Rotational Grazing System Research Articles

The Effects of a Rotational Cattle Grazing System on Elk Diets in Arizona Piñon–Juniper Rangeland

I t is not uncommon to hear statements such as these in the western United States. Dietary overlap between cattle and wild herbivores such as elk or deer has been 1 reported in various regions, seasons, and ecosystems. Competition between two species occurs when a shared resource is in limited supply or when the presence of one species disturbs the other. The simple fact that space and forage resources are shared might or might not, however, constitute a negative interaction between cattle and elk. 1 Studies in central Arizona 2 found that although diet similarity was high in certain years and seasons, there was actually little inter-specific competition between cattle and elk overall. Factors such as scale, season, and forage availability influ- ence the likelihood and degree of competition. Overgrazing isdetrimentaltosustainedlivestockandwildlifeproductivity. Livestock grazing can, however, be applied to positively manipulate habitat for wildlife. A review by Krausman et al. 3 cites a Montana case study in which a rotational cattle graz- ing system “maintained productive cover and forage for elk while enhancing native vegetation condition on all of the managed areas.” DOI: 10.2458/azu_rangelands_v34i1_t olleson

Crecimiento en pastoreo rotacional de toretes de razas criollas Romosinuano y Blanco Orejinegro en Colombia

RESUMENObjetivo. Evaluar el crecimiento de toretes de las razas Romosinuno (ROMO) y Blanco Orejinegro (BON) en una prueba de comportamiento en pastoreo rotacional. Materiales y métodos. La prueba fue desarrollada en la Estación Experimental El Nus, en la Región Andina Colombiana, donde se evaluaron 20 toretes BON y 16 ROMO provenientes de quince ganaderías comerciales, los cuales fueron mantenidos en un solo grupo durante 221 días en pastoreo rotacional en franjas con periodos cortos de ocupación, de los cuales 56 días fueron en pastoreo no suplementado y 165 días bajo tres diferentes fases de pastoreo suplementado en el potrero. Se realizaron pesajes cada 28 días y se evaluaron variables como: la evolución en peso, la ganancia total y diaria, la diferencia entre pesajes, la relación consumo peso vivo y la tasa de consumo. Resultados. El peso inicial en la raza BON fue 180.4±36.9 kilos con 9.6±1.74 meses de edad y en la raza ROMO fue de 171.8±32.6 kilos con 10.1±3.2 meses de edad. El incremento general de los individuos entre pesajes fue 0.497 kilos por día para los individuos de raza BON, y 0.366 kilos por día para la raza ROMO. En la prueba de eficiencia la tasa de consumo de suplemento alcanzada fue 64.8% y 71% para BON y ROMO respectivamente, equivalentes a una ingestión de materia seca de 0.47% y 0.53% con relación al peso vivo. Conclusiones. Este trabajo evidencia un mayor desempeño de los individuos de la raza BON comparados con los animales de la raza ROMO e indica una alta variabilidad en la respuesta a un manejo semi-intensivo en las poblaciones en evaluación.

Soil compaction under varying rest periods and levels of mechanical disturbance in a rotational grazing system

Halde, C., Hammermeister, A. M., McLean, N. L., Webb, K. T. and Martin, R. C. 2011. Soil compaction under varying rest periods and levels of mechanical disturbance in a rotational grazing system. Can. J. Soil Sci. 91: 957–964. In Atlantic Canada, data are limited regarding the effect of grazing systems on soil compaction. The objective of the study was to determine the effect of intensive and extensive rotational pasture management treatments on soil bulk density, soil penetration resistance, forage productivity and litter accumulation. The study was conducted on a fine sandy loam pasture in Truro, Nova Scotia. Each of the eight paddocks was divided into three rotational pasture management treatments: intensive, semi-intensive and extensive. Mowing and clipping were more frequent in the intensive than in the semi-intensive treatment. In the extensive treatment, by virtue of grazing in alternate rotations, the rest period was doubled than that of the intensive and semi-intensive treatments. Both soil bulk density (0–5 cm) and penetration resistance (0–25.5 cm) were significantly higher in the intensive treatment than in the extensive treatment, for all seasons. Over winter, bulk density decreased significantly by 6.8 and 3.8% at 0–5 and 5–10 cm, respectively. A decrease ranging between 40.5 and 4.0% was observed for soil penetration resistance over winter, at 0–1.5 cm and 24.0–25.5 cm, respectively. The intensive and semi-intensive treatments produced significantly more available forage for grazers annually than the extensive treatment. Forage yields in late May to early June were negatively correlated with spring bulk density.

