Thread by @drsplace

I feel like there's a lot of confusion about digestive systems & dietary classifications of different animals. As an animal scientist, I'm part of a small subset of people on 🌎actually bothered by this. So, a thread of recycled material from my days of teaching @okstateafs

You can classify animals by the digestive anatomy & the type of diet animals consume (typically consume, as there are plenty of examples of "herbivores" occasionally eating animal sourced foods). Anatomy can be things like stomach structure & where most fermentation takes place

There are animals that have most microbial fermentative capacity BEFORE their gastric stomach (e.g., low pH stomach like our own). These animals are classified as "pre-gastric" fermenters. Ruminants are pre-gastric fermenters

There are animals that have most microbial fermenative capacity AFTER their gastric somach - these animals are called "hindgut fermenters"

We can further classify animals by their stomach structure: 1. simple stomached animals or monogastric animals 2. animals with complex stomachs like ruminants, and pseudoruminants

Of the common farm animals, pigs & chickens are both monogastric omnivores. Which means "vegetarian fed" hen claims you see on egg carton labels are misleading - chickens aren't vegetarians! 🐓 will eat other 🐓 if given the opportunity. 🐖would eat you given the opportunity.

Cattle, sheep, buffalos, & goats are all ruminant herbivores. They have different feeding behaviors, but are all incredibly efficient at converting fibrous plant material into human usuable products - meat, milk, wool, etc. They're better at it than hindgut herbivores like horses

And yes, ruminants produce methane gas, or rather methanogens that live in their pregastric stomach compartments do. It comes out the animals mouth during a process called eructation, or you can call it belching if you want. Methanogens are a key part of rumen ecosystem

Methanogens use "waste" products from fermentation, which is why they are critical to normal rumen function. If methanogens are removed with no alternate outlet for the waste (H2) then rumen fermentation ⬇️. The complexity of the rumen ecosystem is why mitigating CH4 isn't easy

While we use the word ruminate to talk about thinking, it's a complex process of regurgitating, re-chewing, re-salivating, & re-swallowing food. Ruminants are prey species so they evolved to eat quick and then chew their food again later in safety. They chew a lot, like hrs/day

While all animals have microorganisms living in their digestive tracts, ruminants have an incredibly unique symbiotic relationship. The microbes digest their feed, provide them high quality protein & other essential nutrients (e.g. B12), & the microbes get a fully equipped condo

Bacteria, protozoa, fungi, archaea, and viruses (bacteriophages) all live in the rumen. There are well over 10 billion cells in every mL of rumen fluid, so every mL of rumen fluid has more microbes than people on planet earth.

These microorganisms, & specifically the microbial enzymes that breakdown cellulose, are why ruminants can eat what we cannot & get nutritional value from it. This is why ruminant livestock "use" so much of the earth's surface - because they are some of the few critters that can.

So, a thread that started about animal digestive classifications ends with an ode to why #ruminantsareawesome. They're solar-powered, mobile, self-replicating bioreactors providing milk, meat, wool, leather, draft power, fuel, fertilizer, wealth, & security to humanity