Microbiological quality of raw goat's and ewe's bulk-tank milk in Switzerland

Abstract

A total of 407 samples of bulk-tank milk (344 of goat's milk and 63 of ewe's milk) collected from 403 different farms throughout Switzerland, was examined. The number of farms investigated in this study represents 8% of the country's dairy-goat and 15% of its dairy-sheep farms. Standard plate counts and Enterobacteriaceae counts were performed on each sample. Furthermore, the prevalence of Staphylococcus aureus, Campylobacter spp., Shiga toxin-producing Escherichia coli, Salmonella spp., and Mycobacterium avium ssp. paratuberculosis was studied. The median standard plate count for bulk-tank milk from small ruminants was 4.70 log cfu/ml (4.69 log cfu/ml for goat's milk and 4.78 log cfu/ml for ewe's milk), with a minimum of 2.00 log cfu/ml and a maximum of 8.64 log cfu/ml. Enterobacteriaceae were detected in 212 (61.6%) goat's milk and 45 (71.4%) ewe's milk samples, whereas S. aureus was detected in 109 (31.7%) samples of goat's milk and 21 (33.3%) samples of ewe's milk. Campylobacter spp. and Salmonella spp. were not isolated from any of the samples. However, 16.3% of the goat's milk and 12.7% of the ewe's milk samples were polymerase chain reaction (PCR)-positive for Shiga toxin-producing E. coli. Seventy-nine (23.0%) goat's tank-milk and 15 (23.8%) ewe's tank-milk samples were PCR-positive for insertion sequence 900, providing presumptive evidence for the presence of M. avium ssp. paratuberculosis. These results form the basis for determining the microbiological quality standards for goat's and ewe's milk. Moreover, the data presented form part of the risk assessment program for raw milk from small ruminants in Switzerland.