Response of commercial layers to housing at different cage densities and heat stress conditions. 1-physiological indicators and immune response

Abstract EN

An experiment was conducted to determine the effects of heat stress and different cage densities on blood indices and Immune response.

The hypothesis that, commercial layers, caged at lower densities, react less intensely, to heat stress, than would the hens caged at higher densities was also tested.

A total of 936, Lohman Selected Leghorn (LSL) hens, fifty eight weeks old, were used in this experiment.

These hens were originally housed, at eighteen weeks of age, as follows : 1- The first group (468 hens) was housed in a conventional open-sided house (Heat Stressed).

2-The second group (468 hens) was housed in a conventional open-sided house with desert cooling systems (Control).

Pullets were placed at 4, 5, 6, 7, 8 and 9 birds per cage in wire cages (60 cm wide by 50 cm deep and 40 cm height).

At 58 weeks of age, the first group was exposed to high environmental temperatures, ranging from 40-42°C and 65-70% relative humidity (five hours daily for seven consecutive days).

After each daily heat exposure, the hens were exposed to the normal ambient temperature of the season (20-26 OC and 60-65% relative humidity).

The control group was exposed to the ambient temperatures of the season, ranging from 20-26°C and 60-65% relative humidity.

Data were collected during the period of heat stress exposure.

Results indicated that rectal temperature and Heterophil : Lymphocyte ratios (H : L ratios) of heat-stressed birds, increased significantly as compared to the control group, at the first and last days of heat stress.

However, red blood cell count, packed cell volume, hemoglobin concentration, plasma total protein, globulin and serum potassium levels, of heat stressed birds, decreased significantly as compared to the control ones, when tested at both the first and last day of heat stress.

Plasma albumin and serum calcium levels, of heat stressed birds, decreased significantly as compared to the control group, only at the first day of heat stress.

Also, heat exposure reduced antibody titers against sheep red blood cells (SRBC's) on 3, 5 and 7 days post immunization.

No significant detrimental effects, due to heat stress, on serum calcium and potassium levels, were observed, when hens were housed at the lowest cage density (4hens / cage), at the first day of heat stress.

At the last day of heat stress, plasma proteins, serum calcium and potassium levels, and H : L ratio, were also not affected, when hens were housed at the lowest cage density.

Antibody titers against SRBC's, were significantly reduced due to heat stress, when hens were housed at 9 per cage, on the 3rd day post immunization.

On the 5th day post immunization, when 8 or 9 hens were housed per cage, antibody titers against SRBC's also, decreased significantly, due to heat stress.

Under heat stress conditions, hens caged at low densities (4 or 5 birds / cage) had significantly lower rectal temperatures, and higher serum calcium and potassium levels, when compared to hens at higher cage densities.

Significantly higher antibody titers against SRBC's and lower H : L ratios were also observed when hens were caged at lower densities.

It was concluded that, hens caged at low densities were less affected by heat stress than those at higher cage densities.