The first study determined the effect of wash severity on zero time losses of hay, soyabean meal (SBM), fishmeal (FM) and absorbent cotton wool (ACW) using ten polyester fibre bags for each sample type and wash severity. Bags were washed in an automatic washing machine (Zanussi Z919T) with cold water using the following programmes: B (cotton wash), D (fast colours), G (non-fast colours), H (rinses) and R (woollens). To satisfy the analysis of variance, the zero time loss results were transformed using the square root of the data value plus 1.0. The transformed means (back transformed means are shown in parentheses) for wash programmes B, D, G, H and R were 4.46 (20.3%), 4.48 (19.1%), 4.47 (19.0%), 4.27 (17.2%) and 4.08 (15.6%) (SED = 0.021) respectively. Washing procedure was found to affect sample types differently ( P < 0.001), but the magnitude of losses was always observed to be in the order B > D = G > H > R. The total weight of water, programme duration and slow spin time were found to be the most important factors affecting DM losses. The second study investigated the effect of wash severity and repeated washing on the DM disappearance profile of hay using three mature rumen cannulated cows fed a silage: barley diet (80:20, DM basis). Eight bags containing hay were incubated in each cow for each time period (72, 48, 24, 18, 6, 3, 0 h) thus providing duplicate bags from each cow for the wash programmes B, G, H and R. Washing severity was found to significantly affect the degradation profile of hay ( P < 0.001), largely due to programme H. The magnitude of overall mean disappearances was B > G > H > R with means of 45.9, 43.2, 42.8 and 40.4% (SED = 0.378) respectively. The influence of spin drying was assessed in the third study by washing (programme R) ten bags containing hay, five bags were allowed to drain and then removed whilst the remaining five were spin dried, this process was evaluated three times. Spin drying bags at the end of the washing process did not significantly increase DM losses ( P = 0.113) from the bags. The effect of number of bags washed together was investigated in the fourth study by washing (programme R) either 1, 5, 10, 20, 40, 60 or 120 bags containing hay at a time. No practical effect of bag density during the wash process was observed. The final study investigated the effect of the number of bags incubated in the rumen on the 24 h DM degradability of hay. Bag numbers in rumen were found to have a negligible effect on DM losses from in situ bags. It was concluded that washing procedure can substantially affect DM disappearance values and there is a need for standardisation. Crown Copyright