Research Article

 

Seasonal Impact on Growth Performance, Economic Feasibility, Hematological Indices, and Blood Biochemical Composition of Broiler Chickens

 

Fardos A.M. Hassan, Rehab Reda*

Animal Wealth Development Department, Faculty of Veterinary Medicine, Zagazig University, 44511, Egypt.

 

Received | June 12, 2021; Accepted | July 25, 2021; Published | November 15, 2021

*Correspondence | Rehab Reda, Animal Wealth Development Department, Faculty of Veterinary Medicine, Zagazig University, 44511, Egypt; Email: rehabreda268@yahoo.com; RRsayed@zu.edu.eg

Citation | Hassan FAM, Reda R (2021). Seasonal impact on growth performance, economic feasibility, hematological indices, and blood biochemical composition of broiler chickens. J. Anim. Health Prod. 9(4): 471-478.

DOI | http://dx.doi.org/10.17582/journal.jahp/2021/9.4.471.478

ISSN | 2308-2801

Copyright © 2021 Reda and Hassan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

 

Introduction

 

The poultry sector is characterized by rapid growth, worldwide, and broilers are the preferred type of poultry, raised mainly for meat (Mallick et al., 2020). The broiler industry differs from other livestock production in that broilers have the shortest life cycles, low capital investment, high returns, and quick turnover (Bhende, 2006). In the near future, the global demand for poultry meat is projected to grow exponentially. By 2050, a 33% increase in the world’s population is expected (UNO, 2015), necessitating a 70% increase in food production. Chicken constitutes an inexpensive protein supply for humans; consequently, the demand for poultry meat is likely to increase to enable feeding this vast human population (Ramachandran, 2014; Osti et al., 2017).

 

Genetic and environmental factors can influence the growth characteristics of broilers (Okere, 2014). Choosing the most appropriate season for raising broilers is crucial for increasing productivity (Koknaroglu and Atilgan, 2007). Seasonal variations, climatic changes, and increasing extremities in weather patterns, are major nongenetic factors affecting broiler productivity and profitability (El-Faham et al., 2017). This study aimed to aid broiler farmers in choosing optimal rearing facilities for specific environmental and weather conditions and to achieve favorable broiler performance (May and Lott, 2000). When the thermo-neutral ambient temperature was increased, the feed consumption of 4–8-week-old broilers exhibited a significant decrease (Yahav et al., 1996; Singh et al., 2019). When broilers are exposed to high temperatures, their feed consumption declines and their daily nutrient intake decreases to minimize metabolic heat production and preserve homeothermy (Abu-Dieyeh, 2006). By contrast, low ambient temperatures increase feed intake, body weight gain, feeding effectiveness, and survivability as the broiler chicken adjusted easily to less temperatures than higher ones (Ali et al., 2015).

 

Additionally, fowls react to high temperatures with physiological changes like many other animals which minimize the negative impacts of the hot climate (Donkoh, 1989). The health status of broiler chickens can be assessed using hematological parameters. Numerous factors including conditions of microclimate and macroclimate, raising methods, season, and pathological factors affect blood values (Mohamed et al., 2012). Increased metabolic energy requirements because of low temperatures are concomitant with changes in the hematological and biochemical parameters of the blood. Broiler chickens that are subjected to low temperatures exhibit increased hematocrit value, hemoglobin (Hb) concentration, serum protein, and glucose (Yahav, 2002). Serum triiodothyronine (T3) is associated with temperature regulation in broilers and is a vital growth promoter. A circulating T3 concentration was reported to correlate positively with feed intake and negatively with temperature (Blahova et al., 2007). This study investigated the seasonal influence on growth parameters, hemato-biochemical indices, and the economic value of broilers.

 

Materials and Methods

This study was consistent with the ethical standards and regulations established by the Local Laboratory Animal-Care Committee (Faculty of Veterinary Medicine, Zagazig University). The Committee on Institutional Ethics approved the experimental procedure (Approval No. ZU-IACUC/2/F/36/2021).

