Igor Justin Carassai

Relações planta-animal em ambiente pastoril heterogêneo: processo de ingestão de forragem

Com o objetivo de avaliar o efeito da estrutura de uma pastagem nativa nos parâmetros que compoem o processo de ingestao de forragem de ovelhas e bezerras em pastejo, foram estabelecidas quatro alturas de pasto (4, 8, 12 e 16 cm), em delineamento estatistico inteiramente casualizado, com quatro tratamentos e duas repeticoes no tempo e no espaco. A massa do bocado e a taxa de ingestao foram estimados por diferenca de peso vivo corrigido para a perda de peso metabolico, durante 45 minutos. Os movimentos mandibulares de apreensao e mastigacao foram registrados pelo aparelho IGER Behaviour Recorder. A profundidade do bocado foi obtida em 40 perfilhos marcados por unidade experimental, em medicoes realizadas antes e apos o pastejo. Observou-se correlacao positiva entre a altura do pasto e a massa de forragem, e negativa com a densidade de forragem. A profundidade de bocados apresentou relacao linear e positiva com o aumento da altura do pasto e nao diferiu entre especies animais. Acima de 9,5 cm de altura do pasto, a profundidade do bocado das ovelhas nao compensou a pouca densidade de forragem nos estratos mais superiores, o que reduziu a massa do bocado. A mesma resposta foi observada a partir da altura do pasto de 11,4 cm para as bezerras. Com o aumento da massa do bocado, houve diminuicao na taxa de bocados e aumento na taxa de mastigacao. A taxa de ingestao foi maior nas alturas em que a massa de bocados foi tambem superior, o que evidencia a correlacao positiva entre as duas variaveis. Nessas condicoes, para aumentar o consumo de ovelhas e bezerras em campo nativo, a estrutura ideal de manejo requer manutencao de altura do pasto entre 9,5 e 11,4 cm, respectivamente.

Estratégias de manejo da oferta de forragem para recria de novilhas em pastagem natural

O experimento foi realizado com o objetivo de avaliar o desenvolvimento de novilhas de corte dos 15 aos 28 meses de idade mantidas em pastagem natural sob diversos manejos da oferta de forragem. Avaliaram-se quatro ofertas fixas ao longo do ano (4, 8; 12 e 16% do peso vivo, PV) e tres ofertas de forragem variaveis (8-12; 12-8; e 16-12%, de modo que o primeiro valor corresponde a oferta utilizada na primavera e o segundo aquela empregada no restante do ano). Foram utilizadas novilhas de corte mesticas sob pastejo continuo com taxa de lotacao variavel para avaliacao do peso vivo, do escore de condicao corporal, do ganho medio diario e da aptidao reprodutiva pela dosagem de progesterona no sangue. Para caracterizacao do pasto, foram avaliadas a massa de forragem (MF), a altura do pasto (ALT) e a area efetivamente pastejada (AEP). Na oferta de forragem de 4%, os animais apresentaram reducao acentuada de peso no fim do verao e outono, por isso, essa oferta de forragem foi eliminada. O peso vivo, o escore de condicao corporal e o ganho medio diario nao diferiram entre as ofertas de forragem; as variacoes ocorreram somente entre as estacoes. Aos 26 meses de idade, a probabilidade de estro das novilhas nao diferiu entre as ofertas de forragem, embora a oferta de forragem de 16-12% tenha resultado em probabilidade de estro de 50%. Aos 28 meses de idade, a oferta de forragem de 16-12% resultou em maior probabilidade de estro (86%) e nao diferiu das ofertas de 16% (50%) e 8-12% (50%), as quais promoveram estrutura do pasto mais adequada, ou menos limitante, ao habito de pastejo das novilhas.

Eficiência bioeconômica da adubação de pastagem natural no sul do Brasil

O objetivo deste trabalho foi avaliar as producoes vegetal e animal e a resposta economica de uma pastagem natural submetida a adubacao de correcao e doses de nitrogenio durante a estacao de crescimento 1998/99. O experimento foi conduzido em area da Estacao Experimental Agronomica da Universidade Federal do Rio Grande do Sul (EEA - UFRGS). Em 1996 foram aplicados 3000kg ha-1 de calcario e adubacao correspondente a 500kg ha-1 da formula 5-20-20. Na analise economica, considerou-se um terco destas quantidades como referente a utilizacao na estacao de crescimento 1998/99. Os tratamentos foram doses de nitrogenio (N) na forma de ureia (zero, 100 e 200kg ha-1 de N), em um delineamento de blocos ao acaso com duas repeticoes de area por tratamento. Os animais experimentais foram novilhas de corte com um ano de idade e peso medio inicial de 160kg. A massa de forragem, a taxa de acumulo diario de materia seca, a producao total de materia seca verde e a eficiencia de transformacao do N em producao primaria foram maiores (P<0,1) quanto maior foi a dose de N aplicado. As aplicacoes de 100 e 200kg ha-1 de N elevaram os custos em 104,1 e 208,2%, respectivamente. A aplicacao de 200kg ha-1 de N em pastagem natural apresentou maior producao de peso vivo, margem bruta e eficiencia de conversao do N em produto animal. Quando foram utilizados apenas o calcario e a adubacao N-P-K de correcao, obteve-se o maior retorno financeiro direto. A pastagem natural mostrou resposta positiva a aplicacao de fertilizantes, dentro da amplitude de quantidade destes insumos aplicadas no presente trabalho.

