Grazing Frequency Research Articles

Behavior of beef cattle in silvipastoral systems with eucalyptus

It was aimed to verify the effect of the presence of trees and their heights in silvipastoral system on the intake behavior of Nellore heifers in the summer. Ten heifers for the following systems were used: system without shade, silvipastoral system with 8-meter and 18-meter trees. The data were collected in three days during 12 hours, subdivided in morning (7:15 a.m. to 1. p.m.) and afternoon (1:15 p.m. to 7 p.m.). It was evaluated the times and frequency of grazing, rumination, idle and the percentage of time that the animals remained in the shade; black globe-humidity index, whose average and minimum values (86 and 82) were equal for 8-meter tree system and 18-meter tree system; however they were lower when compared to the without shade system (89 and 86). There was an interaction between the systems and the periods for all the analyzed variables, except for the rumination frequency. For system without shade, the grazing time did not differ between morning (202 min) and afternoon (187 min); however the grazing frequency was lower for the afternoon (3.17). For 8-meter trees systems and 18 meter trees system, the grazing time in the afternoon, respectively, with 195.50 and 219.00 min was higher than in the morning, respectively, with 128.00 and 158.50 minutes. The rumination time was higher in the morning for all systems. The grazing frequency for 8-meter trees was 3.58, for the without shade system it was 3.05 and for 18-meter tree system it was 2.22. A higher idle time and the idle frequency was found in system without shade (97.50 min and 3.80 respectively) in the afternoon. For 8-meter tree system (98.50 min and 4.47 respectively) and 18-meter tree system (127.00 min and 4.27 respectively), they were higher in the morning. The animals remained under shade for an average of 43.49% (with trees with 8 m) and 49.81% (with trees with 18 m) of the time. It was concluded that the presence of trees modify the time and the frequency in grazing and idle; however, it does not influence the time and frequency in rumination.

Behavioural responses of 6-month-old beef calves prevented from suckling: influence of dam's milk yield

The objective of the present experiment was to compare the behavioural response of calves reared by cows of different milk yields to the prevention of suckling with the aid of nose-flaps that allowed the maintenance of social contact with the dam. Twenty Hereford or Hereford × Angus crossbred primiparous cows from a single herd remained with their calves suckling until the beginning of the experiment, in late summer–early autumn. Milk production was determined monthly during the lactation period and the pairs were selected according to the cows’ milk production, for higher or lower milk yield (HMY and LMY, respectively). On Day 0, suckling was prevented by placing a nose-flap anti-suckling device on each calf for 11 days. Calf behaviour was recorded from Day –3 to Day 5, using instantaneous sampling of individual animals in each group, and the calves were weighed monthly since birth, and on Days –8 and 11. Bodyweight profiles for HMY and LMY calves were similar until Day –8; from then on, up to Day 11, HMY calves lost weigh, whereas LMY calves gained weight. Suckling frequency before nose-flaps were fitted was similar for HMY and LMY calves. There was no relationship between the cow’s milk yield and the changes observed in behaviour. Apart from playing, all behaviours were affected by prevention of suckling. The distance between the calves and the dam, and the frequency of grazing and rumination, decreased after nose-flaps were placed, whereas vocalisations, suckling attempts, walking and standing increased. In conclusion, the behavioural responses to prevention of suckling did not differ between the 6-month-old calves reared by cows with high yields and those with low milk yields. The behavioural response of calves that were prevented from suckling but were kept with the dams indicates that the cessation of suckling contributes to the weaning distress of 6-month-old beef calves.

Reversed effects of grazing on plant diversity: the role of below‐ground competition and size symmetry