 

 

Experimental Procedure

This study was conducted in four consecutive seasons (winter, spring, summer, and autumn). In each season, a total of 120 one-day-old male Cobb-500 broilers were obtained from a commercial hatchery. The broilers were grouped in six replicates of 20 birds each. Each group was allocated to a clean floor pen (2 m2; bird density: 10 chicks m−2) covered with a 3 cm layer of sawdust as bedding. Chicks were brooded at 32℃ for the first 3 days, and then the environmental temperature has not been adjusted, depending on the outside weather during the entire period. The relative humidity was maintained between 50% and 60%. The program of lighting during the trail was 23L: 1D. The diet (starter, grower, and finisher; Table 1) was provided as pellets and designed for optimal nutritional performance (NRC, 1994). Water and feed were provided ad libitum. All chicks were vaccinated against Gumboro and Newcastle disease.

 

Growth Performance

Growth parameters were assessed by registering the initial weight on day 1, the final BW on day 42, and the gain in BW was measured as the variance among FBW and initial BW. Feed was withheld for 2 h before weighing the birds. The feed intake per replicate was calculated over the trial period as the difference between provided feed and residual feed. The feed conversion ratio (FCR) was determined as the ratio of feed (g) to weight gain (g) according to (Wanger et al., 1983). The survivability was determined by dividing the number of birds sold by the number of chicks entered. The dead birds during the study were weighed, and all feed losses were collected and weighed in each pen to ensure accurate measurements of feed intake and FCR.

 

Collection of Blood Samples

On the morning of day 42, we collected the blood from the wing veins of animals using a sterilized syringe (5 mL). Three specimens from each replicate were randomly selected (n = 18). An immediate blood sample was preserved in two test tubes, one of which contained an anticoagulant (EDTA) and the further one without. The tube that contained the anticoagulant enabled estimating the packed cell volume (PCV), hemoglobin concentration, and total red blood cell (TRBC) count. The other test tube was stored for approximately 3 h at room temperature and then centrifuged at 3000 rpm for 10 min for biochemical analysis. Hemolysis-free samples for serum were transferred into clean vials and preserved at −20℃ to determine serum glucose, total protein (TP), T3, calcium (Ca), and phosphorus (P).

 

Laboratory Analysis

Examination of blood hematology comprised the following tests: TRBC count was estimated using a Neubauer

 

Table 1: Ingredients and chemical composition of basal diets (as-fed basis).

 

Ingredients	Starter (0 to 10 d)	Grower (11 to 24 d)	Finisher (25 to 42 d)
Yellow maize	56.00	60.60	63.90
Soybean meal (48%)	34.86	29.00	25.00
Maize gluten (60%)	3.50	4.50	4.00
Soybean oil	1.80	2.00	3.66
Calcium carbonate	1.00	1.00	0.90
Dicalciumphosphate	1.80	1.90	1.60
Sodium chloride	0.30	0.30	0.30
Premix*	0.30	0.30	0.30
DL- Methionine (98%)	0.18	0.14	0.11
Lysine, HCl (78%)	0.16	0.16	0.13
Toxenil	0.10	0.10	0.10
Calculated chemical composition†
ME, MJ/kg	12.74	13.00	13.41
CP (%)	23.30	21.44	19.57
EE (%)	4.28	4.60	6.24
CF (%)	2.64	2.55	2.63
Ca (%)	0.97	0.98	0.86
Available P (%)	0.47	0.48	0.41

*Supplied per kg of diet: Vitamin A, 12 000 IU; vitamin D3, 2200 IU; vitamin E, 26 IU; vitamin K3, 6.25 mg; vitamin B1, 3.75 mg; vitamin B2,

6.6 mg; vitamin B6, 1.5 g; pantothenic acid, 18.8 mg; vitamin B12, 0.31 mg; niacin, 30 mg; folic acid, 1.25 mg; biotin, 0.6 mg; Fe, 50 mg; Mn, 60 mg; Cu, 6 mg; I, 1 mg; Co, 1 mg; Se, 0.20 mg; Zn, 50 mg; and choline chloride, 500 mg.

