Effectiveness of various cooling systems during high environmental temperature on production and welfare indices of laying pullets in deep litter system of rearing

Heat stress is one of the major causes for production losses in poultry production, especially in the hot regions of India. The higher susceptibility of poultry birds to heat stress is due to its high body temperature (41°C), much closer to the lethal temperature, which is just around 4°C above the normal body temperature. Poultry birds have insulated feathers and lack sweat glands, so it becomes difficult for them to dissipate heat. Moreover, high metabolic heat production due to high growth rate and egg production in modern poultry breeds further aggravate the situation.
       
High metabolic heat production along with high ambient temperature decreases 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 to 32°C and the decline is much faster when the temperature further rises from 32 to 38°C (Rama Rao et al., 2002). In young broiler stock, nearly 8% mortality and over 10% growth loss occur due to heat stress (Sandercock et al., 2001). In egg laying birds, heat stress caused depressed body weight (Scott and Balnave, 1988), drop in egg production (Muiruri and Harrison, 1991), egg weight (Balnave and Muheereza, 1997) and shell quality (Mahmoud et al., 1996). These adverse effects of heat stress on production performance are generally preceded by suppression of feed intake. All these consequences of heat stress may get further aggravated due to global warming effects in future.
       
Layer house temperature should remain in the thermo neutral range of approximately 18°C to 29°C for expression of their normal behavioral patterns such as time spent in resting, walking around, eating, foraging and drinking water naturally.
       
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 to improve production in poultry birds especially in tropical regions.

This experiment was conducted in deep litter system of housing at the Poultry Research Farm, Department of Livestock Production Management, Guru Angad Dev Veterinary and Animal Sciences University Ludhiana. White Leghorn laying pullets (BV-300) procured from Venky’s India (Ltd.) at 32 weeks of age having similar body weight range and average group weight (n =210).
       
In deep litter system of housing, the size of the pen was 16 x 10 x 10.
       
The pen was divided into two partitions having 35 birds in each partition and following calculations were made.
 
1 Pen                                            = 2 Partitions
In each Partition                           = 35 hens
Hence 2 partitions consists of      = 70 hens
Air circulation for 1 bird                 = 30 cfm
For 70 pullets                               = 30 x 70 = 2100 feet³/min or 59.47 m³/min or 3567 m³/hr
 
A blower fan of size 18 inches with air delivery of 60 m³/min i:e 76.8 kg/min was selected with the objective of lowering the ambient temperature from 35°C to 30°C and increasing the relative humidity from 40% to 60% and 0.0025 kg moisture/kg dry air was required (standard from psychometric chart).
       
The rate of moisture addition = total amount of air delivered /min x total moisture /kg dry air = 76.8 x 0.0025 = 0.192 kg water/min or 11.5 kg/hr or 11.5 litres/hr.
       
Hence, five numbers of foggers each of 0.2 mm diameter with a discharge of 2 litre/hr at a pressure of 30 psi were fitted in front of fan in Fan-fogger cooling system.
       
In Fan-pad system of cooling, exhaust fan of 18 inches was installed to obtain the desired air velocity.
 
Design of Fan-fogger cooling system
 
The fan-fogger system  (Fig 1) consisted of a blower with a copper ring placed in front of it. Fine foggers were placed on the ring, which was connected with a water tank through a high pressure pipe. The water was first filtered and then was pumped into the foggers. The fogger’s on and off-time was controlled through a timer. When the fan and foggers both were in on position, a fine mist was created leading to the cooling of the shed. During the off-time of the fogger, the fan was in running condition so that the required temperature and humidity could be maintained. This on/off cycle of the foggers was repeated throughout the day.
 

 
Design of fan pad cooling system
 
The fan and evaporative pad system (Fig 2) 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 amount 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 18 inches dimension at the opposite end. The water was pumped to the pads through a pump and the pad was kept wet. The cross ventilation of air with wind velocity of 0.5-0.7 m/s through the system cooled the shed.
 

