SummaryThe strong association between polymorphisms in an intronic microsatellite and the coding sequences for (BoLA)-/)/^5i genes, previously described for demonstrating alleles of class II major histocompatibility complex (MHC) in the cow, was examined in sheep to see if similar polymorphisms could be demonstrated in the DRB region of the MHC. The bovine primers LA53 and LA54, previously used to amplify the bovine DRB3 microsatellites. were used with DNA from Australian sheep, eight DRB alleles were identified by length polymorphisms of poiymerase chain reaction (PCR) products amplified from the DRB microsatellite region. Incomplete amplification of both aileles was sometimes found for sheep DNA samples using bovine primers, so a modified primer (LA53b) was used, and found to amplify the microsatellite next to intron 2 of the MHC more reliably than the LA53 primer. Two additional primers {LA31 and LA32), used in amplification of the exon 2 region of bovine DRB3, were used in the sheep, and the PCR products were analysed by single-stranded conformation polymorphism (SSCP). These primers successfully amplified the variable region of the ovine DRB region coded by exon 2, and the SSCP technique demonstrated polymorphisms with sheep DNA. Family studies demonstrated the segregation of alleles, by amplification both of intronic microsatellites and of the exon 2 variable region. Close correspondence was found between the two regions for several alleles. suggesting that the intronic microsatellites were closely linked to DRB-\av\ab\e region alleles. Three families of Merino sheep with ditferent antibody responses to intestinal nematode parasites were examined. The sire group with the highest antibody levels possessed two mierosatellite alleles of closely similar length (alleles 3 and 4) inherited from the sire and present in high frequency in the lambs. In contrast, the other two sires did not possess these two alleles and the alleles were in low frequency in their progeny. Further studies are required in unrelated sheep to confirm whether these two alleles are associated with resistance to nematode parasites.

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Two studies were carried out to measure variation in faecal nematode egg count (FEC) or serum anti-nematode antibody (Ab) concentration in Friesian cattle, and correlations between these traits and subsequent milk yield traits. In Study 1, FEC and Abs were measured in 9-month-old calves and 21-month-old heifers (1996 and 1995 calf crops, respectively), and correlations with the subsequent first-lactation yield traits were estimated in herds calving in late winter (July/August). In Study 2, Abs were measured in mixed-age cows during lactation in each of four groups (summer, autumn, winter, and spring calving mobs), and correlations were *Present address: estimated between Abs and yield in the current lactation. In Study 1, concentrations of the six different Abs (adult and/or third larval stages of four nematode parasite species) were moderately correlated with each other (average correlations of 0.57 in calves and 0.65 in heifers). In Study 2 the average correlation among Abs was 0.74. In Study 1, the average FEC values were 142 and 56 eggs/g in April and June samples collected from calves, and 14 and 28 eggs/g from heifers. Repeatability of FEC over time was moderate in the calves (0.45), but much lower in the heifers (0.13). Correlations between FEC and Ab were low but favourable in sign, averaging -0.24 in calves and -0.12 in heifers, while those between FEC as a juvenile and first-lactation milk or milk-component yields were close to zero, averaging -0.05 for calves and -0.02 for heifers. Correlations between Abs to Cooperia oncophora or Ostertagia L3 antigens and milk or milk-component yields averaged 0.23 and 0.07, for the two age groups in Study 1, respectively, and 0.06 in Study 2. Correlations between these Abs and liveweight averaged 0.14 for calves and 0.17 for heifers. It is concluded that, under the routine herd management conditions applied, concentrations among all Abs studied were consistently correlated, FEC was repeatable in calves, and those calves with a higher Ab response to Cooperia oncophora or Ostertagia L3 antigens tended to show slightly higher first-lactation yields.