Associative effects of ensiling mixtures of sweet sorghum and alfalfa on nutritive value, fermentation and methane characteristics

• Ensiling alfalfa (AF) alone is not practical and unsuitable for making high-quality silage.
• Ensiling sweet sorghum (SS) alone resulted in high fiber and low IVDMD and IVOMD.
• Overall quality of SS-AF silage mixtures was better than the silages prepared from SS or AF alone.
• High quality silages can be made with SS:AF ratios of 20:80 and 40:60.

Combining sweet sorghum (SS) with alfalfa (AF) for ensiling has the potential to improve the nutritive value and fermentation characteristics of resultant silages. However, the optimal combination and the associative effects of SS and AF for ensilage have not been studied. Therefore, the aim of this study was to determine the fermentation characteristic and nutritive value of silage mixtures with six different SS to AF ratios. The two forages were ensiled in air free silos for 150 days at room temperature as mixtures containing 0:100, 20:80, 40:60, 60:40, 80:20, and 100:0 of SS:AF on a fresh weight basis. As the proportion of SS increased in silage, the content of ash, crude protein, saponins, ammonia, acetic acid, propionic acid and pH decreased, while neutral detergent fiber, acid detergent fiber in organic matter, acid detergent lignin, water-soluble carbohydrate, starch, total phenolics and condensed tannins content increased. The silages were evaluated in 24-h incubations with rumen liquor. The in vitro rumen degradability of dry matter and organic matter as well as gas production, pH, ammonia, total volatile fatty acids and methane decreased as the proportion of SS increased in the silage mixtures. This study suggests that high quality silages can be made with SS:AF ratios of 20:80 and 40:60. These silage mixtures offer an opportunity to optimize the nutrient supply for ruminant production.