The sieve tower was dried in a ventilated oven (65 _C) overnight, then cooled down in a desiccator and each sieve weighed again.
Hardness of the feed pellets (25 pellets per sample) was measured as resistance
to axial compression by means of a Kahl pellet tester (Kahl Group) and expressed as
kg/cm2 (Melcion and Delort-Laval, 1981).
Swelling capacity was measured in duplicate as described by Vanstallen (1973).
Briefly, a 1 L glass graduated cylinder with 50 g of sample was filled with water.