An Assessment of the Growth and Profitability Potential of Meat-Type Broiler Strains under High Ambient Temperature

Zia ur Rehman1, Naila Chand1, Rifat Ullah Khan2,*, Sarzamin Khan1 and Muhammad Subhan Qureshi3 1Department of Poultry Science, Faculty of Animal Husbandry and Veterinary Sciences, The University of Agriculture, Peshawar 2Department of Animal Health, Faculty of Animal Husbandry and Veterinary Sciences, The University of Agriculture, Peshawar 3Department of Livestock, Breeding and Genetics, Faculty of Animal Husbandry and Veterinary Sciences, The University of Agriculture, Peshawar Article Information Received 17 March 2017 Revised 04 May 2017 Accepted 24 May 2017 Available online 25 January 2018


INTRODUCTION
B roiler strains most commonly reared in Pakistan are Ross, Hubbard, Cobb and Arber Acre.Various performance traits of these strains such as production potentials, resistance to various diseases and adaptability of these strains in high environmental temperature may adversely affect the farmer's preferences.The information about the performance and management of these strains in the literature of breeder's company not necessarily apply to regional environmental conditions of any particular country (Farran et al., 2000).
High ambient temperature (HAT) is a life-threatening factor for commercial broiler production particularly in hot climates, where poultry producers cannot afford expensive artificial control of high temperature in broiler shed (Deeb and Cahaner, 2001;Khan et al., 2014).High temperature causes economic losses in broiler production due to the poor performance, lower weight gain, and poor feed efficiency (Zhang et al., 2012;Chand et al., 2016).These adverse effects of high ambient temperature are more prominent in chicken genotype having higher body weight and rapid growth than in those with slower growth and lower body weight (Razuki and Al-Rawi, 2007).Different broiler strains respond differently to different environments.The rearing of unsuitable genotype in hot area may result in large economic losses due to the reduced growth, decreased protein gains and higher mortality (Razuki and Al-Rawi, 2007;Berrong and Washburn, 1998).
The testing of different broiler strains in hot climate may provide more useful information relating to specific broiler strains that can produce well in hot and thermo neutral (TN) climates.In view of the above consideration, the present study was conducted to investigate the economic suitability of four commercial broiler strains (Ross, Hubbard, Cobb and Arber Acer) reared in thermo neutral and high ambient temperature (summer season).

MATERIALS AND METHODS
The trial was conducted in a completely randomized design with two temperature zones and four broiler strains.A total of 240 day old broiler chicks of four commercial broiler strains (Ross, Hubbard, Cobb and Arber Acres) of the same age and size were used for the study.In first two weeks, chicks were placed in brooding room and then divided into two groups: thermo neutral zone (TN) and high ambient temperature (HAT).Chicks were fed standard ration as shown in Table I and the chemical composition is given in Table II.Chicks in TN group were housed at constant room temperature (25ºC ± 2ºC and RH 65 ±5%) while chicks in HAT group were kept at high ambient temperature as shown in Table III.Both the groups were kept in two different rooms which were identical in term of size, construction materials and equipment.Chicks in each group were further divided into four sub groups i.e., TN-Ross, TN-Hubbard, TN-Cobb, TN-Arber Acer and HAT-Ross, HAT-Hubbard, HAT-Cobb, HAT-Arber Acer.Each sub group was further subdivided into four replicates having ten chicks per replicate.Feed and water was provided ad libitum.

Performance measurement
Chicks were weighed initially and weekly at seven days interval for six weeks and total body weight gain (BWG) was calculated at the end of trial.Daily feed intake was calculated by subtracting the quantity of feed left from offered.Feed conversion ratio (FCR) was determined on weekly basis.Mortality was recorded during experiment.Economics of each strain used in this trial was calculated in terms of feed cost, gross return and net income.Total expenditure including feed cost per chick plus day old chick price and cost of medicine were included in the total cost per chick.Gross return per chick was computed on per kg (live weight basis) basis according to the market price.Net return was measured by subtracting cost per chick from gross return per chick.

Statistical analysis
Data was subjected to two-way analysis of variance with zone of temperatures and strain as the main effects.The following model was used: Yjkm = µ + βj + αk + γl + ejklm Where, µ is population mean, βj is treatment effect (treatment comprise thermo neutral (TN) zone and high ambient temperature (HAT) zone), αk is the strain effect (four commercial broiler strains Ross, Hubbard, Cobb and Arber Acres), γl is the strain by temperature zone interaction, eijklm is the random error associated to k th chicks and j th is treatment in experimental unit.
Least significant test was used to compare the differences among treatment means.All statistical analysis was carried out using statistical package SAS (1992).

