<p><strong>Background.</strong> The productive variability of the forage is determined by the type of soil and the cultivation system. The use of silvopastoral systems represents an alternative because they can increase forage production and quality. <strong>Objective.</strong> To evaluate the production, the morphological components and the nutritional quality of the biomass of <em>Cynodon plectostachyus</em> (star grass) alone or in association with <em>Leucaena leucocephala</em> (huaxin). <strong>Methodology.</strong> The study was carried out in Tizimin, Yucatan, Mexico. Plots of <em>C. plectostachyus</em> were established in alleys croping of <em>L. leucocephala</em> and in monoculture, in hyperskeletal Luvisols and Leptosols soils. A 2 X 2 factorial design with five repetitions per treatment was used. The biomass production, the forage components and the content of crude protein and neutral detergent fiber were evaluated for one year. <strong>Results.</strong> Forage production, leaf and forage quality did not change according to the cultivation system (p≥0.05). No effect is believed due to the type of soil (p≥0.05). The interaction of the cultivation system with the type of soil increased the NDF content of <em>C. plectostachyus</em> (p≤0.05). <strong>Implications.</strong> The association of <em>C. plectostachyus</em> and <em>L. leucocephala</em> could increase the availability of structural carbohydrates for ruminant nutrition. Likewise, it is essential to consider long-term evaluations that allow to know the improvements in the crude protein content and the biomass production of the grasses in association under silvopastoral systems. <strong>Conclusions.</strong> The association of <em>C. plectostachyus</em> with <em>L. leucocephala</em> in Leptosol soil increases the availability of structural carbohydrates by increasing the stem and dead tissue that can be incorporated as organic matter in the soil.</p>
Palabras clave: acuacultura, insecticidas, peces, CL50, dengue, ecotoxicología RESUMENLa tilapia Oreochromis niloticus es una especie de importancia en acuacultura con un desarrollo promisorio en la península de Yucatán. La bifentrina y la deltametrina son dos piretroides ampliamente utilizados por el sector salud en Yucatán para el control del mosquito Aedes aegypti, vector del dengue. Se evaluó la toxicidad aguda diferencial de Talstar® (sustancia activa, bifentrina) y Biothrine® (principio activo, deltametrina), en juveniles de tilapia O. niloticus. Se usaron ocho concentraciones de Talstar® (2.5 -400 µg/L) y ocho concentraciones de Biothrine® (0.56 -112 µg/L), más un testigo sin insecticida y tres repeticiones por tratamiento. Los signos de toxicidad en los peces bajo la influencia de ambos insecticidas fueron: nadadas erráticas, desbalance e hiperventilación, aunque resultaron más evidentes y en un menor tiempo de aparición, en las concentraciones más altas. El análisis probit reveló que la concentración letal media (CL50) de Talstar® fue de 75.11 µg/L a las 96 horas con intervalos de confianza (95 %) de 58.76 (inferior) y 96.34 (superior) µg/L. La CL50 de Biothrine® fue de 28.36 µg/L a las 96 horas, con intervalos de 23.29 y 35.27 µg/L. Estos valores son considerados como extremadamente tóxicos y alertan por el efecto contaminante potencial que podrían producir en ambientes naturales y de acuacultura. Es necesario continuar con la evaluación de los mecanismos de toxicidad de insecticidas que son utilizados en el sector salud para especies de importancia acuícola en México. Lo anterior por la perspectiva de continuar con su empleo y por el desarrollo del sector en la península de Yucatán.Key words: aquaculture, insecticides, fishes, LC50, dengue, ecotoxicology ABSTRACT Tilapia, Oreochromis niloticus is an aquacultural important species and both, bifenthrin and deltamethrin are two synthetic pyrethroids used by Health Services in Yucatán to control Aedes aegypti mosquito, dengue's vector. Differential acute toxicity of Talstar® Rev. Int.
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