RESUMO. O objetivo deste estudo foi avaliar o comportamento ingestivo de cordeiros em pastagem de... more RESUMO. O objetivo deste estudo foi avaliar o comportamento ingestivo de cordeiros em pastagem de Tifton-85 (Cynodon spp.) em três sistemas de produção: cordeiros desmamados aos 60 dias de idade e mantidos em pastagem; cordeiros mantidos com suas mães em pastagem; e cordeiros mantidos com suas mães em pastagem e suplementados em creep feeding. O delineamento foi em blocos ao acaso com três repetições, utilizando quatro cordeiros-teste por repetição. Na pastagem, avaliou-se a altura, a massa, a composição morfológica e bromatológica da forragem. Na avaliação do comportamento ingestivo registrou-se, do nascer ao pôr do sol, o tempo despendido nas atividades de pastejo, ruminação, ócio, amamentação e alimentação no creep feeding. Avaliou-se, também, a taxa de bocados ao pastejo. Os cordeiros permaneceram maior tempo em pastejo, e os suplementados despenderam menor (p < 0,05) tempo nessa atividade. Cordeiros nãosuplementados apresentaram maior (p < 0,05) tempo de pastejo e menores (p < 0,05) tempos de ruminação e ócio pela manhã. A suplementação em creep feeding alterou (p < 0,05) a distribuição das atividades de pastejo e ruminação, indicando efeito substitutivo de forragem pelo concentrado. Concluiu-se que os sistemas de produção influenciaram o comportamento ingestivo dos cordeiros, não tendo alterado a taxa de bocados destes. Palavras-chave: creep feeding, desmame, pastejo, ruminação, taxa de bocado, Cynodon spp.
RESUMO -Para avaliar as estratégias de alimentação de bovinos em pastejo, quatro novilhas da raça... more RESUMO -Para avaliar as estratégias de alimentação de bovinos em pastejo, quatro novilhas da raça Holandês Preto e Branco foram mantidas em uma pastage m de capim-mombaça ( Panicum maximum Jacq.) com cinco alturas de dossel, em um delineamento inteiramente casualizado, com duas repetições, durante os meses de fevereiro a abril de 2002. Os animais experimentais foram avaliados por meio de testes de pastejo de 45 minutos, durante os quais foram determinados o número de bocados, o número de estações alimentares, o número de passos e o tempo de alimentação utilizando-se cronômetros e contadores. Com o aumento da altura do dossel, o número de estações alimentares diminuiu de forma quadrática ( Ŷ = 16,3199 -0,2424 x + 0,000996 x 2 , R 2 = 0,9328, P = 0,0031), como resultado da maior disponibilidade de forragem, que reduziu a procura por melhores sítios de pastejo. O número de passos entre as estações alimentares aumentou ( Ŷ = 0,7247 + 0,01603 x, R 2 = 0,6172, P = 0,0043), ampliando a exploração do ambiente de pastejo. Quando a massa de forragem aumentou, os animais reduziram as distâncias totais percorridas ( Ŷ = 513,998287 -2,659875 x, R 2 = 0,728076, P = 0,0016), a taxa média de deslocamento ( Ŷ = 11,567445 -0,058396 x, R 2 = 0,724633, P = 0,0013) e, conseqüentemente, a intensidade de utilização da área ( Ŷ = 9,533139 -0,051351 x, R 2 = 0,7708, P = 0,0005), como resultado da elevação da altura do dossel, que garantiu elevado consumo de forragem. Os animais ajustam seus padrões de deslocamento e procura de forragem em resposta à estrutura do dossel forrageiro.
Accurate estimates of bite mass and variations in the short-term intake rate of grazing herbivore... more Accurate estimates of bite mass and variations in the short-term intake rate of grazing herbivores has been historically considered as a fundamental methodological difficulty, a difficulty that increases with the complexity of the feeding environment. Improving these methodologies will help understand foraging behaviours in natural grazing conditions, where habitat structure and interactions among different forages influence feeding decisions and patterns. During the past 30 years, we have been developing the 'continuous bite-monitoring' method, an observational method that allows continuous assessment of foraging behaviours, including bite mass, instantaneous intake rate and food selection, in simple to complex feeding environments. The centrepiece of the method is a 'bite-coding grid' where bites are categorised by structural attributes of the forage to reflect differences in bite masses. Over the years, we have been using this method with goats, sheep, llamas and cattle across a range of different habitats. After reviewing the development of the method, we detail its planning and execution in the field. We illustrate the method with a study from southern Brazilian native Pampa grassland, showing how changes in the forages consumed by heifers strongly affect short-term intake rate during meals. Finally, we emphasise the importance of studying animals grazing in their natural environments to first identify the relevant processes that can later be tested in controlled experiments.
