Of Cows, Milk, Microbes and Cheese.

The rumen of a cow is the organ where the break down of the grass, hay and other foods into usable products occurs. In fact, without the rumen, a cow could not survive (its stomach does not digest these foods), or more correctly without the rumen's collection of microbes (or microbiome) and their fermentation processes, a cow could not survive. These microbes process the cow's feed into usable products (such as short chain fatty acids) or waste products (such as methane).

A talk this week at MIT's Microbiome Group, by Itzhak Mizrahi, illustrated how his and other's work on the rumen microbiome, show that it not only keeps the cows healthy, but also impacts the quality of the milk - and ultimately our cheese.

Understanding the cow's microbiome, will therefore help us understand how to make the best quality milk and thus the best quality cheese.

Itzhak's group noted that by comparing cows with regards to weight, eating habits and excretion products (such as methane), the cows could be divided into low or high efficient feeders. The low efficiency cows tended to produce more methane gas (released through, well, farting) than the high efficiency cows, which they found absorbed higher levels of short chain fatty acids from their digestive systems and produced less waste products.

By analysing a slowly evolving bacterial gene in the microbiome (the 16S rRNA gene), they showed that the microbiome of highly efficient cows was less complex with lower diversity than that of the low efficiency cows. What was driving this selection of microbes in the different rumens? They found that there was a link between about 20 microbes to both the genetics of the cow, but also to the metabolic function these bacteria performed.

They went on to show that not only can cow genetics shape this content, but it could also be selected for by changing the diet. If one type of bacteria's growth slowed in the presence of one type of feed substance, then another would step in, filling this open niche. In fact their work showed clearly that the established phenomenon of niche succession was dynamically at work in the microbiome, and could be influenced by feed content.

So, we know that the microbiome could be dynamically altered by the diet, and was linked to some degree to the genetics of the cow, but where does the calf get its initial microbiome from, and does every calf start with the same microbiome? When does this microbial shaping begin?

In early life, the calf's rumen is tiny and unpopulated with any microbial life, so it all has to be introduced.

They found a link to efficient feeders, quality microbiomes, and how the calf was born: if it was born naturally, it had a quality microbiome tuned to high efficiency; if it was born through c-section, the microbiome was over-diverse and they were inefficient feeders.

They proposed that highly tuned microbe-containing faecal matter from the mother cow entered the calf during normal birth through the birth canal, whereas c-section born cows had a cleaner birth, a later implantation, and of a different source (other multiple cows, from the sheds).

It could be that the quality of our milk and cheese relies on a calf getting a good oral dose of poop during its birth.

Many proposals and suggestions arose from this work including:

  • Feed your cows quality grass, and fodder etc. to maintain a quality microbiome, which will in turn provide quality and microbial-rich milk.

  • Quality microbiomes will also reduce the amount of methane produced by cows globally (hello, climate change)

  • Allow calves to be born naturally whenever possible, and make sure that there is transmission of the mother's microbiome to the calf.

Cheese is a complex substance, and consumers and cheese professionals often - and understandably - focus on the transformation of milk to cheese. However, these extra layers of complexity at the dairying level, make a complete understanding of the microbiome of milk and how it flows through to cheese even more challenging, yet also, in many ways, make a simple chunk of cheese so much more beautiful.

#science #cheese #milk #dairy