Grazing is known as one of the key factors for diversity and community composition in grassland ecosystems, but the response of plant communities towards grazing varies remarkably between sites with different environmental conditions. It is generally accepted that grazing increases plant diversity in productive environments, while it tends to reduce diversity in unproductive habitats (grazing reversal hypothesis). Despite empirical evidence for this pattern the mechanistic link between modes of plant–plant competition and grazing response at the community level still remains poorly understood. Root‐competition in particular has rarely been included in theoretical studies, although it has been hypothesized that variations in productivity and grazing regime can alter the relative importance of shoot‐ and root‐competition. We therefore developed an individual‐based model based on plant functional traits to investigate the response of a grassland community towards grazing. Models of different complexity, either incorporating only shoot competition or with distinct shoot‐ and root‐competition, were used to study the interactive effects of grazing, resource availability, and the mode of competition (size‐symmetric or asymmetric). The pattern predicted by the grazing reversal hypothesis (GRH) can only be explained by our model if shoot‐ and root‐competition are explicitly considered and if size asymmetry of above‐ and symmetry of below‐ground competition is assumed. For this scenario, the model additionally reproduced empirically observed plant trait responses: erect and large plant functional types (PFTs) dominated without grazing, while frequent grazing favoured small PFTs with a rosette growth form. We conclude that interactions between shoot‐ and root‐competition and size symmetry/asymmetry of plant–plant interactions are crucial in order to understand grazing response under different habitat productivities. Our results suggest that future empirical trait surveys in grassland communities should include root traits, which have been largely ignored in previous studies, in order to improve predictions of plants’ responses to grazing.

Influência dos fatores abióticos no fluxo de biomassa e na estrutura do dosel.

Em gramíneas tropicais, taxas de aparecimento e alongamento de folhas e a duração de vida das folhas são características influenciadas pelos fatores de crescimento como: luz, temperatura, água e fertilidade do solo que por sua vez são afetados pelo manejo adotado: altura, índice de área foliar, frequência e intensidade de pastejo, dentre outros. O entendimento das respostas destas variáveis às diferentes condições de manejo é essencial à formulação de práticas de manejo mais aperfeiçoadas, fundamentadas em conceitos morfofisiológicos. Muitas informações sobre a influência dos fatores abióticos na estrutura do dossel das gramíneas tropicais têm sido geradas no Brasil, o que muito têm contribuído para o nosso entendimento sobre o crescimento das gramíneas e a dinâmica do fluxo de biomassa do pasto. Entretanto, o uso direto destes fatores no manejo de pastagens é ainda incipiente. Portanto, é apresentada e discutida a influência dos fatores abióticos no fluxo de biomassa e na estrutura do dossel, resultados gerados ao redor do mundo e algumas possibilidades de seu uso para orientação do manejo, direta ou indiretamente.

The behavioural, digestive and metabolic characteristics of fishes with different foraging strategies

To test the hypothesis that digestion has a more notable physiological effect on ambush foragers than on active foragers, we investigated the behavioural, digestive and metabolic characteristics, as well as the postprandial locomotory capacity, of four species of juvenile fish distributed along the Yangtze River, China, with distinct foraging strategies. The ambush foraging southern catfish (Silurus meridionlis) had the fewest movements per minute (MPM), lowest per cent time spent moving (PTM), slowest critical swimming speed (Ucrit), lowest maintenance metabolism (VO2rest) and lowest maximum locomotory metabolism (VO2max)). However, the southern catfish had the highest feeding level and maximum feeding metabolism (VO2peak) and the greatest decrease in Ucrit after consumption of a large meal. Thus, this fish is highly adapted to its ambush behavioural strategy and sedentary life style. In the herbivorous grass carp (Ctenopharyngodon idellus), a low digestive capacity led to little change in postprandial locomotory performance, which benefits its frequent grazing behaviour. In this species, the greater amount of energy spent on routine activity and avoiding predators versus Ucrit might be related to its herbivorous life style and high predation risk. The active foraging crucian carp (Carassius auratus) adopts a unique high energy cost strategy that allows for high capacity in both routine activity and digestion, and the great flexibility of its cardio-respiratory capacity (increased VO2max after feeding) guarantees a small decrease in Ucrit even after maximum feeding. Finally, the sluggish foraging darkbarbel catfish (Pelteobagrus vachelli) has low digestive and locomotory capacity, but its energy-efficient venomous defence strategy may be related to its abundance. These results show that the digestive, behavioural and metabolic strategies differ among these fish species. The locomotory capacity in the sedentary fishes decreased profoundly after feeding, whereas it decreased little or not at all in the active fishes. The maintenance of high locomotory capacity after eating in the active fishes is probably related to a large metabolic capacity, a lower digestive capacity or an improvement in cardio-respiratory capacity after feeding.

