The association between bulk tank milk analysis for raw milk quality and on-farm management practices

The primary objective of this thesis was to investigate the association between raw milk bacterial quality and on-farm management practices in Prince Edward Island dairy herds. Secondary objectives included identification of lipolytic and proteolytic bacteria in pasteurized milk and investigation of the role of mastitis associated pathogens in elevated bacterial counts in bulk tank milk (BTM).To achieve the primary objective, 4 studies were conducted. In the first study, BTM quality was evaluated biweekly in all PEI dairy herds over a two year period (March 2005 to March 2007), using total aerobic (TAC), preliminary incubation (PIC), laboratory pasteurization (LPC), coliform (CC), and somatic cell (SCC) counts. The results of this study showed weak correlations among the bacterial counts which suggests that each count gives different information in relation to management practices. With the exception of SCC, other milk quality parameters had moderate to high coefficient of variation, which indicates that herd assessments should not rely on a single measurement. In general, there was no consistent seasonal pattern over the 2 year study period for TAC, PIC, and LPC, although all counts tended to be low in winter. The CC and SCC were always highest in summer.In the second study, the association between laboratory test results and on-farm management practices was assessed using data from a mail out survey. The survey covered 4 main areas: general farm demographics and management, cow cleanliness and hygiene, milking procedures and mastitis control, and equipment maintenance and cleaning. The response rate of the survey was 65%. The TAC and PIC were positively associated with the amount of soiling on the teats prior to udder preparation and manual cleaning of the bulk tank. Additionally, various methods of premilking udder preparation were important, with pre-dip followed by drying being superior to other methods in reducing the bacterial counts. The LPC was positively associated with the presence of a plate cooler and inadequate frequency of acid washing, whereas having a water purification system was protective. Finally, for CC, clipping udder hair and automated washing of the bulk tank were protective, whereas increasing herd size and inadequate frequency of acid washing were risk factors.In the third study, the association between BTM bacterial quality and management practices was further investigated using a case control study (January 2006 to May 2007). Cases and controls were defined based on the results of all bacterial counts. On-farm evaluation included observation of basic management practices, evaluation of equipment hygiene and cooling efficiency, and scoring of cow and environmental hygiene. The results identified udder hygiene, milking system wash solution temperature and chemistry, and milk house water quality as important factors for bacteriological quality of BTM.In the forth study, four case-control groups were evaluated to determine specific on-farm risks for each of TAC, PIC, LPC, and CC. The results of this analysis showed that TAC and PIC were mainly associated with cow and stall hygiene, washing the teats with water and not using teat pre-dip, and having dirty teats after udder preparation. The LPC and CC were related to equipment hygiene, with high counts being associated with low temperature of the cleaning solution, high water hardness score, and high alkalinity of the alkaline detergent wash.One of the secondary objectives was to characterize lipolytic and proteolytic bacteria in pasteurized milk. In this study, BTM from 100 farms was subjected to laboratory pasteurization. The lipolytic and proteolytic activity of the surviving bacteria was determined under conditions that approximate poor refrigeration. The predominant isolates from pasteurized milk were Gram-positive rods (83% mainly Bacillus spp.), followed by Gram-positive cocci (17% mainly Staphylococcus spp.). Most of the isolates showed proteolytic or lipolytic activity or both, which indicate their potential of causing spoilage of pasteurized milk.Another secondary objective was to investigate the role of mastitis-associated pathogens in elevated TAC in BTM. In 17 (19%) out of 89 samples that had high (>10,000 cfu/ml) TAC, mastitis-associated pathogens had a significant proportional contribution (≥0.25) to the TAC. While the majority of high bacterial counts were not associated with mastitis organisms, mastitis-associated pathogens can be present in very high numbers in bulk tank milk and can contribute to elevated TAC.In conclusion, TAC, PIC, LPC, and CC are of considerable value for identifying practices that could influence milk quality. Lipolytic and proteolytic bacteria which survive pasteurization, particularly Bacillus spp., represent a big challenge to the shelf life of pasteurized milk. Although not common, mastitis associated pathogens could be associated with elevated TAC in BTM.Source: Dissertation Abstracts International, Volume: 70-08, Section: B, page: 4547