Since the early 2000s forages and supplementary feeds utilised on New Zealand dairy farms have changed but the potential consequences of those changes on the spore populations in the raw milk are unknown. To investigate the potential effect that the bacterial spore populations within the feeds can have on the bacterial spore populations in raw milk, samples of raw milk and the feeds consumed were analysed for their spore populations.
Bacterial spore selection and detection was based on standard microbiological methods, with a heat treatment at 80°C for 12 min to select for spores, followed by detection using two agars and three different incubation temperatures, to capture a wide spectrum of psychrotrophic, mesophilic and thermophilic spores.
From this analysis, the highest counts of bacterial spores were found in tuber-feeds (fodder beet (Beta vulgaris) and turnips (Brassica rapa)) and palm kernel expeller (made from Elaeis guineensis) followed by pasture silage (Lolium Perenne + Trifolium Repens) and feed concentrates. Low counts of spores were present in raw milk samples.
The bacterial spores found were identified using a MALDI-TOF-MS Biotyper (Bruker). These data showed that ~ 70 % of the bacterial spore species identified in milk, could also be identified in feeds from the same farm. The results also showed variations in the diversity of the spore populations between different feed samples, milk samples and different farms.
This study indicates that the bacterial spore populations within cow feeds could influence the spore populations present in the raw milk.