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Somatic cell count (SCO data collected on individual cows since 1991 were obtained from National Milk Records. Following validation genetic and phenotypic parameters were estimated from the lactation average SCCfor 63 424 Holstein/Friesian (HOD, 7966 Ayrshire (AYR) and 14 509 Jersey (JER) animals. The first three lactations were included in the analyses. The heritabilities (h 2 ) for first lactation log SCC (LSCC) were 0-11 (s.e. 0-01), 0-12 (s.e. 0-02) and 0-09 (s.e. 0-03) for the HOL, ]ER and AYR breeds respectively. Estimates for herd sire interaction (c 2 ) effects ranged from 0-01 to 0-02. Analysis of the first three lactations with a repeatability model produced similar h 2 and c 2 estimates. Permanent environment estimates ranged from 0-21 to 0-25. Heritabilities of individual test day LSCC ranged from 0-04 (s.e. 0-02) to 0-10 (s.e. 0-03). Genetic correlations between SCC and milk, fat and protein yield for the HOL breed were 0-06 (s.e. 0-05), 0-14 (s.e. 0-06) and 0-09 (s.e. 0-06) respectively. Genetic evaluations were obtained for 666 595 and 9136 animals for Holsteins and Ayrshires, providing evaluations on 13 525 and 1713 bulls respectively in each breed. The range of LSCC predicted transmitting abilities (PTA) was ±25% although the proportion of bulls with reliability >0-50 was low at 0-17 and 0-05 for HOL and AYR respectively.The correlations between the LSCC PTAs for HOL bulls with at least 50 daughters and their genetic evaluations for linear type were essentially zero for body and some udder traits. Significant negative correlations were obtained for a number of traits including foot angle (-0-14), fore-udder attachment (-0-19) and udder depth (-0-19) and a positive correlation for teat length (0-15). SCC evaluations will be implemented by the Animal Data Centre. Reliabilities will be lower than production because of the lower h 2 for SCC and the lower progeny group size since only 0-80 of recorded cows have SCC records.

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First lactation records for production traits (milk, fat and protein yields) and 17 linear type traits for 7169 Ayrshire heifers were analysed to estimate genetic parameters for type traits and to examine the relationship between type and production traits. A multivariate restricted maximum likelihood procedure fitting a sire model with sire relationships included was used for all analyses.Heritabilities for production traits were approximately 0·3 and genetic correlations among them were high (>0·84). The estimates of heritabilities for type traits were mainly low to moderate ranging from 0·04 to 0·42. Angularity (0·80), beef shape (0·49), foot angle (0·53) and stature (0·46) had higher heritabilities. Generally phenotypic correlations among type traits were lower than the genetic correlations. The highest negative genetic correlation was between rear legs side and rear legs rear (-0·95) and the highest positive correlation between chest width and beef shape (0·93).Genetic correlations between type and production were low to moderate and were similar for milk, fat and protein yields. The genetic correlations between the production traits and chest width, udder depth and beef shape were negative but were positive between production and angularity, rear udder width and teat placement side.

The rationale for a method of computing selection indices for dairy cows is outlined. It uses predicted transmitting abilities of sires from a best linear unbiased prediction or similar method of evaluation together with mean transmitting abilities (cow indices) of dams to estimate herd genetic levels. Indices for individual cows are computed using deviations from those of contemporaries in the herd of her sire's transmitting ability, her dam's index and her own production in each lactation.The method is being used in the UK, cow indices being expressed as transmitting abilities relative to the same fixed genetic base as for sire evaluation.