The digestibility of the non-protein constituents (almost entirely carbohydrate) of ruminant fodders is shown to be a function of the level of the crudefibre and crude-protein components.
The effect of increasing crude fibre in the diet is to depress the digestibility of carbohydrate, irrespective of the level of crude protein associated with it.
The effect of crude protein on the digestibility of carbohydrate is only well marked when its concentration in the dry feed lies below some 5%, that is when the feed is below approximate maintenance levels. Increasing the crude-protein content of the diet from some 2 to about 5% leads to increased digestibility of carbohydrate, but thereafter in the range of some 6–30% crude protein the protein effect is very slightly depressing to carbohydrate digestibility and is apparently quite negligible at average crude-fibre concentrations to be expected at any given level of crude protein.
The implications of the various aspects of this paper are that the variability in digestibility of the non-nitrogenous component of ruminant feeds depends mainly on the respective levels of crude protein and crude fibre in the diet and to a very much lesser extent, if at all, on the species of ruminant or class of feed, be it silage, roughage or even mixture.