Effects of short-term variations in temperature and air pollution on daily cattle mortality in the Netherlands

Abstract

BACKGROUND: Extreme temperatures and air pollution are both associated with increased mortality risk in humans. However, the effects of temperature and air pollution on cattle have not been investigated much before. OBJECTIVES: The objective was to estimate the short-term effects of air pollution, heat and cold on cattle mortality. METHODS: Daily data on cattle mortality, weather conditions and mean levels of PM10, O3, NH3, and NO2 of the Netherlands during 2012–2017 were collected. Then, these associations were investigated with time–series regression using distributed lag non–linear models (DLNM) including lags up to 25 days. Effects of temperature were expressed as those associated with extreme and moderate heat or cold, defined as Temperature Humidity Index (THI) values below the 1st and 5th percentile, and above the 95th and 99th percentile of the national THI distribution. Effects of air pollutants were expressed per 10 µg/m3 change in daily mean concentrations. RESULTS: A significant effect of temperature on cattle mortality was found amongst all age groups. For instance, the younger calves (0–14 days) showed a cumulative RR of 2.13 (95%CI: 1.99 – 2.28) for extreme heat and the older calves (15-55 days) showed a cumulative RR of 1.50 (95%CI: 1.37 –1.64) for extreme cold. There were some significant short-term associations between air pollutants and cattle mortality but none of these persisted during the whole over cumulative lags of 0-25 days. For example, exposure to O3 in the youngest calves resulted in a cumulative RR of 1.09 (95%CI: 1.04 – 1.4) for lag 0-7 and 1.09 (95%CI: 1.03 - 1.16) for lag 0–25. CONCLUSIONS: Both high and low temperatures were associated with increased mortality amongst calves of 15-55D, whereas associations in older calves (56D – 1Y) were only observed for low temperatures and in calves of 0-14D and cows >2Y only for high temperatures. Associations of air pollution with mortality in all age groups were not consistent, except for the effect of ozone of lag 0-7 and lag 0-25. This caused a significant excess mortality risk among all ages, only for cows of 1-2Y it was insignificant.