Association of tropical forage grasses in pastures: interactions between sward characteristics and grazing animals

• Autor(a) principal: Otaviano, Emanoella Karol Saraiva
• Data de Publicação: 2023
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/11/11139/tde-04012024-102025/
• topic: In vitro fermentation; Comportamento ingestivo; Estrutura do dossel; Fermentação in vitro; Ingestive behavior; Multispecific pastures; Nutritive value; Pastagens multiespecíficas; Sward structure; Valor nutritivo

Increasing forage plant diversity in pastures through simultaneous cultivation of forage grasses with complementary characteristics can result in more efficient use of resources, making the system more resilient and sustainable. Although there are several studies focusing on mixtures of forage species from temperate climate, annual species, or mixtures of grasses with legumes, there is little information in the literature regarding mixtures of tropical forage grasses. The general hypothesis of the study was that the association of tropical forage grasses with different functional characteristics generates spatial and temporal complementarity in the exploitation of resources, resulting in improved nutritional value of the forage throughout the year and better distribution of leaves along the vertical profile of the canopy, resulting in greater rates of herbage intake and nutrients. The general objective was to identify and to describe changes in canopy structure of three tropical perennial forage grass species cultivated in monoculture and in association. In addition, to understand the interactions between pasture characteristics and grazing animals, aiming at identifying characteristics of mixtures that can provide increased nutritional value and forage consumption. The experiment was conducted in Piracicaba, SP, Brazil, from December/2020 to March/2022. Treatments corresponded to three tropical forage grasses: Andropogon gayanus cv. Planaltina (Andropogon gambagrass), Panicum maximum cv. Massai (Massai guineagrass) and Brachiaria brizantha cv. BRS Piatã (Piatã palisadegrass) cultivated in monoculture and in association (based on the same proportion of viable pure seeds). Defoliation management was common to all treatments, corresponding to 35 cm pre-cut height and 17.5 cm post-cut height. The results indicated that the association was mainly comprised of Massai guineagrass throughout the experimental period. However, the proportion of species in the mixture was dynamic and varied throughout the seasons. These variations influenced the botanical composition and the vertical distribution of morphological components of the herbage mass, which shaped the ingestive behavior of the grazing animals. Andropogon gambagrass had the smallest herbage bulk density throughout the year and greater presence of weeds, which resulted in smaller rates of herbage intake. However, this treatment presented the greatest content of crude protein throughout the experiment. Differences in chemical composition among treatments throughout seasons of the year influenced differences in in vitro incubation variables, such as methane production, kinetics, and parameters of ruminal fermentation. Although the association did not present greater nutritional value or reduction in methane emissions, other parameters were superior, such as the concentration of ammonia nitrogen and in vitro degradability of dry matter and neutral detergent fiber. In conclusion, the association showed similar or superior results to the best monocultures for the studied variables, which reveals promising results for the use of association of tropical forage grasses. This represents an opportunity to enhance ecosystem services provided by pastures by increasing the number of species in the area.