Succession of floodplain grasslands following reduction in land use intensity: the importance of environmental conditions, management and dispersal

Summary Classical ecological theory predicts a succession towards plant communities that are determined by environmental conditions. However, in ecological restoration, species composition often remains different from the predicted target community, compromising the success of restoration measures. We analysed the relative importance of environmental conditions, management and distance to source populations for floodplain grassland succession following re‐conversion from intensive to traditional use. The study was established at 33 grassland sites in central German river valleys. Species composition, environmental variables, past and current management, and the distance to source populations of characteristic species of traditional management (indicator species) were recorded and compared using multivariate statistics. We further tested the speed of colonization by two indicator species, Silaum silaus and Serratula tinctoria, along transects from source populations into unoccupied fields. The species composition of the successional grassland was mainly determined by elevation, total soil nitrogen, distance to remnant species‐rich grasslands and frequency of mowing or grazing. Elevation and distance were negatively, and frequency was positively related to the occurrence of late successional species. Colonization by indicator species was only dependent on the distance to source populations; other explanatory variables were not significant. Migration from adjacent source sites of S. silaus and S. tinctoria into re‐converted grasslands was slow, reaching only 40 m and 15 m after 15 years. Synthesis and applications. The results demonstrated the limitations of the deterministic view on plant succession and the high relative importance of propagule availability in grassland restoration. Natural colonization will only be successful if source populations of the target species are adjacent to the restoration sites. Artificial introduction techniques are recommended to overcome dispersal barriers.

Rendimiento y dinámica de crecimiento estacional de ballico perenne, pastoreado con ovinos a diferentes frecuencias e intensidades

The objective of the present study was to assess perennial ryegrass seasonal herbage accumulation, growth rate (GR), tiller population density (TPD) and weight (TW) at different grazing frequencies and intensities. Treatments consisted of two grazing frequencies (14 and 21 d in the rainy season and 35 and 42 d in the dry and cold seasons) and three grazing intensities: (hard 4-6 cm), medium (6-8 cm) and lax (8-10 cm) in a completely randomized block design with a factorial 2x3 arrangement and three replicates. In the rainy season herbage accumulation was 28 % greater (P<0.05) at 21 d grazing frequency than at 14 d grazing frequency (4,457 vs 3,457 kg DM ha-1). In the cold and dry seasons herbage accumulation at 35 d interval produced 27 % more herbage than at 42 d interval (2.270 vs 1,787 kg DM ha-1). Medium intensity grazing yielded more herbage than both hard and lax in the three seasons. The highest GR was recorded in the rainy season, especially in August at 21 d frequency and medium intensity. The highest TPD (8,042 tillers m-2) was recorded also in August and tended to drop in September. Tiller weight had the greatest influence on herbage yield at 21 d frequency in the rainy season, and TPD increased herbage yield at the beginning of the following rainy season.

Behavioural changes at weaning in 6-month-old beef calves reared by cows of high or low milk yield

The objective of this experiment was to determine the differences in behavioural changes observed in 6-month-old beef calves at weaning in relation to milk yield availability from their dams. Eighteen Hereford or Hereford × Angus crossbred primiparous cows from a single herd remained with their calves suckling until the beginning of the experiment (194.1 ± 1.9 days after calving). On day 0, calves were moved to a 100-m2 corral far from their mothers, which were taken to a field more than 1000 m away, and returned to the original paddock on day 1. Milk production was determined monthly during the lactation period in 14 of the 18 cows. Calves’ behaviour was recorded using instantaneous sampling of individual animals in each group every 10 min from 0800 to 0950, 1200 to 1350, and 1600 to 1750 hours. Recordings were performed from day –3 to day 5, except on day 0. The calves from the five cows with higher milk yield (HMY) and the calves from the five cows with lower milk yield (LMY) were considered for data analysis. Milk yield was greater in HMY than LMY cows throughout all the lactation. HMY calves tended to suckle more frequently than LMY calves. There were no differences in average daily gain after weaning between HMY and LMY calves. However, HMY calves were heavier at weaning than LMY calves. The frequency of grazing, ruminating, walking and standing differed between HMY and LMY calves, and was affected by weaning. For example, calves from HMY cows spent less time grazing before and after weaning than calves from LMY cows. There were also interactions between group and time on the frequency of these behaviours. Overall, we conclude that the behaviour of 6-month-old beef calves at weaning differed according to their mothers’ milk yield, and their developmental growth stage.

