Abstract
Research has shown that total bacterial count (TBC), which is the bacterial growth per ml of milk over a fixed period of time, can be decreased by good hygiene and farm management practices. The objective of the current study was to quantify the associations between herd management factors and bulk tank TBC in Irish spring calving, grass-based dairy herds. The relationship between bulk tank TBC and farm management and infrastructure was examined using data from 400 randomly selected Irish dairy farms where the basal diet was grazed grass. Herd management factors associated with bulk tank TBC were identified using linear models with herd annual total bacterial score (i.e., arithmetic mean of the natural logarithm of bulk tank TBC) included as the dependent variable. All herd management factors were individually analysed in a separate regression model, that included an adjustment for geographical location of the farm. A multiple stepwise regression model was subsequently developed. Median bulk tank TBC for the sample herds was 18,483 cells/ml ranging from 10,441 to 130,458 cells/ml. Results from the multivariate analysis indicated that the following management practices were associated with low TBC; use of heated water in the milking parlour; participation in a milk recording scheme; and tail clipping of cows at a frequency greater than once per year. Increased level of hygiene of the parlour and cubicles were also associated with lower TBC. Herd management factors associated with bulk tank TBC in Irish grazing herds were generally in agreement with most previous studies from confinement systems of milk production.
Highlights
Total bacterial count (TBC) is the bacteria growth per ml of milk over a fixed period of time (Blowey and Edmondson 1995)
There was no significant association between the level of S. aureus and total bacterial score (TBS)
When the combined management factor regression model was developed, the cumulative effect of best practices, such as participation in a milk recording scheme, heated water in the parlour, washing of the walkways before milking, the shed in good condition, tails ringed or clipped at a frequency of greater once a year and clean cubicles, was calculated as 20,167 cells/ ml, i.e., milk total bacterial count (TBC) was expected to be 20,167 cells/ml lower when these best practices were in place compared to the poorest alternative within each variable
Summary
Total bacterial count (TBC) is the bacteria growth per ml of milk over a fixed period of time (Blowey and Edmondson 1995). According to Bramley and McKinnon (1990), the three main areas or sources of microbial contamination are from within the udder subsequent to synthesis, the exterior of the udder and the surface of milk handling and storage equipment. Jayarao et al (2004) documented that herd size and farm management practices influence bacterial counts in bulk tank milk. Hogan et al (1990) reported that bedding material was a source of bacteria, and Natzke (1981) documented that an increased plate loop count was associated with poor maintenance of the milking machine. The objective of the current study was to quantify the associations between herd management factors and bulk tank TBC in Irish spring calving, grass‐based dairy herds
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