Department of Animal and Poultry Science,
University of Saskatchewan,
Saskatoon, SK,
Canada
Research was completed to examine the effects of day length (12L:12D; 16L:8D; 20L:4D) on the performance and health of broiler chickens as assessed from day of hatch to the end of processing. Growth was reduced in a linear fashion with decreased day length while feed efficiency improved and the incidence of mortality and condemnations (cellulitis, dark carcasses) decreased. The data support the use of shorter day lengths in broiler production, both from an economical and animal welfare standpoint.
Introduction
Lighting programs for broilers have been examined many times over the last 30 years, with many different program types using variable lengths of dark periods and a wide range of patterns (Classen and Riddell, 1989; Gordon, 1994; Buys et al., 1998; Rozenboim et al., 1999; Scott, 2002). Some general concepts tend to hold true in comparisons of lighting regimes which provide darkness to continuous or near continuous light.
Exposure of birds to darkness:
- reduces early body weight but compensatory growth frequently results in equal weight at marketing;
- improves feed efficiency (reduced metabolism and activity during darkness, a more concave growth curve with less maintenance requirement, less carcass fat); and
- improves bird health with emphasis on metabolic problems such as sudden death syndrome (SDS), ascites and leg disorders.
Research using a wide range of species including poultry has also demonstrated that dark exposure, likely through the hormone melatonin, improves immune function (Kirby and Froman, 1991). This suggests that darkness exposure may also benefit the bird’s ability to combat infectious disease.
Despite the extensive research, there is a need to re-examine lighting principles using modern genotypes that have been selected for improved health and hence may not benefit from dark exposure to the same degree. In addition, most if not all lighting research, has failed to provide comprehensive data on losses beyond the farm gate (death in transit and lair age, condemnations). Since lighting programs affect bird health on farm and approximately one third of birds dead at shackling (DAS) are the result of farm based pathology (Classen et al., 2002), it is probable that lighting programs can affect DAS. Epidemiological evidence has indicated that darkness exposure may be one of a number of factors increasing the incidence of cellulitis (Elfadil et al., 1996). Cellulitis is the most important cause of condemnations in Canada and has increased markedly in the last decades (Kumor et al., 2001). Therefore, understanding how management affects its incidence has important economic implications. The objectives of this research were to compare the effects of day length on broiler performance and welfare using the Ross 308 broiler (considered to have high health standards) and in particular to pay attention to the post farm-gate response criteria such as losses in transit to slaughter and due to condemnations at the slaughtering plant.
Materials and Methods
Three lighting treatments were compared to investigate the impact of day length on response criteria. They consisted of 12L:12D, 16L:8D and 20L:4D. A total of 9000 Ross 308 chicks were randomly assigned 1000 per room (500 males and 500 females) to one of nine rooms. Rooms were environmentally independent and each lighting treatment was assigned to three rooms (3 replications per lighting program). All broilers were initially given 23L:1D but were switched to experimental day lengths on day 4 of the experiment. Light intensity was initially 20 lux and was reduced to 10 lux on day 7 where it remained for the remainder of the 35-day experiment.
Birds were fed starter (0.7 kg/bird; 3010 kcal AME/kg; 12.50 g total LYS/kg), grower (1.1 kg/bird; 3145 kcal AME/kg; 11.25 g total LYS/kg) and finisher (to trial end; 3175 kcal AME/kg; 10.00 g total LYS/kg) diets ad libitum. Broiler management followed industry convention for temperature and ventilation.
Birds were given 0.09 m2 floor space per bird. Feed was supplied in tube feeders (0 to 28 days, 13 per room, 35 cm diameter; 28 to 35 days, 13 per room, 43.75 cm diameter) and water using Plasson waterers (12 per room, 43.75 cm diameter).
Birds were weighed as a room at 0, 14 and 35 days of the trial while sample weights of 100 birds per room were taken at 7, 21 and 28 days. Feed intake was measured on a room basis. Dead birds were recorded, weighed and examined for cause of death. At 33 days, 50 birds per room were randomly selected to assess flock uniformity (individual weights) and bird mobility (subjective gait score; Kestin et al., 1992). On day of slaughter, lights came on in rooms 10 h before loading, and feed and water were withdrawn 4 and 8 h after lights came on, respectively. Final body weights were obtained within moving modules approximately 10 to 12 h after lights on. During this same time, sample birds were assessed for digestive tract clearance and skeletal gross pathology (16 birds per treatment). Birds were kept separate according to room during transit to and at the processing plant to allow collection of DAS and condemnation data.
Statistical analysis was conducted as a one way ANOVA using the Proc GLM procedure of SAS Institute Inc (1990). Duncan’s Multiple Range Test was used to separate means when the ANOVA was significant and regression analysis was used as appropriate. Differences were considered significant when P<0.05.
