Mortality, production performance, water intake and organ weight of the heat stressed broiler chicken given savory (Satureja khuzistanica) essential oils through drinking water

Abstract

An experiment was conducted to examine the effects on mortality, production performance, water intake (WI) and organ weight of Satureja khuzistanica essential oil (SkEO) using 720 one-day-old Arian broiler chicks in a 42-day trial. Experimental treatments were addition of 0 (control−), 200, 300, 400 and 500 mg/L SkEO or 500 mg/L polysorbate-80 (control+) into drinking water. The birds were kept under natural ambient temperatures 4–6°C above standard recommendation from days 22 to 42 of age. Addition of SkEO into drinking water at 200 and 500 mg/L decreased weight gain (P < 0.05) of the birds from days 29 to 35 of age with no differences in feed intake (FI) and feed conversion ratio (FCR) compared to control groups (P > 0.05). Addition of 300 and 500 mg/L SkEO into water increased mortality rate of the birds mainly from days 29 to 42 of age. The calculated European broiler index was greater for the birds receiving drinking water supplemented with 400 mg/L of SkEO compared with the other birds. In conclusion, administration of SkEO at 400 mg/L through drinking water to heat stressed broiler chickens may result in improved production performance efficiency.

Keywords:

• broiler chicken
• heat stress
• pancreas
• gall bladder
• Satureja khuzistanica
• water intake

1. Introduction

Extreme ambient temperature is probably the most prevalent environmental stressor adversely affecting welfare, health and production economics in the broiler industry (Borges et al. 2004). The major consequence of heat stress in growing birds is depressed weight gain occurring mainly due to decreased feed intake (FI) and elevated energy expenditure to reduce body temperature (Lott 1991; May & Lott 1992; Belay & Teeter 1993). Therefore, exploration of any avenue towards heat stress relief which improves feed and water intake (WI) may offer a thermoregulatory and performance advantage to heat stressed broilers. Many research studies focused on diet modifications to alleviate hot environmental conditions for heat stressed broilers. In such studies the prime concern was the use of adding supplemental vitamins (McKee & Harrison 1995), electrolytes (Borges et al. 2003, 2004; Ahmed & Sarwar 2006), probiotics (Zulkifli et al. 2000), prebiotics (Riad et al. 2010), organic acids (Goksoy et al. 2010) in the feed or water to minimise the impact of heat stress in broilers. Recently, research finding has noticed the use of phytogenic feed additives to modulate the harmful effect of heat stress in broiler chickens (Suderman & Solikhah 2011; Zeinali et al. 2011). Zeinali et al. (2011) reported that in heat stress condition dietary selenium and turmeric powder could have a beneficial effect on health and plasma lipids in broiler chicken. Suderman and Solikhah (2011) showed that Pluchea indica L. leaf meal at 20 g/kg exhibited beneficial effects on weight gain, FI, WI, but not feed conversion ratio (FCR), in heat stressed broiler chicks.

Satureja khuzistanica Jamzad is a plant well known for its remedial properties in traditional medicine (Zargari 1990). The aerial parts of S. khuzistanica collectively contain up to 3% of an essential oil spectacularly rich in carvacrol (up to 94%; Khosravinia et al. 2013). Carvacrol is a phenolic, caustic and bitter-tasting compound with good stability (ARS 2002) demonstrating antioxidant (Cuppett & Hall 1998) and antimicrobial (Burt 2004) effects. Accordingly, it has been reported that S. khuzistanica essential oils (SkEO) have antioxidant (Abdollahi et al. 2003; Radonic & Milos 2003) and antibacterial (Azaz et al. 2002) effects mainly in experiments conducted under standard managerial practices and normal environmental conditions. Considering the scarce experimental results available on administration of phytogenic extracts to heat stressed avian species, this study, was undertaken to examine the effect of SkEO on productive performance of broiler chickens exposed to high ambient temperatures, where it constantly supplemented into drinking water through day 42 of age.

2. Materials and methods

2.1. Preparation of essential oil

The aerial parts of S. khuzistanica were manually harvested during the flowering stage of the plant in Khorraman farm, Khorramabad (33°48′ N and 48°35′ E), Iran. ¹ The collected materials were air dried at ambient temperature in the shade and hydro distilled using a Clevenger type apparatus for 5 h, giving yellow oil in 3% yield. The oils were dried over anhydrous sodium sulphate and stored at 4°C. A sample of the bulk was analysed based on the methods used by Hadian et al. (2011) and the composition is presented in Table 1.

Table 1. Essential oil composition of S. khuzistanica.

