Vitamin E supplementation during the dry period in dairy cattle. Part I: adverse effect on incidence of mastitis postpartum in a double-blind randomized field trial.

A randomized, controlled field trial with dairy cows demonstrated an adverse effect of vitamin E supplementation during the dry period on mastitis incidence in early lactation. This study was conducted on farms with historically high rates of mastitis to investigate the benefit of vitamin E supplementation on udder health; however, the outcome showed an adverse effect. The aim of the study was to evaluate whether daily supplementation of 3,000 IU of vitamin E to dairy cows during the dry period could improve udder health in commercial herds with a high incidence of mastitis. On 5 dairy farms, dry cows were randomly divided into 2 experimental groups: a high and a low group. Both groups received a dry cow mineral mix providing 3,000 or 135 IU of vitamin E/cow per day, respectively, between dry-off and calving for a mean period of 8 wk. Providing 3,000 IU of vitamin E exceeds NRC standards, but this amount has been used in previous studies. The experiment, as well as the majority of the statistical analysis, were carried out blinded. Blood was sampled 3 times before calving and on calving day. Serum was analyzed for vitamin E and cholesterol. Vitamin E and the vitamin E:cholesterol ratio were analyzed as dependent variables in mixed models and Student's t-tests to study trends in time and differences between groups. Relative risk calculation and survival analysis were used to study the effect of supplementation on mastitis incidence in the first 3 mo of lactation. The results showed that vitamin E supplements increased both absolute vitamin E and the ratio of vitamin E to cholesterol in blood. In the high group, significantly more subclinical and clinical cases occurred, showing the same trend on all farms. In this study, an initial vitamin E level at dry off above 14.5 µmol/L was a risk factor for clinical mastitis, suggesting that the vitamin E status at the start of the dry period is important. It is recommended to work out exactly at what threshold vitamin E is harmful for udder health before new trials with high dosages of vitamin E are started. Additionally, further research is required to investigate the mechanism by which vitamin E affects udder health.

Vitamin E supplementation during the dry period in dairy cattle. Part II: oxidative stress following vitamin E supplementation may increase clinical mastitis incidence postpartum.

The aim of this study was to evaluate, retrospectively, which physiological states influenced the effect of vitamin E supplements during the dry period on the level of oxidative stress at 2 wk antepartum. Furthermore the effect of oxidative stress at 2 wk antepartum on the risk of clinical mastitis in early lactation was investigated. Cows experience oxidative stress around calving. Vitamin E is able to decrease oxidative stress by scavenging free radicals. Normally, vitamin E radicals formed when vitamin E reacts with free radicals are regenerated by a network of other antioxidants, termed the "vitamin E regeneration system" (VERS). In case of vitamin E supplementation, VERS should be sufficient to regenerate formed vitamin E radicals; if not, oxidative stress might increase instead of decrease. Additionally, the level of oxidative stress and vitamin E might be important physiological states to evaluate before supplementation. In a clinical trial, 296 cows on 5 farms were randomly divided into 2 groups, supplemented with a mineral mix between dry off and calving that supplied 3,000 or 135 IU/d, respectively. Blood samples collected at dry off and 2 wk antepartum were analyzed for vitamin E, reactive oxygen metabolites, ferric-reducing ability of plasma, glutathione peroxidase, and malondialdehyde. Cows were allocated retrospectively into 8 subgroups based on the level of oxidative stress, vitamin E, and VERS status at dry off. To evaluate whether differences in physiological states at dry off influenced the effect of vitamin E supplementation on the level of oxidative stress, group effects (supplemented vs. control) were studied with Student's t-test for all 8 subgroup at 2 wk antepartum. Differences in physiological states at dry off influenced the effect of vitamin E supplements. In 2 insufficient VERS subgroups, the supplemented group had higher levels of free radicals at 2 wk antepartum compared with the control group. Relative risk calculation was used to study the effect of oxidative stress at 2 wk antepartum on the incidence of mastitis in the first 100 d of lactation. Higher levels of oxidative stress at 2 wk antepartum were related to higher risk of clinical mastitis. In conclusion, not every dry cow responded well to high vitamin E supplementation. This subgroup analysis provides a possible explanation for the unexpected adverse effects observed in the clinical trial.

Growth of Escherichia coli in whole and skim milk from endotoxin-induced mastitic quarters: in vitro effects of deferoxamine, zinc, and iron supplementation.

A marked growth inhibition of Escherichia coli 0101 K99 F41 was observed in whole and skim milk collected from inflamed quarters 18 and 36 h after intramammary administration of .1 mg E. coli lipopolysaccharide. Individual cow variation in the ability of milk from endotoxin-infused quarters to inhibit growth of E. coli was found. Growth inhibition of E. coli was observed in milk from endotoxin-infused quarters and was most pronounced in skim milk sampled at postinfusion h 18, and incubated at 38 degrees C. The mechanism by which bacterial growth was depressed was probably of noncellular origin. Addition of Fe (45.5 micrograms/ml) and Zn (2.7 micrograms/ml) to whole and skim milk sampled from inflamed quarters at 18 h after endotoxin infusion resulted in a growth-promoting effect. Addition of deferoxamine (6 mg/ml) depressed bacterial growth. Effects of Fe, Zn, and deferoxamine on bacterial growth did not differ in whole and skim milk. No clear relationship was observed between reduction in Zn concentrations in skim milk from inflamed quarters at 18 h after endotoxin infusion and growth inhibition of E. coli in the same samples.