Effect of time delay from sample collection and sample analysis on bulk milk somatic cell count in dairy herds

Daily bulk milk somatic cell count in dairy herds can be used as an evaluation and monitoring tool of productive process and farm management, as well as an indicator of udder health. Since a daily count is not always feasible, we decided to evaluate the effect of time elapsed from milk sample and the execution of somatic cell count (SCC). 84 bulk milk samples from 12 commercial dairy herds, stored with bronopol at a temperature of +2 - +4 C were analyzed four times every three days with Bentley Somacount 150 (Bentley Instruments, Chaska, MN) for a total of 336 values of SCC. Statistical analysis was performed using R software, and a mixed effects model with the single SCC used as random effect was performed. The model obtained, using log(SCC) is : log(SCC)= 5.8366-0,002164 x number of days from sample. Beta coefficient is statistically significant with p<0.0088. An analogue model, using time I, II, III and IV instead of the number of days from sample to analysis, shows that only at time IV there is a significant, though low, decrease in SCC. The results of this study show that log(SCC) is influenced by time passed from sample collection to analysis, but this decrease is not biologically relevant, at least until 15 days from the sample collection. We can conclude that bulk milk samples for somatic cell count, correctly preserved and analyzed till 15 days from sample, don't suffer any variation with biologically relevant significance.