Intermittent Lighting: Impact on Gut Health and Performance of Broiler Chickens

Three animal experiments were conducted to assess the effects of intermittent lighting
 (IL) on the performance and gut health of broiler chickens. 
 The first experiment studied the impact of light intermittency on the resilience of
 broilers to a sub-clinical necrotic enteritis challenge. Performance, lesion score,
 digesta viscosity and short chain fatty acid (SCFA) production were determined
 following the induction of sub-clinical necrotic enteritis in birds raised under both
 continuous lighting (CL, 18L:6D) and IL (1 h of light [L]:3 h of dark
 [D]:1L:3D:1L:3D:1L:3D:2L:6D). Particular attention was given to the days following
 the infection to understand how lighting programs influence the coping mechanisms
 developed by birds challenged by an enteric disease. Birds raised under IL were more
 efficient than those raised under CL in particular during the height of infection. Most
 importantly, the innate protective mechanism of broilers to reduce feed intake in case
 of enteric diseases was outweighed by the voracious appetite of CL birds.
 The primary objective of the second experiment was to understand whether
 improvements in nutrient (nitrogen and starch) digestibility would explain the
 apparent efficient advantage of birds raised under IL. Also, light intermittency and its
 interaction with exogenous enzymes was ascertained in terms of broiler performance,
 feed transit time, plasma metabolites, and nitrogen and starch digestibility. Within IL
 birds, the progression of protein and starch digestion through time and the changes in
 plasmatic metabolites were studied. Neither nitrogen nor starch digestibility could
 explain the improvement in feed efficiency for IL birds. Also, IL did not further
 improve the effects of exogenous enzymes in terms of performance and nutrient
 digestibility. However, results obtained reflect the phenomenal ability of broilers to
 withstand regular intervals of feed deprivation by regulating feed digestion and
 nutrient metabolism. 
 A third experiment attempted to explain efficiency improvements of IL birds through
 reduced heat increment and thus increased net energy of feed. In order to achieve that,
 an energy assay using closed-circuit respiratory chambers was performed to allow for
 the calculation of metabolizable and net energy of feed, and total heat production, heat
 increment, and respiratory quotient of broiler chickens. None of the parameters was affected by light intermittency; however, the methods used in this study might have
 limited the extent to which the results could be interpreted. 
 In parallel with a larger experiment, bone-related characteristics of IL and CL birds
 such as breaking strength and mineralization were assessed and associated with legproblem-related culls, growth rate and Ca and P levels in plasma. Results reflected the
 tight regulation of mineral plasmatic concentrations. Most importantly, the slower
 initial growth of IL birds in comparison with CL birds was identified as the main driver
 for the more complete mineralization and the stronger tibias in these birds. Also, birds
 raised under IL presented lower percentage of culling due to leg-related problems.
 Finally, results of an ancillary study designed to measure feed intake in IL and CL
 birds, particularly during periods of darkness, are shown. Albeit limited in scope and
 time, data generated indicate that a large proportion of feed consumption in IL birds
 occurs in the dark. Findings contradict the initial – and widely accepted – assumption
 that ‘feed intake during periods of darkness is largely negligible’ and encourage
 further research on this topic, specifically with focus on behaviour.
 This research revisited and expanded some of the IL-related topics studied in the 1970s
 through the 1990s and reminded of the importance of ancestral organ physiology and
 feeding behaviour for the progress of an exceptionally technologically advanced
 poultry industry.
 In summary, this work reveals the potential of IL programs, in particular one with
 recurring intervals of 1 h of light and 3 h of darkness, to enhance performance and
 manipulate nutrient intake, to manage gut health, and to improve skeletal integrity in
 fast-growing broilers. Manipulating the use of the crop and the other parts of the
 digestive tract through intermittent feeding has great potential to help overcome some
 of the current challenges in poultry productio