Studies on in situ degradation of feeds in the rumen 3. The effect of freezing forages before and after rumen incubation

Freezing forages before rumen incubation and the in situ residues postincubation has become standard practice, but few results have been published regarding the effects of freezing on in situ dry-matter degradability (DMdeg). Two studies were undertaken to investigate the effect of freezing following rumen incubation. In the first study, hay and prefrozen silage were assessed and in the second, the effect of prefreezing of silage was also compared. Three mature rumen-cannulated cows were fed a diet consisting of silage and barley (80:20 DM basis). The sequence of bag incubation was such that all bags were removed from the rumen at the same time and could either be washed immediately or frozen (−20°C) for 54 h before washing. Freezing bags after rumen incubation, before washing was not found to have an effect on DMdeg in study 1, but in study 2 reduced mean DMdeg and effective degradability of silage (P = 0.014 and P = 0.009, respectively) were observed. Silage frozen prior to rumen incubation was also found to have lower effective degradability values than silage not frozen before rumen incubation (P = 0.006) and the lag time of silage not prefrozen was longer than any other treatment. It was concluded that freezing can significantly affect the DM degradability characteristics measured in situ but that the effects are small and of limited practical significance.