Role of host and environment in mediating reduced gastrointestinal nematode infections in sheep due to intensive rotational grazing

We have previously reported marked reductions in faecal worm egg counts (WECs) and drenching frequency in sheep on an intensive rotational grazing system (IRG) in a cool temperate environment with summer-dominant rainfall. These experiments were designed to determine the role of the host and environmental factors in mediating this. The role of host factors was investigated by administering a fixed larval challenge in each of the 4 seasons of the year to groups of 20 young sheep on three different management systems, including IRG. This comprised a mixed larval challenge containing infective larvae of Haemonchus contortus and Trichostrongylus colubriformis 7 days after short-acting anthelmintic treatment. A range of measurements was then made up to day 35 post-challenge. The role of environmental factors was determined by assessing pasture infectivity in four seasons using faecal worm egg counts (WECs) and pooled faecal culture of worm-free tracer sheep. The management systems were high input (HI) with high fertiliser inputs high stocking rate and relatively long grazing periods; typical New England management system (TYP) with moderate fertiliser inputs and stocking rate and relatively long grazing periods and; Intensive rotational grazing (IRG) with moderate fertiliser inputs and stocking rate but very short (mean 5 days) grazing periods and long (mean 103 days) rest periods. IRG sheep had higher mean WEC at 28 and 35 days after fixed larval challenge than HI and TYP sheep in spring (IRG: 9500±1000; HI: 4000±1000; TYP: 7200±1000 eggs/g, P<0.01) and summer (IRG: 8400±750; HI: 5300±800; TYP: 4400±700 eggs/g; P<0.001) and also had lower liveweights during these seasons. There was no difference in WEC after the autumn challenge (IRG: 5100±450 HI: 4500±450; TYP: 4200±450 eggs/g; P∼0.36) but IRG had lower WEC than TYP following the winter challenge (IRG: 2900±400; HI: 2300±400; TYP: 4300±400eggs/g, P<0.01). The tracer sheep (used to determine pasture infectivity) on IRG had significantly lower WECs during winter, spring and summer than those under the other management systems. Faecal culture and larval differentiation revealed that faeces from tracers on IRG contained significantly lower proportions of H. contortus and significantly higher proportions of Trichostrongylus spp. and Teladorsagia circumcincta than faeces from tracers on the HI and TYP treatments. Thus, when IRG was most efficacious for worm control, during spring and summer when short graze and long rest periods were maintained, sheep on this system exhibited greater susceptibility to larval challenge while tracer sheep indicated lower pasture infectivity. This demonstrates that the effects of IRG on WEC are mediated by reduced larval challenge rather than increased host resistance to infection.

Impact of different grazing systems for bovine cattle on the soil microbiological and chemical characteristics

The objective of this work was to study the effect of grazing systems: rotational, continuous and the absence of cattle, in pastures of Brachiaria brizantha on microbial activity (respiratory, potential nitrification, solubilizing, and enzymatic) and on the chemical attributes (contents of organic carbon, total nitrogen, organic phosphorus, and moisture) of Eutrustox soil over one year. Eight Canchim breed animals were used. The samples were collected in the four seasons from 2005 to 2006. The average of organic C, organic P, and moisture contents, as well as potential nitrification and solubilizing activity and urease and acid phosphatase activities were significantly higher in the spring and/or summer than in autumn and/or winter. The total nitrogen amounts did not vary among seasons. While the respiratory activity was larger during winter and summer, cellulase activity was smaller during spring than in the other seasons. Except for organic P, higher values of the variables studied were observed in the rotational grazing. The results indicate that the hot and rainy season and the rotational grazing system cause increases in the soil microbiological and chemical attributes.

