Effect of narasin inclusion on in vitro fermentation parameters and methane production in different diets used for feedlot cattle

• Grant number: 25/17229-8
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: November 01, 2025
• End date: July 31, 2026
• Field of knowledge: Agronomical Sciences - Animal Husbandry - Animal Nutrition and Feeding
• Principal Investigator: Daniel Montanher Polizel
• Grantee: Emanuele Dias de Souza
• Host Institution: Faculdade de Engenharia (FEIS). Universidade Estadual Paulista (UNESP). Campus de Ilha Solteira. Ilha Solteira , SP, Brazil

Abstract

Current livestock production requires highly efficient systems, especially in the face of increasing competition with other agricultural crops and the growing demand for sustainability. High-concentrate diets are commonly used in intensive systems due to their ability to enhance animal performance, and their effectiveness can be further improved through the use of additives such as ionophores. Narasin is an ionophore with the potential to modulate the ruminal environment by increasing propionate production, reducing methane emissions, and improving energy utilization efficiency. This study aims to evaluate the effects of including 13 mg of narasin per kg of dry matter (DM) on ruminal fermentation parameters, total gas production, methane production, and in vitro digestibility using different high-concentrate diets. The experiment will be conducted using ANKOM gas pressure modules (ANKOM RF Gas Production System). Rumen fluid will be collected from two rumen-cannulated Nelore steers. The gas pressure modules will be randomly assigned to treatments. For each bottle, three grams of sample (on a DM basis), 140 mL of artificial saliva (McDougall's buffer), and 10 mL of rumen fluid will be used. A 2 × 4 factorial arrangement will be used, with factor 1 being the inclusion or not of 13 mg of narasin/kg of dietary DM, and factor 2 being different high-concentrate diets commonly used in Brazilian feedlot systems. The diets will be characterized as follows: (1) high inclusion of ground corn (high starch); (2) inclusion of citrus pulp (pectin source); (3) high inclusion of DDGS; and (4) diet with high fat content (cottonseed). Two analysis rounds will be conducted. In each round, four bottles per treatment (replicates) will be prepared, with half using inoculum from steer A and the other half from steer B (to account for animal variation). Gas pressure readings will be continuously monitored every 15 minutes. After bottle opening, final pH of the fluid will be measured, and two 10 mL aliquots will be collected from each bottle for analysis of short-chain fatty acids and ammonia nitrogen. The remaining residue in the bottles will be dried at 55°C and subsequently washed with neutral detergent. The residue will be quantified to assess in vitro dry matter digestibility. The experimental design will follow a randomized complete block design, with the block defined by the analysis round and the donor animal. Data will be analyzed using the MIXED procedure of SAS 9.4. Effects will be considered significant at P ¿ 0.05 and trends at 0.05 < P ¿ 0.10.