RESULTS
Mean feed intake per chick of four different broiler strains reared in TN and HAT zone is given in Table IV.On day 28, in TN zone, significantly higher (P< 0.05) feed intake was found in Hubbard and Cobb strains, while in HAT zone, higher (P< 0.05) feed intake was recorded in Ross and Arber Acer.On day 35, similar trend was recorded in TN and HAT zones.On day 42, in TN zone, no significant difference was found in feed intake.On day 42, in HAT zone, higher feed intake was recorded in Ross followed by Arber Acer and Cobb, while lowest feed intake was recorded in Hubbard.In TN zone, over all feed intake was significantly (P<0.05)higher in Cobb and Hubbard,   while in HAT zone, significantly higher (P< 0.05) overall feed intake was recorded in Ross and Arber.Mean weight gains per chick of four different broiler strains reared in TN and HAT zone is given in Table V. Temperature zone significantly (P< 0.05) affected weigh gain in different broiler strains on all recorded stages except day 28.On day 28, in thermo neutral zone, significantly higher (P<0.05)weight gain was recorded in Cobb and Hubbard strains followed by Ross and Arber Acer.On day 28, in HAT zone, higher (P< 0.05) weight gain was found in Arber Acer and Ross followed by Cobb and Hubbard strains.On day 35, in TN zone, significantly (P< 0.05) higher weight gain was found in Cobb and Hubbard.On day 35, in HAT zone, significantly (P< 0.05) higher weight gain was recorded in Arber Acer and Ross followed by Cobb.On day 42, in TN zone, weight gain was higher in Cobb followed by Hubbard and Arber Acer, while lowest weight gain was recorded in Ross.On day 42, in HAT zone, significantly (P< 0.05) higher weight gain was recorded in Ross, while it was lower in all other strains.Total weight gain was significantly (P< 0.05) higher in Hubbard and Cobb in thermo neutral zone, while higher total weight gain was recorded in Ross and Arber Acer in HAT zone (Table V).Mean FCR per chick of four different broiler strains reared inTN zone and HAT zone is given in Table VI.On day 28, in TN zone, significantly (P< 0.05) lower FCR was recorded in Hubbard.On day 28, in HAT zone, significantly (P< 0.05) lower FCR was recorded in Arber Acer.On day 35, FCR was significantly lower and the same in all strains in TN zone, while it was significantly (P<0.05)higher and the same in all the four strains in HAT zone.On day 42, in TN zone significantly (P<0.05)lower FCR was recorded in difference were recorded in FCR.On day 42, in HAT zone, no significant difference was recorded in mean FCR.Overall FCR in TN zone was significantly lower (good) in Hubbard followed by Cobb and Arber Acer, while overall FCR in TN zone was the poor (high) in Ross.
In HAT zone, the lowest overall FCR was recorded in Arber Acer followed by Ross, Hubbard and Cobb.Overall FCR was also significantly (P< 0.05) lower (good) in TN zone as compare to HAT zone.Overall mortality of four different broiler strains reared in TN and HAT zone is presented in Table VII.In TN zone, no significant difference was found among the strains.In HAT zone, higher (P< 0.05) mortality was recorded in Cobb followed by Hubbard, Ross and Arber Acer.
Economics of the experimental chicks in terms of feed price, gross return and net return per chick is given in Table VII.In TN zone, significantly (P< 0.05) higher feed price was recorded for Ross and Cobb followed by Arber Acer and Hubbard.Feed cost of Arber Acer in TN zone was not different from Ross and Cobb.In HAT zone, significantly (P< 0.05) higher feed cost per chick was recorded in Ross and Arber Acer.Gross return per chick was significantly higher and same in all the four strains in TN zone.In HAT zone, significantly (P< 0.05) higher gross return per chicks was recorded in Ross and Arber Acer.In TN zone, significantly higher net return per chick was recorded in Hubbard and Cobb.In HAT zone, significantly (P< 0.05) higher net income per chick was recorded in Ross and Arber Acer.Net return per chick for Hubbard strain in HAT zone was not different from Cobb.

