Storage of fresh and ensiled forages by freezing affects fibre and crude protein fractions

Abstract

The effect of freezing on fibre and crude protein fractions of forages was determined. Fresh and ensiled lucerne and fresh bromegrass were processed immediately after collection or stored at −25°C for 1 day or 1, 6 or 12 months before drying at 55°C. Samples were frozen quickly by submersion in liquid nitrogen or slowly at −25°C. Samples which were not frozen were processed immediately or after 1 h delay at room temperature. All treatments were replicated (n = 3). Samples were analysed for crude protein (CP), trichloroacetic acid soluble CP (TSCP), phosphate buffer soluble CP (BSCP), neutral detergent insoluble CP (NDCP), acid detergent insoluble CP (ADCP), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent sulphuric acid lignin (lignin) and ash. Freezing decreased BSCP and increased NDCP by more than 40% for bromegrass. Freezing also changed NDF, ADF, lignin, ash, CP and ADCP in different ways depending on forage type and length of time frozen. No significant effects were observed for method of freezing or a 1-h delay in processing. An additional experiment showed that freeze-drying resulted in less insoluble protein than ovendrying. Prior freezing of forages appeared inconsistently to change the extent of gaseous loss during drying, and resulted in precipitation of protein. These changes also affected fibre estimates. Fresh forages should not be frozen and thawed before analysis of protein or fibre fractions.