Results
Data from the experiment are shown in Tables 1 and 2. Birds on the 12L:12D lighting program were smaller at 14 days than broilers given the other lighting programs. At 35 d, there was a positive linear effect of day length on body weight with the difference between the two extremes (12 and 20 h) being 85 g or approximately one day’s growth. The reduction in growth rate was associated with the reduced feed intake seen with shorter day lengths. Feed efficiency as measured as feed to gain ratio, and feed to gain ratio with mortality correction, improved in a linear fashion as day length decreased.
There was a negative relationship between percent mortality (SDS, ascites) and day length. Bird mobility was poorer for birds on the 20L:4D treatment but the values were very low for all treatments indicating good skeletal quality. This was supported by a low incidence of culls due to leg disorders. Bird uniformity, within 10 or 15% of the mean was unaffected by lighting treatment. Digestive tract clearance and skeletal pathology in birds examined on day of slaughter were not affected by lighting program (data not shown). Bird death during transport and lairage was not affected by treatment but the loss for the 20L:4D treatment was nearly twice as high as the other treatments. The increased number of deaths was primarily due to chronic heart failure. Total condemnations increased with longer day length (Table 2), with the majority of the increase due to cellulitis and dark carcasses.
Discussion
This research confirms earlier work that decreased day length decreases growth rate, but increases feed efficiency and bird health (reducing SDS, ascites), even in a modern genotype with decreased losses due to metabolic disease. Therefore, it points to the continued value of dark exposure in today’s broiler industry. However, it was of interest that there was only a minor effect of day length on bird mobility and no effect on skeletal quality as judged by mortality/culls and gross pathology. This suggests selection for improved skeletal condition is successful in this genotype despite continued increases in growth rate.
The effect of lighting on the incidence of condemnations and in particular cellulitis was dramatic and appears to contradict epidemiologic research. It is often assumed that scratches are the origin of cellulitis and that increased darkness exposure increases scratches. Although scratches are likely an important risk factor in the development of cellulites, this research indicates a benefit of darkness exposure which may be the result of an associated increase in immunological capability. More research is required to confirm this effect but for the time being, it can be stated that darkness exposure is one of the factors that influences cellulitis and it should be used to help reduce the incidence of this important class of condemnations. The effect of day length on dark carcass condemnations is probably associated with chronic heart disease. This mechanism is supported by the reduction in ascites seen during the broiler production cycle. The failure of lighting treatment to affect digestive tract clearance is of interest and indicates that the use of dark periods does not pose a problem of increased contamination during slaughter if birds are given an appropriate feed withdrawal period, preferably on farm.
In conclusion, day length affects productivity of broiler chickens by affecting growth, feed efficiency and bird losses due to mortality, death during transit and lairage and condemnations. While increased dark exposure reduced growth rate, it had positive effects on feed efficiency, and bird well being and welfare.
References
- Buys, N., Buyse, J., Hassanzadeh, M., Ladmakhi, M. and Decuypere, E. (1998). Poultry Science, 77:54-61.
- Classen, H.L., Knezacek, T., Audren, G.P., Stephens, S., Crowe, T., Barber, E.M., Olkowski, A.A., Mitchell,
- M.A. and Kettlewell, P.J. (2002). Saskatchewan Agriculture, Food and Rural Revitalization ADF Final Report
- 19990256, 57 pages (http://www.agr.gov.sk.ca/apps/adf/adf_admin/reports/19990256_10122002133328.pd).
- Classen, H.L. and Riddell, C. (1989). Poultry Science, 68:873-879.
- Elfadil, A.A., Vaillancourt, J.-P., Meek, A.H. and Gyles, C.L. (1996). Avian Diseases, 40:677-689.
- Gordon, S.H. (1994). World’s Poultry Science Journal, 50:269-282.
- Kestin, S.C., Knowles, T.G., Tinch, A.E. and Gregory, N.G. (1992). Veterinary Record, 131:190-194.
- Kirby, J.D. and Froman, D.P. (1991). Poultry Science, 70:2375-2378.
- Kumor, L.W., Olkowski, A.A., Gomis, S.M. and Allan, B.J. (1998). Avian Diseases, 42:285-291.
- Rozenboim, I., Robinzon, B. and Rosenstrauch, A. (1999). British Poultry Science, 40:452-457.
- SAS Institute Inc. (1990). SAS User’s Guide: Statistics. SAS Institute Inc., Cary, NC.
- Scott, T.A. (2002). Canadian Journal of Animal Science, 82:375-383.
From Proceedings of the “16th Australian Poultry Science Symposium”, New South Wales, Australia.
