Abstract
To optimise udder health at the herd level, identifying incurable mastitis cases as well as providing an adequate therapy and culling strategy are necessary. Cows with clinical mastitis should be administered antibiotic medication if it is most likely to improve mammary cure. The somatic cell count (SCC) in milk of the monthly implemented Dairy Herd Improvement (DHI) test represents the most important tool to decide whether a cow has a promising mammary cure rate. Differential cell count (DCC) facilitates the specification of the immunological ability of defence, for example by characterising leukocyte subpopulations or cell viability. The aim of this study was to assess the DCC and cell viability in DHI milk samples regarding the cytological (CC) and bacteriological cure (BC) of the udder within a longitudinal study, thereby gaining a predictive evaluation of whether a clinical mastitis benefits from an antibiotic treatment or not. The cows enrolled in this study had an SCC above 200,000 cells/mL in the previous DHI test. Study 1 assessed the CC by reference to the SCC of two consecutive DHI tests and included 1010 milk samples: 28.4% of the mammary glands were classified as cytologically cured and 71.6% as uncured. The final mixed logistic regression model identified the total number of non-vital cells as a significant factor associated with CC. An increasing amount of non-vital cells was related to a lower individual ability for CC. Cows which were in the first or second lactation possessed a higher probability of CC than cows having a lactation number above two. If animals developed a clinical mastitis after flow cytometric investigation, the BC was examined in study 2 by analysing quarter foremilk samples microbiologically. Taking 48 milk samples, 81.3% of the mammary glands were classified as bacteriologically cured and 18.7% as uncured. The percentage of total non-vital cells tended to be lower for cows which were cured, but no significance could be observed. This study revealed that the investigation of the proportion of non-vital cells in DHI milk samples can enhance the prognosis of whether an antibiotic treatment of clinical mastitis might be promising or not. Prospectively, this tool may be integrated in the DHI tests to facilitate the decision between therapy or culling.
Highlights
Reducing the use of antibiotics in mastitis treatment requires a strict application only in bovine udders that have a promising cure rate
The differential cell count (DCC) in milk indicates an increase in the mean percentage of macrophages [7,15], while the main type of cells recruited into the mammary gland in the course of a persistent inflammatory accumulation are polymorphonuclear leukocytes (PMN) [15,17]
In study 1, 1010 composite milk samples from 442 cows were included: 287 samples (28.4%) from 215 cows had an somatic cell count (SCC) below 200,000 cells/mL the month following the flow cytometric investigation, and 723 samples (71.6%) from 320 cows had an SCC above 200,000 cells/mL at the following Dairy Herd Improvement (DHI) test
Summary
Reducing the use of antibiotics in mastitis treatment requires a strict application only in bovine udders that have a promising cure rate. To estimate the individual udder health status as precisely as possible, the count of leukocyte proportions can reveal the mammary ability to defend against invading pathogens [6] Researchers such as Hageltorn and Saad [7] have already analysed leucocyte populations by flow cytometry and found differences in the differential cell count (DCC) of healthy and diseased udders. The DCC in milk indicates an increase in the mean percentage of macrophages [7,15], while the main type of cells recruited into the mammary gland in the course of a persistent inflammatory accumulation are PMN [15,17]. The results aimed to provide reliable clusters of differentiation between cows with a favourable prognosis of mammary cure and those with a poor prognosis
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