Compound	RI	Composition (%)
α-Thujene	925	0.24 ± 0.14
α-Pinene	933	0.15 ± 0.05
Myreene	981	0.26 ± 0.19
α-Terpinene	1013	0.24 ± 0.12
p-Cymene	1017	1.26 ± 0.86
Limonene	1026	0.13 ± 0.04
(Z)-β-Oeimene	1036	0.54 ± 0.08
γ-Terpenene	1053	0.74 ± 0.23
Trans-sabinene hydrate	1081	0.17 ± 0.02
Terpin-4-ol	1163	tr
α-terpinole	1175	0.42 ± 0.45
Thymol	1266	tr
Carvacrol	1282	92.16 ± 0.46
Thymyl acetate	1329	tr
β-Caryophyllence	1425	0.16 ± 0.01
α-Humulene	1427	tr
β-Bisabolene	1501	tr
Trans-β-bisabolene	1522	0.10 ± 0.01

RI, retention indices determined relative to n-alkanes (C₆–C₂₄) on a DB-5GC column; tr, trace (<0.05%).

2.2. Experimental flock

A total number of 720 one-day-old as-hatched Arian broiler chicks were obtained from a commercial hatchery and housed in a concrete floor, cross-ventilated windowless shed. The chicks were randomly assigned to 36 pens (100 × 180 cm) arranged in 6 rows (blocks/replicates) in parallel with the longitudinal wall of the shed at flocking density of 12 birds/m². Corn and soybean meal-based prestarter, starter, grower and finisher diets (Table 2) were provided to the birds for ad libitum consumption throughout the experimental period. In six distinct tanks with the same size water was supplemented with different doses of SkEO or polysorbate-80 and provided to the birds on a daily basis. The remaining of water in each pen was measured by volume. The shed was equipped with wet pad-and-fan cooling system to reduce the ambient temperature. Nonetheless, average temperature during day and night hours ranged from 32°C to 35°C and 28°C to 30°C, respectively, during 21–42 days. Therefore, from 21 days of age the birds were exposed to seasonal extreme ambient temperatures. All procedures used in this experiment were based on Animal Care Guidelines, Animal Ethics Committee at the Shiraz University, Iran.

Table 2. Effect of essential oils of S. khuzistanica on average daily weight gain (g) in broiler chicken up to days 42 of age.

		Essential oils of S. khuzistanica (mg/L)							Trend
Weight gain	Control+	0	200	300	400	500	SEM	P value	Linear	Quadratic
1–7 days	16.61	16.90	16.78	16.91	16.92	16.98	0.09	0.798	0.245	0.563
8–14 days	26.29	26.41	26.26	26.21	27.17	25.31	0.29	0.555	0.267	0.642
15–21 days	41.31	41.72	40.19	41.52	39.40	40.90	0.32	0.148	0317	0.128
22–28 days	72.62	74.72	76.05	73.48	74.91	74.48	0.46	0.359	0.453	0.086
29–35 days	81.36^b	87.72^a	87.48^a	80.00^b	85.00^ab	80.29^b	0.87	0.008	0.384	0.021
36–42 days	82.43	81.43	79.60	85.62	86.07	83.00	1.25	0.686	0.184	0.102
1–42 days	53.43	54.81	54.39	53.96	54.91	53.49	0.23	0.246	0.452	0.561

Control+, the birds received drinking water supplemented with 500 mg/L polysorbate-80 throughout the trial; SEM, standard error of mean.

^a–gMeans within a row without a common superscript differ significantly (P < 0.05).

The effects of six experimental treatments consisting supplementation of drinking water with 0 (control−), 200, 300, 400 and 500 mg/L SkEO or 500 mg/L polysorbate-80 (control+) were examined in 6 replicates of 20 birds each. Polysorbate-80 is an emulsifier used to disperse SkEO in water at a 1:1 ratio (v/v). Mortality was recorded upon occurrence. Body weight gain, FI and WI were measured weekly and their data were used to generate data on FCR and FI:WI ratio in addition to a European broiler index (EBI) as (Euribrid 1994): At day 21 of age, 1 male bird and at 42 days of age 8 birds (4 males and 4 females) per pen were killed (with our stunning) by slicing the carotid artery and jugular vein, bled for 120 s, scaled at 60°C for 90 s, and picked using a rotary drum picker individually and eviscerated. After evisceration, the carcasses were individually weighed (CW) and the data were presented as a percent of live weight (CY). The proportional weight of abdominal fat (AF), liver, pancreas, duodenum and gall bladder was also expressed proportional to carcass weight.

