Udder health implications of premature bovine mammary regression. II. Collateral intramammary reactions in quarters milked normally during 168-hour milk stasis in opposite quarters.

This investigation has shown that collateral intramammary reactions (CIR's) occur when secretory disturbances in one quarter lead to corresponding changes in one or more of the other, unperturbed, quarters of the same udder. Compared with normal baseline values, the mean values and variations of bovine serum albumin (BSA), beta-N-acetyl-D-glucosaminidase (NAG), mannose (MAN), galactose (GAL) and glucose (GLU) showed slight increases under CIR conditions. Fluctuations of the carbohydrates preceded changes of somatic cell counts (SCC), BSA and NAG in milk. SCC and NAG showed significant negative correlations with MAN, GAL and GLU, the latter being the only parameter significantly correlated with each of the other parameters. The data suggest that the cow's stress control system responded to the milk stasis in the unmilked quarters, by initiating a form of general stress that affected the whole udder. This aggravated regressive conditions in the unmilked quarters and provoked CIR's in the normally-milked quarters. The CIR's amounted to a transient, regressive, compensatory re-adjustment of lactational homeostasis under conditions of acute general stress. CIR's similar to those investigated could also occur in close association with other local and general stressful conditions, disturb the natural defence of the udder and account for fluctuating mammary resistance to bacterial infection.