Increased global demand for soybean and rapeseed meal, and associated fluctuations in their availability and price has resulted in greater interest in home grown, protein-rich forage sources for ruminants. Alfalfa (Medicago sativa) and red clover (Trifolium pratense) are of interest due to their high protein content, but often contain insufficient digestible undegradable protein to meet cow requirements. Tannins can protect protein in forages from microbial degradation by forming a complex in the rumen that dissociates in the abomasum. The effect of the addition of hydrolysable tannins to alfalfa and red clover silage at ensiling on the intake, performance and whole tract digestibility were therefore studied. Twelve multiparous dairy cows received one of 4 dietary treatments in each of 4 periods of 28 d duration, in a Latin square design with measurements taken in the final 7 d of each period. The proportion of alfalfa (A) or red clover (RC) to corn silage was 40:60 (DM basis), and all dietary treatments contained 55:45 forage to concentrates (DM basis). There were 4 dietary treatments; A or RC silage ensiled without or with hydrolysable tannins. Hydrolysable chestnut tannin was added at ensiling at 25 g/kg DM. Cows were fed once daily at 0800h and milked twice daily. Acid insoluble ash was used as an indirect marker for whole tract digestibility. Data were analyzed as a Latin square design using Genstat (v. 17). DMI was highest (P < 0.01) in cows when fed A (mean values of 22.1 and 19.8 kg DM/d for A and RC respectively). There was no effect (P > 0.05) of treatment on milk yield, fat or protein content with mean values of 38.1 kg/d, 41.5 and 33.7 g/kg respectively. Dietary treatment had no effect (P > 0.05) on OM or nitrogen digestibility, with mean values of 0.687 and 0.629 kg/kg respectively. In conclusion, cows offered red clover had a similar level of performance as those fed alfalfa silage but ate 2.3 kg DM/d less, and the inclusion of hydrolysable tannins in alfalfa and red clover silage had no benefit on performance or whole tract digestibility.