Vitamin E supplementation and udder health: A meta-analysis

The objectives of this study were to conduct a meta-analysis on available literature to estimate the magnitude and significance of the weighted summarised effect of Vitamin E status on udder health. Inclusion criteria for studies were one or more groups of cows with given values of vitamin E status or supplemental levels, cow/herd plasma or serum vitamin status or ratios of these to cholesterol or total lipids, vitamin E dosage, route of dosage, period of administration and duration of study. Papers with an abstract in English published between 1984 and 2003 were located through a literature search based on examination of computerised scientific databases and cross-referencing citations in retrieved papers. Fourteen out of 34 papers that addressed the relationship between vitamin E and udder health were eligible for use in the meta-analysis. Vitamin E supplementation was on average associated with a 14% reduction in the risk of intra-mammary infection (IMI). Vitamin E supplementation was also associated with a reduction in milk somatic cell counts (SCC) by a factor of 0.70 and a 30% decrease in the risk of occurrence of clinical mastitis (CM). The observed heterogeneity between studies could be explained by control and supplemental vitamin E levels, their differences and concurrent Selenium supplementation. Publication bias was evident in the meta-analysis. In conclusion, results support the hypothesis that Vitamin E supplementation during the dry and early lactation periods is associated with lower IMI, SCC and CM. However for practicality, dosages, when to start and how to proceed with supplementation and costs need to be determined.