Effects of herbivore grazing on the physiognomy of the coralline alga Spongites yendoi and on associated competitive interactions

The territorial gardening limpet Scutellastra cochlear occurs along the south and southern west coasts of South Africa, whereas one of its primary food items, the encrusting coralline alga Spongites yendoi, extends much farther north along the West Coast. A combined analysis of geographic variation in limpet grazing frequency and a limpet-manipulation experiment was used to study the interaction between the limpet and its coralline food. The coralline comprised most (c. 85%) of the limpet's diet whereas fleshy algae from the limpet's garden comprised c. 7%. Grazing caused the thallus of the coralline to be thin and smooth; in the absence of herbivory, or under low grazing frequencies, the crust became thick and highly protuberant. Grazing weakened the coralline's interference (overgrowth) competitive ability and also reduced its fecundity. In spite of these two apparently negative impacts, the intimate herbivore–coralline association between S. cochlear and S. yendoi showed characteristics of a facultative mutualism. Grazing by S. cochlear reduces the coralline's thallus thickness and consequently increased its lateral margin extension rate. Thinner forms of the coralline grew five times faster than thicker forms. An increased lateral growth results in the thinner form of the coralline being very abundant on the south and southern west coasts, occupying as much as 79% of the substratum in the lower eulittoral zone. Thinner forms of S. yendoi were also less burrowed by boring organisms and more strongly attached than thicker forms of the coralline. Grazing by S. cochlear has thus conferred the advantages of faster lateral growth (i.e. success at exploitation competition) and stronger attachment. The coralline and fleshy algae from the limpet's garden were equally high in organic content on a volume basis. This suggests that the crude food value per bite in the coralline and fleshy algae is comparable. This study has shown that incompletely overlapping distributions between strongly interacting species along a broad geographical gradient is not just a significant feature of the ecology of terrestrial, but also of marine ecosystems.

Balanço do carbono orgânico no solo sob integração lavoura-pecuária no sul do Brasil

A integração lavoura-pecuária tem apresentado um avanço recente em áreas historicamente utilizadas com pecuária de corte extensiva no sul do Brasil. O inadequado manejo das pastagens de inverno associado ao uso da monocultura da soja no verão podem limitar o aporte de resíduos vegetais ao solo e reduzir os estoques de C orgânico do solo. O objetivo deste trabalho foi avaliar o impacto do aumento da freqüência de pastejo no inverno e de sistemas de culturas de verão no estoque de C orgânico total do solo (COT). O experimento, realizado por quatro anos sob sistema plantio direto, seguiu um delineamento de blocos ao acaso, em arranjo bifatorial 3x3, com quatro repetições. O fator A foi constituído por três intervalos de pastejos durante o inverno: sem pastejo (SP), pastejo a cada 28 dias (P28) e pastejo a cada 14 dias (P14). O fator B constou de três sistemas de culturas de verão: monocultura de soja (Mon-S), monocultura de milho (Mon-M) e rotação anual de soja e milho (Rot-S/M). Foram quantificadas as adições de C ao solo via resíduos vegetais e os estoques de COT do solo segundo os métodos de camada e massa equivalentes de solo. O aumento da freqüência de pastejo diminuiu o aporte de C oriundo das pastagens de inverno de 5,3 Mg ha-1 no tratamento SP, para 1,7 e 1,3 Mg ha-1 nos tratamentos P28 e P14, respectivamente. O milho foi a cultura que proporcionou o maior aporte de C ao solo, com uma média de 6,0 Mg ha-1, enquanto a soja adicionou apenas 2,2 Mg ha-1. Os estoques de C orgânico calculados com base em camadas equivalentes de solo foram superestimados nos tratamentos P14 e P28 e subestimados no tratamento SP em comparação aos resultados obtidos com base nas massas equivalentes de solo, que foram utilizados para comparação dos sistemas de manejo. Os estoques de C orgânico nas camadas de 0-0,025, 0,025-0,05 e 0,05-0,10 m foram linearmente relacionados à adição anual de C pelas culturas (pastagem + culturas anuais), sendo necessária a adição de 4,48 Mg ha-1 ano-1 para a manutenção do estoque original de C orgânico da camada de 0-0,10 m. A baixa adição de C ao solo pelos resíduos vegetais no tratamento P14 resultou numa emissão líquida estimada de C para a atmosfera (0,05 a 0,27 Mg ha-1 ano-1 ), enquanto o solo no tratamento SP atuou como um dreno de C atmosférico (0,19 a 0,30 Mg ha-1 ano-1). No tratamento P28, o comportamento do solo como fonte ou dreno de C dependeu do sistema de cultura de verão, tendo sido estimada uma emissão líquida de C do solo sob Mon-S (0,04 Mg ha-1 ano-1 ) e uma retenção líquida de C sob Mon-M (0,15 Mg ha-1 ano-1 ) e Rot-S/M (0,11 Mg ha-1 ano-1 ). O maior intervalo entre pastejos, durante o inverno, associado à utilização do milho no verão contribuiu para maiores adições de resíduos vegetais e acúmulo de C orgânico no solo.

