The apparent digestibility of crude protein by non-ruminants and ruminants

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Abstract
The apparent digestibility of crude protein by the non-ruminants, pigs, horses, rats, man and the rabbit, is shown to be related to the crude protein content of the feed, and the form of the relationship is similar to that for ruminants. With non-ruminants the apparent digestibility of crude protein is markedly depressed by the crude fibre content of the feed, whereas with ruminants the depression is only slight. The relevant equations show that pigs are much more sensitive to crude fibre than horses and rabbits, and both the latter react more markedly to crude fibre than do the ruminants. Despite the apparently significant differences between the equations for the ruminant and nonruminant herbivores, it is shown that over the normal range of crude protein and crude fibre content in feedingstuffs suitable for herbivores, the apparent digestibility coefficient of crude protein is similar for all. In other words, despite different abilities to cope with crude fibre, the herbivores as a class digest crude protein in normal feeds to much the same extent. On the other hand, the pig, an omnivore, is shown to be very markedly affected by the crude fibre content of such feeds.