Introduction

Modern broilers grow at an extremely rapid rate and convert feed to meat with an exceptional efficiency. However, the rapid growth and conversion efficiency are associated with an increased susceptibility to various stress conditions. The metabolic heat along with high ambient temperature decreases the feed intake and body weight by 15% and 23% respectively, in broiler birds (Yalcin et al., 1997). There is a decline of about 1.72% in feed intake for every degree Celsius rise in ambient temperature from 18^oC to 32^oC this decline is much faster when the temperature rises from 32^oC to 38^oC (Rama Rao et al., 2002). Behaviour patterns of birds were divided into two normal and aggressive as suggested by Estevez et al., 2003. Both kind of behavior get affected during heat stress condition. Panting was considered as potential indicator of heat stress. Thermo neutral zone for poultry birds should remain in the range of approximately 18^oC to 29^oC. Panting was found minimum in this thermo neutral zone. At high ambient temperature (31^oC), body temperature of bird rises and respiratory rate (panting) increases to dissipate heat by evaporative cooling. Various studies have been conducted to protect poultry birds from high ambient temperature through cooling of poultry houses using fans and air coolers. Evaporative pads, fogger pads and fogger nozzles can also be used as a good alternate to control heat and its effects in broiler houses (Weaver, 2002). The extent of heat stress can be expressed as an index value, which is a measurement of combined effects of temperature and humidity on the bird. This stress index can be monitored and controlled using different cooling systems in poultry shelters to increase the comfort and improve production in birds. Therefore, the present study was planned with the objectives to compare the effectiveness of different cooling systems on the behavior and welfare of broiler chicks during heat stress period.

Material and Methods

The present study was conducted on 480, sexed day-old healthy broiler chicks. All chicks were randomly divided into 12 groups, each having 40 no’s on similar body weight range, sex ratio and average group weight basis. The birds were provided with either Fan-Pad (FP) or Fan-Fogger (FF) during hot-dry period (April to May). Exhaust-Fan (EF) and Ceiling-Fan (CF) against the control (without any cooling) were used during hot-humid period (July to August) as cooling devices. In the deep litter system, the size of the shed was 16 x 10 x 10 ft³ and each bird provided 1 ft² floor space in their respective group shed.

Design of Cooling Systems

Fan – Fogger System

The Fan-Fogger system consist a blower with the copper ring placed in front of it. Fine foggers (3 in number) each having diameter of 0.2mm capable of producing mist with a pressure of 30psi at the rate of 2 lit/hr, were placed on the ring at the height of 3’ from the ground, which were connected with water tank through a high pressure pipe. Filtered water was pumped into the foggers and its on/off–timing was regulated through a timer. When switched on, foggers created a fine mist to help cooling the shed. During the off-time of the fogger, fan remained in the running condition. This cycle of on and off time was 30 seconds and 60 seconds, respectively and repeated throughout the day.

Fan-Pad System

The fan and evaporative pad system consisted of cellulose pads which were made up of cellulose paper haised in G.I casing with a water distributor through a P.V.C header. The intricately woven cellulose pads were efficient to provide necessary quantity of water to achieve maximum cooling of air coming in contact. The evaporative pads were placed at one end of the shed and exhaust fan of 24” dimension at the opposite end. The water was pumped to the pads through a pump and the pad was kept wet. The crossing air with the wind velocity of 0.5-0.7m/s through the system cooled the shelter.

Ceiling Fan System

Ceiling fan (56”) was used for air circulation during hot-humid season. Ceiling fan was hanged at the roof, in the center of building at the height of 10’.

Exhaust Fan System

Exhaust fan (24”) was used for air circulation and ventilation during hot-humid season. Exhaust fan was fixed in the one end of treatment pen at the 6’ of height.

The chicks were reared from day 1 till 42 days of age under standard conditions of housing and management except the cooling systems. No cooling system was operated till second week of rearing as birds were provided with optimum temperature of brooding. The temperature and humidity in the house were recorded three times (9:00am, 12:00pm, and 3:00pm) in a day with data-logger (SIKA Electronics, MH 3350). Mortality, if any, was also recorded daily. Rectal temperature was noted by digital thermometer at around 2 O’clock in the afternoon. The behavioural status of the birds was recorded using handy cam video recorder (SONY 755E) and the responses of the birds to the temperature and humidity variations in all the treatment groups were examined. The observations were taken for two hour every day from 3 to 6 weeks age of broiler chicks. Birds were observed for various behavioural expressions viz., stereotype pecking, panting, pushing, sitting, eating, drinking and lying (chicks had both hocks at the ground). Pecking at the drinkers, feeding troughs and at the pen wall was considered as stereotype pecking. The birds were also observed for the normal expression of the behaviour like dust bathing, litter scratching, head scratching, body preening, wing preening, preening to uropygial gland, wing flapping and leg stretching. The birds were also recorded and examined for any type of leg abnormalities problem. The data recorded on various parameters were analyzed for statistical differences by analysis of variance (Snedecor and Cochran, 1989). The treatment means were compared by using the Duncan^’s Multiple Range Tests (Duncan, 1995).

Results and Discussion

During Hot-Dry Period

Microclimatic conditions of treatment poultry shed indicated that the average ambient temperature of the shed in FF and FP groups was 1.96 and 2.78°C lower than the control group (Table 1).