†Calculated according to NRC (1994) tables.

ME: Metabolisable energy, CP: Crude protein, EE: Ether extract, CF: Crude fibre, Ca: Calcium, P: Phosphorus.

 

hemocytometer after appropriate dilution (Campbell, 1995); the hematocrit value was measured through a method of capillary micro-hematocrit using a Janetzki centrifuge (Kelly, 1979); and Hb concentration (using Drabkin’s solution diluent) was estimated using cyanmethemoglobin according to (Ritchie et al., 1994). Regarding biochemical indices, the concentration of glucose was estimated with an enzymatic method on the basis of the glucose oxidase reaction, using a kit (Spinreact, SA, Spain). An automated biochemical analyzer was used to estimate TP (g/L) using a biuret technique adapted by Gornall et al. (1949) and Kohn and Allen (1995). Colorimetric techniques were used to determine serum Ca and P. A biochemical analyzer was used to measure the serum level of total T3 IMMULITE 1 (DPC). Analysis of the proximate composition of the test ingredient was performed by AOAC (2000).

 

Economic Feasibility of Broiler Chickens

The potential profitability of the studied broiler chickens was evaluated using a partial budgeting technique provided in the following:

 

Cost of feed/kg BW = [(Feed consumption per bird × Cost of 1 kg feed)/Final weight] (Eq. 1)

 

Total cost/kg BW = [Total costs per bird/Final BW per bird] (Eq. 2)

 

Where total costs included total feed costs, the price for the one-day-old chicks, and the costs for litter, labor, veterinaries, electricity, and miscellaneous items.

 

Profit/kg BW = Price of kg live BW − Total cost per kg BW (Eq. 3)

 

Profit–cost ratio = Profit per kg BW/Total cost per kg BW (Eq. 4)

 

Statistical Analysis

One-way analysis of variance was performed to analyze the data with SPSS, after normality was ensured using the Shapiro–Wilk test and variance homogeneity among experimental units was verified using Levene’s test. Replicate or individual birds were used as the experimental units for all statistical analyses. The mortality percentages were converted into Arcsin values and then retransformed after analysis into the initial values. The significance among values of means was estimated using the Bonferroni test with the significance level at (P < 0.05).

 

Results

 

Growth Performance

The results revealed that seasonally changing environmental temperatures exerted the main influence on broiler performance, health conditions, and physiology. A significant seasonal effect was observed in the final weight, BW gain, FCR, and livability percent (Table 2). Feed consumption and initial BW exhibited no significant effect. Among the groups from all seasons, those raised in winter exhibited the highest FBW and body weight gain (BWG; P = 0.005 and 0.006, respectively). The FCR was significantly lower (P = 0.024) in winter than it was in the other seasons. Additionally, livability percent was within the normal range, however, a significantly lower percent was observed in summer (P = 0.011), followed by winter, spring, and autumn.

 

Economic Evaluation

Birds raised in winter incurred a significantly lower total cost per kg BW compared with those raised in summer, spring, and autumn (Table 3, P = 0.005). Additionally, they generated the highest value in terms of profit/kg BW, profit–cost ratio (P > 0.001), and the price of kg live BW (P = 0.007), in comparison with the birds of the other seasons. Regarding the feed costs, differences between seasons were insignificant (P > 0.05).

 

Hematological and Biochemical Parameters

Table 4 presents the seasonal influence on the hematological parameters. The birds raised in winter exhibited higher hematological indices PCV (P = 0.001), Hb (P = 0.009), and TRBC count (P = 0.032) when compared with those raised in summer, which exhibited the lowest ones. The biochemical parameters (blood glucose, TP, T3, Ca, and P) were significantly higher in winter than in summer, spring, and autumn (P = 0.026, P = 0.015, P = 0.004, P = 0.001, and P = 0.012, respectively; Table 5).

