Influence of the Season on the Nutritive Value and Gas Production of Opuntia ficus-indica and Agave americana L. in Ruminant Feed

SIMPLE SUMMARY: The Opuntia ficus-indica, and the Agave americana L., are invasive plants, widespread across various countries, that are used by farmers as an alternative water source for ruminants in the summer. The goal of this study is to assess their nutritive value and potential throughout the year, so that their use in diets can be optimized. Both plants are very rich in water, minerals, and energy, but low in crude protein and fibre. Although a decrease in digestibility is observed in the summer, both plants can be a viable feed supplement for ruminants in both the winter and the summer, providing a cheap and eco-sustainable alternative water source. Opuntia ficus-indica, and the Agave americana L., can be fed to ruminants when associated with dried fodder, or incorporated into high crude protein diets for ruminants. ABSTRACT: Using invasive plants in animal production can provide an economical and eco-sustainable competitive advantage in a globalized market. The Opuntia ficus-indica and the Agave americana L. are invasive plants historically used by Azorean farmers as an alternative ruminant water source in the summer. This study aims to better understand their properties and how they vary throughout the year, so their use to complement animal diets can be optimised. Six samples of each species were collected on the Terceira Island during 2 growth seasons: winter (January 2021) and summer (September 2021), and their chemical composition, in vitro digestibility, and gas production, were determined. Significant (p < 0.05) differences were found in all parameters between the summer and the winter, with larger variations in both fibre (NDF and ADF) and digestibility parameters found between the Opuntia and the Agave. Gas production was greater in the summer for Opuntia and in the winter for Agave. Even though the digestibility was lower in the summer, we found that both plants offer a viable ruminant feed complement in both seasons, providing a cheap and eco-sustainable alternative water source, that can be associated to dry forage and compound feeding stuff with a high crude protein content when designing ruminant diets.