Forage yield and nitrogen nutrition dynamics of warm-season native forage genotypes under two shading levels and in full sunlight

The successful achievement of a highly productive understorey pasture in silvopastoral systems depends on the use of well-adapted forage genotypes, showing good agronomic performance and persistence under shading and grazing. In this study, the herbage dry matter yield (DMY) and nitrogen nutrition dynamics were determined in three native warm-season grasses (Paspalum regnellii, Paspalum dilatatum and Paspalum notatum) and a forage legume (Arachis pintoi) under two shading levels compared with full sun. The experiment was conducted in the Campanha region, Bage, state of Rio Grande do Sul, Brazil, during two evaluation cycles (2008/2009 and 2009/2010). Three shade cloth levels (0%, 50% and 80% of light restriction) were applied to the forage genotypes in a split plot design, in which shading levels were the main plot and forage genotypes were the subplots, with three replications. P. regnellii showed the highest accumulated DMY (1500 and 1700 g m-2, respectively, for the first and second evaluation cycles) at all shading levels and showed no DMY decreased under the heavy shade (80%). Average DMY over the four genotypes under the 50% shade level was higher or equal compared with full sun. Influence of rainfall was observed on the DMY performance of all genotypes: the positive effect of moderate shading (50%) on P. dilatatum and P. notatum DMY was associated to a low soil water availability status. Increased shading level resulted in high nitrogen nutrition index values on grasses, in comparison with full sun. All genotypes performed well under the moderate shading level, but the DMY of both P. regnellii and P. dilatatum and the herbage N content in P. notatum and A. pintoi of all genotypes stood out, showing that those main genotypes are promising to grow in silvopastoral systems at the Campanha region in southern Brazil.

Impact of nitrogen fertilization on the forage characteristics and beef calf performance on native pasture overseeded with ryegrass

The overseeding of ryegrass (Lolium multiflorum Lam) on sub-tropical native pastures increases the availability and quality of forage in the cold season. However, soil chemical amendment and nitrogen use can affect the floristic composition, with consequences to the primary and secondary production. In a randomized complete block design with three replications, the effect of nitrogen fertilization (40, 90 and 140 kg/ha of nitrogen) on native pasture overseeded with ryegrass in two consecutive years was assessed regarding production and composition of pasture and performance of beef calves. In both years, the forage accumulation rate and forage production responded linearly to the increase in nitrogen rates as a result of increased participation of ryegrass. The lower efficiency of responses in 2008 was due to the increased participation of dead material and the reduction of ryegrass in the forage sward. In 2007 there was an increasing substitution of the participation of native grasses by ryegrass with increasing nitrogen rates. Native legumes and other species were almost not affected by nitrogen fertilization. The average daily weight gain of the animals responded linearly to nitrogen rates in 2007, and quadratically in 2008. The stocking rate and gain per hectare increased linearly in both years, with greater responses in 2007. The production and composition of forage and livestock production are improved by the use of nitrogen, but the efficiency of responses can be affected by sowing date and nitrogen fertilization.

Fertilization and oversowing on natural grassland : effects on pasture characteristics and yearling steers performance

The objective of this study was to evaluate the vegetal and animal production of a natural pasture on a Mollisol soil in the region of Campanha, in RS. The experimental design consisted of complete randomized blocks with three replicates, which enables the comparison between natural unfertilized pastures with fertilized pastures and pastures fertilized and overseeded with Lolium multiflorum, Lotus corniculatus cv. Sao Gabriel and Trifolium repens cv. Lucero (NPO). Data were submitted to the analyses of variance considering seasons of the year as time repeated measurements. Aberddeen Angus calves of about nine months of age were used in continuous stocking with variable stocking rate in order to maintain forage offer at 13% of live weight. Data were collected between July 7th (2007) and May 3rd (2008), totaling 302 days. Fertilized and oversown pastures showed higher green forage mass mainly in the spring, as result of higher dry matter (DM) accumulation rate. Average daily live-weight gain for fertilized pasture (0.581 kg/day) was higher than for natural pasture (0.473 kg/day). Higher live-weight gains were obtained in the fall (0.869 kg/day). Stocking rate showed interaction with the seasons of the year, with higher stocking rates obtained in oversown pasture (701 kg of LW/ha) and fertilized pasture (667 kg of LW/ha) during the spring. Live-weight gain per hectare from natural pasture (224 kg LW/ha) was lower than on fertilized (310 kg LW/ha) and over-sown pasture (287 kg LW/ha). Forage mass, dry matter content, forage allowance and pasture height explained 61% of the average live weight gain. Despite the good performance of native grasslands in this region in its natural condition, the utilization of different inputs as fertilization and oversowing of winter cultivated species promoted positive differences in forage production and its distribution along the year and in animal yield.

