Bovine mammary gland involution, as a part of the reproductive cycle in dairy cows, is a very important remodeling transformation of the mammary gland for the subsequent lactation. There is considerable incentive to accelerate mammary gland involution to improve udder health, shorten the dry period, and simplify the management process by reducing dietary changes. The complex process of mammary involution is characterized by morphological changes in the epithelial cells and mammary tissue, changes in the composition of mammary secretions, and changes in the integrity of tight junctions. Involution is facilitated by elements of the immune system and several types of proteases and is coordinated by various types of hormones. This review first describes the involution process and then argues for the need to accelerate it. Last, this review focuses on various intervention methods for accelerating involution. Our aim is to provide a comprehensive overview of bovine mammary gland involution as well as potential techniques and new opinions for dry cow management.

The transition from lactation to the dry period in dairy cows is a period of high risk for acquiring new intramammary infections. This risk is reduced when the involution of the mammary gland is completed. Accordingly, approaches that speed up the involution process after drying-off could reduce the incidence of mastitis. The current study aimed to develop a biological response modifier that could be injected into cow teats to promote immune cell migration and speed up involution. Chitosan, a natural polysaccharide derived from chitin, is able to trigger host innate immunity. We developed 2 formulations made from either high- or low-viscosity chitosan. Both are liquid at room temperature but form a hydrogel at body temperature. In the first experiment, each udder quarter of 7 Holstein cows in late lactation was randomly assigned at drying-off to receive one of the following intramammary infusions: 2.5 or 5 mL of 5% (wt/vol) low-viscosity chitosan hydrogel, 5 mL of 5% high-viscosity chitosan hydrogel, or 5 mL of water. Milk (mammary secretion) samples were collected from each quarter on d -4, -1 (drying-off), 1, 3, 5, 7, and 10. Milk somatic cell counts and the concentrations of involution markers such as BSA, lactate dehydrogenase, and lactoferrin were measured in each sample. In comparison with the control, the chitosan hydrogel infusions significantly hastened the increases in somatic cell counts, BSA and lactoferrin concentrations, and lactate dehydrogenase activity in mammary secretions. No major differences between sources or volumes of chitosan were observed for the measured parameters. The compatibility of this approach with an internal teat sealant was verified in the second experiment. Each udder quarter of 8 Holstein cows was randomly assigned at drying-off to receive one of the following intramammary infusions: 5 mL of 2% low-viscosity chitosan hydrogel, 4 g of an internal teat sealant, a combination of sealant and chitosan, or 5 mL of water. Milk (mammary secretion) samples were collected from each quarter on d -4, -1 (drying-off), 5, and 10 to measure involution markers. These results suggest that chitosan hydrogel infusion hastened mammary gland involution and activate immune response, which may reduce the risk of acquiring new intramammary infections during the drying-off period. Those results were not affected by the presence of the teat sealant, showing that both approaches are fully compatible and could be used in combination.

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