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In order to meet the greater nutrient requirements of higher yielding dairy cows, concentrate feed levels have increased, and this has led to an increased demand for quality protein ingredients such as soya bean meal and rapeseed meal. As some protein ingredients, especially soya bean meal (SBM), are often imported from countries outside the European Union (EU), this has left the dairy sector vulnerable to instability of supply, price volatility, and the unavailability of non-genetically modified (GM) protein crops. For these reasons, there is interest in the potential of locally grown high protein grain and forage crops to replace imported protein feeds. Field bean (Vicia Faba) (FB), a grain legume, may provide an alternative to imported protein feeds. It can be successfully grown in some of the wetter and more northerly regions of Europe. However, FB is known to contain a number of antinutritional factors, and caution is often adopted when including FB in dairy cow diets. Experiments 1 and 2 examined the effect of FB inclusion level in the diet on cow performance, while Experiment 3 examined the effect of FB processing method on cow performance. Red clover (RC) is a forage legume of particular interest within the UK and Ireland where it has the potential to produce high annual dry matter (DM) yields. In addition, RC silage normally has a higher protein content than grass silage (GS). Furthermore, as a legume, RC has the ability to fix atmospheric nitrogen (N), thus reducing the need for inorganic fertiliser N. However, due to its high protein content, and the associated reduction in N use efficiency, RC silage is often offered in mixtures with grass silage. While a number of studies have examined the nutritive value of swards containing RC and GS mixtures, each of these have evaluated silage produced from a single harvest. Consequently Experiment 4 examined the effects of offering dairy cows grass silages and grass-red clover (RCGS) silages produced from three consecutive harvests (H) over a full production year (harvested early summer, late summer and autumn), on N and energy utilisation and subsequent animal performance. The main parameters examined within Experiments 1 – 4 were dry matter intakes (DMI), milk yield, milk composition, live weight, body condition (BCS), blood metabolites, fertility parameters, N and energy (E) utilisation efficiency, and methane (CH4) production. Experiment 1 (Chapter 2) examines the impact of FB inclusion in the diets of mid-lactation dairy cows. Sixty mid-lactation dairy cows were used in a four treatment continuous design (ten weeks duration) experiment. All cows were given ad libitum access to grass silage, and were supplemented with 10.0 kg concentrate/cow/day. Concentrates offered contained 0, 166, 333 or 473 g FB/kg concentrate (treatments FB0, FB1.7, FB3.3 and FB4.7, respectively), with the FB partially replacing soya bean meal and rapeseed meal. On completion of the 10 week experiment, ration digestibility was measured using four cows from each treatment. While there was a trend for milk protein content (linear: P = 0.081) to decrease with increasing FB inclusion levels, FB inclusion had no effect on silage dry matter DMI, total DMI, milk yield, milk fat content, milk fat yield, milk protein yield, milk fat + protein yield, live-weight change and body condition score change. Similarly, FB inclusion had no effect on DM, organic matter and gross energy (GE) digestibility coefficients, although there was a linear increase in N digestibility (P = 0.041) with increasing FB inclusion levels. Faecal N/N intake (P < 0.042) and milk N/N intake (P = 0.047) decreased with FB inclusion, while energy utilisation was unaffected. Field bean inclusion had no effect on any of the CH4 production parameters measured. The results of this study demonstrate that FB can be included in dairy cow diets at levels up to 4.1 kg DM /day with few negative effects on cow performance. Experiment 2 (Chapter 3) examines the effects on cow performance and nutrient utilisation of including high levels of FB (up to 8.4 kg/cow per d) in the diet of early lactation dairy cows. Seventy-two dairy cows were used in a 3 treatment continuous design (from calving until week 20 of lactation) experiment. All cows were given ad libitum access to a mixed ration comprising grass silage and concentrates (45:55 on a DM basis). Concentrates offered contained either 0, 349, or 698 g FB/kg concentrate (treatments FB0, FB-Low and FB-High, respectively), with the FB completely replacing SBM, rapeseed meal (RSM), maize gluten and wheat in the concentrate with the FB-High treatment. Following completion of the 20 week experiment, ration digestibility, nutrient utilisation and CH4 production were measured using 4 cows from each treatment. None of silage DMI, total DMI, or milk yield were affected by treatment. Cows on FB0 had a higher milk fat content than those on FB-High, whilst cows on FB0 and FB-Low had a higher milk protein content than those on FB-High. Field bean inclusion increased the degree of saturation of milk fat produced. Milk fat yield, milk protein yield and milk fat plus protein yield were higher with FB0 than with either of FB-Low or FB-High. Treatment had no effect on the digestibility of DM, organic matter, N, GE, and neutral detergent fibre (NDF), whilst digestibility of acid detergent fibre (ADF) was higher with FB0 than FB-High. Neither the efficiency of GE or N utilisation, nor any of the CH4 production parameters examined, were affected by treatment. Similarly, none of the fertility or health parameters examined were affected by treatment. The reduction in milk fat observed may have been due to the higher starch content of the FB-High diet, while the reduction in milk protein may have been due to a deficit of methionine in the diet. Experiment 3 (Chapter 4) examines the effect of post-harvest treatment of FB on cow performance and nutrient utilisation. 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 bean crop was dried at 80oC for four hours to achieve a moisture content of 16%, before being left to cool. Beans were then either coarsely rolled (Dry-CR) or finely milled (Dry-FM). The remaining 1/3 of the bean 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 with treatments Dry-CR and Dry-FM comprised a common ‘pre-mix’ (600 g/1000 g concentrate) with the remaining 400 g per 1000 g concentrate comprising FB (coarsely rolled and finely milled beans, respectively). With treatment Moist-P, the same concentrate pre-mix was used (600 g/1117 g concentrate), while the moist FB were incorporated at 517 g/1117 g concentrate, the higher inclusion reflecting their lower DM content. 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 total DMI, milk production or milk composition. Similarly, live weight and BCS 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/GE intake and a higher milk N/N intake, although this appears to have been driven largely by differences in intakes. The results have shown that acid preservation of moist field beans 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.