Thiamine modulates the mammary inflammation, antioxidant function and lactation performance in lactating sheep under heat-stress conditions

This study investigated the effect of dietary thiamine supplementation on mammary inflammation, antioxidant function and lactation performance of heat-stressed Hu ewes. Twenty-four lactating Hu ewes (parity 1–2; days in milk = 14 ± 1 d; milk yield = 1.25 ± 0.08 L/d) with body weight of 52.6 ± 2.7 kg and body condition score of 2.62 ± 0.12 (0 = emaciation, 5 = obesity) were selected. After a 7-d acclimation period, the ewes were randomly allocated into three treatments and raised for 21 d under different ambient temperatures: thermoneutral group without supplementation (CON), heat stress group without supplementation (HS), and heat stress group with dietary thiamine supplementation at 100 mg/kg dry matter intake (DMI) (THS). Each group consists of 8 repetitions, and each repetition involves 1 ewe. THS group significantly increased milk yield, milk fat, lactose and protein levels, except for DMI, compared with HS group ( P < 0.05). The THS group significantly decreased DMI, milk yield, milk fat, lactose and protein levels compared with CON group ( P < 0.05). Milk fatty acid (FA) production of preformed FA, C18:0, C18:1n9c, C18:2n6c, C18:3 and C20:3 of THS group significantly decreased compared with HS group ( P < 0.05). Milk FA production of preformed FA, C18:0, C18:1n9c, C18:2n6c and C20:3 of THS group significantly increased compared with CON group ( P < 0.05). Arginine, leucine, valine, alanine, and aspartate productions in milk of THS group were significantly higher than those in HS group ( P < 0.05). Relative to the HS group, total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) activities and triglyceride content were significantly higher in the THS group ( P < 0.05), while malondialdehyde (MDA) and TNF-α, IL-6, and IL-1β levels significantly declined in the THS group ( P < 0.05) in mammary vein blood and mammary tissue. Relative to the HS group, the protein abundances of lactose synthesis related proteins (GLUT1, GLUT3, and LALBA), milk fat synthesis related proteins (FASN, SCD, and PPARγ) and milk protein synthesis related proteins (CAT1, EAAT3, and ASCT2) were significantly higher in the mammary tissue in the THS group ( P < 0.05). Relative to the CON group, the protein abundances of lactose synthesis related proteins (GLUT1, GLUT3, and LALBA), milk fat synthesis related proteins (FASN, SCD, and PPARγ) and milk protein synthesis related proteins (CAT1, EAAT3, and ASCT2) were significantly lower in the mammary tissue in the THS group ( P < 0.05). These results suggest that thiamine supplementation could mitigate mammary inflammation, improve mammary antioxidant function and lactation performance.