiio Anual da Sociedade Brasileira de Zootecnia. Piracicaba-SP: FEALQ, v.38. p.l85· 186.

Poli, C.H.E.C., Z. Castilhos, J .K. Trindade, P.c.F. Carvalho, E.C. Pinto, C. Semmelman, A.B. Soares & E . Guerra. 2001a. Efeito da distribui~ao vertical de especies forrageiras no processo de sele~ao de dieta em dois tipos de pastagem nativa melhorada. En: Reuniiio Anual da Sociedade Brasileira de Zootecnia, 2001, Piracicaba-SP' Anais daXXXVIII ReuniiioAnual da Sociedade Brasileira de Zootecnia. Piracicaba-SP: FEALQ, v.38. p.128-129.

Poli, C.H.E.C., J .M. Rosito, A.G. Shirmer, P.R. Boggiano & P.C.F. Carvalho. 2001b. Leaffragment identification of subtropical native grass species. En: International Grassland Congress, 2001, Sao Pedro. Proceedings of the XIX International Grassland Congress. Piracicaba: FEALQ, p.300-301.

Pontes, L.S ., P.C.F. Carvalho, E .O. Silveira, C. Nabinger, L.M.G. Rosa, A.B. Soares, C.H.E.C. Poli & J .K. Trindade. 2001. Eficiencia de utilizacao de azevem (Lotium multiflorum Lam) manejado a diferentes alturas. En: Anais da XXXVIII Reuniiio Anual da Sociedade Brasileira de Zootecnia. Piracicaba-SP: FEALQ, v.38. p .263-264.

COURSES

Carvalho, P.C.F. 1999. Interface Planta-Animal. Post-graduation in Animal Science, Porto Alegre .

Carvalho, P.C.F. 1999. Estudos Aprofundados na Interface Planta-Animal. Post­graduation in Plant Production, Cur itiba.