 

Discussion

 

Seasonal Effect on Growth Performance of Broilers

Table 2 presents the seasonal influences on the growth parameters of broilers. A significant seasonal effect was observed in final values for BW, BWG, FCR, and percent of livability, as birds raised in winter exhibited superior values for FBW, BWG, and FCR (2766.67, 2720 g/bird, and 1.64, respectively) followed by birds raised in autumn, summer, and spring. This is consistent with a previous study reporting the highest BW in winter (Osti et al., 2017). In contrasting studies (Nembilwi, 2002; Thirumalesh et al.,, 2012), the weight of broilers was not affected by the season. A significantly (P < 0.05) higher FBW observed in winter may be a consequence of high feed utilization, which might be attributable to the more appropriate microclimate. Previous studies have reported 18℃–23℃ as an ideal temperature (Aengwanich and Simaraks, 2004; Al-Aqil et al., 2009; Yakubu et al., 2007). At this temperature, birds can control their heat balance relatively well and require low levels of energy for their activity (Syafwan et al., 2011). Hence, broilers adapt to lower temperatures more easily than to higher ones (Manning and Wyatt, 1990). The lower BW, BWG, and higher FCR during summer and spring in this study were likely because of the high temperature. This meant that the bird had to balance heat production and heat loss, for example, through panting. This behavior incurs a metabolic cost in terms of energy, resulting in a higher FCR (Abu-Dieyeh, 2006). Also, the significantly higher (P < 0.05) livability percent for birds raised in the autumn, spring, and winter could be due to a more appropriate temperature for broiler chickens. By contrast, the low livability percent of broiler in summer could be due to heat stress and a lowered immune response, which can cause heatstroke, increased pathogens, and finally death (Sarma et al., 2019; El-Faham et al., 2017). However, the overall livability was above 95%, which is considered normal for broiler chickens.

 

Seasonal Effect on the Profitability of Broilers

Regarding the economic feasibility, a significantly (P < 0.01) lower total cost/kg BW, higher profit, and profit–cost ratio were observed in winter, which is consistent with the findings of Iqbal et al. (2012) who reported the 1 kg live broiler production cost to vary considerably among farms, seasons, and countries. The highest production cost was observed in summer and was attributable mainly to a higher FCR. The production cost per unit at high temperatures is higher than that at low temperatures because of the energy expenditure incurred by body heat dissipation processes; this lowers the production efficiency at high temperatures (McDowell, 1972). However, the highest profit in winter may attributable to the higher market price, because the market price of live broiler was the prime factor affecting the profitability of the birds (Roy, 2000; Raha, 2007; Ali et al., 2015). These findings are consistent with Rahman et al. (2003) and Ramdur et al. (2010) they also found that higher profits for broiler production occur in winter with the highest profit-cost ratio than in other seasons and less sale value per bird in the summer season.

 

Seasonal Effect on the Hematological Parameters of Broilers

Physiological reactions in broilers respond to seasonal and environmental temperature variations. Poultry belongs in the category of homeothermic birds that can live comfortably in a relatively small thermal neutral zone. In this study, significantly higher hematological values of PCV,

 

Table 2: Effect of seasons on production performances of broiler1

 

	Seasons
Items 2	Winter	Spring	Summer	Autumn	SEM3	P-value
Initial BW (g/bird)	46.27	40.15	44.40	42.50	0.122	0.128
Final BW (g/bird)	2766.67a	2516.28b	2636.81ab	2730.95a	17.23	0.005
TFI (g/bird)	4459.17	4325.83	4410	4521.80	31.64	0.253
BWG (g/bird)	2720.40a	2476.13c	2592.41ab	2688.45a	14.76	0.006
FCR (feed: gain)	1.64b	1.75a	1.70ab	1.68ab	0.019	0.024
Livability (%)	96.04b	97.83 ab	95.20c	97.97a	0.120	0.011

Means bearing different superscripts within the same row are significantly different (P< 0.05).

1Results are presented as the means of 6 replicate pens with 20 birds per pen.

2BW: Body weight, TFI: Total feed intake, BWG: Body weight gain, FCR: Feed conversion ratio

3SEM: Standard error of the mean.