Table 1: Effect of different cooling systems on micro climate, mean rectal temperature and survivability

Mean value bearing different superscripts in a row differ significantly (p<0.05); *THI = THI = T_d – (0.55 – 0.55RH) (T_d – 58) where, T_d= dry bulb temperature (°F), RH = relative humidity (%)

The numerical difference for the temperature among all the treatment groups was statistically significant. The relative humidity achieved in FP group was significantly higher than FF group (44.65%) and control group (39.21%). This increase in the relative humidity in the FP pen was also statistically significant than that in FF pen. The rectal temperature was significantly higher in the control group than FF and FP groups. It was indicated that FP (98.23%) group had significantly higher survivability rate than the control (95.04%) group. Behavioural response of broiler chicks under different treatment groups have been represented as percentage of the observation period (Table 2).

Agonistic Behaviour

The birds under cooling treatments had less frequency of agonistic behavioural expressions like pecking and avoiding compared to those of control group except pushing behaviour. Both the FP and FF groups had comparatively lower pecking percentage than the control group. However, the variation among all the treatment groups was non-significant. Significantly lower percentage of avoiding was observed in FP group followed closely by FF group. The control group had higher (p < 0.05) percentage of avoiding than both the treatment groups. However, the opposite trend was observed among the treatment groups with respect to pushing against the expectations. The numerical difference in pushing behaviour however, was non-significant in all the groups. This variation in agonistic behaviour of broiler chicks attributed to strong influence of cooling treatments in relieving the birds from heat stress compared to control group birds reared without any cooling.

Table 2: Agonistic and Non-agonistic behaviour of broiler chicks under different cooling system groups during hot-dry summer months

Mean values bearing different superscripts in a row differ significantly (p<0.05)

Non-Agonistic Behaviour

Data for non-agonistic behaviour (Table 2) indicated that the percentage of dust bathing, lying, sitting and standing was significantly higher in the cooling treatments. Birds of FP and FF groups spent more time (p < 0.05) in dust bathing, litter scratching, body preening, wing flapping, leg stretching, preening to wing or uropygial gland and eating against the control group. Panting behaviour was significantly higher in control group than both the treatment groups.

During Hot-Humid Period

Microclimatic conditions indicated 0.24°C and 0.22°C lower shed temperature (P<0.05) respectively, in EF and CF groups than the control group (Table 3).

Table 3: Effect of different cooling systems on micro climate, mean rectal temperature and survivability rate of broiler chicks from 3 to 6 weeks of age during hot-humid summer months

Mean value bearing different superscripts in a row differ significantly (p<0.05); *THI = THI = T_d – (0.55 – 0.55RH) (T_d – 58) where, T_d= dry bulb temperature (°F), RH = relative humidity (%)

The values for relative humidity differed significantly among all the treatment groups. The birds in control group also had significantly higher rectal temperature (107.9°F) than both the treatment groups. However, EF group had significantly lower rectal temperature than that in CF group. Behavioural response of broiler chicks under different treatment groups have been represented as percentage of the observation period (Table 4).

Table 4: Agonistic and Non-agonistic behaviour of broiler chicks under different cooling system groups during hot-humid summer months

Mean values bearing different superscripts in a row differ significantly (p<0.05)

Agonistic Behaviour

The data recorded for agonistic behaviour indicated that the FP group had significantly lower pecking percentage than the control group. However, CF group had statistically similar value of pecking as in EF and the control group. Same trend followed by avoiding behaviour in which, the control group had higher (p< 0.05) percentage of avoiding than both the treatment groups. However, the opposite trend was observed among the treatment groups with respect to pushing against the expectations. However, the numerical difference in pushing behaviour was non-significant in all the groups. This variation in agonistic behaviour of broiler chicks attributed to strong influence of cooling treatments in relieving the birds from heat stress compared to control group birds reared without any cooling.

Non-Agonistic Behaviour

Data for non-agonistic behaviour (Table 4) indicated that the EF group had significantly higher percentage of dust bathing, head scratching, litter scratching, wing flapping, lying, sitting and standing than the control group. Birds of EF spent more time (p<0.05) in dust bathing, head scratching, litter scratching, wing flapping, lying, sitting and standing against those in the control group. However, CF group had statistically similar values for all these activities as in EF and control group. Lying and panting behaviour differed significantly among all the treatment groups. The EF and CF groups had higher body wing and uropygial gland preening, leg stretching compared to control group but the difference for these activities among all the groups was statistically non-significant. In which, EF had significantly lowest value for lying and panting followed by CF group compared to control group.

These results indicated that the cooling systems especially FP system (hot-dry period) and EF system (hot-humid period) were efficient enough to relieve the birds from the adverse effects of heat stress. Similar results were reported by Dagtekin et al., 2009 and Bayraktar et al., 2004. Both the cooling systems in the present study were able to curb down mortality rate effectively. Andrew et al., 1993, also reported high mortality among the control group than those under different cooling system. In the present study the birds under FF system (hot-dry period) and CF system (hot-humid period) of cooling performed significantly better than the control group. The response of birds to adverse environmental changes like high temperature in the form of panting was significantly higher in control group than both the treatment groups. The increased expression of agonistic behaviour by the control birds was indicating of minimizing the heat production by the birds. Control group birds had significantly higher (p<0.05) panting as an attempt to combat heat stress through evaporative heat loss. Whereas, lower percent of panting in birds of all the FP, FF, EF and CF groups indicated cooling in the shed might have led to reduced heat production or body temperature of birds thus lowered evaporative heat loss through panting. On the other hand, birds of FP, FF, EF and CF groups had more non-agonistic behavior, indicating less effect of heat stress and in turn on behaviour of birds. Spinu et al., 2003, also noticed increased time spend in lying in summer by the broiler breeder hens to minimize the heat production.

Conclusion

All cooling systems were very efficient to reduce effect of heat stress in broiler birds during summer month. Fan-Pad during dry summer and Exhaust Fan during humid summer was found more valuable in reducing the adverse effect of heat stress on broiler chick’s performance.

References

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