Natural Heat Stress Affects Physiological, Hematological and Hormonal Parameters in North African Ram Breeds

Walid Mâaoui1,2, Mohamed Amine Ferchichi2, Jihen Toumi3, Bayrem Jemmali2*, Naceur M’hamdi1 and Abderrahmen Ben Gara2

1National Agronomic Institute of Tunisia, Carthage University, 43 Avenue Charles Nicolle, Tunis 1082, Tunisia

2University of Carthage, LR13AGR02, Mateur Higher School of Agriculture, Mateur, Tunisia

3Central Analytical Laboratory of Animal Feeds, Tunisia

ABSTRACT

To study the ability of sheep to maintain their homeothermy in a North African natural heat stress condition, three Tunisian sheep breeds the Barbarin (BTR), Queue Fine de l’Ouest (QFO) and Noire de Thibar (NTB) were used. A total of twelve (4 per breed) rams were used in this study, for the period of 3 months from March to June. During this period, the ambient temperature varied from 12.5 °C to 32 °C, relative humidity from 49% to 94% and the temperature humidity index (THI) from 50 units to 85 units. The THI values exceeded the borderline of thermal stress, resulting a higher rectal and skin temperature, heart and respiratory rates (P<0.05). The rectal temperature (RT) varied from 39.41 °C to 39.38 °C for BTR, from 39.20 °C to 39.52 °C for QFO and from 39.51 °C to 39.72 °C for NTB. A significant (P<0.05) decrease in thyroxine (T4) from 16.58 pmol/l to 7.52 pmol/l for BTR rams, from 10.99 pmol/l to 6.34 pmol/l for QFO rams and from 12.43 pmol/l to 6.91 pmol/l for NTB rams. TSH hormone decrease significantly from a comfort situation to a stressful situation for BTR (0.124 mUI/l to 0.039 mUI/l), QFO (0.132 mUI/l to 0.065 mUI/l) and NTB (0.113 mUI/l to 0.057 mUI/l). No change in tri-iododthyronine (T3) and a no significantly decrease for cortisol hormone, from 6.91 ng/l to 2.83 ng/l for BTR, from 9.69 ng/l to 4.20 ng/l for QFO and from 7.65 ng/l to 2.42 ng/l for NTB. These responses allowed animals to efficiently dissipate heat, maintain a physiological rectal temperature, and avoid thermal stress. Blood samples were taken and analyzed during two different periods: no stress and heat stress to study the relationship between homeothermy and hematological (RBC, WBC, Hb, Ht, Pl, PCV, MCH, and MCHC), biochemical (glucose, cholesterol, total protein) and hormonal (T4, T3, Cortisol and TSH) parameters responses.

Article Information

Received 19 August 2023

Revised 20 November 2023

Accepted 04 December 2023

Available online 14 March 2024

(early access)

Published 06 May 2025

Authors’ Contribution

MW, MAF and JT designed the study

and wrote the manuscript. MW, MAF,

JT, NM and BJ performed the field work. ABG, MW and BJ analyzed the data.

Key words

Heart rate, Heat stress, Hematological parameters, Rams, Rectal temperature, Temperature humidity index, Thyroxine

DOI: https://dx.doi.org/10.17582/journal.pjz/20230819131031

* Corresponding author: [email protected]

0030-9923/2025/0003-1331 $ 9.00/00

Copyright 2025 by the authors. Licensee Zoological Society of Pakistan.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Introduction

To feed the world’s rising population, crop and animal production must become more intensive and efficient globally, particularly in the intertropical zone (Renaudeau et al., 2012; Scholtz et al., 2013). However, the climate change anticipated the raise of the mean temperatures in temperate regions. Agriculture, biodiversity, energy sector, hydrology, human and animal health could all suffer as a result of the rising temperature (Solymosi et al., 2010). Negative impacts of climate change on animal production parameters are: (1) An increase in atmospheric CO2 levels and temperatures will have a major impact on feed quantity and quality (Chapman et al., 2012). (2) A water scarcity will have an impact on the livestock industry, which needs water for animal drinking, feed crops, and manufacturing activities (Thornton et al., 2009). (3) A higher temperature may accelerate the development of diseases and parasites that spend part of their life cycle outside of their host, putting animals at risk (Patz et al., 2000; Harvell et al., 2002; Karl et al., 2009). (4) Temperature, humidity, species, genetic potential, life stage, and nutritional status all influence heat stress in livestock. Because livestock in lower latitudes are generally better acclimated to high temperatures and drought, livestock in higher latitudes will be more affected by higher temperatures than livestock in lower latitudes (Thornton et al., 2009).

