ASSESSMENT OF VARIATION OF RESISTANCE TO HORN FLY ( Haematobia irritans irritans L.) ASSOCIATED WITH PLASMA PARAMETERS IN BEEF CATTLE

Research work was carried out in two farms, 300 km apart, in the province of Buenos Aires, Argentina in order to answer the question whether it exists or not animal variability regarding resistance to horn fly ( Haematobia irritans irritans L.) and if resistance can be traced to identifiable blood parameters. Flies were counted and blood samples taken from 13 heifers in farm A; from 19 heifers in farm B. Readings were made every 15 days during spring, summer and autumn when horn fly activity is at its peak. Data were recorded for two years in farm A (1995/96 and 1996/97) and one year in farm B (1995/96). Blood samples underwent electrophoretical analysis in order to identify plasma proteins as percentage area of albumin (band 7). Data were analyzed by the proc GLM of SAS. Significant differences were found in both farms for heifers (P