The effects of photoperiod, light intensity and their interaction on blood acid-base balance, metabolites, and electrolytes in broiler chickens under environmentally controlled conditions were examined in two trials at USDA, Agricultural Research Service (ARS), Poultry Research Unit in Mississippi State.

Researchers found that continuous exposure of broiler chickens to varying light intensities had a minor effect on blood physiological variables, whereas the short photoperiod markedly affected most blood physiological variables without inducing physiological stress in broilers.

In the journal, Poultry Science, Hammed Olanrewaju and colleagues report a 3×3 factorial experiment in a randomised complete block design was used in this study. In each trial, all treatment groups were provided 23 hours of light and one hour of dark (23L:1D) with 20 lux of intensity from placement to seven days of age and then subjected to the treatments.

The nine treatments consisted of three photoperiods:

• long/continuous (23L:1D) from days 8 to 56
• regular/intermittent (2L:2D), and
• short/non-intermittent (8L:16D) from days 8 to 48 and 23L:1D from days 49 to 56

The three light intensities (10, 5.0 and 0.5 lux) were imposed from day 8 to day 56 at 50 per cent relative humidity. Feed and water were provided ad libitum.

Venous blood samples were collected on days 7, 14, 28, 42 and 56.

Main effects indicated that short/non-intermittent photoperiod significantly (P<0.05) reduced bodyweight, pH, partial pressure of oxygen, saturated oxygen, Na⁺, K⁺, Ca²⁺, Cl⁻, osmolality, triiodothyronine (T3) and total protein along with significantly (P < 0.05) elevated partial pressure of carbon dioxide, haematocrit, haemoglobin and lactate concentrations.

In addition, there were no effects of photoperiod on HCO₃⁻, glucose, anion gap, and thyroxine (T4).

Plasma corticosterone was not affected by photoperiod, light intensity or their interaction.

There was no effect of light intensity on most of the blood variables examined. Acid-base regulation during photoperiod and light intensity exposure did not deteriorate despite a lower pH and higher partial pressure of CO₂ with normal HCO₃⁻.

These results indicate that continuous exposure of broiler chickens to varying light intensities had a minor effect on blood physiological variables, concluded Olanrewaju and colleagues, whereas the short photoperiod markedly affected most blood physiological variables without inducing physiological stress in broilers.

Reference

^{Olanrewaju H.A., L. Purswell, S.D. Collier and S.L. Branton. 2013. Interactive effects of photoperiod and light intensity on blood physiological and biochemical reactions of broilers grown to heavy weights. Poult. Sci. 92(4):1029-1039. doi: 10.3382/ps.2012-02792}