RELATIONSHIPS BETWEEN MILK ELECTRICAL CONDUCTIVITY, DAILY MILK YIELD, AND MILKING ABILITY OF PRIMIPAROUS AND MULTIPAROUS COWS

The new techniques for automation of the milking process allow for early diagnosis of mastitis. Diagnosis of subclinical mastitis should be a priority for every producer aiming to obtain raw milk of highest possible cytological quality. The analyses were performed based on herd milking data for Polish Holstein-Friesian cows yielding an average of 9500 kg milk. The herd consisted of 180 lactating cows, data from almost 152 000 milkings were obtained. Correlations were calculated between milk electrical conductivity vs. daily yield and milking ability of primiparous and multiparous cows. The numerical data were statistically analysed using multifactorial analysis of variance. An increase in milk electrical conductivity and thus deteriorating udder health were paralleled by a significantly lower milk yield in both primiparous and multiparous cows. In primiparous cows, the decrease was 4.7 kg (from 32.0 with milk electrical conductivity of <= 5.50 mS/cm to 27.3 kg with conductivity of >7.00 mS/cm). A notably greater reduction in productivity was observed for multiparous cows (5.5 kg) between the extreme ranges of milk electrical conductivity. In both primiparous and multiparous cows, milking time increased progressively with increasing range of milk electrical conductivity (from 366 to 372 s and from 369 to 379 s, respectively). Milk yield per minute decreased by 0.41 kg (from 2.23 to 1.82 kg/min.) in older cows and by 0.32 kg (from 2.05 to 1.73 kg/min.) in primiparous cows. The deteriorating udder health caused a significant decrease in daily milk yield of the primiparous and multiparous cows in every lactation period. For both primiparous and multiparous cows, the highest milk yields per minute (2.08, 2.20, 2.20 and 1.88; 2.57, 2.37, 2.18 and 1.96 kg/min., respectively) in all lactation periods were observed when milk electrical conductivity (<= 5.50 mS/cm) was indicative of very good udder health. In summing up, it is concluded that throughout lactation, in both primiparous and multiparous cows, daily milk yield decreased with increasing electrical conductivity of the milk and thus with deteriorating udder health. Furthermore, milk electrical conductivity had a significant effect (in the interaction with lactation period and daily milk yield of the cows) on milkability traits.