The effect of environmental temperature on immune response and metabolism of the young chicken

The effect of environmental temperature on immune response and metabolism was studied in young chickens. Immunization was performed by injecting intramuscularly 0.5 ml packed SRBC (sheep red blood cells) in both thighs of 32 days old pullets ( WarrenSSL ). The ensueing immune response was evaluated by determining haemagglutinin anti-SRBC antibody titers and the number of plaque forming spleencells. The pullets were kept in climate controlled respiration chambers allowing accurate regulation and maintenance of climatic conditions. Thermal demand of the imposed conditions was measured by determining metabolic rate and performance before as well as after immunization. The following three aspects were studied separately: 1. The effect of the immune response to SRBC on growth rate and energy gain; 2. The effect of environmental temperature on the immune response to SRBC 3. The relation between thermal effects on the immune response to SRBC and energy metabolism.The effect of the immune response to SRBC on metabolic rate and performance characteristics can only be accurately assessed if compared with an appropriate control-treatment. Because injection perse was shown to reduce heat production for at least 2 to 4 hr after injection, controls were sham-immunized with PBS (phosphate buffered saline). Feed intake, body weight, growth rate and metabolizability of gross energy were not significantly affected by SRBC-injection, but SRBC-injected pullets were eating more while gaining less than PBS-injected pullets. The magnitude and composition of energy gain were influenced by immunization. Immunized pullets retained significantly (P < 0.01) more energy. deposited significantly (P < 0.05) more fat and had a significantly (P < 0.01) lower derived maintenance requirement of metabolizable energy than sham-immunized pullets during day 1 to 5 after injection. During day 6 to 10 after injection, SRBC-injected pullets deposited significantly (P < 0.05) less fat than PBS-injected pullets. It remains to be investigated whether vaccinations have similar effects on metabolic rate and growth traits.The effect of environmental temperature on the immune response to SRBC can only be described in terms of deviations from data gathered at a standard temperature. Such a standard temperature should be included in all research on this area, because significant differences in immunological data within temperature between experiments were found in all cases. In this research a 25 C environment was chosen as the standard control.This standard temperature of 25 C was shown to be near or at the lower critical temperature (T cr ) of the animals used in this research. The T cr depended on feeding level and time of day. Restricted-fed (about 80% of adlib . intake) pullets had a T cr of 27.9 C. This is about 2 C above that of adlib . fed birds. However, the difference in thermoregulatory heat below and above T cr in adlib . fed pullets was significant only if activity free heat production data were used. Below T cr thermoregulatory heat (about 0.345 W.kg -1. C -1seemed to be independent of feeding level. At night, with lights off, T cr was about 3 C lower than the calculated 24-hr value. At daytime T cr was above 30 C and could not be calculated.The effect of moderate temperatures (about 10 C deviating from T cr ) on the immune response was investigated in 4 experiments, using 2 climate respiration chambers. In each experiment the standard temperature of constant 25 C was maintained in one chamber. The temperature regimens in the other chamber were as follows: a constant temperature of 15 or 35 C or a temperature, which fluctuated between 10 and 20 C (10-20 C) or between 30 and 40 C (30-40 C). Total antibody titers at day 5 after injection, the day of peak titers, were increased significantly (P < 0.01) at 10-20 C, 35 C and 30-40 C compared to the antibody titers at 25 C. 2-Mercapto-ethanol resistant antibody titers at day 5 after injection were increased significantly (P < 0.05) at 35 C and 30-40 C. Thermal effects on antibody titers at the other sampling days (day 0 and 10 after immunization) were not significant. The effect of feeding level and degree of acclimation on antibody titers was investigated within each temperature regimen. Restricted feeding at low or high temperatures increased antibody titers at day 5 after injection. Exchange of pullets, prior to immunization, to low or high temperatures decreased total antibody titers at day 5 after injection. With respect to the humoral immune response it can be concluded that, if regressive effects of environmental temperature are to be expected, a change in temperature at the moment of immunization may be more important than the absolute temperature itself.More extreme low temperatures than the above mentioned, i.e . below 15 C, tended to reduce total antibody titers at day 5 after immunization in restrictedfed pullets. The investigated cold conditions were a constant temperature of 10 C and a temperature which fluctuated between 5-15 C. The results suggest that temperatures lower than the last mentioned may depress the immune response to SRBC if compared to the increase in immune response at moderate conditions.In all experiments physiological data were gathered before as well as after immunization. At the moderate low temperatures feed conversion (g feed/g growth) was higher (P < 0.05) than at 25 C. Feed intake was increased by 12.9% (at 15 C)and 10.5% (at 10-20 C) compared to intake at 25 C. Growth rate and protein gain were not significantly affected by low temperatures. High temperatures reduced (P < 0.05) feed intake (15.9% at 35 C and 14.9% at 30-40 C) and growth rate (12.3% at 35 C and 12.5% at 30-40 C) compared to 25 C. Protein gain and feed conversion were not significantly affected by high temperatures. The combined immunological and physiological data indicate that at moderate non-optimal, i.e . non-thermoneutral, conditions a positive relationship exists between immune responsiveness and metabolic rate. At extreme deviating temperatures this relationship may be reverted due to a prevalent non-specific, stress, response. The increased fat deposition found at such extreme temperatures may be an indication for the severity of the imposed conditions.The results of this research indicate also that it is more important that appropriate minima and maxima are not trespassed than that the temperature is fixed. Such fluctuating temperatures have no reducing effect on performance characteristics and immune function if compared to constant temperatures. It remains to be investigated whether thermal effects on immune responsiveness are similar to thermal effects on disease resistance.