The effect of ambient temperature and relative humidity in postpartum dairy cows on productive and reproductive performance and biochemical blood indices in the subsequent lactation

This study evaluated the effects of ambient temperature (T) and relative humidity (RH) during the postpartum transition period on dairy cows’ milk performance, fertility, and immunometabolic blood indices in the subsequent lactation. A total of 100 Polish Holstein-Friesian cows originating from five commercial dairy farms were categorized into three groups based on average T (<16 °C, 16-20 °C and >20 °C) and RH (<65%, 65-75%, and >75%) on the calving day(0d), and days7, 14, 21 after calving. With increasing T and RH postpartum, the average daily milk yield during the first 150 days in milk decreased gradually, and the differences between T <16 °C and >20 °C and RH <65% and >75% groups were approx. 3.48 and 2.78 kg, respectively. Milk of cows exposed to increased T and RH was lower in protein, and lactose and higher in fat, milk urea, and somatic cell count. It was also characterized by altered fat composition. Ambient T during the postpartum period had a negative effect on cows’ fertility, which, however, was not affected by RH. The increasing T from <16 °C to >20 °C resulted in the later manifestation of the first estrous(by 27.7 days), a more extended artificial insemination service period (by 19.4 days), a higher number of insemination services per conception (by 0.92 on average), more days open (by 43.3 days), and a longer calving interval (by 43.3 days). Within ranges used in this study, increasing T, and RH during the period from d 0 to d 14 postpartum led to decreased body condition score on day 21 by approx. 0.48 and 0.51 points, respectively. Furthermore, T and RH on a calving day were associated with altered biochemical blood indices on d 21 after calving, indicating a more severe negative energy balance and a state of inflammation. The results of this study suggest that dairy cows that calve when T >16 °C should be provided cooling to ensure optimal environmental conditions for high milk production and prevent economic losses associated with reduced milk yield and low fertility.