Seasonal nitrate levels in the soil solution of an organic pasture managed for nature conservation

Extensive management of pastures is considered as an option to enhance nature conservation in agricultural landscapes. Partial reduction of the grazing frequency from four to two rotations and discontinuing the tending of sod and sward have been tested for extensive management of a mixed pasture at the Nova Scotia College of Agriculture in Truro since 2004. It is not well known how extensification affects the N cycle of organic pastures without mineral fertilizer or manure applications. Moisture and temperature of the topsoil and nitrate content of the leachate extracted with ceramic suction cups at 0.5 m depth were monitored prior to grazing and during sward regrowth in the first and second rotation in spring of 2005 and 2006. In each year, more than 75 % of all samples contained less than 2.5 mg NO3-N L-1. A significant seasonal nitrate dynamic suggests that plant N uptake reduces nitrate leaching in the first rotation, while soil biological activity increases N supply due to soil warming in excess of plant uptake, thus raising the nitrate level in the second rotation. Extensification significantly reduced soil temperature with a concomitant albeit small decrease of nitrate levels in the soil leachate. The pasture cycled nitrogen very tightly with little room for leakages as a result of imposed treatments during the spring season. Key words: Pasture, organic, temperature, nitrogen, leaching

The importance of grazing intensity and frequency for physiological responses of the tropical seagrass Thalassia hemprichii

Seagrass grazing is an intrinsic disturbance in primarily tropical and subtropical areas. While there is a general parabolic response in seagrass growth to grazing intensity, there is less knowledge on the role of grazing frequency, as well as potential interactions between grazing intensity and frequency. This study experimentally investigated physiological responses in Thalassia hemprichii to simulated (leaf cutting) grazing regimes with different intensities (25% vs. 75%) and frequencies (1 times vs. 3 times) over 35 days in Chwaka Bay (Zanzibar, Tanzania). The results showed that the two high-intensity treatments (75% removal) had 37–41% lower growth rate than the low-intensity/low-frequency treatment, and rhizome sugar and starch content were both affected in a similar way. A 36% lower starch content in the simulated low-intensity/high-frequency regime (25% × 3) compared to the one of low-intensity/low-frequency (25% × 1) also shows an interaction between grazing intensity and frequency. This suggests that high-intensity (and to some extent frequency) grazing regimes, in comparison to low-intensity regimes, could negatively affect T. hemprichii growth, energy reserves, and thereby the ability to deal with additional stress like light limitation or grazing.

