This experiment investigated the effects of different levels of bile acid (BA) additives in diets on the lactation performance, serum antioxidant metabolites, and serum biochemical indices of 60 multiparous mid-lactation dairy cows. The cows were randomized to receive one of the four homogeneous treatments, with the BA preparation supplemented at 0, 6, 12, and 18 g/head/d. The experiment lasted for 14 weeks. The first 2 weeks were the pre-feeding period. The milk yield and composition data were recorded weekly, and the dry matter intake and antioxidative blood index were analyzed on the 6th, 10th, and 14th weeks of the study. On the 84th day of the experiment, the experimental group exhibited significantly higher levels of total protein and albumin, by 57.5% and 55.6%, respectively, compared to the control group (p < 0.05). On both the 28th and 84th days of the trial, the experimental group showed a markedly higher lipase content compared to the control group, by 26.5% and 25.2%, respectively (p < 0.05). Furthermore, the experimental group displayed notably elevated levels of superoxide dismutase, glutathione peroxidase, and total antioxidant capacity, surpassing the control group by 17.4%, 21.6%, and 8.7%, respectively. In conclusion, BA additives improve the serum antioxidant indices of dairy cows, thereby enhancing the performance of these cows.

Tea tree oil (TTO) plays an important role in regulating lipid metabolism and has anti-inflammatory properties. In postpartum dairy cows, dry matter intake (DMI) is dramatically decreased, resulting in lipid metabolism disorder and the systemic pro-inflammatory response. However, the effects of TTO on glucolipid metabolism and immunity in postpartum dairy cows remain uninvestigated. Therefore, this study aimed to evaluate the effects of TTO on production performance, serum biochemical indicators, and immunity in postpartum dairy cows. Our results demonstrate that DMI tended to increase (p = 0.07) in the total mixed ration (TMR) diets supplemented with 0.01% TTO/dry matter (DM) basis relative to that in the control group. The 4% fat-corrected milk (FCM) content in the 0.01% and 0.02% TTO groups showed an increase (p = 0.09) compared with that in the control. Remarkably, the levels of globulin (GLO) and immunoglobulin G (IgG) were elevated (p < 0.05) in the TMR diet supplemented with 0.02% TTO compared to those in the control group. The TTO caused no profound changes in cholesterol (CHO), triglyceride (TG), high-density lipoprotein (HDL), or low-density lipoprotein (LDL). Notably, 0.02% TTO increased (p < 0.05) the serum glucose concentration relative to that in the control group. In conclusion, our results demonstrate that TTO could improve glucolipid metabolism and enhance immunity in postpartum dairy cows. It may be a novel resolution strategy for body condition recovery and the improvement of milk performance.

Excessive lipid mobilization will snatch cell membrane lipids in postpartum dairy cows, which may impair the function of immune cells, including peripheral mononuclear cells (PBMCs) and polymorphonuclear granulocytes (PMNs). Acetate, as a precursor and the energy source of milk fat synthesis, plays a key role in lipid synthesis and the energy supply of dairy cows. However, there is little information about the effect of sodium acetate (NaAc) on the immune function of PBMC and PMN in postpartum dairy cows. Therefore, this study aimed to evaluate the effects of NaAc on the immune functions of PBMCs and PMNs in postpartum dairy cows. In this experiment, twenty-four postpartum multiparous Holstein cows were randomly selected and divided into a NaAc treatment group and a control group. Our results demonstrated that the dietary addition of NaAc increased (p < 0.05) the number of monocytes and the monocyte ratio, suggesting that these postpartum cows fed with NaAc may have better immunity. These expressions of genes (LAP, XBP1, and TAP) involved in the antimicrobial activity in PBMCs were elevated (p < 0.05), suggesting that postpartum dairy cows supplemented with NaAc had the ability of antimicrobial activity. In addition, the mRNA expression of the monocarboxylate transporters MCT1 and MCT4 in PBMCs was increased (p < 0.05) in diets supplemented with NaAc in comparison to the control. Notably, the expression of the XBP1 gene related to antimicrobial activity in PMN was upregulated with the addition of NaAc. The mRNA expression of genes (TLN1, ITGB2, and SELL) involved in adhesion was profoundly increased (p < 0.05) in the NaAc groups. In conclusion, our study provided a novel resolution strategy in which the use of NaAc can contribute to immunity in postpartum dairy cows by enhancing the ability of antimicrobial and adhesion in PBMCs and PMNs.