The core temperature of sheep range between 38.3 and 39.9 °C. They are able to maintain their temperature in this range even the environmental conditions are disadvantageous. On the other hand, the range of thermal settings in which the maximum of the welfare and productivity of agricultural animals like ewes and rams is quite narrow, so sheep’s physiology, behavior, and energy expenditure are altered in order to maintain a stable core temperature in this restricted range (Silanikove, 2000; Al-Dawood, 2017; Johnson, 2018). Non-essential functions such as growth, reproduction, and milk production might be affected by the environmental conditions and the productivity can be restricted in thermal conditions. Depending of breed age and physiological state, the top threshold temperature from which thermoregulatory mechanisms are substantially tested and begin to involve significant energy expenditure ranges from 25 to 31 °C (Hopkins et al., 1978; Silanikove, 2000; Al-Dawood, 2017).

Many parameters can be controlled to study the effect of environmental conditions on sheep and specially rams, but very little is known about this subject. The most important parameter to follow, is the testicular temperature, which must be maintained below core body temperature for most mammals, including sheep, in order to produce motile and morphologically normal spermatozoa (Setchell, 1998). At ambient temperatures of 20-30°C, the ram has intra-testicular temperatures range between 33-35°C, indicating a rectal-testicular temperature gradient of 4-6°C (Marai et al., 2008, 2009; Kahwage et al., 2018; Barragán Sierra et al., 2021; Van Wettere et al., 2021). Multiple studies have examined the effects of higher testicular temperature on ram ejaculation output and quality using local or whole-body heating. However, few research have looked at the impact of temperature on sperm quality across North African meteorological condition. In the other hand, earlier research has found that both absolute temperature in different regions of the testes and the testicular thermal gradient are useful predictors of semen quality (Menegassi et al., 2015) and fertility in pasture-raised animals (Lunstra and Coulter, 1997).

The temperature humidity index (THI) is a heat stress index that takes account of both temperature and relative humidity. It is commonly used to evaluate the severity of heat stress in livestock animals. This indicator was created as a weather safety measure in order to control and reduce heat stress-related losses. The THI includes the impacts of both ambient temperature and relative humidity in one index, that’s why it is widely used in hot places around the world as a realistic indicator for the degree of stress on livestock animals caused by weather conditions (Habeeb et al., 2018; Thom, 1959). Some authors have recently employed this parameter to study the influence of heat stress on animal physiological parameters like rectal temperature, heart rate, respiration rate, skin temperature (Sejian et al., 2012), and blood parameters (Sejian et al., 2012).

The objectives of this paper were to study physiological, blood, biochemical and hormonal parameters of rams when they were exposed to heat stress conditions, to fined crucial threshold values, and to determine the most affected markers.

MATERIALS AND METHODS

In this trial, The Experimental Animal Use Ethics Committee of National Agronomic Institute of Tunisia has previously approved (protocol No 05/15). It took place in the farm of the Heigh School of Agriculture of Mateur in North of Tunisia (latitudes 37° 04’ North and longitudes 9° 62’ East), between March and June 2021. This subhumid area region shows a typical Mediterranean climate, the annual average rainfall is between 400-500 mm. A hot and extremely dry air from the Sahara Desert characterize the dry season, which extend from June to September. Nonetheless, when subtropical marine air masses converge in the region during the dry season, some convective clouds develop occasionally. Summer is usually hot and dry season in Tunisia. The continental zones are characterized by daily maximum temperatures surpassing 40°C (Verner et al., 2018). An automated meteorological station 300 meters away from the animal allows the recording of climatic parameters such as ambient temperature (Ta, °C) and relative air humidity (RH, percent). In addition of the climatic data provided by the automatic weather station and to have more exactitude, temperature and humidity were controlled in the feeding area by a thermos hygrometer (Testo 608-H1, Entech Industrial Solution Co.,Ltd, Thailand). The THI was calculated according to the formula described by Thom (1959).

THI = 0.8*Ta + ((HR/100) * (Ta-14.3)) + 46.4

With Ta is the daily ambient temperature in °C, HR is the daily relative air humidity in %.

