Farm management factors associated with bulk tank total bacterial count in Irish dairy herds during 2006/07

Total bacterial count (TBC) is the bacteria growth per ml of milk over a fixed period of time [2]. High TBC milk should be avoided since some bacteria (Staphylococcus aureus, Escherichia coli and Streptococcus agalactiae) found in raw milk can cause diarrhoeal disease and food poisoning [7]. After pasteurisation, the risk of illness to humans can occur by recontamination of milk through milk pipes and stored milk residues or by thermoduric bacteria (Bacillus cereus) which can survive pasteurisation [7]. Bacteria can also have a negative effect on dairy products. For example, Alteromonas putrefaciens causes a surface taint in butter, and E. coli can spoil milk and dairy products by gas production during storage [7]. Accordingly, milk quality is required to be within certain thresholds according to European law ([5], Council Directive 92/46/EEC); total bacterial count must not exceed a geometric average of 100,000 per ml over two months, with at least two tests per month. Additionally, incentives (TBC less than 30,000) and penalties are applied by milk processors to help ensure high milk quality. Recent research indicates a general tendency for bulk tank TBC in Ireland to decrease between the years of 1994 to 2003, but this was followed by an increase between 2003 and 2004 [1].Milk is synthesised in epithelial cells of the mammary gland and is virtually sterile when secreted into the alveoli of the udder [26]. Thus, contamination of milk largely occurs subsequent to milk synthesis. According to Bramley and McKinnon [3], 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. Bacteria can multiply through poor hygiene and sanitation and subsequently be flushed into the bulk tank, increasing the TBC [9]. An increase in TBC can be related to mastitis organisms, environmental contaminants, dirty milking equipment or failure of refrigerati