Relationship between aerosols and bacteria in different japanese dairy housing and their mitigation methods

概要

The objectives are to elucidate relationships between aerosols and bacteria, and their dependence on environmental factors during all the seasons (spring, summer, autumn, and winter) in different types (open type, enclosed type, tie-stall, and calf) of dairy houses, and to find out the effectiveness of an air cleaner machine (ACM) in reducing aerosols and bacteria in an enclosed type dairy house during winter in Tochigi, Japan.

The concentrations of all sizes of aerosols were higher during the summer in open house. The concentrations of 0.3–2.0 µm aerosols were higher in summer, but the concentration of 2.0–10.0 µm aerosols was higher in winter in enclosed house. The concentrations of total aerobic, S. aureus, and E. coli during the summer in open, tie-stall, and calf houses were high. But high concentrations of total aerobic, S. aureus, and E. coli were found in enclosed house during winter. The E. coli concentration in calf house was higher than concentrations in open, enclosed, and tie- stall house during summer. There were significant differences (p < 0.05) of total aerobic, S. aureus, and E. coli in both open and enclosed house during all seasons. The highest significant difference of total aerobic, S. aureus, and E. coli was found between summer and winter in both open and enclosed house.

The highest airflow within the enclosed house observed during summer than all other seasons and lowest airflow within the enclosed house observed during winter. The airflow difference between summer and winter in the enclosed house causes a difference in concentrations of aerosols and bacteria in the enclosed house. There was no airflow difference found in the open house during different seasons. There were seasonal differences in temperature and RH both in the open and enclosed house. The most significant differences were found between summer and winter in both open and enclosed house. The highest VPD observed during the warmer months in the dairy houses except for the enclosed type house where lowest VPD found during the summer.

There were a total of 78 (57 positive and 21 negative) relationships observed among aerosols, bacteria, and environmental factors in different houses in different seasons. Among 78 relationships, 11 positive relationships between aerosols and bacteria (i.e., bacteria concentration increased with increased aerosol concentration), four negative relationships between aerosols and bacteria (i.e., bacteria concentration decreased with increased aerosol concentration), 13 positive and one negative relationship between temperature and bacteria, two positive relationship between RH and bacteria, 15 positive and one negative relationship between aerosols and temperature,

five positive and four negative relationships between RH and aerosols, six negative relationships between aerosols and airflow, six positive and two negative relationships between aerosols and VPD, and five positive and three negative relationships between aerosols and VPD were observed.

The four positive relationships of aerobic bacteria with 0.3–5.0 µm aerosols, one positive relationship of Salmonella spp. with 0.5–1.0 µm aerosols during the winter, every two positive relationships of S. aureus and E. coli with 2.0–10.0 µm aerosols, and one negative relationship of Salmonella spp. with 1.0–2.0 µm aerosols, observed during the summer in calf houses. One negative relationship of E. coli with 1.0–2.0 µm aerosols during the summer and one positive relationship of S. aureus with 2.0–5.0 µm aerosols during the autumn in open house. One positive relationship of E. coli with 5.0–10.0 µm aerosols during the spring, two negative relationships of S. aureus with 0.3–0.5 and 2.0–5.0 µm aerosols during the summer in the enclosed house. During winter in calf house, the higher total aerobic and S. aureus concentrations correlated with higher temperatures, but these concentrations gradually decreased with decreasing temperature.

There was a significant difference (p < 0.01) of 2.0–5.0 and 5.0–10.0 µm aerosols observed in the exhaust air of the ACM. There was a significant difference (p < 0.05) of total aerobic and S. aureus, and complete disappearance of E. coli also found in the exhaust air. The reduction of 0.3–0.5, 0.5–1.0, 1.0–2.0, 2.0–5.0, and 5.0–10.0 µm aerosols were 49.44%, 55.46%, 45.09%, 63.43%, and 93.11%, respectively, and total aerobic, S. aureus, and E. coli were 84.86%, 82.22%, and 100.00%, respectively in the exhaust air. The overall reduction of 0.3–0.5, 0.5–1.0, 1.0–2.0, 2.0–5.0, and 5.0–10.0 µm aerosols were 0.09%, 1.06%, 3.11%, 5.04%, and 8.05%, respectively, and total aerobic, S. aureus, and E. coli were 7.00%, 9.55%, and 61.56%, respectively in the central air. But just after one hour of stopping the ACM, the concentration of 0.3–0.5, 0.5–1.0, 1.0–2.0, 2.0–5.0, and 5.0–10.0 µm aerosols increased to 2.06%, 0.07%, 0.26%, 2.42%, and 6.34%, respectively, and the concentration of total aerobic, S. aureus, and E. coli increased to 8.13%, 7.93%, and 184.13%, respectively in the central air.