According to Moran (2005), the THI values obtained indicate: < 72 = thermal comfort zone (TCZ); > 72 = thermal stressful zone (TSZ). In addition, the THI was calculated at the time of physiological data collection to allow for real-time assessment of environmental circumstances.

A total number of twelve clinically healthy mature Tunisian breed rams aged between 3 and 4 years were used in this study. The breeds were divided in three groups, 4 animals for each group. The first one is composed by Tunisian Barbarin sheep (BTR, n = 4; BW= 67 ± 7.81 Kg; Age = 3.2 years) with a white fat-tailed breeds. The second one is composed by Queue Fine de l’Ouest Tunisian sheep, with a white breed (QFO, n = 4; BW = 56 ± 2.00 Kg; Age = 3.5 years), the last one composed by the Noire de Thibar Tunisian sheep with a black breed (NTB, n = 4; BW= 64 ± 9.16 Kg; Age = 3.4 years).

All of the rams were confined on a single lot of 25 m2 (L =5 x l=4.5 m, 1.8 m2/animal) without pasture and no exposition to direct solar radiation. The animals were maintained in well-ventilated sheds with a one open side and asbestos roofing at 3.0 meters height, with a normal hygienic condition.

Oat hay (3 Kg/animal/day) and 350 g/animal/day of a commercial concentrate were included in the diet (ground corn, crushed barley, bran, soybean meal, calcitic lime, and mineralized salt). The animals were watered and fed twice a day (0800 h and 1800 h), and they had unlimited access to the feeding trough.

The variables: respiration rate (RR), heart rate (HR) and rectal temperature (RT) were measured weekly in the afternoon (from 1100h-1400h). The RR (*breath/min) was measured by counting flank movements for one minute by an observer positioned beside the animals. The HR (beats/min) was monitored with a veterinary stethoscope, counting the number of hart battements for 15 sec then multiplied by four. A transrectal digital thermometer was used to measure the RT (°C) after 15 sec of its introduction, the thermometer beeped and displayed the temperature reading to one decimal point.

The skin temperatures monitored were forehead temperature (FOT, °C), right shoulder temperature (RST, °C), left shoulder temperature (LST, °C), top of shoulder temperature (TST, °C), rump temperature (RUT, °C), chest floor temperature (CFT, °C) and scrotal temperature (SCT, °C). An infrared thermometer (Berrcom JXB-178, Berrcom Factory, China) was used to measure skin temperatures in various body locations.

Blood samples were obtained from the jugular vein at the same time of day in two periods (no stress and heat stress), into 5-ml vacutainer tubes, three tubes per animal and period (two vacutainer tubes with Lithium Heparin and one tube with EDTA). Due to a time restriction, this blood was delivered to the Physiology Laboratory in an ice carrier and preserved at a low temperature. Firstly, with Auto Hematology Analyzer (Rayto RT-7600; Rayto Life and Analytical Sciences Co., Ltd.; China), EDTA blood samples were analyzed to determinate blood metabolites such as red blood cell count (RBC), white blood cell count (WBC), hemoglobin (Hb), hematocrit (Ht), platelets (Pl), packed cell volume (PCV), mean corpuscular hemoglobin (MCH) and the mean corpuscular hemoglobin concentration (MCHC). Secondly, the heparinized blood samples were centrifugated during 5 to 10 min with 3000 rpm to recover plasma. Glucose, total protein, cholesterol and alkaline phosphatase (ALP) were measured using an (RT-2100 C. Microplate reader; Rayto Life and Analytical Sciences Co., Ltd.; China). Finally, cortisol and free tri-iodothyronine (T3) concentrations were determined using an enzyme linked fluorescence assay (ELFA) equipment, while the concentrations of thyrotropin (TSH) and free thyroxine (T4) in blood plasma were determined using (Simens IMMLITE 1000 Immunoassay equipment; Siemens Healthineers Headquarters; Germany).

The following formula was the statistical model used to examine the effects of heat stress on ram breeds, as well as the interactions, on ram physiological parameters, skin temperatures, blood components, biochemical and hormonal compositions:

Were Yijkl is the observation for the physiological parameters, μ, overall mean, HSCi, heat stress classes (thermal comfort zone, thermal stressful zone), Brj Breed of the rams (BTR, NTB and QFO), HSCi*Brj Interaction heat stress classes and breed, eijkl is Random error.

