Prepartal liver glutathione and its association with lactation performance, metabolism, and health outcomes in transition dairy cows.

Our objective was to determine the association of prepartal liver glutathione (GSH) concentration with lactation performance parameters, metabolism and inflammation, and gene expression in transition dairy cows. Sixty Holstein dairy cows were enrolled at -21 ± 3.3 d relative to calving and remained on trial until 30 DIM. All cows received the same close-up diet from -21 DIM until calving (1.67 Mcal/DM and 13.5% CP) and lactation diet from calving until 30 DIM (1.80 Mcal/DM and 17.7% CP). A liver biopsy was performed in all cows at -8 d (±3.2 d) relative to calving, and total GSH was measured using a commercial colorimetric kit. This metric was used to retrospectively classify cows by GSH as high (HGSH; n = 15), medium-high (MHGSH; n = 15), medium-low (MLGSH; n = 15), and low (LGSH; n = 15). Liver samples were collected at -8, 7, and 21 DIM, and blood samples at -21, -10, 2, 7, 14, and 21 DIM to evaluate oxidative stress, metabolism, inflammation, and liver function biomarkers. Statistical analysis was performed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC) with the preplanned contrast to test a linear effect with increasing levels of GSH. A linear increase in prepartal energy balance (EB; from -1.55 to 1.11 Mcal/d) and postpartal BCS (from 3.00 to 3.16) was observed as prepartal liver GSH increased from LGSH to HGSH groups, suggesting an association between prepartal liver GSH and energy metabolism around parturition. This effect was also associated with a trend for a linear increase in prepartal DMI as prepartal liver GSH increased across groups. We observed a linear increase in ECM (from 50.2 to 54.7 kg/d) and milk protein yield (from 1.33 to 1.46 kg/d) as prepartal liver GSH levels increased. Neither reactive oxygen metabolites nor antioxidant capacity measured via ferric reducing antioxidant power were altered according to prepartal liver GSH. However, there was a linear increase in the total thiol groups of plasma as prepartal liver GSH increased, suggesting some level of antioxidant protection. A linear increase in total (from 0.83 to 1.74 nmol/mg), reduced (from 0.66 to 1.37 nmol/mg), and oxidized forms of GSH (from 0.07 to 0.17 nmol/mg) was observed in the liver as prepartal liver GSH levels increased. The hepatic activity of g-glutamyl transpeptidase at -8 DIM was greater in MHGSH cows compared with LGSH and HGSH. At -8 DIM, a linear upregulation of genes related to GSH metabolism, including GCLC, GGCT, and GSR, was observed as prepartal liver GSH increased, suggesting that transcriptional regulation may contribute to the GSH phenotype observed in this study. These results emphasize the importance of maintaining adequate hepatic GSH reserves before calving to support metabolic adaptation and lactation performance. Future research should explore the direct effect of GSH on lactation performance and oxidative stress protection, as well as nutritional and management factors to enhance hepatic GSH synthesis before calving.