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May 15, 2023

Let the Rumen do the Heavy Lifting

When it comes to milk solids components, the most efficient path of production

When it comes to milk solids components, the most efficient path of production is via rumen microbial synthesis, according to Dr. Isaac Salfer, Assistant Professor of Animal Science at the University of Minnesota.

Salfer told the audience of a recent I-29 Moo U Dairy Podcast, "Butterfat and Protein," that the production of both fat and protein in milk is most economical when the cow manufactures it herself.

He said milkfat is produced from one of two sources: (1) preformed fatty acids, generally with 16 carbons or more, that come directly from feedstuffs; and (2) de novo-synthesized fatty acids, which usually have 16 carbons or less, and are the product of the volatile fatty acids – typically acetate - which are produced via rumen fermentation.

Rumen pH is highly influential on how milkfat production can be maximized through de novo synthesis. "Milkfat synthesis in the mammary gland can be affected by the presence of bioactive fatty acids produced during rumen fermentation," Salfer explained.

"Lower rumen pH is undesirable, because it encourages fatty acids to undergo alternative biohydrogenation," he added. "Biohydrogenation – the process of rumen microbes converting unsaturated fatty acids to saturated fatty acids -- is a normal process in the rumen. But when rumen pH is low, even for short periods of time, biohydrogenation follows an alternate pathway and produces the bioactive fatty acids that reduce milkfat synthesis. They produce bioactive fatty acids that essentially act like hormones and can directly reduce milkfat production."

Salfer said there is a direct and well-recognized correlation between rumen acidosis and suppressed milkfat production. But even minor fluctuations in rumen pH throughout the day can impact milkfat synthesis. "If we leave the bunk empty for two hours and cows come back and slug feed, the rumen pH can drop fairly quickly, potentially below 5.4," he noted. "Bioactive fatty acid production kicks in and suppresses overall milkfat production."

That's where management practices like correct stocking density, ample bunk space, and pushing up feed frequently can make a real difference in fat production. "Anything you can do to get cows eating more frequently will help stabilize the rumen and support your fat test," said Salfer.

Milk protein, too, has two main production sources: (1) dietary protein that escapes the rumen and makes its way to the small intestine; and (2) microbial protein that is synthesized within the rumen by microbes.

Salfer quoted a nutritionist colleague who said, "The cheapest and best protein source you can feed cows is actually starch." This is because starch is used as energy by rumen microbes, which leads them to synthesize more microbial protein – which is a high-quality protein source for the cow. He went on to explain that achieving the sweet spot between feeding high levels of starch – yet not causing rumen acidosis – will stimulate rumen microbial growth and maximize microbial protein synthesis.

Beyond these fundamentals, Salfer said protein production can be enhanced in some cases with feed additives like rumen-protected amino acids and specific rumen undegradable protein (RUP) commodity feed sources. Some enzymes and yeast additives have been shown to improve fiber digestibility and boost fat production.

There also is a distinct seasonal pattern to component production. Salfer said his research has shown that fat and protein production peaks in late December to early January, and hits a seasonal low around July 1. The spread between high and low is about 0.3 pounds of milkfat and 0.15 pounds of protein per cow per day.

"This seasonal pattern is very consistent and naturally-occurring in the cow," noted Salfer. "If your components are steady year-round and you’re not seeing that seasonality in your herd, you may be missing out on some of the genetic potential of your cows and potential value of the milk they produce."