Recria de cordeiras em pastagem nativa melhorada submetida à fertilização nitrogenada: 1. Dinâmica da pastagem

It was evaluated the effect of nitrogen fertilization (100 and 200 kg/ha of N as urea) on the components of forage production of an improved native pasture with 3.12 ha (paddocks - 0.52 ha). Control areas without application of N were used, using a complete block design with two replications. Paddocks were grazed by lambs in a continuous stocking and variable stocking rate to keep forage allowance of 16% LW. In spring of 2004, pasture was uniformly fertilized with 250 kg/ha of 5-20-20 and N doses were applied during experimental period (summer 2005). Total forage on offer and rate of forage disappearance were not affected by treatments nor the periods of evaluation. Total herbage mass diminished significantly with time and was affected by N doses as function of the accumulation verified prior to the experimental period. All other studied variables showed no significant effect of N due to water deficit. There was no herbage accumulation during the first part of experimental period and accumulation rate only became positive in the last half period. As consequence, herbage height and herbage mass diminished significantly with time. Green forage mass showed inverse behaviour in relation to dead material percentage. The quadratic response of this later component was initially characterized by high values that diminished by the final period with the reestablishment of normal rainfall. By this reason, the green forage allowance was very low and interacted in time with N doses. Volumetric density presented low values when compared to values previously observed in this kind of pasture. However, a tendency for higher values was verified at the end of the observations period. The herbage height and herbage mass presented high correlation (r = 0.87) indicating that herbage height can be a good estimator of herbage mass, in these conditions. In the situation of water deficit, nitrogen fertilization does not contribute to the expression of more intense responses of the studied variables.

Floristic and vegetation structure of a grassland plant community on shallow basalt in southern Brazil

Few studies have adequately described the floristic and structural features of natural grasslands associated with shallow basalt soils in southern Brazil. This study was carried out on natural grazing land used for livestock production in the municipality of Santana do Livramento, in the Campanha region of the state of Rio Grande do Sul, Brazil. The aim of the study was to describe the floristic and structural diversity of the area. The floristic list obtained comprises 229 plant taxa from 40 botanical families, with a predominance of the families Poaceae (62), Asteraceae (28), Fabaceae (16) and Cyperaceae (12). The estimated diversity and evenness in the community were 3.00 and 0.874, respectively. Bare soil and rock outcrops accounted for 19.3% of the area, resulting in limited forage availability. Multivariate analysis revealed two well-defined groups among the sampling units. One group showed a high degree of internal aggregation, associated with deep soils, and was characterized by the presence of tussocks, whereas the other was less aggregate and was characterized by prostrate species growing on shallow soil. Ordination analysis indicated a gradient of moisture and of soil depth in the study area, resulting in different vegetation patterns. These patterns were analogous to the vegetation physiognomies described for Uruguayan grasslands. Overall, the grassland community studied is similar to others found throughout southern Brazil, although it harbors more winter forage species. In addition, the rare grass Paspalum indecorum Mez is locally dominant in some patches, behaving similarly to P. notatum Fl., a widespread grass that dominates extensive grassland areas in southern Brazil.

Atributos físicos do solo sob intensidades de pastejo e métodos de pastoreio com cordeiros em integração lavoura‑pecuária

The objective of this work was to evaluate possible alterations in the soil bulk density and total porosity due to lamb trampling, under different grazing management after no-tillage summer crop. The experiment was carried out in the layers 0-2.5, 2.5-5 e 5-10 cm of an arenic Ultisol, in an annual ryegrass pasture with forage allowance of 2.5 and 5.0 of animal potential consumption, under continuous and rotational stocking. An ungrazed area was used as check. Grazing intensities and methods did not affect soil bulk density and total porosity. It is possible to use areas with this kind of soil texture, with cover crops for lamb grazing in the winter, without alterations on soil physical attributes, caused by animal trampling, reach harmful levels for subsequent crops.

Carcass characteristics and meat quality of Aberdeen Angus steers finished on different pastures

The present study was conducted to assess carcass features, physicochemical and sensory parameters of meat from steers finished on three types of pastures: natural pasture; natural pasture improved, fertilized and oversown with winter species; and annual summer grassland. The experiment was conducted from December 14, 2009 to November 30, 2010, with treatments distributed in a completely randomized design with a different number of replicates. Animals were used as experimental units. Experimental animals were Aberdeen Angus steers with twenty months of initial age and 354±27.4 kg of live weight, on average. The highest average daily gains were obtained for the annual summer grassland. There was no effect of treatments on carcass conformation. The highest carcass yield was obtained on the improved natural pasture. Forequarter yield, side cut yield and longissimus muscle area were similar between the pastures. Moisture and total lipids were not affected by the pasture. Thawing and cooking losses were higher in improved natural pasture and lower in sorghum pasture. Regardless of the treatment, the meat had luminosity ranging from intermediate to dark, high in red, high in yellow, and considered within the normal range for beef. Meat of higher shear force was found in natural pasture, and lower shear force was observed in meat from annual summer grassland. Average live weight daily gain explained 18% of the shear force. Sensory evaluation by duo-trio test showed differences between samples from distinct pastures in flavor. All the studied systems allow for desirable characteristics in carcass and meat.