Circadian rhythms and adaptive development: how understanding circadian rhythms during meat chicken incubation could improve development and timing of the hatch window

Adult chickens utilise external circadian cues to schedule their daily cycles. In other taxa, developing embryos can actively entrain the timing of life transitions to a circadian rhythm (Villamizar et al., 2013, Saunders, 2002), but we currently have a poor understanding of how circadian rhythms develop in meat chicken embryos. Commercial poultry are not exposed to diurnal light changes during incubation, removing the possible use of such cues for optimising hatch timing. Synchronising hatching is expected to reduce the hatch window and potentially improve both welfare and performance, as chicks would experience reduced wait times for access to feed and water (Careghi et al., 2005).

We hypothesised that circadian cues throughout incubation could benefit both hatching synchrony and post-hatch development. We tested the influence of two environmental circadian cues throughout incubation (light and temperature) on Ross308 broiler embryos using a 2 × 2 full factorial experimental design (n = 12 batches, 3 batches/treatment). Once hatched, chicks (n = 275) were individually tagged and raised in randomised mixed floor pens following breed guidelines until day 14. To quantify the hatch window, incubators were checked every 30 minutes and hatched chicks were counted. Lastly, to quantify differences in post-hatch development, all chicks were weighed, tarsus was measured, and a subset of chicks (n = 137) were scanned in a quantitative EchoMRI body composition analyser on days 1, 7 and 14. Hatch window and developmental variables were statistically analysed using one-way ANOVAs.

Initial data showed no significant effect for circadian light and temperature cues to increase the length of incubation before hatching of the first chick (n = 12 hatch windows, 277 eggs, P > 0.05). There were no significant treatment effects on chick weight or tarsus length (both n = 277 chicks, P > 0.05) at 1, 7 or 14 days post-hatch, and no significant effect on chick body composition (n = 137 chicks, P > 0.05). Whilst pilot data from our initial experiment provided no evidence that circadian light or temperature rhythms influenced the onset of hatching or development; we suggest that there is potential for other triggers to influence hatch timing and potential for the poultry industry to employ these to reduce the time before day-old chicks have access to feed and water. Future research should focus on improving the hatch window through means of replicating natural environmental conditions or focusing on particular light wavelengths.