2.3. Statistical analysis

The statistical model used to analyse the collected data was:

where Y_ijkl is the dependent variable, µ is the general mean, SkEO_i is the fixed effect of SkEO (i = 6; control+ and 0, 200, 300, 400, 500 mg/L SkEO), S_j is the fixed effect of sex (j = 2), B_k is the random effect of block (k = 6; 1, 2, 3, 4, 5 and 6) and ε_ijkl is the residual error. For the variables evaluated at 21 days of age, sex was omitted from the model. The data were analysed using PROC MIXED of SAS Institute 9.1 (2002). The least significant differences test was used for multiple treatment comparisons using the least significant means statement of SAS Institute 9.1 (2002) with letter grouping obtained using the SAS pdmix800 macro (Saxton, 1998). For the different statistical tests, significance was declared at P ≤ 0.05. The REG procedure of SAS Institute 9.1 (2002) was used to provide regression models for assessment of relation between SkEO and WI.

3. Results

In this study, average daily weight gain (DWG), FI, WI, FCR and FI:WI ratio were determined and analysed for the period from 1 to 42 days of age in weekly periods. Addition of SkEO into drinking water at 200 and 500 mg/L decreased DWG of the birds in days 29–35 of age compared with the control− birds (P < 0.05; Table 2). The mean DWG of the treated birds was not different from control groups in all other periods (P > 0.05). There were no significant differences in FI among the birds receiving SkEO and the control groups (P > 0.05; Table 3). The mean FCR was not affected by supplementation of SkEO in drinking water but overall FCR was tended to be improved by 3.5% in birds receiving 400 mg/L SkEO (P < 0.058; Table 3).

Table 3. Effect of essential oils of S. khuzistanica on average daily feed intake and feed conversion ratio in broiler chicken up to day 42 of age.

		Essential oils of S. khuzistanica (mg/L)							Trend
	Control+	0	200	300	400	500	SEM	P value	Linear	Quadratic
Feed intake (g)
1–7 days	19.26	19.67	19.40	19.02	19.19	19.53	0.104	0.4158	0.2345	0.2013
8–14 days	36.62	36.17	36.45	37.01	36.50	36.29	0.114	0.2258	0.6571	0.7201
15–21 days	60.01	60.95	60.03	60.71	59.86	61.46	0.252	0.3129	0.5321	0.1234
22–28 days	136.58	132.36	133.27	132.07	132.17	129.78	0.898	0.2511	0.4561	0.2340
29–35 days	183.41	175.65	176.13	175.15	175.41	175.52	1.603	0.6742	0.2913	0.4521
36–42 days	189.77	199.85	204.82	210.97	196.04	214.24	2.754	0.0672	0.3912	0.1219
1–42 days	104.27	104.11	105.08	105.82	103.18	106.14	0.466	0.4356	0.2345	0.0912
Feed conversion ratio (g feed:g gain)
1–7 days	1.141	1.185	1.158	1.125	1.135	1.151	0.007	0.1603	0.2048	0.4193
8–14 days	1.393	1.377	1.408	1.418	1.351	1.437	0.014	0.5144	0.2834	0.2006
15–21 days	1.440	1.477	1.494	1.466	1.523	1.504	0.010	0.1280	0.2817	0.3510
22–28 days	1.829	1.824	1.754	1.798	1.765	1.745	0.013	0.1652	0.3461	0.4123
29–35 days	2.099	2.160	2.022	2.192	2.066	2.191	0.026	0.3171	0.3116	0.4218
36–42 days	2.369	2.430	2.592	2.465	2.278	2.599	0.042	0.1801	0.4760	0.1812
1–42 days	1.903	1.948	1.930	1.963	1.880	1.985	0.011	0.0581	0.1823	0.1456

Control+, the birds received drinking water supplemented with 500 mg/L polysorbate-80 throughout the trial; SEM, standard error of mean.

^a–gMeans within a row without a common superscript differ significantly (P < 0.05).

Table 4. Effect of essential oils of S. khuzistanica on water intake, water:feed ratio in broiler chicks up to 28 days of age.

