Relationships between milk somatic cell counts, production index
and dry cow therapy in seasonal dairy herds
K.L. Macmillan; G.F. Duirs and I.S. Hook
Ruakura Animal Research Station, Hamilton; National Dairy
Laboratory, Hamilton and Wellington-Hawke's Bay Livestock Improvement
Association, Palmerston North
Proceedings of the New Zealand Society of Animal Production.
1980, 40: 180-188
Milk samples were cell counted from 12,233 cows in 106 herds
which were production tested on five occasions during the 1978-9 season.
The data were codes 0, 1, 2 or 3 for cell counts of less than 250 x 10³,
250 to 500 x 10³, 501 to 750 x 10³, and greater than 750 x 10³ cells/ml,
respectively. The five scores for each cow were summed. The
relationship between seasonal score and geometric mean cell count (GM)
was described by the equation GM = 46.1 + 19.1 (score) + 4.02 (score)²
(r² = 0.98). Scores for each age category tended to be distributed into
four subgroups comprising animals with low, medium, high or very high
scores. Whereas 86.5% or 2-year-olds were in the low-scoring subgroup,
only 53.0% of mature cows were in this category. The respective
percentages in the very high subgroup were 0.8 and 7.1.
Regression analyses showed that for each unit increase in seasonal score
amongst the mature cows, the Production Index (PI) declined by 0.63 (±
0.06). In 2-year-olds the decline was not significant (0.19 ± 0.19).
On a population basis, only 3.9% of cows were in the very high-scoring
subgroup, but because their average cell count level was 1085 x 10³
cells/ml, they contributed 25.3% of all the cells. The identification
of these cows through cell counting could allow bulk milk cell counts
to be significantly reduced by culling.
The use of dry cow therapy produced a small but significant increase in
early lactation PI (101.9 vs 99.7). This PI difference was not
sustained for the whole of lactation (102.0 vs 101.7).
Keywords: NZSAPAB;
Last Updated 12-09-1998