Influence of Grazing Frequency on Cynodon Grasses Grown in Peninsular Florida

Bermudagrass and Stargrass are among the most important of the warm-season perennial grasses used for livestock grazing and hay production in warmer regions of the world. The purpose of this experiment was to test four stargrasses (Cynodon nlemfuensis Vanderyst var. nlemfuensis) and four bermudagrasses (C. dactylon L. Pers.) at four grazing frequencies (GF) for dry biomass (DB) yield, nutritive value, and persistence. Experimental design was a split-plot arrangement of a randomized complete block with three replications. The main plot consisted of GF (2, 4, 5, and 7 weeks) and grass entries (cvs. Stargrass 2000, Florona, Okeechobee, and Ona Pasture No. 2 stargrass; Bermudagrass 2000, Jiggs, World Feeder, and Tifton 85 bermudagrass) as subplots. There was a grass entry × GF interaction for DB yield during the warm-season. Decreasing GF from 2 to 7 weeks resulted in a linear increase in DB yield and generally a linear decrease in CP and IVDOM. Bermudagrass 2000 and Jiggs bermudagrass were generally the two highest yielding entries at GF of 2 (3.4 and 3.1), 4 (6.5 and 5.7), 5 (6.9 and 7.9), and 7 weeks (9.3 and 8.2 ton/acre), respectively, and most persistent. Delaying GF from 2 to 7 weeks decreased CP and IVDOM by 39 and 22%, respectively. Winter forage production was highest for Bermudagrass 2000 and Jiggs and averaged 1.1 ton/acre when harvested after 12 weeks regrowth.

Atributos físicos do solo em sistema de integração lavoura-pecuária sob plantio direto

A compactação do solo é um dos principais fatores responsáveis pela queda da produtividade das culturas agrícolas. Por isso, o impacto causado pelo pisoteio bovino sobre o solo e os conseqüentes reflexos nos atributos físicos densidade do solo, porosidade do solo, resistência mecânica à penetração e infiltração de água no solo, em área manejada sob sistema integração lavoura-pecuária, foram investigados em experimento de campo, no município de Jari, na região do Planalto Médio do Rio Grande do Sul, Brasil. Foram avaliados três sistemas de manejo da pastagem de inverno (aveia-preta, Avena strigosa Schreber + azevém, Lolium multiflorum Lam.), caracterizados pela freqüência de pastejo: (1) Sem Pastejo (SP), (2) Pastejo a cada 28 dias (P28) e (3) Pastejo a cada 14 dias (P14). Além disso, foi avaliada a influência da cultura de verão, soja [Glycine max (L.) Merr.] ou milho (Zea mays L.), em rotação com as pastagens de inverno, em amenizar ou agravar a ação compactadora do pisoteio bovino. A compactação do solo, avaliada pela sua densidade, concentrou-se na camada de 0-0,05 m de profundidade, porém houve redução de sua macroporosidade até a camada de 0,10-0,15 m, no sistema com a maior freqüência de pastejo (P14). A resistência mecânica do solo à penetração atingiu valores de 2,61 e 2,49 MPa nos tratamentos P14 e P28, respectivamente, nas profundidades de 0,05 e 0,08 m, enquanto as áreas que não foram pastejadas mantiveram valores inferiores a 1,66 MPa. A taxa de infiltração de água no solo foi alterada significativamente pelo pisoteio bovino e pela cultura de verão antecedente. Com a cultura de milho, o solo mostrou-se menos sensível ao pisoteio bovino, ao passo que com a cultura de soja na maior freqüência de pastejo (P14) a taxa de infiltração de água no solo foi reduzida. A cultura de soja proporcionou os maiores valores de macroporosidade nas camadas avaliadas e, quando conjugada à menor freqüência de pastejo (P28) ou à ausência de pastejo (SP), observaram-se as maiores taxas de infiltração de água no solo.

Effects of two mixtures of perennial ryegrass cultivars with contrasting heading dates, and differing in spring‐grazing frequency and silage harvest date, on characteristics of silage from first‐cut swards

