Is there a special mechanism behind the changes in somatic cell and polymorphonuclear leukocyte counts, and composition of milk after a single prolonged milking interval in cows?

• Background: A single prolonged milking interval (PMI) e.g. after a technical stop in an automatedmilking system is of concern for the producer since it is associated with a short-lasting increase inmilk somatic cell count (SCC), which is a major quality criterion used at the dairy plants. Thecontent of polymorphonuclear leukocytes (PMN) and how the milk quality is influenced has notbeen much investigated. The SCC peak occurs without any obvious antigen challenge, possiblyindicating a different leukocyte attraction mechanism after a PMI than we see during mastitis.Methods: Composite cow milk samples were taken at the milkings twice daily during 7 days beforeand 5 days after a PMI of 24 h. Milk was analyzed for SCC, PMN, fat, protein and lactose, and atsome occasions also casein and free fatty acids (FFA).Results: During the PMI the proportion of milk PMN increased sharply in spite of marginallyincreased SCC. The peak SCC was not observed until the second milking after the PMI, in theafternoon day 1. However, the peak SCC value in morning milk did not occur until one day later,concomitantly with a decrease in the proportion of PMN. After declining, SCC still remainedelevated while PMN proportion was decreased throughout the study as was also the milk yield,after the first accumulation of milk during the PMI. Milk composition was changed the day after thePMI, (increased fat and protein content; decreased lactose, whey protein and FFA content) but thechanges in the following days were not consistent except for lactose that remained decreased therest of the study.Conclusion: The PMI resulted in increased SCC and proportion of PMN. Additionally, it gave riseto minor alterations in the milk composition in the following milkings but no adverse effect on milkquality was observed. The recruitment of PMN, which was further enhanced the first day after thePMI, appeared to be independent of milk volume or accumulation of milk per se. Hence, we suggestthat there is a special immunophysiological/chemoattractant background to the increased migrationof leukocytes into the milk compartment observed during and after the PMI.

Subject headings

LANTBRUKSVETENSKAPER  -- Veterinärmedicin (hsv//swe)

AGRICULTURAL SCIENCES  -- Veterinary Science (hsv//eng)

LANTBRUKSVETENSKAPER  -- Husdjursvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Animal and Dairy Sience (hsv//eng)

Publication and Content Type

ref (subject category)

art (subject category)