Subclinical mastitis (SM) is a major concern in the dairy industry because it causes economic losses and can lead to clinical mastitis. The mechanisms of the onset and progression of SM are not fully understood, and a new procedure for the detection and appropriate prediction of SM leading to clinical mastitis is necessary for dairy cow management. Inflammatory cytokines such as interleukin (IL)-6 are known to be present in inflamed mammary glands at the onset of mastitis, and IL-6 concentrations correlate with the levels of inflammation. In this study, the detection of IL-6 was examined for the evaluation for the future prediction of SM in 77 quarter milk samples from 20 cows. IL-6 concentrations in quarter milk were measured by sandwich ELISA, and the data were compared with milk somatic cell count (SCC) levels to diagnose SM. Average IL-6 concentration was significantly higher in SM quarter milk (207·0±441·6 pg/ml) than in healthy control quarter milk (12·6±33·4 pg/ml, P<0·01). Results of the cross-tabulation table show that SM prediction accuracy based on IL-6 concentration was almost equal or superior to SM prediction accuracy based on SCC. The detection of IL-6 in milk indicated SM earlier than did the detection of elevated SCC. Thus, the detection of IL-6 in milk could be a future prediction marker for SM.

Determination of somatic cell count (SCC) is used worldwide in dairy practice to describe the hygienic status of the milk and the udder health of cows. When SCC is tested on a quarter level to detect single quarters with high SCC levels of cows for practical reasons, mostly foremilk samples after prestimulation (i.e. cleaning of the udder) are used. However, SCC is usually different in different milk fractions. Therefore, the goal of this study was the investigation of the use of foremilk samples for the estimation of total quarter SCC. A total of 378 milkings in 19 dairy cows were performed with a special milking device to drain quarter milk separately. Foremilk samples were taken after udder stimulation and before cluster attachment. SCC was measured in foremilk samples and in total quarter milk. Total quarter milk SCC could not be predicted precisely from foremilk SCC measurements. At relatively high foremilk SCC levels (>300×103 cells/ml) foremilk SCC were higher than total quarter milk. At around (50–300)×103 cells/ml foremilk and total quarter SCC did not differ considerably. Most interestingly, if foremilk SCC was lower than 50×103 cells/ml the total quarter SCC was higher than foremilk SCC. In addition, individual cows showed dramatic variations in foremilk SCC that were not very well related to total quarter milk SCC. In conclusion, foremilk samples are useful to detect high quarter milk SCC to recognize possibly infected quarters, only if precise cell counts are not required. However, foremilk samples can be deceptive if very low cell numbers are to be detected.

Automatic milking systems have made possible the separation of high- and low-quality milk at the udder quarter level during the milking process. The aim of this study was to investigate the composition and yield of milk from individual udder quarters to determine whether deteriorated milk composition occurs in udders that are assumed to be healthy and whether quarters with high-quality milk are found in udders with high milk somatic cell count (SCC). Milk samples were collected on one occasion from 90 cows at udder quarter level and cow composite level. The milk was analyzed for content of total protein, whey protein, casein, fat, lactose, citric acid and SCC; milk yield was registered. The cows were divided into three groups depending on the SCC of their composite milk. Cows in group 1, cow composite SCC < 100 000 cells/ml, were assumed to have healthy udders. However, instances of increased SCC and decreased milk quality were discovered in one or more udder quarters of approximately 30% of the group. Cows in group 2, cow composite SCC of 100 000 to 300 000 cells/ml, and group 3, cow composite SCC > 300 000 cells/ml, were assumed to have affected udders. However, the majority of these cows had one or more udder quarters in which increased SCC and deteriorated milk quality were not detected. Calculations of bulk-tank milk values, when separation of milk from affected udder quarters was performed, indicate that SCC changes to a much greater degree compared to the other milk components. These results show that milk from affected udder quarters suffers compositional changes, but calculations of simulated separation indicate that the compositional changes in bulk-tank milk are small. The effect of separation of milk from individual udder quarters on bulk-tank milk needs to be further studied.