 

Table 3: Effect of seasons on cost of production and profitability of broiler1

 

	Seasons
Items 2	Winter	Spring	Summer	Autumn	SEM3	P-value
FC ($/kg BW)	0.65	0.71	0.70	0.71	0.009	0.253
TC ($/kg BW)	0.89c	1.12a	1.05b	1.02b	0.023	0.005
Price of kg live BW($)	1.76a	1.72a	1.39b	1.25b	0.055	0.007
Profit ($/kg BW)	0.87a	0.60b	0.34c	0.23c	0.014	<0.001
Profit-cost ratio	0.98a	0.54b	0.32c	0.23c	0.019	<0.001

 

Means bearing different superscripts within the same row are significantly different (P < 0.05).

1Results are means of 6 replicate pens of 20 birds per pen.

2BW: Body weight, FC: Feed cost, TC: Total cost, cost of one kg feed = 0.42$

3SEM: Standard error of the mean.

 

Table 4: Effect of seasons on hematological indices of broiler1

 

	Seasons
Items 2	Winter	Spring	Summer	Autumn	SEM3	P-value
PCV (%)	37.92a	31.33bc	29.63c	32.80b	1.899	0.001
Hb (g/dl)	13.88a	11.73bc	11.03c	12.96b	0.568	0.009
TRBC (million cell/mm3)	2.67a	2.24b	2.16b	2.33ab	0.009	0.032

Means bearing different superscripts within the same row are significantly different (P < 0.05).

1Results are means of 3 samples from each replicate pens.

2PCV: Packed cell volume, Hb: Hemoglobin concentration, TRBCS: Total red blood cells,

3SEM: Standard error of the mean.

 

Table 5: Effect of seasons on some blood biochemical compositions of broilers1

 

	Seasons
Items 2	Winter	Spring	Summer	Autumn	SEM3	P-value
Blood Glucose (mg/dl)	213.79a	181.44b	164.10b	198.03ab	5.1332	0.026
Total Protein (g/l)	38.60a	33.79bc	31.60c	37.60ab	2.391	0.015
T3 (ng/ml)	2.59a	1.03b	0.98b	1.84a	0.235	0.004
Ca (mmol/l)	3.17a	2.39b	2.29b	2.56b	0.502	0.001
P (mmol/l)	2.74a	2.25b	2.01b	2.40ab	0.019	0.012

Means bearing different superscripts within the same row are significantly different (P < 0.05).

1Results are means of 3 samples from each replicate pens.

2T3: Triiodothyronine, Ca: Calcium, P: Phosphorus.

3SEM: Standard error of the mean.

 

 

Hb, and TRBC count were observed in winter (37.92%, 13.88 g/dL, and 2.67 million cell/mm3, respectively), because of an elevated energy demand due to the cold temperatures. This means that the cardiovascular system must adapt to the altered energy needs of the body. Therefore, the increase in hematocrit (PCV), hemoglobin, and blood volume was observed in broilers subjected to low ambient temperatures, which is consistent with the results of Blahova et al. (2007). Moreover, Yahav and Hurwitz (1996) reported that the decline in hematocrit value for the Cobb strain during summer could be due to a decrease in the erythrocytes count, which is caused by increased damage in erythrocyte or hemodilution. Additionally, the lower levels of Hb concentration in the summer could be due to high temperatures changing the spread of iron in the organisms of birds, which has been described by Vecerek et al. (2002) and Comito et al. (2007). The results demonstrated that the high ambient temperature in summer reduced the TRBC count. This is in harmony with the findings of Khan et al. (2002), who reported that elevated temperatures lead to a decline in TRBC count, which might be caused by diminished oxygen consumption. This, in turn, may be accompanied by a simultaneous decrease in the production of red blood cells due to a lower basal metabolic rate.

