[Does selection for characteristics of the udder, teats, ease of milking and udder health offer any prospects of improvement of resistance to mastitis? (author's transl)]. / Biedt selectie op kenmerken van uier, spenen, melkbaarheid en uiergezondheidskenmerken een perspectief voor de verbetering van de weerstand tegen mastitis?

Improvement of resistance to mastitis by indirect selection for udder traits, ease of milking and milk cell counts is discussed. --Selection for less pendulous udders with shorter teats is practised. Genetic variation in udder and teat measurements between and within sub-populations of Dutch Friesian (DF) and Meuse-Rhine-IJssel (MRY) cattle in first lactations is important (Table 1). --Selection for ease of milking based on an ease of milking test of progeny groups has been practised since 1962. An optimum peak flow of about 2.9 kg/minute is attained in the DF and MRY breeds (Graph 1). --A field trial in 1587 DF and 1139 MRY cows showed that culling for problems of udder health after three lactations (DF 10%, MRY 20% of the cows culled) is of more importance than culling for hard milking (DF 6%, MRY 4%) (results in 3.3). --There was no relationship between the incidence of clinical mastitis (DF 20%, MRY 22%) in the third and fourth lactations and the peak flow tested in the first lactation (Table 2). --There was a positive correlation between peak flow and lactation milk yield (DF r = 0.23, MRY r = 0.19) (Table 3). --The incidence of leaking milk just before milking is slightly lower in the DF breed than in the MRY breed and related to the peak flow (Table 4). --Milk cell counts tested in DF and MRY progeny groups in first lactations showed genetic variations (DF log cell count 2.43 sigma 0.32 h2 = 0.30). --Determining milk cell counts in progeny groups during the last part of the first lactation (when differences are more marked than during the first part of lactation) may provide a basis for indirect selection for resistance to mastitis (Graph 2). There are prospects of improvements of udder health by indirect selection for udder and teat conformation traits. Selection for ease of milking is of minor importance in this regard. Further research is required to show that selection for udder traits during first lactations, e.g. a small proportion of daughter in the classes showing high milk cell counts, may provide a basis for selection for a lower incidence of mastitis in the older cows.

[Milk cell count as a selection criterion in breeding dairy cattle with improved resistance to mastitis]. / Het melkcelgetal als selectiecriterium bij het fokken van melkvee met een betere weerstand tegen 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)

Effect of bull selection for somatic cell count in first lactation on cell counts and pathogens in later lactations.

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.