RESULTS

Climate variables

Figure 1 present the changes of the climatic elements during the experiment period registered with the automatic weather station. The period from March to June is the changing period from spring to summer. The Ta varied from 12.5°C to 32°C, RH from 49% to 94% and the THI from 50 units to 85 units.

 

Table I. Least square means of heat stress effect on skin temperatures, physiological, hematological and biochemical parameters of three Tunisian rams breed (BTR, QFO, NTB).

Variables	Thermal comfort zone (TCZ) (Ta= 18.27±3.67 °C; THI= 62.77 ± 4.52)			Thermal stress zone (TSZ) (Ta= 33.41±4.54°C; THI= 77.66 ± 3.93)			Significance
	BTR	QFO	NTB	BTR	QFO	NTB	C1	C2	C3
Phycological parameters RT (°C) RR (breath/min) HR (beat/min)	39.41 44.59 87.70	39.20 44.88 88.29	39.51c 42.81 89.03	39.38 56.00 102.57	39.52 60.22 104.22	39.72b 57.00 105.88	NS 0.0026 <.0001	0.024 <.0001 <.0001	NS <.0001 <.0001
Skin temperature FOT TST RST LST RUT CFT SCT	33.07 35.20 34.78 35.04 35.32 33.62 33.55	33.11 35.29 35.31 35.48 35.02 34.04 33.90	33.71 35.06 35.27 35.26 35.26 33.78 33.21	37.55 37.61 37.21 36.89 37.12 37.12 36.17	37.98 38.26 37.85 37.68 38.22 37.51 37.08	37.70 38.25 37.93 37.41 38.18 37.47 37.11	<.0001 <.0001 <.0001 0.0042 0.0042 0.0003 0.0145	<.0001 <.0001 <.0001 0.0003 <.0001 0.0001 0.0014	<.0001 <.0001 <.0001 0.0004 <.0001 <.0001 0.0001
Hematological parameters RBC (nb x 109/l) WBC (nbx 1012/l) Hb (g/dl) Ht (%) Pl (nb x 109/l) PCV (%) MCH (pg) MCHC (g/dl)	10.05 8.40 11.00 25.20 323.50 29.90 13.07 43.75	8.75 7.95 11.05 25.40 338.75 30.02 13.32 44.00	7.92 7.65 9.70 22.20 308.00 27.90 12.75 44.00	11.40 7.45 13.80 34.87 290.75 35.82 9.12 32.55	10.30 7.37 11.72 30.80 251.00 34.67 8.95 33.62	11.35 6.72 11.67 30.07 265.25 30.92bc 9.37 32.67	NS NS NS 0.0030 NS 0.0018 <.0001 <.0001	NS NS NS NS 0.0007 0.0102 <.0001 <.0001	NS NS NS 0.0120 0.0163 NS <.0001 <.0001
Biochemical parameters Glucose (g/l) Cholesterol (g/l) Total protein (g/l) ALP (UI/l)	0.45 0.41 62.96 188.27	0.41 0.33 71.68 197.19	0.25 0.42 72.63 184.87	0.38 0.64 73.00 96.25	0.29 0.64 84.25 117.25	0.32 0.52 57.90 84.00	NS 0.0464 NS 0.0057	NS 0.0095 NS 0.0139	NS NS NS 0.0029
Hormonal composition Thyroxine (pmol/l) Tri-iodothyronine (pmol/l) Cortisol (ng/l) TSH (mUI/l)	16.58 2.61 6.91 0.124	10.99a 4.54 9.69 0.132	12.43b 2.85 7.65 0.113	7.52 2.76 2.83 0.039	6.34 2.91 4.20 0.065	6.91 3.15 2.42 0.057	<.0001 NS NS 0.0046	0.0004 NS NS 0.0206	<.0001 NS NS 0.0464

 

RR, respiration rate, HR, heart rate; RT, rectal temperature; FOT, forehead temperature; RST, right shoulder temperature; LST, left shoulder temperature; TST, top of shoulder temperature; RUT, rump temperature; CFT, chest floor temperature; SCT, scrotal temperature.

Hb, hemoglobin; Ht, hematocrit; Pl, platelets; PCV, packed cell volume; MCH, mean corpuscular hemoglobin; MCHC, mean corpuscular hemoglobin concentration; ALP, alakaline phosphate; TSH, thyrotropin.

a, difference is statistically significant between BTR and QFO for the same parameter in the same thermal situation; b, difference is statistically significant between BTR and NTB for the same parameter in the same thermal situation; c, difference is statistically significant between QFO and NTB for the same parameter in the same thermal situation; C1, Difference between BTR for the same parameters in TCZ and TSZ conditions; C2, Difference between QFO for the same parameters in TCZ and TSZ conditions; C3, Difference between NTB for the same parameters in TCZ and TSZ condition.