 

Seasonal Effect on the Biochemical Indices of Broilers

Blood biochemical indices serve as an effective indicator of bird health and determining them allows identifying metabolic alterations (Filipović et al., 2007). In this study, serum glucose, Ca, and P concentrations were significantly decreased throughout the summer compared with those in spring, autumn, and winter seasons, with birds raised in winter exhibiting the highest values. The decrease in glucose concentration, Ca, and P during the summer might be an outcome of the decrease in feed intake. However, it could also be caused by the increased consumption of water as a response to heat stress, which leads to hemodilution and thereby a reduction in carbohydrate consumption. This finding is in the line with the previous research carried out by Abdalla and Nawal (2009). Additionally, the birds raised in winter exhibited a significant (P < 0.05) elevation in the concentration of TP when compared with birds raised in other seasons. This could be a result of the increase in feed consumed by the birds accompanied by a higher digestibility of protein because of the low temperatures (Mohamed et al., 2012). Temperature affects T3, a hormone that influences feed consumption and weight gain. The circulating concentration of T3 seems to be correlated positively with feed intake and negatively with temperature (Stojevic et al., 2000). In this study, significant changes in T3 concentration were observed. The serum values of T3 were higher in winter (2.59 ng/mL) than in autumn, spring, and summer. This result is consistent with the results of Yahav (2002).

 

Conclusion

 

To conclude, Cobb-500 commercial broiler chickens exhibited the most favorable production and economic performance (including the highest profit at the lowest cost of producing 1 kg meat) in winter. Additionally, the highest hemato-biochemical values were also observed in winter. Thus, the preferred season for small-scale broiler farmers to earn the highest profit is winter, although they must take extra care during the chick period. Additionally, farmers may seek to control environmental variables to obtain better livability, FCR, and body weight in summer.

 

Acknowledgments

 

The authors wish to thank the Egyptian Knowledge Bank Editing SPOC Office for the proofreading of the manuscript.

 

Conflicts of interest

 

The authors declare that there are no conflicts of interest.

 

authors contribution

 

R.R. designed the study plan, gathered literature, and compiled the manuscript. F.A.M.H. provided technical assistance in writing and revising the manuscript. All the authors read and approved the final manuscript.

 

References

 

• Abdalla MA, Nawal ME (2009). Effects of sesonal change in the thermal environment on physiological responses of unsexed broilers to dietry supplementation of antithroild drug carbimazole. Middle-East J. Sci. Res. 4:122-126.

• Abu-Dieyeh ZHM (2006). Effect of high temperature per se on growth performance of broilers. Int. J. Poult. Sci. 5(1): 19-21. https://doi.org/10.3923/ijps.2006.19.21.

• Aengwanich W, Simaraks S (2004). Pathology of heart, lung, liver and kidney in broilers under chronic heat stress. Songkanakarin J. Sci. Technol. 26(3):417-424.

• Al-Aquil A, Zulkifi I, Sazili A, Omar A, Rajion M (2009). The effects of the hot, humid tropical climate and early age feed restriction on stress and fear responses, and performance in broiler chickens. Asian-Australian J. Anim. Sci. 22(11):1581-1586.

• Ali MY, Jahan SS, Das AK, Islam MA (2015). Seasonal influence on productivity and profitability of small and medium scale broiler farming in Bangladesh. Int. J. Livestock Research. 5(5): 21-29. https://doi.org/10.5455/IJLR.20150424053857.

• Association of Official Analytical Chemists (AOAC) (2004). Official methods of analysis, volume 2, 18th edition. AOAC, Arlington, VA, USA.

• Bhende MJ (2006). Production and cost of broiler meat: a case study. Karnataka Agricultural Development and Rural Transformation Center, Research Report. Institute for Social and Economic Change, Bangalore.

• Blahova J, Dobsikova R, Strakova E, Suchy P (2007). Effect of low environmental temperature on performance and blood system in broiler chickens (Gallus domesticus). Acta Vet. Brno. 76: 17-23. https://doi.org//10.2754/avb200776S8S017.

• Campbell TW (1995). Avian Haematology and Cytology, Lowa State University Press, Ames, Lowa.

• Comito RW, Reece WO, Trampel DW, Koehler KJ (2007). Acid-Base balance of the domestic turkey during thermal panting. Poult. Sci. 86:2649-2652. https://doi.org/10.3382/ps.2007-00248.