Origin, Persistence, and Resolution of the Rotational Grazing Debate: Integrating Human Dimensions Into Rangeland Research

The debate regarding the benefits of rotational grazing has eluded resolution within the US rangeland profession for more than 60 yr. This forum examines the origin of the debate and the major reasons for its persistence in an attempt to identify common ground for resolution, and to search for meaningful lessons from this central chapter in the history of the US rangeland profession. Rotational grazing was a component of the institutional and scientific response to severe rangeland degradation at the turn of the 20th century, and it has since become the professional norm for grazing management. Managers have found that rotational grazing systems can work for diverse management purposes, but scientific experiments have demonstrated that they do not necessarily work for specific ecological purposes. These interpretations appear contradictory, but we contend that they can be reconciled by evaluation within the context of complex adaptive systems in which human variables such as goal setting, experiential knowledge, and decision making are given equal importance to biophysical variables. The scientific evidence refuting the ecological benefits of rotational grazing is robust, but also narrowly focused, because it derives from experiments that intentionally excluded these human variables. Consequently, the profession has attempted to answer a broad, complex question—whether or not managers should adopt rotational grazing—with necessarily narrow experimental research focused exclusively on ecological processes. The rotational grazing debate persists because the rangeland profession has not yet developed a management and research framework capable of incorporating both the social and biophysical components of complex adaptive systems. We recommend moving beyond the debate over whether or not rotational grazing works by focusing on adaptive management and the integration of experiential and experimental, as well as social and biophysical, knowledge to provide a more comprehensive framework for the management of rangeland systems. El debate sobre los beneficios del pastoreo rotativo ha eludido una resolución en el ámbito de la profesión del manejo de los pastizales naturales en los EE.UU. por más de 60 años. Este foro examina el origen del debate y las principales razones de su persistencia en un intento por identificar un terreno común para su resolución y para buscar lecciones sustantivas de este capítulo central de la historia de la profesión del manejo de los pastizales naturales de EE.UU. El pastoreo rotativo fue un componente de la respuesta institucional y científica a la severa degradación de pastizales que ocurrió a comienzos del siglo 20 y desde entonces se ha transformado en la norma profesional para el manejo del pastoreo. Quienes manejan el pastoreo han encontrado que los sistemas rotativos pueden facilitar el logro de objetivos de manejo diversos, pero los experimentos científicos han demostrado que los sistemas de pastoreo no necesariamente contribuyen al logro de objetivos ecológicos específicos. Estas interpretaciones parecen contradictorias, pero sostenemos que pueden ser reconciliadas si son evaluadas dentro del contexto de sistemas adaptativos complejos en los que las variables humanas tales como el fijar metas, el conocimiento empírico, y la toma de decisiones reciben la misma importancia que las variables biofísicas. La evidencia científica refutando los beneficios ecológicos del pastoreo rotativo es robusta, pero con un foco estrecho, porque proviene de experimentos en los que se excluyeron intencionalmente las variables humanas. Por lo tanto, la profesión ha intentado dar respuesta a una pregunta amplia y compleja - si se debiera o no adoptar el pastoreo rotativo – con un enfoque necesariamente estrecho de investigación de procesos ecológicos. El debate sobre el pastoreo rotativo persiste porque la profesión de manejo de los pastizales aún no ha generado un marco de manejo e investigación que pueda incorporar tanto los componentes sociales como biofísicos de sistemas adaptativos complejos. Recomendamos ir más allá del debate sobre si el pastoreo rotativo “funciona” o no, y enfocar el debate en el manejo adaptativo y la integración de conocimiento experimental y empírico, así como el conocimiento social y biofísico, para proveer un marco más amplio para el manejo de sistemas de pastizales naturales.

Effects of probiotic supplementation on liveweight gain and serum cortisol concentration in cattle

PROBIOTICS are preparations from the culture of live microorganisms. They have been shown to have beneficial effects when used as growth promoters (Ferreira and others 2009) and as immunostimulants (Arenas...

