Genetic parameters and evaluations for somatic cell counts and its relationship with production and type traits in some dairy breeds in the United Kingdom

Abstract 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 (h2) 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, JER and AYR breeds respectively. Estimates for herd sire interaction (c2) effects ranged from 0·01 to 0·02. Analysis of the first three lactations with a repeatability model produced similar h2 and c2 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 h2 for SCC and the lower progeny group size since only 0·80 of recorded cows have SCC records.