 

Physiological parameters

In this study, according to Table I, only the RT for NTB rams has a significant difference between breed in thermal stress conditions. No changes are observed between RT breeds in a comfort situation and a stressful situation, except for QFO rams (39.20 °C with TCZ conditions; 39.52 °C with TSZ conditions). For the RR (BTR = 56.00 breath/min; QFO = 60.22 breath/min; NTB = 57 breath/min) and HR (BTR = 102.57 beat/min; QFO = 104.22 beat/min; NTB = 105.88 beat/min) no significant difference between breeds in a thermal stress condition have been reported.

In the other hand, skin temperatures: FOT, RST, LST, TST, RUT, CFT and SCT were higher, moving from spring to summer for all genotypes (Table I). The SCT had the lowest skin temperature for all the ram’s breed.

Hematological parameters

Some changes in the blood parameters of animals exposed to high temperatures have been recorded (Table I). In fact, RBC and Hb increase no significantly from TCZ to TSZ situation and no change was registered in WBC parameters during the experiment. However, Ht increase significantly for BTR rams from 25.20 % to 34.87 % and NTB rams from 22.20 % to 30.07 %. Contrary, Pl decrease significantly for QFO rams (338.75 109/l in TCZ conditions vs 251.00 109/l in TSZ conditions) and NTB rams (308.00 109/l in TCZ conditions vs 265.25 109/l in TSZ conditions). On the other hand, we found that PCV increase with a significative difference with BTR (29.90 % vs 34.67 %) and QFO (30.02 % vs 34.67 %). Finally, MCH and MCHC decrease significantly for the three types of breeds from a comfort to a stressful situation.

Biochemical parameters

Minor changes in the biochemical parameters of rams from a TCZ to TSZ situation (Table I). The glucose decreases non significantly for all the ram breeds, form 0.45 g/l to 0.38 g/l for BTR, from 0.41 g/l to 0.29 g/l for QFO and from 0.25 g/l to 0.32 g/l for NTB. Cholesterol increases significantly (P<0.05) only for BTR and QFO rams. No changes in total protein and a significantly decrease for ALP parameters from 188.27 109/l to 96.25 109/l for BTR, from 197.19 109/l to 117.25 109/l for QFO and from 184.87 109/l to 84.00 109/l.

Hormonal parameters

Hormonal response of animals to high temperature (Table I) was examined. A significant (P<0.05) decrease in thyroxine (T4) from 16.58 pmol/l to 7.52 pmol/l for BTR rams, from 10.99 pmol/l to 6.34 pmol/l for QFO rams and from 12.43 pmol/l to 6.91 pmol/l for NTB rams. TSH hormone decrease significantly from a comfort situation to a stressful situation for BTR (0.124 mUI/l to 0.039 mUI/l), QFO (0.132 mUI/l to 0.065 mUI/l) and NTB (0.113 mUI/l to 0.057 mUI/l). No change in tri-iododthyronine (T3) and a no significantly decrease for cortisol hormone, from 6.91 ng/l to 2.83 ng/l for BTR, from 9.69 ng/l to 4.20 ng/l for QFO and from 7.65 ng/l to 2.42 ng/l for NTB.

DISCUSSION

According to temperature and humidity conditions (temperature between 13 to 38.5°C and humidity between 18 to 64.5%, THI between 56.1 to 37.1). Bouraoui et al. (2002), in an arid zone, had found difference in the averages of THI values (68±3.75 units vs. 78±3.23 units for the spring and summer periods, respectively). In comparative research, Bellagi et al. (2017) studied the effect of heat stress on Holstein and Tarentaise dairy cows and showed that the average values per month between 2009 and 2014 of Ta, RH, and THI from five public weather stations in the North of Tunisia were 18.8°C, 68.9%, and 64.0 units, respectively. The monthly means of Ta and THI reached their highest points in August (28.1°C and 76.6 units, respectively) and their lowest points in February (10.7°C and 52.1 units, respectively). The standard deviations of the three parameters were 0.81°C, 2.30%, and 1.22 units, respectively. In conclusion, there were no significant climatic difference amongst the five locations. According to Djelailia et al. (2020), Holstein dairy cows raised in the south arid zone of Tunisia were subject of heat stress from June to September with monthly THI values exceeding the critical threshold which is 72 units. During this period, THI ranged from 73±1.74 to 79±3.01. In the feeding area, the temperature and the THI were characterized by TCZ conditions equal to 18.27±3.67°C and 62.77±4.52 units respectively. Whereas, the TSZ conditions were: 33.41±4.54°C for temperature and 77.66±3.93 units for THI.