AbstractThis experiment quantified the effects of: (i) heading date of perennial ryegrass, (ii) grazing frequency in spring and (iii) date of silage harvest, on the ensilability of herbages harvested for silage, and on the conservation and estimated nutritive value of the resultant silages. Replicated field plots with two perennial ryegrass mixtures (intermediate‐ and late‐heading cultivars) were subjected to three spring‐grazing regimes (no grazing, grazing in late March and grazing in both late March and late April) and were harvested on four first‐cut harvest dates between 20 May and 21 June. Herbage from each of the four replicates of these 24 treatments was precision‐chopped and ensiled unwilted and with no additive in laboratory silos. Herbage from the sward with the intermediate‐heading cultivar had a higher (P &lt; 0·001) dry‐matter (DM) content and buffering capacity than that from the late‐heading cultivar, whereas water‐soluble carbohydrate concentrations increased (P &lt; 0·001) with more frequent grazing in spring. Later harvesting enhanced herbage ensilability through an increased (P &lt; 0·001) DM content and reduced (P &lt; 0·001) buffering capacity and pH. Fermentation profiles of the silage were not markedly influenced by the cultivar mixture used but grazing in both late March and late April resulted in a more extensive fermentation with the acids produced increasingly dominated by lactic acid. The concentrations of acetic acid, and to a lesser extent, ethanol declined as silage harvest date was delayed. Overall, the relative effects of grass cultivar mixture were smaller than those of spring‐grazing treatment or silage‐harvesting date although on any given harvest date the herbage from the intermediate‐heading cultivar mixture was easier to preserve as silage than herbage from the late‐heading cultivar mixture. Delaying the harvesting of the late‐heading swards by 8 d removed the differences related to growth stage in buffering capacity, pH and DM content.

Fotossíntese foliar do capim-xaraés [Brachiaria brizantha (A. Rich.) Stapf. cv. Xaraés] e modelagem da assimilação potencial de dosséis sob estratégias de pastejo rotativo

Objetivou-se com este trabalho quantificar a fotossíntese foliar ao longo do período de rebrotação e modelar a fotossíntese de dosséis vegetativos em função da arquitetura foliar e do ambiente luminoso em pastagens de capim-xaraés [Brachiaria brizantha (A. Rich.) Stapf.] submetidas a estratégias contrastantes de pastejo rotativo. Na fase inicial de rebrotação, o potencial fotossintético foi pequeno, em média 10,4 µmol CO2 m-2 s-1 e, no tratamento de maior intervalo de pastejo (100% IL), esse potencial foi ainda menor (3,3 µmol CO2 m-2 s-1), o que pode comprometer o desenvolvimento das plantas. No dia médio (DM) do ciclo, ocorreram os maiores valores de fotossíntese foliar, em média 26 µmol CO2 m-2 s-1. No pré-pastejo, o tratamento 95%, que apresentou os menores intervalos de pastejo (22 dias), continuou com os maiores valores de fotossíntese foliar (26,1 µmol CO2 m-2 s-1). Enquanto isso, os tratamentos com maiores intervalos de pastejo (28 e 32 dias, respectivamente para o tratamento 28 dias e 100% IL) tiveram seus valores de fotossíntese foliar reduzidos (21,3 e 24,5 µmol CO2 m-2 s-1). No tratamento de maior freqüência de pastejo (95% de IL), o menor intervalo de pastejo e a manutenção de menor IAF médio (2,08) resultaram em maior entrada de luz no interior do dossel. O manejo adequado do capim-xaraés deve ser feito com intervalos de pastejo inferiores a 28 dias, a fim de possibilitar maiores valores de fotossíntese de dossel ao longo do ciclo de rebrotação.

Site use of grazing cattle and sheep in a large-scale pasture landscape: A GPS/GIS assessment

