Towards an optimum mixing protocol for on-farm bulk milk sampling

This paper describes the application of a bottom-sampling technique to dynamically monitor creaming and mixing in bulk milk tanks and determine optimum mixing protocols for milk sampling. Creaming onset in field experiments occurred between 40 and 50 min. Bottom-sampling data determined after 3 h of creaming indicate that the mean mixing time required to ensure a homogenous sample for composition testing is 57 s, and there is a less than 1% probability that an individual tank would require more than 2 min of agitation. Bottom and top-sampling statistics determined after 1 h of creaming indicate mean mixing times of 20 and 34 s, respectively, and predict that individual tank mixing times will exceed 46 and 64 s, respectively, less than 1% of the time. Bacterial cell counts were directly correlated with fat content, but somatic cell counts were independent of fat content. Based on these results, it is recommended that hourly agitation of bulk tanks as currently prescribed in many jurisdictions should be maintained, but the duration of intermittent agitation should be reduced from 5 to 2 min to reduce the impact of agitation on fat globule stability. If hourly agitation is effected during milk storage, agitation time before sampling can be reduced from 5 to 2 min. This will save time for drivers and trucks and reduce the potential impact of agitation on fat globule stability.