The non-selective antibiotic treatment of dairy cows at the last milking in lactation was studied for its influence on the reduction in the occurrence of infectious processes in the udder after calving. The herd of 120 dairy cows, on an average, was housed in the K 98 cow-house and in a calving house equipped with the traditional technology. The non-selective treatment was performed in 125 dairy cows in the form of single administration of Oxymykoin foam (Galena) (70 cows) and Chronicin foam (Galena) (55 cows) after the last milking in lactation. The treatment of 53 bacteriologically positive cows with Oxymykoin foam had 86.8% therapeutic effectiveness; this indicates the excellent effectiveness of the preparation. Five additional new infections arose in this group of cows treated with Oxymykoin. The treatment of 36 bacteriologically positive cows with Chronicin foam had the effectiveness of 63.9%; in almost 2/5 of the treated cows (13 animals) the bacteria causing mastitis persisted in the post-parturient period. Eight new infections occurred in this group of treated cows. The results of the non-selective antibiotic treatment of dairy cows after the last milking in lactation prove the good effectiveness of the method reducing the percentage of infected cows in the period after calving.