Reducing Methane Emissions using Unconventional Feed Ingredients and Bioactive Compounds in the Diet: In Vitro Studies

The growing human population is increasing the demand for food, particularly animal-based products like meat and milk, leading to a need for more livestock production. This growth creates competition for feed resources and farmland, putting additional pressure on the environment. A major environmental issue from livestock, especially cattle and sheep, is the emission of methane, which significantly contributes to climate change. At the same time, increased human populations are producing more agro-industrial waste, posing further environmental risks. Using these agro-industrial by-products, which contain beneficial bioactive compounds, as animal’s feed could offers a practical way to reduce methane emissions from ruminants, lessen competition for human food resources, and lower environmental pollution from waste disposal. This thesis investigates innovative dietary strategies specifically aimed at reducing methane emissions from ruminants through dietary modifications, the use of feed additives and advanced feeding technologies. The first study was based on a review that we published earlier, which explored the potential of various fruits and vegetable by-products as alternative feed sources for ruminants. Through this review, we identified a gap in the literature concerning the use of mango and avocado by-products. Given their high bioactive compounds, such as phenolic compounds, we decided to investigate these by-products as potential feed ingredients and feed additives for ruminants. In this study, we examined mango and avocado by-products as feed ingredients and supplements through two experiments. The first experiment evaluated the nutritional composition, in vitro dry matter digestibility, and fermentation characteristics to assess their suitability as ruminant feed. The second experiment tested the effects of micro encapsulated phenolic extracts from these by-products, assessing their potential to optimize rumen function and reduce methane emissions. Results indicated that mango peel, mango seed kernel, and avocado seed were particularly promising due to their high digestibility and fermentation efficiency. Furthermore, microencapsulated fruit peel by-products showed potential as feed supplements for reducing in vitro methane production. The third study assessed the effects of L-Carvone, an essential oil active compound, on rumen fermentation, dry matter digestibility, and methane production. At a medium dose of 250 μL/L, L-Carvone significantly reduced methane production without compromising in vitro dry matter digestibility. Higher doses (500 μL/L) were more effective in reducing methane, though they negatively impacted digestibility. In the fourth study, the effects of bakery by-products on rumen degradability, fermentation characteristics, and methane yield were evaluated. The results showed that feeding bakery by-products significantly reduced methane production without affecting digestibility, suggesting their potential as an effective strategy for mitigating methane emissions from ruminants. Together, these in vitro studies studies demonstrate that by-products from various industries, often considered waste, can be repurposed as valuable feed ingredients for livestock. By utilizing these by-products, which contain bioactive compounds, and incorporating pure essential oil compounds such as L-Carvone, we can potentially reduce methane emissions, alleviate food-feed competition, and minimize environmental pollution, offering sustainable solutions to the environmental challenges posed by livestock production.