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A atividade pecuária no Brasil é basicamente representada pelo sistema pastoril. No entanto as adversidades edafoclimáticas promovem uma falta de uniformidade na oferta e qualidade de forragem, acarretando na maior intensificação dos sistemas de produção. A busca por alternativas de alimentação visando à melhoria no desempenho animal, tem sido objeto de muitas pesquisas, como o uso de forrageiras adaptadas a determinadas condições ambientais. Geralmente, estas plantas podem apresentar compostos que alteram a produção animal, seja positiva ou negativamente. Dentre estes compostos, destacam-se os taninos condensados (TC) que são compostos polifenólicos oriundos do metabolismo secundário das plantas. Em concentrações elevadas (6 a 12 % da matéria seca (MS)) eles reduzem a palatabilidade, o consumo, atividade enzimática, digestibilidade de proteínas e carboidratos, e consequentemente reduzem o desempenho animal. Porém, quando esse consumo é médio ou baixo (2 a 5 % da MS), permite uma eficiência na utilização da proteína dietética, formando complexos através de ligações de hidrogênio, assim, acaba protegendo a proteína da degradação ruminal, aumentando o fluxo de aminoácidos para absorção intestinal. Além de melhorar a eficiência proteica da dieta, pode-se dizer que os TC reduzem a produção de metano, e trazem benefícios no controle de parasitas gastrintestinais, melhora o desempenho reprodutivo, desenvolvimento fetal, a resposta do sistema imunológico, as concentrações séricas de hormônio, a produção de lã e lactação. O uso de plantas com baixa concentração de taninos condensados pode ser uma boa estratégia nutricional para ruminantes, desde que seu mecanismo de ação sobre o metabolismo proteico seja considerado. Esta revisão tem como objetivo, trazer algumas respostas ao uso de TC na alimentação de ruminantes, com o foco nas alterações da fisiologia digestiva do rúmen, que se torna responsável pelas consequências secundárias dos taninos sobre a produção animal.

Tropical pasture canopy characteristics can alter lamb ingestive behavior. Our study evaluated the ingestive behavior of young lambs in different tropical pastures to identify which variables interfere in their grazing activity. Two years of study were carried out with 54 weaned lambs distributed in three different pasture canopies: 1) monoculture of an upright grass, guinea grass (Panicum maximum; GG); 2) monoculture of a shrubby legume pigeon pea (Cajanus cajan; PP) and 3) contiguous paddock with half GG and half PP (GP). The experiment was set out in a randomized complete block design (3 blocks). Lamb ingestive behavior was observed from sunrise to sunset with records every 5 minutes. To identify the main variables that affected lamb grazing activity, a multivariate analysis of the Decision Tree was performed. Our results showed that there was no difference in the ingestive behavior parameters of young lambs in different canopies (P > 0.05). There was interaction among the canopies and the experimental periods for the variables idleness time and biting rate (P ≤ 0.05). Lambs in all canopies showed more idleness time in the first evaluation period. Lambs in canopies containing grass (GG and GP) exhibited greater bites per minute throughout the experimental period. Lamb grazing time increased 40% as experimental period progressed and plants matured. The Decision Tree identified leaf:stem ratio as the variable that most influenced lamb grazing time in GG and GP canopies while in the PP, grazing time was directly related to canopy height. The behavior of young lambs on tropical pasture is variable as there is a change in the behavioral response to canopy characteristics over time. In addition, the grazing time of these animals can be estimated by means of variables related to canopy structural characteristics (leaf:stem ratio and height) together with chemical variables.

The efficiency of grazing ruminant production systems is directly associated to the animals' ingestive behavior, and to structural characteristics of the pastures. The objective of this study was to evaluate the ingestive behavior of young lambs grazing three different heights of Capim Aruana (Panicum maximum). The experiment was carried out in two consecutive years, in which 30 tester lambs (4–5 months old) were equally divided into three paddocks (treatments) corresponding to different average sward heights of Aruana grass: (1) Tall-75 cm; (2) Medium-50 cm; and (3) Short-25 cm in a randomized block design. Ingestive behavior assessments were carried out every 28 days through 10-min observations of the main activities of the animals (grazing, ruminating, idling) and biting rate, from sunrise to sunset. In addition, the productive and qualitative characteristics of the pastures were assessed. Despite differences in pasture structure, grazing time (GT) and idling time were similar among treatments (P = 0.4266 and P = 0.2939, respectively). The shortest ruminating time (RT, P = 0.0181) was recorded in the treatment of lowest sward height. Lambs grazing on this treatment also showed 23% more bites per minute (P= < 0.0001) than animals in the Tall and Medium treatments. A Decision Tree analysis was performed for GT, identifying in a hierarchical order that the initial weight of the animals and sward height explained 62% (R2 = 0.621) of the variation, representing the variables with the greatest influence on GT. Initial body weight explained 48% of the model. Thus, our research shows that the different sward heights of Capim Aruana mainly alter the lamb's RT and biting rate, and that the animals' initial body weight is a key factor influencing GT, given that this variable makes lambs more susceptible to changes in sward height.