Field beans (FB, Vicia Faba) is a crop which can be grown within Northern and Western areas of Europe, and which has potential to partially replace imported protein ingredients in ruminant rations. However, in these regions beans are frequently harvested with a moisture content in excess of 16%, and as such must be treated to prevent mould growth. This study was designed to examine the impact of moist preservation of FB using propionic acid, and the extent of physical treatment of dried FB, on dairy cow performance and nutrient utilisation. Eighteen mid-lactation Holstein-Friesian dairy cows were used in a three-period (each of four weeks duration) change-over design experiment. The FB crop used in the experiment (Var. Boxer) was harvested at a moisture content of approximately 25%. Three treatments, each comprising a different post-harvest treatment of FB, were examined. Following harvest, approximately 2/3 of the FB crop was dried at 80°C for four hours to achieve a moisture content of 16%, before being left to cool. Dried FB were then either coarsely rolled (Dry-CR) or finely milled (Dry-FM). The remaining 1/3 of the undried FB crop was coarsely rolled and the beans then treated with propionic acid at a rate of 20 litres/ton fresh beans (Moist-P). Cows on all three treatments were offered a mixed ration comprising grass silage and concentrates (forage: concentrate ratio of 60: 40 on a dry matter basis). The concentrate component of the diet comprised a common ‘pre-mix’ representing 65% of the concentrate on a DM basis, with the remaining 35% of concentrate on a DM basis comprising FB (either dry coarsely rolled, dry finely milled or moist acid treated). The experimental concentrates were designed to achieve an intake of FB of approximately 3.5 kg per day with each treatment. At the end of the 12 week experimental period, 4 cows from each treatment were subjected to a ration digestibility evaluation. Treatment had no effect on dry matter intakes, milk production or milk composition. Similarly, live weight and body condition score were unaffected by treatment (P>0.05). None of the digestibility coefficients examined was affected by treatment. Cows offered the Moist-P diet had a higher milk energy/gross energy intake, and a higher milk nitrogen/nitrogen intake, although this appears to have been driven largely by differences in intakes. The results have demonstrated that acid preservation of moist FB is equally as effective as conventional drying of beans, while degree of processing post drying (coarsely rolled vs finely milled) had no effect on subsequent cow performance.