Partitioning of vitamin E in lactating dairy cows at two levels of vitamin supplementation

Vitamin E (VE) is a key lipid-soluble antioxidant involved in protecting biological membranes from oxidative damage and supporting immune functions. Supra-nutritional levels improved immune responses in some instances. We hypothesized that VE overfeeding could play an important role especially when heat stress occurs. The objective of this study was to evaluate the partitioning of VE to milk following the administration of two levels of VE in two seasons. Fourty-six multiparous Holstein cows (BW 750±78.8 kg) of a commercial dairy herd located in the Parmigiano Reggiano cheese-production area (N° of cows 883±48; milk yield 36±1.5 kg/d) were selected 7 days after calving, including 22 and 24 cows that calved during the winter (October to November) and summer (May to July) seasons, respectively. Cows assigned to two pens, balanced for parity and date of calving, received 2 hay-based total mixed ration (-TMR- aNDF 36 %DM, starch 27 %DM, CP 14.4 %DM, EE 2.6 %DM) supplemented with high (HVE; 8000 mg/d) or low (LVE; 1600 mg/d) doses of VE. Animals were observed from 7 to 150 days in milk (DIM). The girth circumference was measured individually at the beginning of the trial to estimate the BW and metabolic BW. Feed intake was measured weekly on a pen base by difference between the amount of feed delivered and orts. Meanwhile, the TMR of each group was sampled and chemically analyzed. Plasma samples were collected from the coccygeal vein at 7, 20, 60 and 150 DIM, and analyzed for the metabolic profile and VE content. Milk yield was recorded, and milk samples were collected individually 3 times per season during the milk samplings performed by the breeder association. Milk quality was determined by MilkoscanTM while VE content was determined using an iCheck fluorometer–spectrophotometer (iCheck Vitamin E; BioAnalyt GmbH, Teltow, Germany). Data were statistically analyzed by generalized linear models using SPSS software (IBM SPSS Statistics for Windows, Version 29.0; IBM Corp., Armonk, NY). An increase in the DMI was observed in the summer season in the HVE vs LVE group (29.2 vs 28.0; p=0.027), although metabolic profile, milk yield and quality were similar between groups. The highest daily VE secretion in milk was observed in the HVE group during the winter season (222 and 146, 133 and 105 mg/d, for HVE and LVE in winter season, HVE and LVE in summer season, respectively), while no differences were found in the LVE group between seasons. The plasmatic content of VE was higher in the HVE group (p<0.001), and especially in the winter season reaching 382 mg/d. A higher proportion of VE partitioned to the milk on the VE assumed was observed for the LVE group (p<0.001) especially in the winter season (7.71 vs 5.44 for winter vs summer; p<0.001), indicating a possible better absorption efficiency. The retention of VE was always higher in the HVE group (p<0.001), with the highest observed in the summer season (9109 vs 8981 mg/d; p=0.003). Similar results were found considering the proportion of VE retained on the assumed (93.7 vs 84.78 for HVE vs LVE in winter season, p<0.001; and 95.6 vs 89.06 for HVE vs LVE in the summer season, p<0.001).