The mean THI recorded in the hottest seasons of the year, spring and summer, can moderate stress of the rams (Kahwage et al., 2018). During physiological evaluations, Marai et al. (2007), indicated that the THI is an environmental condition that help the setting up of severe to very severe stress, which increase in the afternoon, when Ta rise.

In high ambient temperature, animals are forced to activate many thermoregulatory mechanisms. The physiological processes of the body are greatly influenced by the changes of environmental temperature (Wojtas et al., 2014). According to this study RT varied from 39.41 °C to 39.38 °C for BTR, from 39.20 °C to 39.52 °C for QFO and from 39.51 °C to 39.72 °C for NTB (Table I). The increase in the RT by around 1°C above the physiological comfort limits (20 to 30°C) may hinder vital function in animal production, essential functions, necessitating more investigation (Silanikove, 2000). the capacity of Morada Nova and Santa Inês hair sheep breeds to maintain homeothermy was studied by Kahwage et al. (2018). It showed that Santa Inès animals exhibited somewhat higher RT (0.2-0.3 °C) than Morada Nova animals. In the other hand, the physiological adaptation shown by both breeds favored the action of heat dissipation mechanisms and the rams were able to sustain homeothermy even in the seasons when the heat load was the most intense. In our study, from comfort to a stressful situation, the respiration rate (RR) varied from 44.59 to 56.00 breaths/min for BTR, from 44.88 to 60.22 breaths/min for QFO and from 42.81 to 57.00 breaths/min for NTB (Table I). Generally, in sheep the normal respiratory rate (RR) varied between 25 and 30 breaths/min (Arruda and Pant, 1984). The animals intensify thermolysis by the respiratory system with the increasing of the RR from 40 to 60 breaths/min (Silanikove, 2000). Kahwege et al. (2018) indicated that the RR in Morada Nova and in Santa Inès rams had higher values moving from spring to summer. It increases from 58.4±3.2 breath/min to 62.6±3.7 breath/min for the firth breeds and from 57.9 ± 2.8 breath/min vs 56.3±3.2 breath/min for the second one, indicating that the respiratory evaporative mechanism had been activated to prevent hyperthermia.

Heart rate (HR) varied with the seasons and times of day, with greater values in the afternoon for both breeds (Table I), especially from spring to summer, NTB animals had higher HR (105.88 beats/min) than QFO animals (104.22 beats/min) and then BTR animals (102.57 beats/min). A compensatory reaction to the requirement to redirect blood flow to the capillaries in order to promote heat dissipation following peripheral vasodilatation, HR also increases in the afternoons in the spring and summer (Fadare et al., 2013). Due to this, the animals of both genotypes were able to keep their RT temperatures within the species’ physiological range, which has a maximum threshold of 39.9 °C (Marai et al., 2007). Various study indicated an increase in heart rate from comfort to heat stress conditions: Wojtas et al. (2014) with Merinos rams noted 90.23 beats/min in comfort conditions and 107.79 beats/min in heat stress conditions, Kahwege et al. (2018) reported higher HR in summer than in winter for Santa Inès (85.5±1.2 vs 84.8±1.3 beats/min) and Morada Nova (91.2±1.3 vs 92.2±1.5 beats/min).

In the present experiment, the increase in FOT, RST, LST, TST, RUT, CFT and SCT were observed from spring to summer (Table I). The highest levels of skin temperatures seen during the hottest seasons of the year were registered in the afternoon and they are linked to the higher thermal load that happens naturally during that period of time (Barros et al., 2015), causing rams of both genotypes to cumulate body thermal energy (Kahwege et al., 2018).