Aspectos clínicos, parasitológicos e produtivos de ovinos mantidos em pastagem de capim-aruana irrigado e adubado com diferentes doses de nitrogênio

This work aimed to evaluate clinical, parasitological and productive parameters of crossbred lambs under a rotational grazing system of Panicum maximum cv. Aruana grass fertilized with four doses of nitrogen (75, 275, 475 and 675 kg ha-1 year-1). Eighteen lambs were used per treatment, totaling 72 animals. The following parameters were evaluated: daily weight gain (DWG), total weight gain (TWG), stocking rate (SR), meat production, number of fecal eggs per gram (EPG) and coproculture. Deworming was accomplished according to conjunctiva color compared using the Famacha&copy; card. DWG and TWG were greater (p < 0.05) in the animals under pasture fertilized with 75 kg ha-1 year-1. However, SR and EPG were greater (p < 0.05) in the animals kept in pastures with 675 kg ha-1 year-1. There were no significant differences among nitrogen levels for the different colors of ocular mucosa or the number of animals dewormed. A prevalence of 80.0 to 93.0% of Trichostrongylus sp. was found. The deworming based on the evaluation of conjunctiva color did not reduce EPG into desirable levels for any of fertilized doses of nitrogen. The nitrogen dose of 475 kg ha-1 year-1 in Aruana grass allowed greater productive performance per hectare.

Losses of N2O, CH4 and NH3 from a grass sward used for overwintering beef heifers

This study evaluated losses of N2O, CH4 and NH3 from a rotational grazing system for overwintering beef cattle which spend 1 month on pasture. The cattle density was 71 heifers/ha and they were moved weekly to a new feeding area within the main pasture. The N2O, CH4 and NH3 losses were determined in two feeding areas that were severely trampled (ST) or less trampled (LT) and in a control area from which cattle were excluded. The N input to the pasture was measured. The NH3 losses were measured by micrometeorological mass balance in two periods with heifers present. The N2O and CH4 were measured using a closed chamber method with 9 chambers within each area on 10 occasions after heifers were removed from the pasture. The N input was 510kgN/ha. The NH4-N contents in the clay loam topsoil were 45, 28 and 11kg/ha in the ST, LT and control areas, respectively. Losses of NH3 were low due to rainy and cold conditions, corresponding to maximum 0.3kgN/ha/d. The soil was water logged and this, with the cold conditions, may have lowered N2O emissions. Maximum N2O losses were 7, 30 and 18gN2O-N/ha/d from ST, LT and control areas, respectively.This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

Desempenho de vacas leiteiras em pastagem de alfafa suplementada com silagem de milho e concentrado e viabilidade econômica do sistema

Avaliou-se o efeito da substituição parcial de silagem de milho por pastagem de alfafa no desempenho de vacas leiteiras e na viabilidade econômica do sistema. Utilizaram-se 24 vacas da raça Holandesa, em estádio médio de lactação, em delineamento em blocos ao acaso. Os tratamentos foram: dieta à base de silagem de milho em confinamento, silagem de milho substituída parcialmente por pastejo restrito (PR) e pastejo irrestrito (PI) de alfafa. O sistema de pastejo foi rotacionado, e a quantidade de concentrado igual em todos os tratamentos. A massa de forragem foi de 2.338 e de 1.878kg de MS/ha, e a oferta de 1,8 e 4,2kg de MS/100kg de peso vivo, nos tratamentos PR e PI, respectivamente. A produção de leite não diferiu entre os tratamentos, cujas médias foram de 25,9; 25,8 e 25,2 litros por vaca por dia no confinamento, no PR e no PI, respectivamente. A produção diária de leite por área foi de 59,3L/ha no PR e de 63,0L/ha no PI, enquanto no confinamento foi de 45,7L/ha. A substituição parcial de silagem de milho por alfafa em pastejo não limitou o desempenho produtivo dos animais e mostrou-se economicamente vantajosa em relação ao confinamento.

