ron2
Posted : 9/1/2006 6:17:47 AM
Here's my ditch-digging, shakespeare-quoting, non-expert understanding of the differences between animal protein and vegetable or grain protein.
Meat is, (oversimplified) protein and cellulose. Cellulose is fiber and passes through. Protein is amino acid chains and, in meat, is accompanied by nitrogen. Excess or unneeded nitrogen is filtered out by the kidneys and passes through in the urine. Plant protein is not accompanied by nitrogen and is referred to as NFE (nitrogen free extract). In a dog food, they find the amount of animal protein by doing a nitrogen count and multiply by a conversion factor. In plant matter, there are other elements, such as minerals and carbohydrates. A digestive system processes the nutrients at a certain rate. So, the system must get the required nutrition out of the food in a certain time period before it passes on. Meat will get the protein in quicker because it has less "other" ingredients competing for entry into the system. But some of the "other" nutrients are necessary for the health of the dog. Here is where, I think and someone may correct me, ash comes into play. Ash is just that, the "burned up" residue of mineral leftover after burning meat. In the cooking process, there will be "ash", or mineral residue. Dogs have no use for burnt minerals. So, that is also in the system taking up space. In some dogs, it may be interfering with nutrient absorption. In a cat, an obligate carnivore, this can become crucial.
It is noteworthy, IMO, that all ingredients are ground fine before being used in a kibble recipe. Then cooked at a low temperature in the extrusion process. Both the grinding and the heat in a low cooking render the ingredients, especially the plant matter, more digestible and usable by the animal.
So, if a kibble has meat for the first ingredient, and considering that the necessary fat can only be added at the end, due to process interference if it were added earlier, the dog would then get it's crucial load of protein and fat up front, with the other ingredients coming along as they can to round out the nutritional profile, as necessary. IMHO, nutrient absorption is similar to fluid dynamics. Fluid flows in the path of least resistance, much as heat will flow to cold. So, kibbles in the stomach the protein and fat first will get absorbed first and the others as the can be before the GIT moves everything along.