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Thirty-four dairy farms in the south central zone of Chile were evaluated in order to describe the functioning of the milking machines with respect to vacuum, pulsators, milklines and cluster characteristics and their relationship with somatic cell count (SCC) and milk yield (MY). An inadequate nominal vacuum level (NVL) was one factor that influenced negatively SCC. The increase of SCC was more accentuated in those milking machines with high-lines than mid- and low-lines. MY was also negatively influenced by an inadequate high NVL. Higher MY value was found in those farms which had < 44 kPa NVL. In all cases, effective vacuum reserve deficit (EVRD) produced SCC above international recommendations. The EVRD effect was not significant (P > 0.05) on MY. There was no influence of the pulsation type on SCC and MY, but in all cases the association pulsation-pulsator produced an SCC above international recommendations. A highly significant positive correlation between milkline height and SCC was found (r = 0.41; P < 0.01). Only low-lines presented SCC within recommended international levels. Milking machines with a small capacity cluster volume showed higher SCC. Low-lines with a large claw (300-350 mL) had lower SCC (P < 0.05) compared with mid-lines. No significant influence of claw capacity on MY was found. Cows with a high SCC level produced below the optimal level. Good milking machine functioning and maintenance might be the only solution in order to obtain maximum benefits at the studied farms. [ABSTRACT FROM AUTHOR]