The effect of 40 genetic markers (blood groups and biochemical polymor
phisms) on 5 haematological parameters (haematocrit, haemoglobin conce
ntration, red blood cells count, white blood cells count and different
ial leucocyte count) was studied in 179 fighting bulls to investigate
whether genetic background was related to stress endurance. Analysis o
f data was carried out by Harvey's methods (1977). Environmental facto
rs (season, management before the bullfight, ''encierro'' and suffered
punishment), body constitution and pedigree were also included in the
analysis. The A, B and S system of cattle blood groups, erythrocyte c
arbonic anhydrase (Ca) and transferrin (Tf) genotypes showed a signifi
cant effect on all studied parameters. Our results show that fighting
bulls with the H antigen and those without A, G(2) and G(3) antigens h
ad lower haematocrit and haemoglobin concentrations than the average p
opulation, whereas the fighting bulls with Ca-s/Ca-s and Tf(A)/Tf(E) g
enotypes showed a higher reversal of the leukocyte differential count
than the average population. These results may suggest a better adapta
tion to resistance to stress in animals displaying H antigens and Ca-s
/Ca-s, Tf(A)/Tf(E) genotypes and in those without A, G(2) and G(3) ant
igens.