Validation of relationship between milk resistance and daily yield of dairy cows

The reduced value of resistance (R) of milk (<167Ω) or increased conductivity (EC) >6.0 mS/cm indicate the growing number of ions in milk during the initial phase of mastitis. The aim of this study is to demonstrate a linear (verified by a validation procedure) dependency between R and mean daily yield (MDY), which could be used for current monitoring and forecasting of milk yield in dairy cow herds. Although the topic has frequently been examined, a validated model for prediction of MDY based on R has still not been presented.

Data from 118 dairy cows were analyzed in the study. The validation of model dependency R↔MDY was performed by the live-one-out method (LOO).

The minimum geometrical/arithmetical mean of R milk was observed during the 1st month of lactation and was 53.40/254.86 Ω. However, the maximum geometrical/arithmetical mean of R milk was observed during the 7th month of lactation and has 189.62/574.51 Ω. The final model was described by the curve equation MDY = -04461 × R% + 51.58 where R% - percentage share of cows in a herd whose R oscillated within the limits 49.38-154.32 Ω.

Complete predictivity of the model within the above mentioned limits ("prognostic range") was confirmed by the results of validation of the model. The developed model enables the efficiency of a herd at specified percentage share of cows of defined milk R value to be determined.