[Milk cell count as a selection criterion in breeding dairy cattle with improved resistance to mastitis]

The cell counts in the milk of female progeny of thirty-one bulls of the Meuse-Rhine-IJssel breed were determined in three breeding areas in the Netherlands, viz., in the provinces of Overijssel, Gelderland and North Brabant. The individual cell counts of the milk of 1,741 females in their first lactations were determined in study I. Eleven bulls, the female progeny of which showed high or low average cell counts in the milk, were selected on the basis of these results. The quarter milk of older females sired by these eleven bulls was studied (bacteriological examination and determination of cell counts). Females in their first and second lactations were examined in study II. This was done in 1,071 females sired by ten of the initially selected eleven bulls. The heritability of the cell counts in the milk of the females sired by thirty-one bulls, which cows were in their first lactations, was 0.081. On the basis of geometric means of the cell counts in the milk of the females in their first lactations, the rank order of the bulls which had sired them corresponded inadequately with that of half-sibs in their third and fourth lactations. In study II, the similarity in rank order of these two age groups was much better: groups of female progeny averaging low cell counts and percentages in their first lactations corresponded with low cell count averages and percentages of quarters of older half-sib progeny in their third and fourth lactations, which quarters were found to be positive on bacteriological examination. There were some differences in rank order.(ABSTRACT TRUNCATED AT 250 WORDS)