Impact of severe nutrient restriction before dry-off on inflammatory-, hepatic-, and immune-related indicators from dry-off through the transition period.

Drying off high-producing dairy cows can induce inflammatory responses associated with mammary involution, particularly when milk yield remains high at milking cessation. Nutrient restriction is often used to reduce milk yield to ∼15 kg/d before dry-off, a level considered favorable for mammary involution. However, restriction can also alter metabolic status during late lactation and the effects of this strategy on systemic inflammatory status and liver function during the subsequent transition period remain unclear. The objective of this study was to determine whether a severe reduction in dietary nutrient supply before dry-off affects systemic inflammatory status, liver function, and selected immune-related indicators during dry-off and the subsequent transition period. Thirty-two Holstein cows arranged in 16 pairs were initially enrolled and assigned at the pair level to either receive ryegrass hay ad libitum as the sole feed for 7 d before dry-off (NR) or to continue receiving the lactation diet (CTR). After exclusion of cows that did not meet the inclusion criteria, 26 cows producing more than 15 kg/d remained in the final dataset (NR, n = 13; CTR, n = 13). Treatments were applied at the pair level, whereas biological measurements were collected at the individual cow level. After dry-off, carried out 55 d before the expected calving, both groups received only ryegrass hay for 7 d, and free access to water was always provided. Blood samples were collected at -7, -3, 0, 1, 4, 7, 14, and 28 d from dry-off (DFD), and -14, -3, 3, 7, 14, and 28 d from calving (DFC). Milk samples were collected at -7, -3, and 0 DFD and 7, 14, and 28 DFC for SCC determination, bacteriological culture, and flow cytometry analysis. Restriction reduced milk yield by 62% before dry-off. Dry-off significantly altered blood cell count and plasma concentrations of inflammatory biomarkers. Milk SCC increased during restriction but was similar afterward. Overall differences between treatments in blood cell counts were limited. Similarly, no differences in CD3+, CD4+, CD8+, and CD11b+ milk cell populations were detected. Compared with CTR, in NR monocyte count was lower and eosinophils higher at 0 DFD. Lower haptoglobin and reactive oxygen metabolites concentrations at 4 DFD suggested a different temporal pattern of the systemic response after dry-off, potentially consistent with an earlier onset of involution-related changes. Nevertheless, after calving, NR cows had lower albumin and paraoxonase, and higher globulin, haptoglobin, bilirubin, AST-GOT, and myeloperoxidase at key time points, consistent with a less favorable inflammatory and hepatic biomarker profile. These findings, together with the previously reported reduction in DMI in NR cows, suggest that severe nutrient restriction before dry-off may alter the timing of dry-off-related responses and impair metabolic and inflammatory adaptation during the subsequent lactation. Further research is needed to decipher the mechanism underlying these long-term effects.