I can see that the end result of cellulose digestion would be energy rich but doesn’t the cow have to put in a heck a lot of time and energy to get that out?
How about feeding a cow straight sugar? How would that work?
I admit that you probably know more about this than I do but it goes against intuition. Why do strict carnivores even exist if grass just sits there and represents such a great source of energy?
Do you have any citations for this?
The reason I question it is that my research indicates that as a class of foods, proteins and carbohydrates both come in at 4 kcal/gram and since “meat” is also going to contain fat at 9 kcal/gram, I can’t see how grass can be higher in calories than meat.
I’m also confused at how cellulose, which is basically chains of glucose can be higher in calories than an equivalent mass of sucrose. My research indicates that both sucrose and glucose come in at 4 kcal/gram so I’m not understanding how equivalent masses of each have different caloric contents.
Yep, but that’s another issue, and because of the way it’s made it has to put a lot of time and energy into extractig energy from meat as well.
Pretty badly. Cows have evolved to eat grass, and that means they have evolved to give the microbes first shot at everthing they swallow. Feeding the microbes sugar means they produce lots of volatiles, lots of alcohol and so forth. Basically the microbes waste a lot of cow-usable material and convert it to stuff that is less usable. It’s fairly wasteful. Horses do fairly well on sugar because they don’t give the microbes much of a showing until the food reached the large intestine.
Grass represenst a great source of energy if you ignore the the indigetsibility, the toxins, the silicon fragments (essentially ground glass) and other nasties it contains. Grass is also very low in many essential nutrients, including protein. As a result animals that eat grass have to use one or both of two solutions. Some, like horses, go through massive amounts of the stuff like horses to get the required nutrient before they are poisoned. That means they have to spend most of the day eating and at risk of predators. Others such as cattle can eat less grass but they have had to evolve some extremely complex internal plumbing to do so and have to live life at a fairly sedate pace with limited intelligence to cope with the time required to process. The energy is their in grass but it takes a lot of time and effort to get out.
In contrast predators can utilise a food supply that represents more readily available energy without the toxins and as such they can live their life at a fast pace. The downside of course is that they can never evolve the gut flora needed to eat grass and so are forced to rely on either the plant eaters or fruits, neither of which permits high population densities and both of which tend to fluctuate wildly. It’s horses for courses. Predators aren’t particularly advantaged or disadvantaged, they just occupy a different niche.
Kinda. The 4kcal/gm thing is based on simply burning a highly variable sample of materials and is a gross generalisation of the way the real world works. All else aside the mammalian digestive tract doesn’t have a problem with burning wet food and as such any relaistic calorific value has to be based on “field weight” not “dry weight”.
The USDA has a very good website if you want more realistic figures. Sorry I can’t directly link, but you can do your own search on Steak, blade, trimmed and bran, wheat, crude. Lean steak comes in at 3.1kcal/gm, while wheat bran (the closest equivalent to grass) comes in at 9.0kcal/gm.
The fat content going to be a big variable, but even so unless somehow our cow is getting extremely high fat content meat it’s going to come in well under.
You answered your own question. Cellulose is a polymer of glucose, sucrose is a disaccharide. Mass for mass celluose simply contains more chemical bonds than sucrose. Every bond between those monomers represents chemical energy in its own right. Hence the material with greater number of bonds has the greater energy.
Thanks for the USDA link!
Cite?
The protein supplement in the feed of high productivity cattle mostly goes into the manufacture of cow proteins, into meat production and the production of milk proteins. The milk production of high productivity cows is so high, it is difficult for them to produce the large amount of protein secreted in the milk from grass alone. The ingested protein, whether directly from plants, from the microbes that populate the stomachs of the cow or from a high protein feed supplement is digested to amino acids, which are absorbed and can be used directly to synthesize new proteins.
Zombie cow thread!