Expression of the tight junction protein zonula occludens-1 during mammary engorgement

C.V. COOPER, K. STELWAGEN, K. SINGH, V.C. FARR, C.G. PROSSER AND S.R. DAVIS

Dairy Biotechnology Group, AgResearch Limited, Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand

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NZSAP 2004 Abstract No. 13 Proceedings of the New Zealand Society of Animal Production 64: 43-47

An increase in tight junction (TJ) permeability occurs during extended milking intervals and is associated with reduced milk secretion. This paper examines temporal changes in the expression of a major TJ protein, zonula occludens-1 (ZO-1), during mammary engorgement. Alveolar mammary tissue was collected from 52 mid-lactation dairy heifers at 0, 6, 12, 18, 24, 36 and 72 h, and at 8 d following abrupt cessation of milking (n = >=6 cows per time point). ZO-1 protein expression significantly decreased during mammary engorgement (P<0.05). Similarly, ZO-1 mRNA expression had halved by 36 h to 8 d post-milking (P<0.05). In a second trial, alveolar tissue was collected from the udder halves of late-lactation dairy cows (n = 4) that were milked unilaterally, either once-daily or twice-daily for 4 days. A 1.7-fold increase in ZO-1 mRNA expression was detected after once-daily milking, compared with twice-daily milking (P<0.05). The down-regulation of ZO-1 during mammary engorgement is consistent with increased TJ permeability. However, the up-regulation of ZO-1 mRNA expression during short-term once-daily milking suggests that TJ function is repaired as the mammary gland adjusts to the extended milking interval. In conclusion, we have identified changes in ZO-1 critical to TJ function in bovine mammary glands.

Keywords: NZSAPAB; bovine; mammary; once-daily milking; tight junction; ZO-1

Last Updated 8/07/2004