Despite all the biotic and abiotic factors affecting foraging by ruminants, there is a common and... more Despite all the biotic and abiotic factors affecting foraging by ruminants, there is a common and fundamental process, which is bite gathering. We hypothesised that because the mechanics of bite formation dominate the foraging process, changes in short-term bite mass are reflected in longer-term animal performance across a wide range of sward conditions. We focus at the meal level of foraging, using experiments in which the effect of abiotic factors and digestive constrains are minimised, making intake rate the main currency. We estimated bite mass across a wide range of structural challenges to large-herbivore foraging in a long-term experiment with heterogeneous native grasslands. A conceptual model was developed for average daily gain, where energy gain and energy costs were proximate causal variables. Energy gain was a function of diet quality and components of daily intake rate, where bite mass was the main component estimated. In turn, components of intake rate were determined by sward structure and bodyweight. Energy costs were a function of bodyweight and abiotic conditions. Finally, sward structure, bodyweight and abiotic conditions were determined by experimental treatments, seasons and years. Then, the conceptual model was translated into statistical models that included variables measured or estimated, and coefficients representing all links in the conceptual model. Weight gain was a function of bite mass, forage characteristics, and animal and abiotic conditions. Models were set up to test whether forage and stocking conditions affected monthly gain beyond the effects through bite mass, after correcting for abiotic factors. Forage mass, height and disappearance did help predict monthly gain after bite mass was included in the model, which supported our hypothesis. However, stocking treatments and season had significant effects not incorporated in bite mass. Although the model explained 77.9% of liveweight gain variation, only 35.2% was due to fixed effects, with 10.8% accounted by bite mass and its interactions. Concomitant experiments showed that sward structure (first with sward height and the second with tussock cover) does determine bite mass and short-term intake rate in the complex native grasslands we studied. Yet, other temporal varying components of monthly gain not correlated with bite mass, temperature or wind, added most of the observed variation in monthly animal performance. Part of the model failure to account for variation in performance may be related to a significant and temporally variable grazing of tussocks. We used a bite mass model that assumed no tussock grazing. In light of these results and a parallel experiment, we conclude that tussock grazing must be incorporated in future versions of the model.
RESUMO. O objetivo deste estudo foi avaliar o comportamento ingestivo de cordeiros em pastagem de... more RESUMO. O objetivo deste estudo foi avaliar o comportamento ingestivo de cordeiros em pastagem de Tifton-85 (Cynodon spp.) em três sistemas de produção: cordeiros desmamados aos 60 dias de idade e mantidos em pastagem; cordeiros mantidos com suas mães em pastagem; e cordeiros mantidos com suas mães em pastagem e suplementados em creep feeding. O delineamento foi em blocos ao acaso com três repetições, utilizando quatro cordeiros-teste por repetição. Na pastagem, avaliou-se a altura, a massa, a composição morfológica e bromatológica da forragem. Na avaliação do comportamento ingestivo registrou-se, do nascer ao pôr do sol, o tempo despendido nas atividades de pastejo, ruminação, ócio, amamentação e alimentação no creep feeding. Avaliou-se, também, a taxa de bocados ao pastejo. Os cordeiros permaneceram maior tempo em pastejo, e os suplementados despenderam menor (p < 0,05) tempo nessa atividade. Cordeiros nãosuplementados apresentaram maior (p < 0,05) tempo de pastejo e menores (p < 0,05) tempos de ruminação e ócio pela manhã. A suplementação em creep feeding alterou (p < 0,05) a distribuição das atividades de pastejo e ruminação, indicando efeito substitutivo de forragem pelo concentrado. Concluiu-se que os sistemas de produção influenciaram o comportamento ingestivo dos cordeiros, não tendo alterado a taxa de bocados destes. Palavras-chave: creep feeding, desmame, pastejo, ruminação, taxa de bocado, Cynodon spp.
