Impact of close-up dry period heat stress on performance, fertility, and immunometabolic blood indices of dairy cows – prospective cohort study

Abstract This study aimed to investigate whether heat stress, as defined by the temperature-humidity index (THI) during the close-up period, had any impact on the productive performance, fertility, and immunometabolic blood indices of dairy cows in the subsequent lactation. The THI on the −7 d before the calving day was negatively associated with fertility parameters such as delayed first estrus postpartum, an elongated calving interval by approximately 32 d, a higher number of services per conception by 1.00, and an elongated artificial insemination service period, days open, and inter-calving period by about 20, 52, and 52 d, respectively. Lactation performance was associated with increasing THI values on −21, −14, and −7 d before calving resulting in decreased milk yield by about 2.30, 2.60, and 2.90 kg, respectively. The study found that the immunometabolic blood indices were associated with increasing THI values during the close-up dry period. The study showed that exposing dairy cows to close-up period heat stress had negative consequences on performance, fertility, and immunometabolic blood indices in the subsequent lactation. Therefore, it is recommended that herd management and barn microclimate changes be implemented earlier, starting from the late dry period, to mitigate the negative impact of heat stress occurrences.