Soya-bean meal and rapeseed meal treated with 0, 0·4 or 0·8 g formaldehyde/100 g crude protein (N × 6·25) was incubated in the rumen in nylon bags with 10 and 40 μm aperture.
Disappearance of dry matter and nitrogenous compounds was reduced with increasing formaldehyde treatment.
The proportion of acid-pepsin soluble nitrogen in the undegraded residues of untreated and treated soya-bean meal was similar to the original samples. For rapeseed meal the proportion of acid-pepsin soluble nitrogen in the undegraded residues decreased with increasing rumen incubation time. This reduction decreased with increasing formaldehyde treatment.
Concentration of amino acids in the undegraded residues did not generally deviate from those in the original samples. However, a distinguishable decrease in the methionine concentration was observed in all the rapeseed meal samples and in glutamic acid concentration in rapeseed meal treated with 0 and 0·4 g formaldehyde/100g- crude protein.
Most of the changes due to rumen incubation were smaller using the 10 μm bags than using the 40 μm bags. However, the bag pore size did not play a decisive role in the conclusions of the results given.