included in the original descriptio

included in the original description for durability (Pfost, 1963). In fact, for each
measurement it is important irrespective of the device used. In addition, (specified)
standard conditions need not be similar to guideline recommendations. While the
individual feed manufacturer should set standards for his own situation, science asks for
a standardised approach for comparative reasons.
In the case where a number of pellets is examined, the CV of data is commonly
lowered by excluding the highest and lowest value. This procedure is rather commonly
applied by for example the Kahl and Schleuniger tests. From a scientific point of view,
this procedure, however, is highly questionable.
It can be concluded that only general descriptions can be given on the magnitude of
the different binding mechanisms. It appears that crystallisation processes taking place in
the pellet during cooling/drying and capillary forces account for the largest part of
binding particles (Schwanghart, 1970). However, other non-discussed phenomena, such
as glass-formation, may play a role as well in creating structure within agglomerates.
Within the scope of animal feed manufacturing these are still poorly understood. More
research is needed to gain knowledge on the effects of different processing conditions
and the magnitude of the different binding mechanisms.
The devices used in animal feed manufacturing most of the time yield a figure which
merely reflects a measurement which consists of a mixture of fragmentation and
abrasion, for instance the Holmen pellet tester. For practical purposes the aim should be
to identify the method which at best reflects the mixture of hardness and durability
which is most closely related to the figures derived from the specific plant at which the
feeds have been produced. For this purpose empirical equipment has been developed
which at present is commonly used in animal feed production: Pfost’s tumbling can, the
Holmen pellet tester and the Kahl hardness tester. Recently, on-line test devices have