Abstract
Solid-liquid separation solids from anaerobically digested dairy cow slurry (hereinafter, separated solids) are used as bedding material, but there are hygienic concerns that such material, being derived from manure, may cause outbreaks of mastitis. In this study, we investigated the hygienic status of separated solids during bedding material preparation and during use as bedding at a dairy farm, using Escherichia coli counts as an indicator. Two days’ worth of separated solids were deposited in a pile. Then, every 2 days, 4 times in total, a new pile of separated solids was redeposited after each existing pile was turned and moved. This resulted in 4 piles, and the fourth pile was then used as bedding. Due to turning, the temperature of the separated solids fl uctuated between 45 °C and 80 °C in the summer and between 40 °C and 70 °C in the winter; throughout the year, the separated solids had experienced temperatures of 55 °C or greater for a total of 100 h by the time of the fourth turning. The E. coli counts in the separated solids immediately after solid-liquid separation were 102 to 103 CFU/g-wet but declined to below the limit of detection in 90 % of the samples prior to placement in stalls. These results indicate that aerobic fermentation of separated solids is effective in eliminating E. coli.
Counts of E. coli in the bedding were below the limit of detection prior to placement in stalls, and then increased rapidly to between 102 and 104 CFU/g-wet within 2–3 h after placement, reaching 104 to 105 CFU/g-wet by 22–23 h after placement. In addition, E. coli counts in unused bedding that remained in front of the brisket locator since the start of the investigation increased to 103 to 104 CFU/g-wet at about 12 h after placement in the stalls. These results did not indicate an inhibitory effect of the separated solids bedding after short-term fermentation on the growth of E. coli. The relation between average barn temperature and average E. coli counts in the bedding during use prior to the placement of new bedding in stalls had a high positive correlation (r = 0.918) in the range of 1.6 °C to 23.7 °C. At temperatures of 22.7 °C or higher, E. coli counts reached a level estimated to be conducive to the outbreak of mastitis (106 CFU/g-wet or greater).
The separated solids bedding was found to have the following characteristics. (1) Moisture at the time of placement in stalls was high, at about 78 %, and because of this, (2) E. coli counts tended to be low when moisture was high; (3) moisture was high and E. coli counts were low when the barn temperature was low; and (4) moisture was low and E. coli counts tended to be high when the barn temperature was high.
