Nutritionists and researchers from as early as the 1950s have been investigating isoacids in dairy nutrition. Now, decades later, their potential role in boosting rumen function, dairy cow productivity, and even environmental sustainability is being visited with renewed interest.
According to Dr. Jeffrey Firkins, Professor of Animal Science, Ohio State University.
“isoacid” is a collective term representing branch-chain volatile fatty acids like isobutyrate, 2-methybutyrate, and isovalerate. All are the result of the degradation of amino acids in the rumen.
Early isoacid research showed that supplementing lactating dairy cow rations with them improved rumen function and production efficiency. Alycia Bales, former graduate student and researcher at Michigan State University, explained that rumen bacteria are commonly divided into two categories: cellulolytic bacteria, which digest fiber; and amylolytic bacteria, which digest starch and sugar.
“Isoacids are naturally produced in the rumen through digestion of protein and are required by cellulolytic bacteria for growth,” noted Bales. “So, maintaining optimal concentrations of isoacids can enhance the growth and activity of cellulolytic bacteria and improve fiber digestion.”
She added that increasing fiber digestion can increase the nutrients produced in the rumen that are needed to synthesize milk fat, so supplementing dairy diets with isoacids could theoretically boost milk fat yield. Isoacids also have been found to influence hormones associated with nutrient utilization for milk production, potentially improving efficiency of the mammary gland.
In the 1980s, isoacids took center stage in dairy nutrition via a feed additive called IsoPlusTM, marketed by the Eastman Kodak corporation. This throwback commercial promoted the product as a supplement that would “help cows produce 4 to 6 pounds more milk per day, with no increase in feed intake, and no harmful side effects.”
Firkins said results from the product were generally favorable and supported by a large body of research. However, Eastman Kodak abruptly discontinued IsoPlus as it navigated seismic business challenges within the company as a whole.
But, Firkins said, much was learned from the product and its associated research, which widely supported the role of branch chain volatile fatty acids for NDF degradability. Deficiency in branch chain volatile fatty acids derived from ration ingredients is common, particularly since nutritionists have started formulating rations with lower levels of rumen degradable protein to reduce nitrogen excretion by dairy cattle.
And, IsoPlus has not disappeared from the marketplace completely. The original product has been reformulated and is commercially available again. It is marketed as Zinpro® IsoFerm® by Zinpro Corporation.
Supplementing cows with isoacids could confer benefits beyond just providing growth factors for cellulolytics, noted Firkins. He said the mechanisms of isoacids also likely lead to a more balanced rumen microbe population and subsequent improved efficiency of microbial protein production, as long as rumen nitrogen levels are sufficient.
Improved fiber digestibility supports increased fatty acid synthesis in the mammary gland by supplying more of the volatile fatty acid acetate, but also through transcriptional regulation. “Improved energy availability probably helps to increase milk production without drawing on body reserves,” observed Firkins. “Because primiparous cows are still growing, they might respond less to isoacids for milk production, but could partition more energy to growth.”
A recent study published in the Journal of Dairy Science, examined the effects of supplementing dairy cow diets with an isoacid blend at 2 forage NDF levels. The researchers found that isoacid supplementation significantly increased milk yield and nutrient digestibility in the high-NDF (21%) group, while it increased average daily gain and decreased milk urea nitrogen (MUN) in the low-NDF (17%) group. Additionally, both groups that received the isoacid supplement showed an increase in milk odd-chain fatty acids (C15:0 and C17:0). Isoacid supplementation did not affect dry-matter intake or feed efficiency in either diet.
The authors said because MUN and urinary nitrogen excretion are highly correlated, the reduction in MUN warrants further research on the potential of isoacids positively affecting nitrogen footprint from dairy cattle.
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