THE EFFECT OF ACETYLSALICYLIC-ACID AND COLD STRESS ON THE SUSCEPTIBILITY OF BROILERS TO THE ASCITES SYNDROME

Acetylsalicylic acid (ASA) inhibits the in vitro formation of many cyc looxygenases, some of which in mammals regulate pulmonary vasoconstric tion. Pulmonary vasoconstriction occurs in some species subsequent to hypoxaemia, through the mediation of cyclooxygenases. If this effect a lso is manifested in broilers, ASA might have a therapeutic potential in ameliorating the pulmonary hypertension syndrome (clinically manife sted as the ascites syndrome) induced by, amongst other factors, expos ure to low ambient temperatures. Male broilers were fed pellets contai ning 500 parts/10(6) of ASA from 3 weeks of age. After 1 week, ASA-tre ated and control (no ASA) groups were moved to a cold environment for 4 weeks. The development of the ascites syndrome was monitored by reco rding haematocrit and mortality with ascites. The plasma levels of two cyclooxygenases, the prostaglandins PGE(2) and PGF(2 alpha), were mea sured in birds in the cold-exposed groups. No differences in haematocr it values, overall mortality or plasma prostaglandins levels were note d between the ASA-treated and control groups during the period of cold exposure. There was an increased mortality in the ASA-treated groups during weeks 3 to 4 of cold exposure, indicating possible inhibition o f a cyclooxygenase vasodilator, which could exacerbate a possible exis ting pulmonary vasoconstriction. The protocol of this field trial does not indicate that ASA might be of therapeutic use in preventing the a scites syndrome in broilers.