The influence of pasturable and stall period diets of dairy cows on the electrical conductivity of milk

Abstract

The aim of this study was to analyse the influence of dairy cows’ diet on electrical conductivity (EC) of milk during pasturable and stall periods and to assess EC relationship with milk yield and somatic cell count (SCC). The experiments were carried out during 2009–2013 with 421 dairy cows which were milked using an automated voluntary milking system “DeLaval VMS” (“DeLaval”, Sweden). All year round the cows were kept untied indoors and fed on farm-made grass silage forage, during pasturable period the diet was supplemented with a fresh legume/ grass mixture. The data consisted of 462582 milking records. The average EC of milk (4.92 ± 0.001 mS cm -1 ) met zootechnical standards. The average milk yield was 25.12 ± 0.020 kg, milk SCC – 188.95 ± 1.032 thousand ml -1 . Milk yield during pasturable period was in average 1.4% lower and SCC was 7.9% higher than during the stall period. The average EC during pasturable period of the experiment was 3.6% higher than during the stall period in all lactations (p < 0.001). The higher (23.03 g) cows’ ruminal N-balance (RNB) during pasturable period had no positive effect on milk yield as SCC increased during that period. The correlation between milk yield and EC of milk during pasturable and stall periods was negative (r = −0.124–−0.226, p < 0.001). The observed SCC was lower than 200 thousand ml -1 in the milk samples where EC was in the range of 4.6 to 5.8 mS cm -1 . As EC increased, SCC had a statistically significant (p < 0.001) rise both in pasturable and stall periods (r = 0.356–0.403). EC of milk could provide an alternative way for early diagnosis of mastitis.