SUMMARYOn an experimental farm 3 dairy breeds were compared with regard to mastitis by various parameters. Higher cell counts and more udder infections were present in the Dutch Red and White (DRW) in comparison with the Holstein Friesian (HF) and the Dutch Friesian (DF). Within the HF breed a negative correlation between cell count and production was established and also in this breed, a negative correlation between maximum rate of milk flow and cell count. There is no evidence that higher procuction and easier milking are connected with more mastitis. On the contrary, within the breeds an opposite trend appeared. Selection against mastitis does not conflict with selection for production and ease of milking. An addition trial revealed that sampling after too quick preparation of the cows before milking resulted in much higher cell counts in quarter samples. Cows which were selected for drying off with antibiotics recovered from their infection but these more susceptible animals maintained a higher cell count to a certain extent.

Somatic cell counts were measured one time on Meuse-Rhine-Ijssel cattle in The Netherlands. Experiment 1 involved 1,741 first lactation daughters of 31 bulls. Eleven bulls with daughters with either high or low average cell count were selected for further study of their daughters in third and fourth lactation. Cell counts and bacteriological tests were performed on 684 of the older daughters. A second experiment was conducted to measure daughters in second lactation and to obtain additional daughters in first lactation. This experiment recorded cell counts of 1,071 daughters of 10 of the bulls selected in Experiment 1. Heritability of the natural logarithm of cell count in first lactation was .081 based on daughters of 31 bulls in Experiment 1. Geometric daughter averages ranged from 206 to 700 X 10(3) cells/ml. Transmitting ability of bulls was estimated by the regressed least squares method. Ranking of bulls on first lactation cell count was different between the two experiments. Management factors and stage of lactation effects could be responsible for these differences. Within Experiment 2, the ranking of bulls on cell counts was nearly identical between first and second lactation. Daughter groups with low average cell count in first lactation in Experiment 2 had low averages in third and fourth lactation although some changes in ranking did occur. These results are consistent with a low to moderate genetic correlation between lactations for cell count. In general, daughter groups with higher average cell count had higher percentage of quarters with mastitis pathogens.

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SUMMARYA field case of mastitis in cows, caused by Mycoplasma agalactiae var. bovis, formed the occasion to conduct an infection experiment. Five lactating heifers were infected in the udder at different times. The cows were slaughtered 2, 5, 7, 9 and 12 days p.i. and the pathological changes were studied. The investigation indicated that the pathological picture differed with time: in the acute stage, the inflammation was characterized by exudation of mostly eosinophils in the alveoli; later on, the mastitis was identified by an interstitial reaction with eosinophils and mononuclear cells, including plasma cells and lymphocytes; in the chronic stage, progressive fibroplasia around ductuli and alveoli, with hypertrophy of alveolar epithelium, was characteristic. The pathological findings are discussed.

The investigation results mentioned led to the hypothesis: "Higher milk cell counts in the 1st lactation daughter groups indicate a higher susceptibility to mastitis and subsequently a higher mastitis prevalence with increasing age". The validity of this hypothesis has been investigated in the presented study by a simple scheme. Older sires were selected for this purpose in order to establish the (different) predicting cell counts in their 1st lactation daughters - and - to examine quarter samples from respective older age groups for the prevalence of mastitis.