Year-round mixed-species grazing at low densities in large-scale pasture systems has become a popular conservation concept as it is assumed to maintain the valuable biodiversity of semi-open cultural landscapes. This study aims to elucidate which vegetation types are preferentially grazed by cattle and sheep and whether the grazing animals change their preferences through the seasons so that year-round grazing leads to a utilization of all habitats. Additionally, we wanted to determine the main factors underlying the site use patterns of the animals. The study was conducted on 180 ha of a nature reserve and former military training area in northern Germany from January to October. Within this area, the positions of one cattle herd and one sheep flock were simultaneously recorded every 5 min using the global positioning system (GPS). For this purpose, we fitted one GPS collar alternately to three different cows and another to three different sheep. If the position of a collared animal had changed more than 6 m but less than 100 m within 5 min grazing was assumed based on a validation of these thresholds by direct observation. Using a geographic information system, we analysed the location data with regard to vegetation characteristics, altitude, and distance from fences, water sources, and a sheep shed. For each month, we determined Ivlev's electivity index of both herbivore species in relation to eight broad vegetation types. We used multiple linear regression to create models that describe the grazing frequencies in the grid cells of the area depending on parameters of those grid cells and their spatial position. Cattle preferred moist and productive habitats, whereas sheep preferred dry and nutrient-poor habitats. Only when feed was in extremely short supply, the animals switched to sites they had previously avoided. Differences in the spatial preferences of the two species were more marked than seasonal changes. Spatial demands of cattle and sheep were largely complementary. Grazing sites with better water availability (i.e. lower distance from the drinking trough and ponds) were significantly preferred by cattle. The sheep preferred grazing sites close to their shed. Our results show that only a combination of different herbivores guarantees that all habitats of such a large low-intensity pasture are grazed and thus are kept in a management status favourable to conservation. However, the positioning of drinking troughs, fences, and sheds should be carefully considered as these facilities seriously influence the site use of the animals.

Capim-tanzânia submetido a combinações entre intensidade e freqüência de pastejo

O objetivo deste trabalho foi avaliar as características estruturais e a produção de forragem do capim-tanzânia (Panicum maximum Jacq. cv. Tanzânia) sob condições de pastejo rotativo, em um Latossolo Vermelho distrófico, num experimento realizado em Campo Grande, MS. Os tratamentos corresponderam a combinações entre três condições de pré e duas condições de pós-pastejo, e foram alocados às unidades experimentais segundo um delineamento de blocos completos casualizados, com três repetições e arranjo fatorial 3x2. As condições de pré-pastejo de 90, 95 e 100% de interceptação de luz (IL) foram atingidas consistentemente com alturas de dossel em torno de 60, 70 e 85 cm, respectivamente. Pastejos iniciados com 90% de IL resultaram em maior número de ciclos de pastejo em relação aos iniciados com 95 e 100% de IL. O acúmulo de forragem foi maior em pastejos realizados com 95% do que com 90 ou 100% de IL, mas não houve diferença entre os tratamentos de 90 e 95% de IL para acúmulo de folhas. O acúmulo de colmos aumentou após os 95% de IL, indicando a importância da freqüência de pastejo como maneira de controlar a estrutura e a composição do dossel.

Management of Lotus corniculatus under dairy cow grazing

The effect of lax or hard dairy cow grazing (residual stubble height of 10 and 5 cm) and grazing frequency (grazing when sward height reached 35 or 20 cm) on persistence, productivity and forage quality of pure pastures of Lotus corniculatus was evaluated over two growing seasons. Keywords: Lotus corniculatus, dairy cows, grazing management

Manejo das pastagens de inverno e potencial produtivo de sistemas de integração lavoura-pecuária no Estado do Rio Grande do Sul

Para avaliar o impacto de diferentes freqüências de pastoreio bovino em pastagens anuais de inverno sobre o rendimento zootécnico e na produtividade de grãos das culturas de verão em sistemas mistos (integração lavoura-pecuária), conduziu-se um experimento a campo no município de Jari-RS. Foram avaliados três tratamentos referentes ao manejo das pastagens de inverno, a saber: sem pastoreios (SP), pastoreios a cada 28 dias (P28) e pastoreios a cada 14 dias (P14); e dois referentes às culturas de verão, sendo elas: soja e milho. A produção animal não foi afetada significativamente pela freqüência de pastoreio adotada, porém notou-se redução na produção de palhada para cobertura de solo à medida que se intensificou a utilização das pastagens. Da mesma maneira, o rendimento de grãos da soja e do milho em sucessão nestas áreas foi reduzido pelo aumento da freqüência de pastoreio. Nas áreas que não receberam pastoreios durante o inverno (SP), o rendimento de grãos de soja e milho foi de 3,2 e 7,8Mg ha-1, respectivamente. O tratamento P28 não diferiu significativamente do tratamento SP quanto ao rendimento de grãos de soja e milho, enquanto que, no tratamento P14, houve a redução no rendimento destas culturas da ordem de 0,78 e 1,29Mg ha-1, respectivamente.