Relationships among rotational and conventional grazing systems, stream channels, and macroinvertebrates

Cattle grazing in riparian areas can reduce water quality, alter stream channel characteristics, and alter fish and macroinvertebrate assemblage structure. The U.S. Department of Agriculture, Natural Resources Conservation Services has recommended Rotational Grazing (RG) as an alternative management method on livestock and dairy operations to protect riparian areas and water quality. We evaluated 13 stream channel characteristics, benthic macroinvertebrate larvae (BML), and chironomid pupal exuviae (CPE) from 18 sites in the Upper Midwest of the United States in relation to RG and conventional grazing (CG). A Biotic Composite Score comprised of several macroinvertebrate metrics was developed for both the BML assemblage and the CPE assemblage. Multi-Response Permutation Procedures (MRPP) indicated a significant difference in stream channel characteristics between RG and CG. Nonmetric Multidimensional Scaling indicated that RG sites were associated with more stable stream banks, higher quality aquatic habitat, lower soil compaction, and larger particles in the streambed. However, neither MRPP nor Mann–Whitney U tests demonstrated a difference in Biotic Composite Scores for BML or CPE along RG and CG sites. The BML and CPE metrics were significantly correlated, indicating that they were likely responding to similar variables among the study sites. Although stream channel characteristics appeared to respond to grazing management, BML and CPE may have responded to land use throughout the watershed, as well as local land use.

GrazeIn: a model of herbage intake and milk production for grazing dairy cows. 2. Prediction of intake under rotational and continuously stocked grazing management

AbstractDecision support tools to help dairy farmers gain confidence in grazing management need to be able to predict performance of grazing animals with easy‐to‐obtain variables on farm. This paper, the second of a series of three, describes the GrazeIn model predicting herbage intake for grazing dairy cows. The model of voluntary intake described in the first paper is adapted to grazing situations taking account of sward characteristics and grazing management, which can potentially affect intake compared to indoor feeding. Rotational and continuously stocked grazing systems are considered separately. Specific effects of grazing management on intake were quantified from an extensive literature review, including the effect of daily herbage allowance and pre‐grazing herbage mass in rotational grazing systems, sward surface height in continuously stocked grazing systems, and daily time at pasture in both grazing systems. The model, based on iterative procedures, estimates many interactions between cows, supplements, sward characteristics and grazing management. The sensitivity of the prediction of herbage intake to sward and management characteristics, as well as the robustness of the simulations and an external validation of the GrazeIn model with an independent data set, is presented in a third paper.

Desempenho de novilhos mantidos em pastagens de capim-elefante e capim-mombaça

Foi avaliado o desempenho de novilhos mantidos em pastagens de capins elefante e mombaça no período de outubro a dezembro de 2006. Adotou-se o sistema de pastejo rotacionado, com oferta regulada de forragem. A área experimental consistia de duas repetições contendo 18 piquetes de 0,25 ha cada, divididos em nove piquetes formados de capim-elefante e nove com mombaça. Os efeitos de tratamentos foram as espécies forrageiras, a repetição de área, a interação entre estes, piquetes dentro da interação e o erro experimental. Este modelo foi usado para analisar os atributos do pasto. Para analisar o consumo, a digestibilidade e o ganho, foram aleatoriamente alocados 24 novilhos para as respectivas interações entre forragem vs. repetição vs. sistema de pastejo, o que totalizou três animais por interação tripla. Os sistemas de pastejo consistiram de pastejo ad libitum (AL) e restrito (PR). O capim-elefante apresentou maior biomassa de matéria seca total (BT) e biomassa de matéria seca verde foliar (BFV). Não houve diferença entre as forrageiras quanto à produção de biomassa de matéria seca verde foliar, no entanto a proporção de folhas foi maior no capim-mombaça. As extrusas apresentaram composição bromatológica semelhante. Apenas o consumo de proteína bruta diferiu entre as forrageiras, sendo este maior para o pasto de mombaça. A alimentação à vontade possibilitou maior consumo de todos os nutrientes em ambas as pastagens. A digestibilidade dos nutrientes foi maior para o capim-elefante, mas não diferiu entre os níveis de alimentação: apenas o teor em proteína bruta foi maior no pasto onde o pastejo foi restrito e o teor de energia bruta do pasto foi maior para o sistema de pastejo à vontade. Apesar das diferenças qualitativas e quantitativas entre as forrageiras, não foram encontradas diferenças quanto ao ganho em peso por animal e por área. Entre os animais com alimentação à vontade, o ganho médio em massa corporal foi de 850 g/dia e o ganho por área de 246 kg/ha durante o período experimental.

