Abstract:

This experiment was conducted to investigate the effects of inulin on production performance, immune response, antioxidant status and hormone levels of lactating dairy cows under heat stress. Twenty-four healthy, high-yield Holstein cows with similar body conditions were grouped in 4 blocks of 6 cows based on days in milk (DIM), milk yield and parity (n=6 in each group) using a completely randomized grouping design. Within each block, cows were randomly assigned to 1 of the 4 treatment groups: a control group without inulin supplementation (CON), and three groups receiving inulin at doses of 200, 300 and 400 g·d^-1 (Inulin-2, Inulin-3 and Inulin-4). The trial period was 10 weeks, including 2 weeks of pre-feeding period and 8 weeks of formal trial period. The study was carried out during the hot summer, with an average temperature-humidity index (THI) greater than 68, indicating that the cows were experiencing heat stress. The results showed that feeding inulin had no significant effect on rectal temperature (RT) and respiratory rate (RR) of heat-stressed dairy cows (P>0.05). With the increase of inulin addition, the milk yield of dairy cows showed a quadratic increase trend, but the difference was not significant (0.05≤P < 0.1), while the milk yield of Inulin-3 and Inulin-4 groups were significantly higher than that of CON group (P < 0.05). With the increase of inulin feeding amount, serum creatinine concentration quadratic significantly decreased (P < 0.05), reached the lowest value in Inulin-3 group, and was significantly lower than that in CON group (P < 0.05). The concentration of serum interleukin (IL) - 1β quadratic significantly decreased (P < 0.05), and the lowest value was observed in Inulin-3 group, which was significantly lower than that in CON group (P < 0.05). The concentration of serum tumor necrosis factor (TNF) -α quadrtic decreased, but the difference was not significant (0.05≤P < 0.1), reaching the lowest value in Inulin-3 group, which was significantly lower than that in CON group (P < 0.05). The serum total antioxidant capacity (T-AOC) showed a quadratic upward trend, but the difference was not significant (0.05≤P < 0.1), reached the highest value in the Inulin-3 group, and was significantly higher than that in the CON group (P < 0.05). In summary, dietary inulin supplementation can alleviate the heat stress of high-yielding dairy cows by improving immune performance, antioxidant status and hormone secretion, and can also increase milk yield and improve milk composition. For lactating cows experiencing heat stress, the recommended dose of inulin is 300 g·d^-1.

Key words: Holstein cows, heat stress, inulin, immune performance, antioxidant properties, hormones, production performance