Analysis of milking performance of cows in different lactations and lactation periods based on the electrical conductivity of milk

Abstract

Milk electrical conductivity (EC) and milk flow rate are potential indicators in selection targeting mastitis resistance [1]. Measurement of milk (EC) is one of the indicators of such diagnosis, because it provides an early warning system by monitoring udder health at each milking [2, 3]. The work aims to determine the influence of the EC of milk on milking indicators of cows at different lactations and lactation periods. During the research, the EC of milk of 375 milking cows, milk yield, duration of milking, average and maximum milk flow were analysed. Cows were divided into three groups according to the EC of milk (< 5.0 mS/cm, 5.0–5.5 mS/cm, > 5.5 mS/cm). Lactation was divided into two groups: 1 lactation, 2 and older lactations. Cows were divided into four groups according to the period of lactation (up to 100 days, from 101 to 200 days, from 201 to 300 days and over 300 days of lactation). Averages, errors of averages, and statistical reliability of data (P) were calculated using Microsoft Excel programme. Differences were considered significant at P < 0.05. We found that cows of the second and older lactation with a milk EC of less than 5.0 mS/cm produced 1.74 kg (P < 0.05) less milk than cows with a milk EC of 5.0–5.5 mS/cm, and 1.77 kg (P < 0.05) less than cows with a milk EC higher than 5.5 mS/cm. As the EC of milk increased, milking duration also increased with the number of lactations and lactation days. In the period up to 100 days of lactation, cows with a milk EC higher than 5.5 mS/cm had a milking duration that was 34 seconds longer than cows with a milk EC lower than 5.0 mS/cm (P < 0.05). Cows of the second or later lactations with a milk EC greater than 5.5 mS/cm had an average milk flow of 0.2 kg/min (P < 0.05) lower than cows with a milk EC of 5.0–5.5 mS/cm, and 0.23 kg/ min (P < 0.05) lower than those with a milk EC lower than 5.0 mS/cm. Cows over 300 days of lactation with a milk EC greater than 5.5 mS/cm had an average milk flow rate and maximum milk flow rate of 0.75 kg/min and 1.29 kg/min lower, respectively, than cows with a milk EC of less than 5.0 mS/cm (P > 0.05). In conclusion, we can state that increased duration of milking and decreased average milk flow can be used as additional indicators for evaluating the udder health of cows.