 
Preparation of poultry house
 
All preparations were made in the poultry house before the arrival of pullets. After removal of all the equipments and old litter, the house was thoroughly cleaned, washed and disinfected. Fan-fogger and Fan-pad systems were installed in the poultry house to cause cooling of different sheds. Two thermo-hygrometers in each pen were fixed to record the temperature and humidity conditions in the shed. This experiment was conducted in deep litter system of rearing. First week of experiment was considered as acclimatization period. Therefore actual data recording was done from 2^nd week onwards till the completion of 10^th week from the start of the experiment (April to Mid-June).
 
Experiment details
 
This experiment was conducted on 210, White leghorn laying pullets reared in deep litter system of housing which consisted of two treatment groups, Fan-fogger system (FF) and Fan-pad system (FP), which were tested and compared with control group (CONTROL), without any cooling system. The pullets were randomly allocated to 6 groups each having 35 numbers and in three replicates. The birds used for the experiment were similar in body weight range and average group weight. The pullet ration was computed using various ingredients procured from the local market (Table 1). Daily feed recording and eggs laid were maintained separately for each group. Feed and water were made available ad libitum all the times. The body weight of all the laying pullets was recorded at the start and at the end of the experiment. All the eggs produced in a group were weighted twice in a week. Egg quality parameters were recorded once in two weeks by selecting eight eggs from each treatment group after one month from the start of experiment. Mortality, if any, was also recorded daily. Rectal temperature was noted twice in a week by digital thermometer in the afternoon at 2 pm. Temperature and humidity of the room was recorded from 4 places in shed, three times in a day using Data logger (SIKA Electronics, MH 3350).The blood sample of 5-10ml was collected by cardiac puncture with a sterilized syringe having anticoagulant into it from four birds from each treatment for evaluation of biochemical parameters.
 

       
Liver tonic (SuperliveTM) 0.25g, Vitamin C 20g, Choline chloride 50g, Trace minerals 50g (Ferrous sulphate, 120mg; Cupric sulphate, 12mg;  Potassium iodide, 1mg; Manganese sulphate, 90 mg; Zinc sulphate, 60 mg; Salinomycin, 500 mg), Vitamin A, 825000IU; Vitamin D₃, 165000IU; Vitamin E, 500mg; Vitamin B₁₂, 0.015mg; Vitamin K, 100mg; Thiamine, 80mg; Riboflavin, 6mg; Vitamin B₆, 160 mg; Niacin, 1200mg; Biotin, 0.2mg; Folic acid, 1.0mg; In addition to these supplements, methionine and cystine (M+C) were also added to fulfil the requirements.
 
Observations recorded
 
The observations which were recorded in this experiment include body weight, temperature - humidity index, feed intake, Hen day egg production (HDEP), Egg weight, rectal temperature, bird behavior, welfare indices, mortality percent and egg quality parameters viz specific gravity (SG), yolk Index, yolk colour, shell thickness.
 
Determination of antioxidant enzymes
 
The activity of lipid peroxidation, superoxide dismutase (SOD) and catalase in erythrocytes was assayed by method of Stocks and Dormandy (1971), Marklun and Marklund (1974) and by Aebi (1983) respectively. The activity of glutathione peroxidase in erythrocyte lysate was assayed by the method of Hafeman et al. (1974) and Glucose-6-phosphate dehydrogenase (G6PD) activity was assayed by the method of Deutsch (1978).
 
Statistical analysis
 
The collected data was subjected to statistical analysis using Software Package for Social Sciences (SPSS Version 16.0) available in the Central library, Guru Angad Dev Veterinary and Animal Sciences, Ludhiana. The recorded data were subjected to one-way analysis of variance (Snedecor and Cochran 1989) and comparison among means was made by Duncan‘s multiple range test with significance level of P ≤ 0.05 (Duncan 1955).

The results of experiment in deep litter system of housing have been presented and discussed as below:
 
Microclimatic conditions
 
The data for microclimatic conditions in the shed, THI, rectal temperature and survivability rate under this experiment has been given in Table 2.
 

