Effects of essential oils alone or in combination with monensin on nutrient flow and digestibility, and in situ and in vitro ruminal parameters of beef cattle

• Grant number: 25/16442-0
• Support Opportunities: Scholarships abroad - Research Internship - Scientific Initiation
• Start date: December 08, 2025
• End date: April 07, 2026
• Field of knowledge: Agronomical Sciences - Animal Husbandry - Animal Nutrition and Feeding
• Principal Investigator: Paulo Roberto Leme
• Grantee: Maria Eduarda Ramos
• Supervisor: Ana Clara Baiao Menezes
• Host Institution: Faculdade de Zootecnia e Engenharia de Alimentos (FZEA). Universidade de São Paulo (USP). Pirassununga , SP, Brazil
• Institution abroad: South Dakota State University, United States
• Associated to the scholarship: 24/16780-0 - Effect of guanidinoacetic acid supplementation in the growing and finishing phase on the metabolomic profile of Nelore bulls, BP.IC

Abstract

High-concentrate diets offer significant benefits for beef cattle, especially when ingredient costs are favorable. However, excessive starch and low physically effective fiber may lead to the accumulation of volatile fatty acids and lactate in the rumen, causing disorders such as ruminal acidosis. Monensin, a widely used ionophore, improves feed efficiency by modulating the ruminal microbiota, but its use as a growth promoter has raised concerns due to potential bacterial resistance. In this context, phytogenic compounds, such as essential oils, have emerged as natural alternatives with the potential to enhance ruminal fermentation, reduce metabolic diseases, and improve animal performance. This study will evaluate the effects of essential oils, alone or in combination with monensin, on intake, digestion, ruminal metabolism, and diet degradability, using Red Angus steers fitted with ruminal, duodenal, and ileal cannulas in a 4×4 Latin square design with a 2×2 factorial arrangement. The essential oil treatment will be provided as a proprietary commercial blend primarily based on cinnamon (Cinnamomum spp.) and other plant extracts, whose exact formulation cannot be disclosed due to confidentiality agreements, but with characteristics comparable to marketavailable products. Evaluations will include in vivo, in situ, and in vitro trials, such as digestibility assays, ruminal acidosis challenge, and measurements of pH, VFA, and lactate. The findings are expected to provide valuable insights for the development of nutritional strategies that combine productive efficiency and sustainability in beef cattle production.