Mixed silage of whole catch crops - crops grown between 2 main crops - and straw might be an alternative forage source for dairy cattle in times of forage shortage, but is still understudied. This research sought to evaluate the effects of feeding mixed silage of rye-vetch-mixture and straw (RVS silage) in replacement of whole crop rye silage on feed intake, ECM yield, milk composition, nutrient digestibility, and metabolic variables of dairy cows. The study was a crossover trial with 10 Holstein and 4 Simmental cows (average 593 kg BW and 53 DIM at the start of the trial) tested in 2 experimental runs of 4 weeks each, whereby the last 2 weeks were used for the measurements. The cows were randomly allocated to one of the 2 diets differing only in the major forage source, either rye-vetch-straw silage (RVSS treatment) or a pure rye silage (RS treatment) as control. The diets were fed as partial mixed rations consisting on a DM basis of 43.8% RVS silage or rye silage, 14.6% corn silage, 14.6% meadow hay, and 27.0% concentrate mixture. The cows were additionally supplemented with 5 kg concentrate per day. Data showed that feeding the RVSS diet tended to decrease the DMI without affecting performance (mean ECM yield: 28.4 kg/d) and mean BW during a sampling period. Feeding the RVSS diet tended to increase dairy feed efficiency (kg ECM/kg DMI), likely due to the higher total-tract apparent OM digestibility of the RVSS diet compared with the RS diet. Furthermore, cows fed the RVSS diet spent significantly more time on rumination per kg intake of physically effective NDF. Diet did not affect the concentration of glucose, BHB, urea, total protein, albumin, triglycerides, cholesterol, liver enzymes and macro minerals in blood. Neither of the diets affected the concentration and proportions of short-chain fatty acids in the rumen fluid and feces. In conclusion, the mixed silage of catch crop and straw holds potential to replace traditional rye silage in the feeding of dairy cows yielding up to 30 kg ECM per day. Feeding the RVSS diet enhanced total-tract apparent OM digestibility and rumination index, without any negative effects on ECM yield, milk composition, BW, ruminal and fecal VFA concentration and key blood variables. Future research may evaluate the potential of mixed silages of catch crop and straw in the feeding of high-producing dairy cows as a viable option to overcome shortages in forage production.