ATP bioluminescence to establish a test procedure for hygiene testing of liners and tubes on farm level An investigation of the effect of ageing on the hygienic status of rubber liners and tubes

When rubber equipment in a milking system ages, physical and chemical deterioration occurs and cracks, crevices, as well as deposits of organic and inorganic material is formed on the surface. Bacterial colonization can accumulate, especially on ageing rubber equipment and if the cleaning procedure is not functioning properly. Formation of biofilm in milking equipment could in turn cause bacterial contamination of bulk tank milk. ATP bioluminescence is a fast and easy way to determine the hygienic status of a surface based on its ATP content, and results are given in relative light units (RLU). The method measures both bacterial contamination as well as residues from other organic material. ATP bioluminescence has previously been assessed in order to investigate the hygienic status of milking equipment but large variations between measurements have been seen and correlations between RLU values and total bacterial count (CFU) have shown deviating results. The aim of this study was to use ATP bioluminescence to establish a test procedure for hygiene testing of liners and tubes that would give reliable and reproducible results. The study also aimed to investigate whether the hygienic status deteriorated as rubber liners and tubes aged and if it was possible to set thresholds for RLU values that could determine when liners should be replaced, based on their hygienic status. The study was carried out on three Swedish farms with milking parlours and the total study period was 7 months. To establish a standard test procedure, several sampling parameters were tested on one of the farms and the effect of each parameter on the obtained RLU values was assessed. The final test procedure was then used on the three farms as liners aged for at least 2400 milkings, and as tubes aged for up to 6 months. CFU was determined for comparison with RLU values on one farm during the whole study, and occasional samples for comparison between CFU and RLU were also taken on another farm. The results showed that RLU values were significantly affected by sampling location on the liner or tube, type of detergent and milk point in the parlour. Liners on the same cluster could show large variations in RLU values, making it difficult to obtain a high reproducibility between measurements. RLU values declined on all three farms when the equipment aged, which may have been due to seasonal effects or that detergent residues quenched the ATP readings. The results from the study indicated that liners and tubes can maintain a clean hygienic status despite ageingif the cleaning procedure is efficient. There was a strong significant correlation between CFU and RLU (r=0.83, p<0.0001). The study also showed that RLU values are individual for each farm and that high RLU values can be obtained even when the number of CFU is low, due to other organic debris such as milk residues remaining in the equipment. Because of individual differences between farms, it was not possible to propose a general threshold RLU level indicating when aged milking equipment should be replaced.