       
The temperature of the pens in FP and FF groups during the experimental period was 31.25°C and 32.18°C, respectively. This was respectively, 2.37 and 1.44°C lower than that in the control (33.62°C) group. This difference in mean shed temperature was highly significant among all the groups. The relative humidity data recorded under different treatment groups was 49.92, 48.25 and 44.08%, respectively in FP, FF and the control group which differed significantly because of moisture addition in air by both the cooling systems. The data for THI under different treatments indicated that THI value was significantly lowered in FP group.
       
Similarly, FF group had significantly lower TH index than the control group though it was not as effectively lowered as was in FP group. Thus, the THI value differed statistically in both the treatment and the control group.
       
The rectal temperature recorded under various treatments indicated that the numerical difference for rectal temperature of birds under all the groups was statistically non-significant.
       
The survivability rate, however, was highest (92.85%) in FP followed closely by FF (91.42%) compared to the lowest (87.14%) in the control group. The difference among treatments for survivability percent was not significant.
 
Production performance
 
The data on production performance and egg quality parameters have been given in Table 3. The percent egg production, however, differed significantly (P<0.05) from 36- 42 weeks of age among all the treatment groups. The highest egg production was observed in FP group (77.13%) than both the FF (73.81%) and the control (72.47%) groups. The egg production was higher in FP and FF groups by 4.66% and 1.34%, respectively, which might be attributed to comfort provided by the cooling systems in the treatment groups in comparison to the control under severe heat stress conditions. The daily feed intake was statistically similar in both FP and the control group during 34 to 42 weeks. However, the cooling systems in treatment groups did not influence feed intake significantly throughout the experiment. The feed intake per unit egg mass was significantly poorer in control groups than both the treatment groups. Better (P<0.05) feed utilization efficiency was registered in FP followed closely by FF with significant difference than both FP and control groups. Similarly, better (P<0.05) efficiency of protein and energy utilization was recorded in order of FP > FF > control throughout the experiment. The average egg size data indicated that FP group had higher egg weight than both FF and control groups throughout the experiment, except at 34, 40 and 42 weeks of age where FF also had similar egg size. However, control group had lowest egg size. Statistically, the data for average egg size differed significantly among all the treatment groups. The pooled data of egg size indicated that both the treatment groups registered higher egg size of 55.84g in FP and 54.47g in FF than the control group with 53.4g of egg size. The average daily egg mass was significantly higher in FP than FF and the control groups throughout the experiment except at 34 weeks of age where FP and FF groups performed statistically similar with respect to egg mass production. However, overall data (Table 3) for daily egg mass also indicated that FP group had significantly higher daily egg mass. The daily egg mass value in FF group was slightly higher but statistically similar to that of control group.
 

 
Egg quality
 
The data on egg quality parameters recorded during experimental period (Table 3) indicated that the egg shell thickness in all the treatment groups was exactly the same. The egg specific gravity was significantly higher in both FP and FF than the control group but there was no difference between FP and FF groups. Slightly higher value of H.U was recorded in FP and FF groups, though the numerical difference between all the groups was not significant. Similarly, yolk index was also numerically higher in FP and FF than the control group. However, the yolk colour score was higher in control group than both the treatment groups. The differences for the yolk index and yolk colour score were, however, non-significant among all the treatments.
 
Antioxidant enzymes
 
The data for antioxidant enzyme level in the blood samples of laying pullets is given in Table 4. In the blood samples of birds, level of G6PD, GPx and catalase were significantly lower (P<0.05) both in FF and FP groups, when compared with control group having highest levels of these antioxidant enzymes, while FF group had statistically similar value for GPx levels than in both control and FP groups. The level of LPO and SOD enzymes in blood samples was numerically highest (P>0.05) in control followed by FF and FP groups, respectively.
 

 
Bird behaviour and welfare
 
Behavioural response of laying pullets under different treatment groups have been represented (Table 5) as average percentage of the observation period.
 