DISCUSSION
Under high ambient temperature, there is heat exchanged between the birds and their surrounding environment (Al-Fataftah and Abu-Dieyeh, 2007).Birds lose heat to their surrounding environments mostly by evaporative heat loss and gain heat from environment at the same time.In addition, heat is produced by feed metabolism.The birds use their physiological mechanism to reduce heat stress during high environmental temperature.Our results are in line with findings of Lara and Rostagno (2013) who found that birds kept under high ambient temperature, consumed 16.4% less feed compared with TN group at 42 days of age.Similarly, Quinteiro-Filho et al. (2010) reported decreased feed consumption in broilers kept at high ambient temperature.Niu et al. (2009) reported decreased feed consumption in broilers subjected to cyclic heat stress (23.9 to 38°C) which is in support to our findings.Al-Fataftah and Abu-Dieyeh (2007) found that increasing temperature decreased feed consumption after four weeks trial by 4.0, 12.4 and 28%, respectively as compared to feed consumption in TN zone (24-28°C).
Under optimum condition, Iqbal et al. ( 2012) reported that Hybro PN consumed significantly less feed compared to Arber Acer, Ross and Hubbard strains.Similarly, Razuki et al., (2011) reported that Hubbard strain consumed more feed then Cobb, Ross and Lohmann strains in heat stress.
The depression in body weight gain at high environmental temperature might be due to decreased feed consumption, inefficient digestion (Hai et el., 2000), decreased concentrations of growth hormones (T3 and T4) in hot environments (Elnagar et al., 2010), reduced enzymatic activities of amylase, trypsin and chymotrypsin (Abu-Dieyeh, 2006), decreased plasma amino acid and energy supply (Temim et al., 2000).At high ambient temperature protein synthesis is reduced (Geraert et al., 1996) and metabolism is impaired (Farrell and Swain, 1978), which might be responsible for reduced growth rate at HAT zone.Strains that perform better at optimum ambient temperature may not maintain their superiority for growth in HAT (Razuki and Al-Rawi, 2007).Moreover, differences between strains in their growth at high ambient temperature are related to their genetic potential for feed intake and growth rate (Razuki et al., 2011) which may be responsible for better performance of Ross and Arber Acer under high temperature zone.Tawfeek et al. (2014) reported 35.47% less body weight for birds kept under high ambient temperature as compared with thermo neutral group at 42 days of age which is supported to our findings.Similarly, Lara and Rostagno (2013) reported 32.6% less weight gain under high ambient temperature as compared with thermo neutral group.Ruzaki and Al-Rawi. (2007) reported that strains that performs better in optimum temperature cannot maintain superiority for growth in high ambient temperature.
The decreased body weight may not only be due to the lower feed intake, but also to a direct effect of environmental temperature on broiler physiology and metabolism (Tawfeek et al., 2014).Our results are in line with findings of Lara and Rostagno (2013), Quinteiro-Filho et al. (2010), Niu et al. (2009), Al-Fataftah andAbu-Dieyeh (2007) and Abu-Dieyeh (2006).The results of present findings are in agreement with those Razuki et al. (2011), who reported that Ross strain exhibited better FCR than Cobb, Hubbard and Lohmann strains in heat stress.Similarly, Farran et al. (2000) reported that Arber Acres has significantly lower feed conversion than Ross and Lohman at 49 days of age.
In the present study, mean mortality and economics of four different broiler strains reared in TN and HAT zone are significantly affected by temperature zone.In hot environment, high mortality in broiler may be due to inefficient evaporative cooling which increase of heat inside the body.When temperature of the body reaches dangerous level, due to continue accumulation heat, the birds' dies from heat prostration (Al-Fataftah and Abu-Dieyeh, 2007).The death from heat prostration may be due to adrenal cortical insufficiency or cardiovascular failure or imbalance of ions (potassium, calcium, sodium, chloride, phosphate, magnesium and sulphate) in the blood (Deaton et al., 1978).Our results are similar to the findings Quinteiro-Filho et al. (2010), Al-Fataftah andAbu-Dieyeh (2007) and Abu-Dieyeh et al. (2006).Iqbal et al. (2012) reported that mortality in Hubbard strains was significantly lower (4.4%)than Hybro PN, Ross 308 and Arbor Acres-strains in optimum conditions.Similarly, Razuki et al. (2011) reported lower mortality in Hubbard strains compared to Rose, Cobb and Lohmann.

CONCLUSION
Ross and Arber Acer performed better in terms of feed intake, weight gain, FCR and are more economical to be reared in hot summer season in tropical climates of Pakistan, while Cobb and Hubbard strains are more suitable in thermo neutral environment.

Table IV .-Feed intake of different broilers strain reared under thermo neutral and high ambient temperature zones.
Mean with different superscript in the same column are significantly different (P<0.05)

Table V .-Weight gain of different broilers strain reared under thermo neutral and high ambient temperature zones.
Mean with different superscript in the same column are significantly different (P<0.05).

Table VII .-Mean (±SE) mortality (%), cost (Rs.), gross income (Rs.) and net income (Rs.) of different broilers strain reared under thermo neutral (TN) and high ambient temperature (HAT) zones.
Mean with different superscript in the same column are significantly different (P<0.05).