Warm, rainy winter onset increases the risk of hard, icy snow layers and the occurrence of mycotoxins in reindeer winter pastures

Abstract

When thick wet snow covers unfrozen ground at the beginning of winter, herders fear the development of a hard, icy bottom snow layer and the appearance of noxious moulds (microfungi) in semi-domesticated reindeer pastures. Such winter onsets were experienced in 2019 and 2021 in the reindeer herding area of Finland, after which significant reindeer losses, along with collapses in calf production and slaughter animals, were encountered. We studied the development of weather and snow conditions in the late autumn and early winter of 2021–2022 and measured snow conditions in March 2022 in 11 reindeer cooperatives. We also collected samples from reindeer winter forage plants for mycotoxin analysis. We found that the weather and snow conditions during the late autumn and early winter of 2021 caused the formation of a hard, icy bottom snow layer and the development of mycotoxins in pastures. Alternariol (AOH) and alternariol monomethyl ether (AME), produced by Alternaria spp., were found in all 33 samples (104–2562, 61–808 µg/kg DM) and zearalenone (ZEN) by Fusarium spp. in 16 samples (14–206 µg/kg). Certain significant correlations in the concentrations of mycotoxins with snow conditions and ground surface temperatures were found. We assume that besides difficult grazing conditions in the winters of 2019–2020 and 2021–2022, the presence of mycotoxins in pastures has contributed to reindeer losses and reduced the body condition, health, and reproduction of reindeer. As onsets of winters become warmer and rainier, the risk of similar pasture conditions in reindeer herding may increase.