Effects of genetic variation on total plasma protein, body weight gains, and body temperature responses to heat stress.

The effects of heat stress (HS) on total plasma protein (PP) concentrations, body weight gains (BWG), and body temperature (BT) were studied in an Athens-Canadian Randombred (ACRB) population and commercial broilers (BR). The populations were maintained at environmental temperatures of 21, 32, and 38 C from 3 to 6 wk of age. The PP, BWG, and mortality (M) were measured at 3, 4, 5, and 6 wk and BT at 6 wk. After 2 wk of HS, the PP of the birds grown at 38 C was lower than that of birds in the 21 and 32 C environment, but differences for the 21 and 32 C groups were not consistent. The ACRB had significantly lower PP than the BR at 4, 5, and 6 wk. There were no phenotypic correlations between PP and BWG within temperature, line, and sex. The decreased BWG of the BR in response to the HS was much more severe than that of the ACRB. The BT of the ACRB (41.5 C) was significantly lower than that of the BR (41.9 C). Birds grown at 38 and 32 C had a higher BT (42.0 and 41.8 C) than at 21 C (41.3 C). The BR showed an increase in M in both the 38 and 32 C environments, but the M for the ACRB was not affected by environmental temperatures.