• Donkoh A (1989). Ambient temperature: a factor affecting performance and physiological response of broiler chickens. Int. J. Biometeorol. 33: 259-265.

• El-Faham AI, Ibrahim SA, El-Safty SA, Hussanien MS, Ali GM, Rayan GN (2017). Field study for seasonal effect on productive performance of broiler breeder chickens. Egyp. J. Nutr. Feeds. 20(2): 131-137. https://doi.org/10.21608/ejnf.2017.104072

• Filipović N, Stojević Z, Milinković-Tur S, Ljubić BB (2007). Changes in concentration and fractions of blood serum proteins of chickens during fattening. Vet. Arhiv. 77(4): 319-326.

• Gornall AG, Bardawill, CJ, David MD (1949). Determination of serum protein by means of the biuret reaction. J. Biol. Chem. 177(2): 751-766. PMID: 18110453.

• Iqpal J, Ashgar AM, Tanveer A, Shamsul H, Sohail HK (2012). Comparative performance of different economic traits of four imported broiler strains under local conditions of Pakistan. Pakistan J. Agric. Res. 25(1):76-82. http://www.pjar.org.pk/

• Kelly WR (1979). Veterinary Clinical Diagnosis, 2nd Edn, Tindal. London, pp: 266-267.

• Khan WA, Khan A, Anjum AD, Zia-Ur-Rehman (2002). Effects of induced heat stress on haematological values in broiler chicks. Int. J. Agric. Biol. 4(1): 74-75. http://www.ijab.org.

• Kohan RK, Allen MS (1995). Enrichment of proteolytic activity relative to nitrogen in preparation from the rumen for in vitro studies. Anim. Feed Sci. Tech. 52(1):1-14. https://doi.org/org/10.1016/0377-8401(94)00711-H

• Koknaroglu H, Atilgan A (2007). Effect of season on broiler performance and sustainability of broiler production. Journal of Sustainable Agriculture. 31(2): 113-124. https://doi.org/10.1300/J064v31n02_08.

• MacDowell RE (1972). Improvement of livestock production in warm climates. W. H. Freeman, San Francisco. http://aims.fao.org/node/122535

• Mallick P, Muduli K, Biswal JN, Pumwa J (2020). Broiler poultry feed cost optimization using linear programming technique. J. of operations and strategic planning. 3(1): 31-57. https://doi.org/10.1177/2516600X19896910

• Manning RO, Wyatt R (1990). Effect of cold acclimatization on the broilers chicks resistance to acute aflatoxicosis. Poult. Sci. 69:388-396.

• May JD, Lott BD (2000). The effect of environmental temperature on growth and feed conversion of broilers to 21 days of age. Poult. Sci. 79 (5): 669-671. https://doi.org/10.1093/ps/79.5.669.

• Mohamed EAA, Ali OHA, Malik HEE, Yousif IA (2012). Effect of season and dietary protein level on some haematological parameters and blood biochemical compositions of three broiler strains. Int. J. Poult. Sci. 11(12): 787-793. https://doi.org/10.3923/ijps.2012.787.793.

• Nembilwi D (2002). Evaluation of broiler performance under small-scale and semi-commercial farming conditions in Northern Province. Dissertation, Degree of Magister Technologiae Agriculture in the Departement of Agricultural Management at Port Elizabeth Technikon, George Campus, Port Elizabeth.

• NRC (1994). Nutrient Requirements of Poultry, 9th revised edn. National Academy Press, Washington, DC.

• Okere I (2014). Growth traits, breast meat yield and quality of broiler genotypes under hot conditions. Iran. J. Appl. Anim. Sci. 4(1): 159-164.

• Osti R, Bhattarai D, Zhou D (2017). Climatic variation: effects on stress levels, feed intake, and bodyweight of broilers. Brazil. J. Poult. Sci. 19(3): 489-496. https://doi.org/10.1590/1806-9061-2017-0494

• Raha SK (2007). Broiler industry in Bangladesh: some issues. Proceedings of the 5th International Poultry Show and Seminar. World’s Poultry Science Association, Bangladesh Branch, Dhaka, Bangladesh, pp. 1-9.

