Effect of temperature stress on circulating biogenic amines in bovine

1. A sensitive, simple and selective Chromatographic method using high performance liquid chromatography was developed to measure circulating levels of histamine (HI), norepinephrine (NE), dopamine (DA) and serotonin (5-HT) as indicators of response to thermal stress in two breeds of cattle. 2. Duplicate exposures for 8 hr to 13°C resulted in significantly elevated plasma NE and DA in longhorns but not in Herefords and suggest a relatively greater sensitivity to the cold (13°C) in the longhorn. 3. Environmental temperatures of 32 and 42°C significantly increased rectal temperatures of both breeds with much higher rectal temperatures in Herefords. 4. The 32 and 42° C effects on circulating NE and DA of Herefords were highly significant but not in the longhorn. However, heat stress significantly elevated HI and 5-HT in the longhorn which may account for their relatively greater heat tolerance based on their lower rectal temperatures.