Lighting Programs for Broiler Production

Implementation of lighting programs adapted to the normal growth rate of chickens, has brought about improvements in the viability of the animals, feed conversion and decrease of physiopathological dysfunctions, such as: Ascites, skeletal problems and sudden death, depending on the duration of light exposure  (Abad, 2005). However, prolonged or continuous exposure to light, without periods of rest (sleep) can cause abnormalities in chickens (for example, tibial discolasia) related to accelerated growth (Sorensen et to the., 1999), which is detrimental to animal welfare, even though their performance results are not compromised (Dale et al., 1996). In the same way, night lightning schemes for broiler chickens will need to receive renewed interest due to new regulations on animal welfare in developed countries, such as the European Community legislation on chicken welfare, which will ban continuous lighting programs. It should be recognized that continuous lighting programs have a detrimental effect on sleep, eyes, physical activity and health conditions of the legs, incidence of ascites and sudden death syndrome (Buyse & Decuypere, 2003).
On the other hand, consumption in the cooler hours of the day would avoid possible heat stress in broiler chickens and, thereby reduce the rates of mortality and abnormalities that may occur in broiler chickens.
In view of the problems raised and the need to expand existing knowledge, this research intends to assess the effect of an alternative lighting program on the productive performance of broiler chickens. For this study, we depart from the hypothesis that a short period of lighting during the night might be enough to increase food consumption to levels that ensure appropriate weight gain.

We used a warehouse of semi-controlled environment, with four rooms, of which the first was used for collective rearing of the BB chicks up to 21 days of age, while the remaining three were divided into five pens of 1 m² each and it was where the different treatments were placed during the course of the experiment. 105 one-day-old hybrid Ross 308 chicks, of both sexes, located in densities of 7 birds/m² were used. During the first three weeks, the birds received the same management; all of them were exposed to continuous light 24 hours a day. In the third week the lights were turned off for a period of one hour, with the aim of getting them accustomed to periods of darkness that would come the following week.
Food and water were provided ad libitum. A commercial diet for the initial stage was offered during the first three weeks, followed by a fattening diet (also commercial) in the following three weeks. After collective rearing was finished and before the trial, chickens were weighed again, balanced by sex and live weight and randomly allocated at a rate of 4 males and 3 females in each experimental unit, according to a totally randomized design to constitute the following treatments: T0: (12 h L:12 h O), natural light only program (L), the rest, darkness (O), T1: (24 h L), continuous lighting program and T2: (14 h L: 10 h O), program L, intermittent, with 12 h natural L plus 2 h artificial L between 23: 00 and 1: 00 am. Animals had 5 hours of darkness before and after these two hours of artificial light at night. 35 birds were used in each treatment, spread evenly over five repetitions. Food consumption, daily weight gain, feed conversion and mortality were assessed during the fourth week of life. Data on production parameters were subjected to variance analysis to verify possible statistical differences among the treatments.

Table 1 shows the productive behavior of birds by treatments during the fourth week of life, noting that food consumption in the chickens in the continuous lighting treatment (T1) was significantly higher (P < 0.05) than the other treatments (T0 and T2).
The possibility of light on a permanent basis, being able to see food, led T1 birds to consume about 15 g/bird/day more than birds in the other treatments, which showed similar behavior between each other (P > 0.05), thus highlighting that exposure to light for 2 additional hours (T2) was not enough to significantly increase the consumption of food compared to T0.
Due to increased consumption in T1, chickens also showed significantly greater weight gains (P < 0.05) and, therefore, higher live weight (P < 0.001) compared to the other treatments, which also turned out to be similar between each other (P > 0.05). These results are consistent with those found by Sorensen et al. (1999), who points out that increases in live weight were associated to increases in light exposure periods.
In regard to feed conversion, it was observed that T0 birds were the most inefficient ones (P < 0.049) at turning food into body tissue; which is possibly related to the fact that they consumed the food under high temperatures, in a heat stress situation, which made the animals adopt behavior pattern to survive this condition. Any environmental stress requires an expenditure of energy by the birds, which means that this energy is diverted to activate physiological mechanisms to dissipate heat and, thus, counteract the adverse effects of stress (Angulo, 1990; Silva et al., 2001).

Table 1. Effect of the lighting programs on the productive behavior of chickens during the fourth week of life.

The other treatments with artificial light at night (T1 and T2) were able to concentrate the consumption of food in times of increased thermal comfort. However, in birds exposed to continuous light (T1), the food conversion situation significantly worsened in comparison to the group that had only 2 hours of light at night (T2); which could be related to the larger number for hours for rest available to this group and, therefore,  to physiological conditions enabling better use of food (Buys et al., 1998).

In previous studies, Ohtani & Leeson (2000) found that in the period between the third and sixth week, the accumulated weight gain and food consumption were significantly higher than in the treatment with intermittent light, although there were no differences (P > 0.05) in the food conversion of variable. Furthermore, other authors agree with these findings, revealing that chickens exposed to light less than 23-23.5 h and 0.5 - 1 (h) of darkness reach greater weight only in the first weeks of life, but at the end of the cycle (42 days) their weight is equal to or less than the weight of those that were exposed to conventional lighting programs (12h: 12h) and intermittent lighting programs (Dale et al., 1996; Renden et al., 1996).

Broiler chickens have a voracious appetite and are capable of eating through the entire photoperiod (Buyse & Decuypere, 2003). Through the contribution of a photoperiod near continuous lighting (23 h light: 1 h darkness), it is assumed that food consumption reaches a maximum, a condition thought as necessary to achieve maximum weight gain as well. Reducing the daily photoperiod, from 23 to 18 hours of light or less, in fact, has a negative effect on the rate of growth, due to the lower consumption of food or minor food efficiency (Robbins et al., 1984). It has been pointed out that if the length of the day is not too short (> 12-14 h light), food consumption during the dark period is negligible (Buyse et al., 1993), which could explain that the additional 2 hours of light were not sufficient to achieve a higher consumption compared to T0. Also, other authors have mentioned that the alternative lighting should be offered to achieve an extension of natural light, thus avoiding interruptions of light (Abad, 2005).

However, it should be noted that broiler chickens learn to eat in the dark, and less recent studies have shown that light is not really essential for food intake to occur properly (Cherry & Barwick, 1962; Squib & Collier, 1979). Likewise, Buyse et al. (1993) point out that animals raised under natural light present two top moments in food consumption: at dawn and at dusk, in other words, the animals become accustomed to eating during the cooler hours of the day and, thus, evade the effect of heat stress.

On the other hand, broiler chickens learn to develop strategies to try to overcome the long night periods without consumption of food. This includes the anticipated increase in food consumption towards the end of the photoperiod, mechanical storage of intake in the gastrointestinal tract and its gradual release during the night (Buyse et al., 1993) and reducing gastric motility (Duke & Evanson, 1976, 1976). During night fasting, night heat production declines by more than 40 per cent (Buyse et al., 1993), as well as the heart frequency and the rectal temperature (Klandort et al., 1978), Decuypere & Kühn, 1984), this reduction in the metabolic rate may be attributed to lower levels of the thyroid hormone at night, 3.3 ', 5-triiodothyronine (T3), stimulating metabolism (Klanford et al., 1978; Buyse et al., 1987). Forecasting food consumption behavior towards the end of the photoperiod needs time to develop (Squibb and Collier, 1979) and this learning process can be accelerated through simulation of sunset (Savory, 1976).

No mortality was reported during the experiment in any of the treatments.

The use of an alternative program of 2 h of light (T2) during the early morning failed to improve significantly neither food consumption nor growth, although it allowed a more efficient use of food by broiler chickens.

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