RESUMO -Para avaliar as estratégias de alimentação de bovinos em pastejo, quatro novilhas da raça... more RESUMO -Para avaliar as estratégias de alimentação de bovinos em pastejo, quatro novilhas da raça Holandês Preto e Branco foram mantidas em uma pastage m de capim-mombaça ( Panicum maximum Jacq.) com cinco alturas de dossel, em um delineamento inteiramente casualizado, com duas repetições, durante os meses de fevereiro a abril de 2002. Os animais experimentais foram avaliados por meio de testes de pastejo de 45 minutos, durante os quais foram determinados o número de bocados, o número de estações alimentares, o número de passos e o tempo de alimentação utilizando-se cronômetros e contadores. Com o aumento da altura do dossel, o número de estações alimentares diminuiu de forma quadrática ( Ŷ = 16,3199 -0,2424 x + 0,000996 x 2 , R 2 = 0,9328, P = 0,0031), como resultado da maior disponibilidade de forragem, que reduziu a procura por melhores sítios de pastejo. O número de passos entre as estações alimentares aumentou ( Ŷ = 0,7247 + 0,01603 x, R 2 = 0,6172, P = 0,0043), ampliando a exploração do ambiente de pastejo. Quando a massa de forragem aumentou, os animais reduziram as distâncias totais percorridas ( Ŷ = 513,998287 -2,659875 x, R 2 = 0,728076, P = 0,0016), a taxa média de deslocamento ( Ŷ = 11,567445 -0,058396 x, R 2 = 0,724633, P = 0,0013) e, conseqüentemente, a intensidade de utilização da área ( Ŷ = 9,533139 -0,051351 x, R 2 = 0,7708, P = 0,0005), como resultado da elevação da altura do dossel, que garantiu elevado consumo de forragem. Os animais ajustam seus padrões de deslocamento e procura de forragem em resposta à estrutura do dossel forrageiro.
Accurate estimates of bite mass and variations in the short-term intake rate of grazing herbivore... more Accurate estimates of bite mass and variations in the short-term intake rate of grazing herbivores has been historically considered as a fundamental methodological difficulty, a difficulty that increases with the complexity of the feeding environment. Improving these methodologies will help understand foraging behaviours in natural grazing conditions, where habitat structure and interactions among different forages influence feeding decisions and patterns. During the past 30 years, we have been developing the 'continuous bite-monitoring' method, an observational method that allows continuous assessment of foraging behaviours, including bite mass, instantaneous intake rate and food selection, in simple to complex feeding environments. The centrepiece of the method is a 'bite-coding grid' where bites are categorised by structural attributes of the forage to reflect differences in bite masses. Over the years, we have been using this method with goats, sheep, llamas and cattle across a range of different habitats. After reviewing the development of the method, we detail its planning and execution in the field. We illustrate the method with a study from southern Brazilian native Pampa grassland, showing how changes in the forages consumed by heifers strongly affect short-term intake rate during meals. Finally, we emphasise the importance of studying animals grazing in their natural environments to first identify the relevant processes that can later be tested in controlled experiments.
Despite all the biotic and abiotic factors affecting foraging by ruminants, there is a common and... more Despite all the biotic and abiotic factors affecting foraging by ruminants, there is a common and fundamental process, which is bite gathering. We hypothesised that because the mechanics of bite formation dominate the foraging process, changes in short-term bite mass are reflected in longer-term animal performance across a wide range of sward conditions. We focus at the meal level of foraging, using experiments in which the effect of abiotic factors and digestive constrains are minimised, making intake rate the main currency. We estimated bite mass across a wide range of structural challenges to large-herbivore foraging in a long-term experiment with heterogeneous native grasslands. A conceptual model was developed for average daily gain, where energy gain and energy costs were proximate causal variables. Energy gain was a function of diet quality and components of daily intake rate, where bite mass was the main component estimated. In turn, components of intake rate were determined by sward structure and bodyweight. Energy costs were a function of bodyweight and abiotic conditions. Finally, sward structure, bodyweight and abiotic conditions were determined by experimental treatments, seasons and years. Then, the conceptual model was translated into statistical models that included variables measured or estimated, and coefficients representing all links in the conceptual model. Weight gain was a function of bite mass, forage characteristics, and animal and abiotic conditions. Models were set up to test whether forage and stocking conditions affected monthly gain beyond the effects through bite mass, after correcting for abiotic factors. Forage mass, height and disappearance did help predict monthly gain after bite mass was included in the model, which supported our hypothesis. However, stocking treatments and season had significant effects not incorporated in bite mass. Although the model explained 77.9% of liveweight gain variation, only 35.2% was due to fixed effects, with 10.8% accounted by bite mass and its interactions. Concomitant experiments showed that sward structure (first with sward height and the second with tussock cover) does determine bite mass and short-term intake rate in the complex native grasslands we studied. Yet, other temporal varying components of monthly gain not correlated with bite mass, temperature or wind, added most of the observed variation in monthly animal performance. Part of the model failure to account for variation in performance may be related to a significant and temporally variable grazing of tussocks. We used a bite mass model that assumed no tussock grazing. In light of these results and a parallel experiment, we conclude that tussock grazing must be incorporated in future versions of the model.
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