Research Note
Rumen Modifiers:
What We Know and Don’t Yet
Feeding to maximize the cow’s genetic potential for milk yield and components involves higher starch diets that can impact the rumen microbiome. Certain feed additives can help mitigate the risk of SARA (sub-acute ruminal acidosis) and knock-on effects to the rumen microbiota. Confirming the efficacy of others, however, requires additional controlled research.
“In any case, before incorporating any rumen modifier additive,” cautions Ohio State’s Dr. Jeffrey Firkins, “know the farm’s forage, feed management procedures, and feeding behavior. Be ready to balance the ration for starch fermentability, which can be affected by grain processing.”
Firkins notes that there is relatively little known about how rumen modifiers can be “strategically used” to influence rumen fermentation in higher starch diets in order to mitigate or reduce the risk of SARA. NASEM 2021 describes several such additives, although in most cases the “mechanism of action” requires more detail.
A recent literature review summarizes ruminal fermentation stoichiometry and possible MOA for a variety of additives, including those with potential to reduce methane emission.
Primarily, rumen modifiers can help avoid lactate accumulation, which occurs under acid forming conditions that suppress digestibility of neutral detergent fiber and presage SARA.
Firkins points to decades of research on rumen additives based on yeast (Saccharomyces cerevisiae), including yeast cultures, and their effect on lactate uptake: “In addition to stimulating lactate usage, yeast products appear to decrease inflammation in the gut and lessen partitioning of nutrients away from milk.”
Likewise, there’s much research supporting the use of monensin, the ionophore approved for lactating dairy cattle feed in 2004, which increases propionate production while inhibiting lactate-producing bacteria. Firkins suggests there may be more potential for monensin in combination with other rumen modifiers.
Both academics and industry are revisiting branched-chain volatile fatty acids (aka isoacids), which were introduced commercially in the 1980s but without wide acceptance. Today, Firkins says, for high-producing cows fed total mixed rations, isoacids can work as rumen modifiers to increase milk yield and reduce nitrogen excretion.
As possible rumen probiotics, Firkins suggests that rumen bacteria such as Megasphaera elsdenii, some strains of Selenomonas ruminantium, and Coprococcus catus are lactate consumers that would benefit from further study.
In addition to supporting dairy productivity, the future of rumen modifiers includes reducing methane emissions, Firkins says: “Many compounds have been tested to suppress methanogenesis, with 3-NOP (3-nitroxypropanol, recently approved for dairy feed) and red seaweed (Asparagopsis taxiformis) having the largest response.”
Combinations of additives spanning multiple MOA “might hold promise.” Yet, Firkins adds: “When using rumen bioactives, we need to understand their modes of action to better justify their usage but also to understand what variables can limit their benefits.”
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