The effect of seasonal changing temperature on blood metabolic indicators in Holstein Friesian cows

The main aim of this research was to study the impact of seasonal temperature variation on metabolic markers in dairy cows, particularly blood parameters that are recognised as indicators of homeostasis. From December 2019 to December 2020, 723 blood samples were collected from 382 lactating Holstein Friesian cows throughout the four seasons. The temperature humidity index (THI) was used to identify the seasons: hot (THI ≥68), or cold (THI <68). Seasons had a significant effect (p < 0.05) on insulin and prolactin levels and no significant effect on non-esterified fatty acids (NEFA). Insulin averaged 9.86 mIU/L in spring, significantly higher than winter (6.30 mIU/L) and autumn (5.92 mIU/L), but did not differ between spring and summer. Prolactin levels increased progressively, they were lowest in autumn (3.78 ng/mL), rose slightly in winter (6.49 ng/mL), and continued to increase in spring (8.58 ng/mL) and summer (11.22 ng/mL). In conclusion, the fluctuation in temperature across the seasons under continental climate significantly impacts specific metabolic markers in dairy cows. Despite these seasonal variations in insulin and prolactin, NEFA levels remained consistent across all seasons. These findings highlight the differential impact of seasonal temperature changes on key metabolic hormones involved in energy balance and lactation in Holstein Friesian cows.