Effects of heat stress and dietary zinc source on performance and permeability of mammary epithelium of lactating dairy cows
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Heat stress may negatively alter the barrier integrity of mammary epithelium, whereas organic source of dietary zinc has been shown to enhance epithelial integrity. The objective of the first study was to evaluate the effect of environmental heat stress and dietary zinc source (zinc-MET complex vs. zinc hydroxychloride) on lactating Holstein cows’ performance and permeability of mammary epithelium. Heat stress impaired cow’s performance and increased gene expression of tight junction proteins in mammary tissue. Replacing a portion of zinc hydroxychloride with zinc-MET complex had no impact on cow performance but improved mammary epithelial integrity. The objective of the second study was to examine the effect of repeated mammary tissue collections during lactation on cow performance and udder health of lactating dairy cows. Lactating cows recovered rapidly from mammary tissue collections and no long term impacts of repeated mammary biopsy procedures on DMI, milk yield and composition, or udder health were observed.