The importance of daylength and darkness exposure on the welfare and productivity of commercial broilers
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The impact of daylength on commercial broilers was studied in two experiments, with birds exposed to one of four lighting programs (14L:10D (14L), 17L:7D (17L), 20L:4D (20L) and 23L:1D (23L)). The first experiment was repeated in a block formation four times, with each block containing two full-room replications and including a total of 16,128 broilers. In addition to daylength, other main effects studied in this experiment were genotype (Ross x Ross 308 and Ross x Ross 708) and gender, and these variables were randomly placed within each room. The second experiment included two replications of each of the four lighting programs described above in a format similar to a commercial situation. The total number of birds in this experiment was 7,552, equally distributed into one of eight rooms, with each room containing equal numbers of male and female Ross x Ross 308 broilers. Lighting programs used graded levels of daylength, which allowed the use of regression analysis as the primary statistical tool to define relationships between variables and daylength (SAS Proc Reg and Proc RSReg). For data involving light, genotype and gender (productivity, mortality, gait score, ocular weights), statistics included SAS General Linear Model to test for differences in genotype and gender, and interactions between the three main effects. In all cases, data not normally distributed were (log+1) transformed prior to analysis. In experiment 1, daylength and body weight were quadratically related at 32 and 39 d of age, with 20L producing the heaviest birds. Although not statistically significant, the data curve at 49d was of similar shape, with both 17L and 20L birds heavier than those raised under 23L. With less replication in experiment 2, differences only approached significance at 31 d of age (P=0.09), but once again, the regression curve was similar in shape. Birds raised under 20L consumed more feed at 39 and 49 d as compared to those under any other lighting program. 23L birds at 39 d ate as much as those raised on 17L, and less than the similar group at 49d. Feed efficiency was impacted quadratically, and birds given the longest dark period were most efficient. The latter birds exhibited the lowest mortality levels, which increased linearly with daylength. Both metabolic and skeletal mortality levels increased linearly with daylength in all periods, and infectious disorders in a quadratic fashion, with the peak found in birds raised under 20L. Average gait score was reduced either linearly or quadratically with increasing daylength, and footpad health at 28 and 35 d of age decreased as daylength lengthened. Eye weight was heavier under 23L only. The behaviour of 2 pens per lighting program of Ross x Ross 308 males was recorded with the use of infrared cameras within two of the experiment 1 trials (27/28d in trial 1 and 42/43 d in trial 2). Using scan sampling techniques at 10 min intervals, the average percentage of time performing various behaviours was calculated for the photophase, scotophase, and 24 h period (6 measurements x 24 h per d). Standing, walking, feeding preening, stretching, dustbathing and foraging decreased (linearly or quadratically) with increasing daylength at both ages in both the photophase and 24 h period. Running was reduced in a similar manner at 27/28 d, and was completely eliminated under 23L. These latter birds no longer performed dustbathing behaviour at 42/43 d of age. Percent of time of all behaviours was similar or only slightly different for birds raised under 14 and 17L. Reactivity was reduced in birds raised under 23L, was intermediate under 20L, and similar for 14L and 17L at 27d of age. To determine if melatonin within the flock was produced in diurnal rhythms, blood samples were collected either six (23L) or eight times (14, 17 and 20L) over the 24 h period (six per time). Samples were analyzed using radioimmunoassay. Diurnal melatonin production patterns were noted for flocks under 14, 17 and 20L, but were not found in 23L flocks. Frequent significant quadratic or linear relationships were noted between behaviour and time during the photophase under both 14 and 17L, and occasionally under 20L. No such relationships were noted under 23L, indicating sporadic timing of behavioural expression amongst the flock. The lack of flock synchronization under 23L may lead to repeated sleep disruption (fragmentation), which results in similar symptoms to total sleep deprivation, including poor productivity, a reduction in health, and poor reactivity leading to increased lethargy.
DegreeDoctor of Philosophy (Ph.D.)
DepartmentAnimal and Poultry Science
SupervisorClassen, Henry L.
CommitteeLaarveld, Bernard; Gomis, Susantha; Gonyou, Harold; Crowe, Trever; Van Kessel, Andrew; Bessei, Werner
Copyright DateNovember 2011