Rotational Grazing Systems and Livestock Grazing Behavior in Shrub-Dominated Semi-Arid and Arid Rangelands

Rotational grazing systems (RGS) are often implemented to alleviate undesirable selective grazing by livestock. At both fine and coarse scales, livestock selectively graze individual plants, patches, communities, and landscapes. Smaller pastures, increased stocking density, and rotation allow managers to constrain livestock movement and determine season and frequency of grazing, potentially limiting selectivity and preventing repeated grazing of preferred plants. However, in arid and semi-arid rangelands, forage growth is limited primarily by precipitation rather than defoliation frequency. When soil moisture is adequate, forage is abundant and defoliation levels are typically low, and repeated, intensive defoliation of preferred plants is less likely than in more mesic areas where more consistent precipitation and soil moisture storage allows animals to establish and maintain spatial hierarchies of grazing patterns. Many southwestern rangelands contain diverse vegetation, which provides quality forage during different times of the year. These spatial and temporal patterns of forage distribution may not be amenable to manipulation with RGS. Tracking data show that livestock often alternate among locations within pasture boundaries and can opportunistically exploit areas with higher quality forage when they are available. Higher stock densities combined with higher stocking rates can increase livestock use of less preferred areas, but overall distribution patterns of intensive-rotational and extensive grazing systems are often comparable at similar stocking rates and distances from water. Management that ensures that grazing of riparian areas does not occur during the critical late summer period may be more beneficial than RGS that periodically defers livestock use throughout the grazing season. In arid and semi-arid shrublands, timely adjustments to animal numbers and practices that improve grazing distribution at regional and landscape scales are more likely to be effective in maintaining or improving rangeland health than fencing and RGS. Los sistemas de pastoreo rotativos (SPR) son utilizados frecuentemente para contrarrestar los efectos no-deseados del pastoreo selectivo del ganado. Tanto a escalas finas como gruesas el ganado pastorea selectivamente plantas individuales, parches, comunidades y paisajes. Potreros más pequeños, mayor densidad animal, y la rotación permiten poner límites al movimiento de los animales y determinar la estación y la frecuencia de pastoreo, limitando potencialmente la selectividad y previniendo el pastoreo reiterado de plantas preferidas. Sin embargo, en pastizales áridos y semiáridos, el crecimiento del forraje está limitado principalmente por precipitación y no por la frecuencia de defoliación. Cuando la humedad edáfica es adecuada, el forraje es abundante y los niveles de defoliación son típicamente bajos, y la defoliación repetida e intensa de plantas preferidas es menos probable que en áreas más mésicas donde la precipitación consistente y el almacenaje del agua en el suelo permiten que los animales establezcan y mantengan jerarquías espaciales de patrones de pastoreo. Muchos de los pastizales naturales del sudoeste de los Estados Unidos contienen vegetación diversa que provee forraje de calidad en distintos momentos del año. Estos patrones espaciales y temporales de distribución de forraje podrían no ser susceptibles a ser manipulados a través de SPR. Datos de monitoreo con GPS demuestran que los vacunos alternan entre lugares dentro de los limites de un potrero y que pueden utilizar áreas de mayor calidad de forraje de modo oportunista cuando las mismas están disponibles. Densidades animales más elevadas combinadas con cargas animales más altas podrían incrementar el uso de áreas menos preferidas pero los patrones globales de distribución del pastoreo de sistemas rotativos intensivos y sistemas de pastoreo extensivos son frecuentemente comparables bajo condiciones similares de carga animal y distancia al agua. Un manejo que asegure la exclusión del pastoreo de aéreas ribereñas (vegas/mallines/humedales) en el período crítico de fines del verano podría ser más beneficial que SPR que periódicamente difieren el uso del ganado durante la estación de pastoreo. En estepas arbustivas áridas y semiáridas ajustes oportunos del número de animales y prácticas que mejoren la distribución del pastoreo a escalas regionales y del paisaje podrían ser más efectivos que la construcción de alambrados y el uso de SPR en mantener o mejorar la salud del pastizal.

