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In Cantabrian Mountains (N Spain), summer pastures are mostly utilized for beef cattle production. This work aimed to study cow and calf performance of two local breeds, Asturiana de los Valles (AV) and Asturiana de la Montaña (AM), grazing at different pasture mixtures from June to October. Data were recorded from 1995 to 2013 in a high mountain area, which was divided in two plots of 30 ha each: one with 70 per cent grassland and 30 per cent Calluna-heathland cover (C30), and another with 30 per cent grassland and 70 per cent heathland cover (C70). The effects of vegetation cover, breed, physiological status and their interactions on body weight (BW) and body condition score (BCS) changes were analysed. In general, AV cows showed worse (P less than 0.001) BW and BCS changes than AM cows (-81 vs. 18 g per day; -0.16 vs. 0.03 BCS units). In C30, cows gained 80 g per day and maintained BCS (0.00), whereas in C70 cows lost 143 g per day and 0.14 BCS points. An interaction (P less than 0.01) between breed and vegetation cover indicated that the differences between breeds mostly occurred in C70 plot. Lactating cows lost BW and BCS, whereas non-lactating cows used to gain BW and BCS (-253 vs. 190 g per day; -0.22 vs. 0.09 BCS units; P less than 0.001). Regarding calf growth, no differences were found between breeds in spite of the greater mature BW size in AV breed, while greater BW gains were observed in C30 than in C70 (769 vs. 557 g per day; P less than 0.001). Cattle from AM breed present a better adaptation to high moun- tain conditions, particularly when the availability of quality pasture is limiting