A correlation between environmental temperature and blood parameters was confirmed in many study (Srikandakumar et al., 2003; Cwynar et al., 2014; Wojtas et al., 2014). The hematological results obtained in the study of Srikandakumar et al. (2003) showed that heat stress in sheep caused an increase in Hb and MCHC, a decrease in RBC and WBC and no change in PCV and MCV parameters. During another experiment and in order to examine heat stress effect and air flow on hematological parameters of Merino Rams, Wojtas et al. (2014) found that only WBC decrease significantly. 

The exhibition to heat stress affects negatively blood metabolites (Marai et al., 2008, 2009; Barragán Sierra et al., 2021). In this study (Table I). Firstly, serum glucose decreases non significatively in the blood of the three genotypes, this result is conformed with many studies (Nazifi et al., 2003; Marai et al., 2009; Cwynar et al., 2014) and in contradiction with others (Al-Haidary et al., 2012; Wojtas et al., 2014). Secondly, the cholesterol increases significantly for BTR (0.41 vs 0.64 g/l) and QFO rams (0.33 vs 0.64 g/l) this result is in conflict with Shaffer et al. (1981), Marai et al. (1995) and Habeeb et al. (1996) studies. Furthermore, when the glucose-saving system is activated, a reduction in blood concentrations of these lipid metabolites is partially related to the mobilization of fatty acids to meet energy requirements (Baumgard and Rohads, 2013; Sejian et al., 2017). Thirdly, in this study no significative change in serum total protein was observed from spring to summer. However, Baumgartner and Parnthaner (1994) observed that the serum total protein levels were significantly (P<0.05) lower in summer than in winter in Karakul sheep. In turn, a significative difference was found with ALP (P<0.05), alkaline phosphatase enzyme activities decrease significantly (P<0.05) in summer compared to winter with Egyptian Suffolk rams (Marai et al., 2009).

Finally, all species, including rams, use their thyroid glands to regulate their body temperatures (Binsiya et al., 2017). Thyroid hormones are secreted less frequently as a result of the heat stress, which leads lower metabolic heat generation and body heat load (Nazifi et al., 2003; De et al., 2017). According to Table I, T4 hormone decrease significantly for the three Tunisian ram breeds form a comfortable situation to heat stress situation (BTR: 16.58 vs 7.52 pmol/l; QFO: 10.99 vs 6.34 pmol/l; NTB: 12.43 vs 6.91 pmol/l) likewise Shalaby (1996) discovered that the exposure of Finn sheep to direct solar radiation in summer decrease the T4 level. Marai et al. (1997) showed that the level of T4 was higher during summer than in winter season in Barki and Ossimi x Suffolk crossbred sheep and finally, no change was founded by De et al. (2017) in T4 concentrations from a comfort to a stressful situation with crossbred rams (Garole x Malpura x Malpura). No change in T3 level hormone and a no significant decrease in cortisol hormone have been observed in this study, which is agree with the finds of Marai et al. (2009). However, a decrease in T3 level was observed with Youssef and Johnson’s (1985) and Marai et al. (1997). In conclusion, TSH secretion decrease significantly with heat stress conditions. Thyroid hormones in the blood are also regarded to be good indicators of an animal’s nutritional status (Riis and Madsen, 1985; Rhoads et al., 2009). It’s seems that thermal stress have a direct effect on the hypothalamus-pituitary axis, resulting the reduction of TSH secretion (Rasooli et al., 2004; Sejian and Srivastava, 2010).

CONCLUSION

The physiological adaptations showed by all genotypes boosted the activity of heat dissipation mechanisms, permitting the Tunisian rams breed to maintain their homeothermy during the hottest season of the year. During the spring-summer transition period, physiological parameters such as RR and HR are affected by heat stress, the RT for NTB rams, the rectal temperature for NTB rams were the most affected by the rise of temperature, which shows that BTR and QFO rams have better adaptative capability. As a result, BTR and QFO males have an adaptative capability to fight the thermal challenges imposed by Noth African climate. Those genotypes have an advantageous physiological characteristic, they can resist to the environmental adversity. The THI elevation also had an effect on hemato-biochemical parameters. Some of them increase, such as RBC, Ht, PCV and cholesterol, while others decreasing, such as Pl, MCH, MCHC and ALP.

Acknowledgement

The authors are grateful to the Coordination for the Improvement of “High School of Agriculture of Mateur” for the financial support for carrying out the research.

Ethical statements and IRB approval

This study was approved by the Official Animal Care and Use Committee of the National Institute of Agronomy of Tunisia (protocol No 05/15).

Statement of conflict of interest

The authors have declared no conflict of interest.

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