Efectos ambientales y parámetros genéticos de variables de crecimiento para un rebaño de ciervo rojo (Cervus elaphus) en cautiverio

The objective was to estimate environmental effects and genetic parameters on growth traits in a flock of farmed red deer of the central Mexican highland. Animals were raised on an intensive rotational grazing system of grass-legume mixed temperate pastures. Evaluated traits were birth (BW), weaning adjusted to 100 d (WW) and yearling (YW) weights. Analyses were performed using the MTDFREML program.

The effects of dairy cow weight on selected soil physical properties indicative of compaction

AbstractThe effect of treading by dairy cows of three different weights on soil physical properties was investigated under different soil moisture deficit (SMD) treatments in the south of Ireland. SMD was used as a readily predicable surrogate for volumetric water content. Animal treading in grassland ecosystems is known to affect soil and vegetation properties, which can influence agricultural system productivity. Treading action can result in reduced soil water infiltration and increased runoff. In Ireland short winter housing and early spring turnout are key elements of low cost grass based production. However, there is potential for soil damage as a consequence of animal treading during early spring and late autumn. This study shows that SMD is the main factor affecting changes in bulk density (BD), soil shear strength, penetration resistance (PR) and total porosity. At high SMD (dry), soil was less sensitive to trampling damage than at low SMD (wet). At SMD 0 mm, BD increased by 6.1% post trampling, whereas it only increased by 3.1, 4.0 and 0.5% at SMD 11, 14, and 29 mm, respectively. Average soil BD was 2.3% greater immediately post trampling, and 4.6% greater in the hoof marks. PR was significantly greater following trampling by the heavy weight cow compared with the light or medium weight cow. There was no significant effect of cow weight on soil water content or soil BD. The results indicate that forecasted SMD can be used as a management input for rotational grazing systems to protect soil quality.

INFLUÊNCIA DE DIFERENTES SISTEMAS DE PASTEJO SOBRE AS PROPRIEDADES FÍSICAS E AGREGAÇÃO EM SOLOS DE CERRADO

The objective of this study was to evaluate soil structure alterations that occurred in a typical Red distroferric Latossol under different grazing systems. In 2004, soil samples from three depths (0-2 cm, 2-7 cm, and 30-35 cm) were collected in a farm owned by the College of Veterinary of the Federal University of Goias, Goiânia, Goias State, Brazil, as it follows: I) soil under pasture with Panicum maximum cv. Tanzania, in a rotational grazing system, clump position (“C”); II) soil under pasture with Panicum maximum cv. Tanzania, in a rotational grazing system, among clumps position (“AC”); III) soil under pasture with Cynodon dactilum cv. Tifton 85, in a continuous grazing system; and IV) soil under Savannah, as reference. The implantation of pastures with Tifton 85 and Tanzania grasses changed physical properties of the soil, through the reduction of macropores (MAC) and increase in soil density (SD). Soils under pastures with Tifton 85 and Tanzania grasses (“C” position) presented larger mean geometric diameter (MGD), if compared to the soils under Savannah and pasture with Tanzania grass (“AC” position). Alterations in soil structure were more significant in the topsoil layer (0-2 cm and 2-7 cm depth). Stocking rates practiced in the pastures with Tifton 85 and Tanzania grasses were excessive and also the main reason for deteriorating physical soil properties. KEY-WORDS: Cynodon dactilum ; Panicum maximum ; continuous grazing system; rotational grazing system; stocking rate.