Agonistic behaviour
 
The data recorded for agonistic behaviour in laying pullets indicated that birds under cooling treatments had less frequency of agonistic behavioural expression 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 than the control group. The control group had highest (P<0.05) percentage of avoiding than both the treatment groups. However, there was no significant difference between FP and FF groups. The opposite trend was observed among the treatment groups with respect to pushing against the expectations. The numerical difference in pushing behaviour was non-significant in all the groups. This variation in agonistic behaviour of laying pullets was 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 5) indicated that the percentage of dust bathing, lying, sitting and standing had significant results with cooling treatments. Significantly more number of birds were performing normal expressions of behaviour like dust bathing, litter scratching and standing in both FP and FF groups compared to the control group. While reverse trend was observed in lying and sitting activities under different treatments with significant difference. Birds of FP and FF groups spent more time (P>0.05) in body preening, leg stretching, preening to wing or uropygial gland and eating than those in the control group. Panting behaviour was numerically highest (P>0.05) in control followed by FF than FP groups, however, FF had statistically similar value of panting behaviour when compared to both FP and the control group.
       
Dagtekin et al., (2009) reported effectiveness of evaporative cooling systems to lower the temperature of poultry houses, thus improving efficiency of feed conversion weight gain and mortality in broiler chicks. The poor performance by the control group compared to cooling treatments in the present study confirms the findings of Kirunda et al., (2001) who reported that egg production in White Leghorn birds decreased when exposed to high environmental temperature. Furthermore, birds exposed to high temperature have been reported to have reduced egg weight, poor shell thickness and lower specific gravity. These results also agree with the findings reported by Mashaly et al., ( 2004) about adverse effects of high temperature on production performance and egg quality parameters in laying hens.
       
On the other hand, Sharma and Gangwar (1985) compared various cooling systems on the basis of performance of broiler chicks and adjudged air coolers or foggers to be effective to improve growth performance of broiler chicks.
       
Ugurulu and Kara (2003) also reported 4.28% higher egg production by hens under evaporative cooling system than in natural ventilated house. In the present study also, both the cooling systems (FP and FF) were able to increase hen-day egg production to the tune of 5.5% and 0.73% during experiment I and 4.66% and 1.34% respectively, during experiment II against the control without any cooling.
       
The data on biochemical analysis indicated that both the treatments were able to provide necessary cooling and in turn comfort, led to the maintenance of the enzyme levels responsible for lipid peroxidation, which are the strong indicators of heat stress in poultry birds. These results confirm the findings of the previous study of Altan et al., (2000), in which higher MDA concentration was reported in the broiler chicks as a response to heat stress. Similar findings were reported by Azad et al., (2010) with respect to MDA, GPx activity in the broiler chicks. Similarly, Lin et al., (2010) and Tan et al., (2010) also reported significantly higher production of antioxidative enzymes like SOD, catalase, GPx along with formation of MDA induced by acute heat stress.
       
The results pertaining to behavioural response by birds with or without cooling under various treatments during experiment I and II, agree with the findings of Estevez et al., (2003) who reported an increase in normal behaviour in the form of locomotory activities with decrease in temperature. On the other hand, there was significant increase in behaviour of lying down or prostration due to increase in environmental temperature was noticed. Moreover, locomotory activities in the present study were also decreased due to exposure to high temperature in the control group than both the cooling groups confirms the findings reported by Maria et al., 2004.

The author wish to express sincere thanks to ICAR, New Delhi for providing financial support during M.V.Sc degree programme in the form of ‘Junior Research Fellowship’ award and financial assistance provided by CIPHET (ICAR) Ludhiana for carrying out this research work entitled “Effect of Cooling System on Thermal Comfort and Production of Poultry birds”. The help and guidance rendered by my Major Advisor Dr. Daljeet Kaur, Assistant Professor and other faculty members of Department of Livestock Production Management, COVS, GADVASU, Ludhiana is thankfully acknowledged.