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 cyclooxygenases, some of which in mammals regulate pulmonary vasoconstriction. Pulmonary vasoconstriction occurs in some species subsequent to hypoxaemia, through the mediation of cyclooxygenases. If this effect also is manifested in broilers, ASA might have a therapeutic potential in ameliorating the pulmonary hypertension syndrome (clinically manifested as the ascites syndrome) induced by, amongst other factors, exposure to low ambient temperatures. Male broilers were fed pellets containing 500 parts/10(6) of ASA from 3 weeks of age. After 1 week, ASA-treated and control (no ASA) groups were moved to a cold environment for 4 weeks. The development of the ascites syndrome was monitored by recording haematocrit and mortality with ascites. The plasma levels of two cyclooxygenases, the prostaglandins PGE2 and PGF2alpha, were measured in birds in the cold-exposed groups. No differences in haematocrit values, overall mortality or plasma prostaglandins levels were noted 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 of a cyclooxygenase vasodilator, which could exacerbate a possible existing pulmonary vasoconstriction. The protocol of this field trial does not indicate that ASA might be of therapeutic use in preventing the ascites syndrome in broilers.