Milk yield and composition, feed intake and stocking rate of crossbread cows in tropical grasses managed in a rotational grazing system

The objective of this study was to evaluate milk yield and composition, dry matter intake, and stocking rate in pastures with tanzania grass (Panicum maximum cv. Tanzânia), star grass (Cynodon nlemfuensis cv. Estrela-Africana), and marandu grass (Brachiaria brizantha cv. Marandu). The grasses were managed in a rotational grazing system with Holstein x Zebu crossbreed cows, with a 30-day resting period and three days of paddock occupation. The pastures were fertilized with 1,000 kg/ha/year using the 20:05:20 (NPK) formula, split in three applications during the rainy season. It was used a complete random block experimental design with three factors being studied and two replications. In the experiment, four cows/paddock were used and, when it was necessary, regulator animals were added in order to obtain a supply of 7% body weight green forage dry matter. The animals were individually fed concentrate at 2 kg/day during the experimental period. Milk yield did not differ among the three grasses, with values of 9.1; 9.1; and 8.7 kg/cow/day for pastures with tanzania grass, star grass and marandu grass, respectively. Similarly, grass did not affect milk chemical composition. Stocking rate was similar among the three grasses, with values of 4.6; 4.5 and 5.0 UA/ha for tanzania grass, star grass and marandu grass, respectively. The highest dry matter intake was observed for tanzania grass with 2.6% of the body weight while stargrass (2.3%) and marandu grass (2.4%) did not differ among each other. The highest dry matter intake on tanzania grass pasture was not reflected on milk yield per animal. Milk yield and composition and stocking rate are similar among the evaluated grasses.

Meadow Fescue, Tall Fescue, and Orchardgrass Response to Defoliation Management

Meadow fescue [Schedonorus pratensis (Huds.) P. Beauv.] represents an alternative to temperate grasses typically used in forage‐livestock systems. Our objective was to compare the productivity, nutritive value, and persistence of diverse meadow fescue cultivars with that of tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] and orchardgrass (Dactylis glomerata L.) when harvested by regimes representing lax and severe hay production and rotational grazing. ‘Azov’ (plant introduction strain cross), ‘Bartura’ (commercial cultivar), and ‘Hidden Valley’ (naturalized population) meadow fescue, ‘Barolex’ tall fescue, and ‘Bronc’ orchardgrass were harvested infrequently (40‐ to 65‐d harvest interval) or frequently (when plants reached 25‐cm sward height) to a 5‐ or 10‐cm residual sward height (RSH) at two Wisconsin locations in 2 yr. Annual dry matter (DM) yield of all grasses was greater when harvested infrequently (7.46 Mg ha−1) than frequently (5.92 Mg ha−1), or at 5 cm (7.52 Mg ha−1) than 10‐cm RSH (5.88 Mg ha−1). Tall fescue and orchardgrass annual yield was greater than that of all meadow fescues when harvested infrequently, but differences among grasses were relatively small when harvested frequently, particularly at 10‐cm RSH. Neutral detergent fiber digestibility (NDFD) of meadow fescue was 30 to 80 g kg−1 neutral detergent fiber (NDF) greater than that of tall fescue or orchardgrass at every harvest in all environments. Meadow fescue cultivars were less persistent than tall fescue after 2 yr, but were usually equal to or more persistent than orchardgrass. Meadow fescue should be considered as a viable alternative to tall fescue and orchardgrass in temperate, managed intensive rotational grazing systems due to its comparable yield and superior digestibility.

Desempenho de Espécies Florestais e Pastagens em Sistemas Silvipastoris no Estado do Pará

Proposing economic and ecological land-use alternatives has been a great challenge for agricultural research in the Brazilian Amazon. The silvopastoral systems (SPS) are promising to integrate trees in the livestock production system and reclaim degraded pastures in the Amazon region. In Municipality of Paragominas, State of Para, nine SPS composed by combination of three tree species (Schizolobium amazonicum, Bagassa guianensis and Eucalyptus tereticornis), planted in 6 m-lane, spaced by 12 m – and three pastures (Brachiaria brizantha, B. humidicola and Panicum maximum / dictioneura B. dictyoneura), planted in the inter-lane space. Steers grazed the one-hectare experimental parcels simulating a rotational grazing system with 14 days - grazing period and 42 days – rest period, and was evaluated during August 1990 to November 1991. From the tree and pasture management point of view, the more promising silvopastoral combinations were, respectively, S. amazonicum - B. brizantha and E. tereticornis - B. brizantha.