• Rahman, KS, Roy K, Dey MS (2003). Production performance of two broiler strains as affected by season under rural environment of Bangladesh. Pakistan J. Biol. Sci. 6(8): 735-737. https://doi.org/10.3923/pjbs.2003.735.737

• Ramachandran R (2014). Current and future reproductive technologies for avian species. J. Adv. Exp. Med. Biol. 752: 23-31. https://doi.org/10.1007/978-1-4614-8887-3_2.

• Ramdur AJ, Khan HSS, Martur MD Mahajanshetti SB (2010). An analysis of seasonality and growth trends in marketing of poultry eggs and chicken in Dharwad district. Karnataka J. Agric. Sci. 23: 632-634.

• Ritchie BW, Harrison JG, Harrison RL (1994). Avian Medicine: Principles and Applications. Wingers Publishing, Inc, Florida.

• Roy BC (2000). Identification of constraints to broiler farming. MS in Poultry Science Thesis. Department of Poultry Science, Bangladesh Agricultural University, Mymensingh.

• Sarma M, Borah MK, Kalita K, Mahanta J, Kalita N, Talukdar J, Deka P, Amonge T, Islam R (2019). Effect of Season on Performance of Broiler Chicken Under Deep Litter System of Management in Assam. Int. J. Livestock Res. 9(7): 246-253. https://doi.org/10.5455/ijlr.20181029040524.

• Singh DK, Singh VK, Paswan VK (2019). Comparative production performance of Hubbard, Vencobb and Vencobb-400 broiler strains during tropical summer season. Indian J. Anim. Res., 53(5): 685-688. https://doi.org/10.18805/ijar.B-3553.

• Stojević ZS, Milinković-Tur, Ćurćija K (2000). Changes in thyroid hormones concentration in chicken blood plasma during fattening. Vet. Arhiv. 70: 31-37.

• Syafwan S, Kwakkel RP Verstegen MW (2011). Heat stress and feeding strategies in meat-type chickens. World’s Poult. Sci. J. 67:653-674.https://doi.org/10.1017/S0043933911000742

• Thirumalesh T, Ramesh BK, Suresh BN (2012). Influence of season on nutrient intake and performance of broilers in arid region of Karnataka. Indian J. Anim. Res., 46(1):78-81.

• United Nations Organisation (UNO) (2015). Department of Economic and Social Affairs website. Available from: http://www.un.org/en/development/desa/news/population/2015-report.html.

• Vecerek V, Strakova E, Suchy P, Vaslarova E (2002). Influence of high environmental temperature on production and haematological and biochemical indexes in broiler chickens. Czech J. Anim. Sci. 47(5):176-182.

• Wanger DD, Furrow RD, Bradley BD (1983). Subchronic toxicity of growth promoters in broiler chickens. Vet. Pathol. 20(3): 253-359. https://doi.org/10.1177/030098588302000311.

• Yahav S, Hurwitz S (1996). Induction of thermotolerance in male broiler chickens by temperature conditioning at an early age. Poult. Sci. 75(3):402-406. https://doi.org/10.3382/ps.0750402.

• Yahav S (2002). Limitations in energy intake affect the ability of young turkeys to cope with low ambient temperatures. J. Therm. Biol. 27(2): 103-108. https://doi.org/10.1016/S0306-4565(01)00021-3

• Yahav S, Straschnow A, Plavnik I, Hurwitz S (1996). Effect of diurnal cycling versus constant temperature on chicken growth and food intake. Br. J. Poult. Sci. 37(1): 43-54. https://doi.org/10.1080/00071669608417835.

• Yakubu A, Salako A, Ige A (2007). Effects of genotype and housing system on the laying performance of chickens in different seasons in the Semi-Humid Tropics. Int. J. Poult. Sci. 6(6):434-439. https://doi.org/10.3923/ijps.2007.434.439