Blood Glucose Levels in Young Chickens: The Influence of Light Regimes

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Young male broiler-cross chickens, five to eight weeks of age were subjected to the following conditions: (1) ad libitum fed and exposed to a 12 hr. light—12 hr. dark lighting regime approximating the normal day light time of the outside environment; (2) fasted 12–31 hrs. and exposed to the same lighting regime as in (1); (3) ad libitum fed and exposed to continuous light or darkness; and (4) ad libitum fed and exposed to a lighting regime of 12 hrs. light and 12 hrs. dark, however, the initiation of the light period was 8 hrs. out of phase with the lighting regime employed in (1). Blood samples were drawn at various times and blood glucose levels determined for each sampling period.The data indicated a normal rhythmic pattern of blood glucose level (elevated during the period of illumination) in ad libitum fed, normally lighted birds and a reduced rhythmic pattern superimposed on the gradually declining blood level in the fasted birds exposed to the same lighting regime. Birds exposed to continuous light showed no rhythmic pattern. Exposure to continuous darkness resulted in an altered rhythm with an elevated period of possibly shorter duration than birds on a normal light regime (1). Birds on an out-of-phase lighting regime exhibited a response to the initiation of illumination similar to the birds in (1). However, these appeared to be a secondary influence of some other controlling factors as there was variation in the data collected indicating a non-uniform response of the birds tested.The conclusion that was drawn was that in other experiments where blood glucose level is used as a physiological indicator appropriate consideration must be given to conditions of feeding, lighting, and sampling time when designing experiments.