22 March 1996

Cell count work is worthwhile

ROUTINE national genetic evaluation of milk somatic cell counts in UK dairy cattle is worthwhile, despite the low proportion of bulls with high reliabilities, limited information and the low heritability of cell counts.

Genetic evaluation can identify extremes but unfavourable links with yield and some udder traits, suggest that a composite index approach may give the best results. Official evaluations are expected to be launched this year.

The case for genetic evaluation of milk cell counts was explained in a presentation by researchers from the Animal Data Centre, Rickmansworth, Herts.

Analysis was based on 666,595 Holstein, 9136 Ayrshire and 8400 Guernsey cows with cell count records, resulting in the evaluation of 13,525 Holstein, 1713 Ayrshire and 849 Guernsey sires.

The findings will be presented as predicted transmitting abilities (PTAs). Positive correlations indicated that higher yields will result in higher cell counts.

The work recognises that mastitis is one of the most costly health problems in dairy cattle and that herd average somatic cell counts have been measured and used since 1977 as a way to identify high levels of mastitis in herds. Optional individual cow cell count recording started in 1991 and about 80% of all cows are now recorded.