Ahstruct.s. Monday 25th March 2002 7 class II loci, for little or no sequence variation is seen in Equine MHC class II genes with respect to the extent of most species (Chu, 1994). This, however, is not the case with polymorphism, haplotypic association between alleles of different domestic equidae (Bailey, 1994). To date, five ELA DRA alleles loci establishing linkage disequilibrium, determining the dis- have been detected by single strand conformation polymorphism tribution of alleles and haplotypes in different breeds/equids, and (SSCP) studies of the second exon of DRA in all equid species. to determine the functional consequences and clinical relevance Here, we report the discovery of new DRA alleles after screening of ELA class II polymorphisms in relation to disease suscept- a random panel of equids using sequenced based typing ibilityiresistance (Sarcoids, Sweet itch, Strangles, Grass sickness, (SBT). The main objective of this programme is to characterise Colic). Room B. 18~00-18~30 19. Genetic regulation of immune traits in cattle by MHC and non-MHC genes GLASS. E.J.” Koslin Institute, Koslin, Midlothian, EH25 YPS Disease is a major source of economic loss to the livestock industry. Understanding the role of genetic factors in immune responsiveness and disease resistance should provide new approaches to the control of disease through development of safe synthetic subunit vaccines and breeding for disease resistance. The major histocompatibility complex (MHC) has been an important focus for infectious disease studies but the relative importance of non-MHC gents influencing immune responsive- ncss has not been well defined. Bovine MHC encodes two distinct isotypes of class II molecules, DR and DQ, and about half the common haplotypes express duplicated DQ genes. Both DR and DQ gcncs are involved in antigen presentation to T cells. In an Room C. Theme - Aquatic Disease analysis of T cell clones, distinct biases to particular restriction elements were observed. In addition inter-haplotype pairings of DQA and DQB molcculcs produced functional molecules. In a vaccine trial with several peptides derived from foot-and-mouth disease virus (FMDV), bovine MHC polymorphisms were cor- related with protection and non-protection. In addition in a second generation cross between Charolais and Holstein breeds of cattle, significant sire and breed effects were observed in responses to an FMDV peptide. These results suggest that both MHC and non-MHC genes play a role in regulating immune traits in cattle. Identifying these other genes and quantifying their relative contributions is the subject of further studies. Room C. 15.15-15.45 20. KEYNOTE: Pathology of gill disease in fish FERGUSON, H.W.*” Veterinary Diagnostic Service, Institute of Aquaculture, University o,f Stirling, Scotland FK9 4LA In two separate surveys of diagnostic submissions covering a reactions of the tissue to various insults. In addition, a range of decade, gill diseases represented the single most important cate- responses to infectious and non-infectious diseases will be covered gory of disease. This overview of branchial disease primarily covers including diatoms, protozoa, and bacteria, notably Flnvohacterium intensively-reared fish in all sorts of environments, both freshwater brunchiophilum, the cause of the economically important and marine. It looks at normal morphology and physiology, and “bacterial gill disease”, which will be studied in some detail. Room C. 15.45-16.00 21. Factors influencing the welfare of farmed Atlantic salmon (Sulmo sahr) in commercial marine cages BELL, A.,*“’ BRON, J.,’ TURNBULL, J.F.,’ ADAMS, C.E.,2 HUNTINGFORD, F.A.3 ‘Institute of Aquaculture, University oJ Stirling, Stirling FK9 4LA, Scotland, UK; ‘Fish Biology Group, University Field Station, University af Glasgow, Glasgow G63 UAW; ‘Fish Biology Group, Division of Environmental and Evolutionary Biology, Institute of Biomedical and Life Sciences, University o,f Glasgow, Glasgow G63 OAW A project was undertaken to investigate the cffccts of stocking at a commercial fish farm. A total of 14 cages were studied over a density on the welfare of farmed Atlantic salmon (S&no salar L.) period of approximately 1 year. The stocking densities ranged