		Essential oils of S. khuzistanica (mg/L)							Trends
	Control+	0	200	300	400	500	SEM	P value	Linear	Quadratic
Water intake (mL/day per bird)
1–7 days	32.86^a	32.86^a	30.29^b	30.00^c	28.57^d	27.14^e	0.353	0.0001	0.0234	0.5691
8–14 days	97.14^b	102.86^a	94.29^d	95.71^c	92.86^e	91.43^f	0.623	0.0001	0.0023	0.3491
15–21 days	162.86^c	161.43^d	177.14^a	167.14^b	167.14^b	154.29^e	1.172	0.0001	0.0021	0.4001
22–28 days	249.00^b	257.43^a	238.86^d	242.57^c	218.57^e	215.71^f	2.572	0.0001	0.0038	0.7412
29–35 days	322.07^a	297.09^c	305.19^b	278.64^d	271.43^e	257.14^f	3.685	0.0001	0.0231	0.4183
36–42 days	351.00^a	328.43^c	328.71^b	314.14^d	300.00^e	281.71^f	3.758	0.0001	0.0052	0.3426
1–42 days	202.49^a	196.68^b	195.75^c	188.03^d	179.76^e	171.24^f	1.810	0.0001	0.0010	0.7250
Water (mL):feed (g) ratio
1–7 days	1.71^a	1.67^a	1.56^b	1.58^b	1.49^c	1.39^d	0.020	0.0001	0.0124	0.5791
8–14 days	2.65^b	2.84^a	2.56^cd	2.59^c	2.54^cd	2.52^d	0.020	0.0001	0.0183	0.2471
15–21 days	2.71^bc	2.65^c	2.95^a	2.76^b	2.79^b	2.51^d	0.025	0.0001	0.0251	0.4021
22–28 days	1.82^b	1.95^a	1.79^b	1.84^b	1.65^c	1.67^c	0.021	0.0001	0.0028	0.6412
29–35 days	1.76^ab	1.69^a	1.74^a	1.60^bc	1.55^cd	1.47^d	0.023	0.0001	0.0049	0.2103
36–42 days	1.85^a	1.68^b	1.62^bc	1.50^c	1.54^bc	1.32^d	0.032	0.0001	0.0131	0.4416
1–42 days	1.94^a	1.89^ab	1.86^b	1.78^c	1.75^c	1.61^d	0.020	0.0001	0.0217	0.6270

Control+, the birds received drinking water supplemented with 500 mg/L polysorbate-80 throughout the trial; Control−, the birds received drinking water with no additive; SEM, standard error for overall mean.

^a–gMeans within a row without a common superscript differ significantly (P < 0.05).

The mean WI was significantly decreased by addition of SkEO in a dose-dependent trend during all weekly periods of age (P < 0.05; Table 5). Supplementation of drinking water with 200, 300, 400 and 500 mg/L SkEO resulted in 0.47%, 4.40%, 8.60% and 12.93% decrease in WI, respectively, from 1 to 42 days of age (Figure 1). A dose-response decrease was also observed in mean FI:WI ratio for all the birds receiving the treated water, but the association was not such consistent as WI (P < 0.01; Table 4).

Figure 1. Effect of S. khuzestanica essential oils on water intake in broiler chicks during days 1–42 of age.

Table 5. Effect of essential oils of S. khuzistanica on carcass weight (CW; g), carcass yield (CY; %), abdominal fat-to-carcass weight ratio (AF:CW) in broiler chicks at 42 days of age.

	CW	CY	AF:CW
Males
Control+	1662.6	40.54	2.442
0	1594.2	31.69	1.969
200	1651.0	38.00	2.294
300	1661.3	35.50	2.131
400	1652.2	32.00	1.940
500	1683.6	38.75	2.300
SEM	14.449	1.202	0.067
P < F	0.1581	0.1859	0.2125
Trends
Linear	0.4510	0.2871	0.4511
Quadratic	0.2672	0.3212	0.1873
Females
Control+	1408.0	41.77	2.970
0	1454.2	36.58	2.500
200	1413.6	45.00	3.127
300	1328.4	38.08	2.866
400	1398.2	37.92	2.722
500	1409.6	36.25	2.557
SEM	15.238	1.203	0.077
P < F	0.2936	0.2910	0.1581
Trends
Linear	0.3321	0.3870	0.6517
Quadratic	0.3642	0.3912	0.1271

Control+, the birds received drinking water supplemented with 500 mg/L polysorbate-80 throughout the trial; SEM, standard error of mean.

^a–eMeans within a column without a common superscript differ significantly (P < 0.05).

Effect of SkEO-treated water on mortality of broiler chickens in days 1–21 and 22–42 of age is depicted in Figure 2. The mean mortality rate was not different for the treated birds compared to the control groups during 1–21 and 22–42 days of age (P > 0.05). However, for pooled data over all periods, addition of 300 and 500 mg/L SkEO increased mortality rate of the birds mainly in the second part of the growing period when the birds were suffering from extreme ambient temperature.

Figure 2. Effect of essential oils of S. khuzistanica on mortality of broiler chickens during 1–21 and 22–42 days of age. The letters inside the columns represent significant difference for mortality percent among treatments for 1–42 days of age. The error bars show standard error for mean mortality over 1–42 days.

The calculated EBI was greater for the birds grown on drinking water supplemented with 400 mg/L of SkEO compared to the other groups (Figure 3). There was no significant effect of SkEO-treated water on carcass weight, carcass yield and AF percentage in male and female birds at day 42 of age (P > 0.05; Table 5).

Figure 3. Effect of essential oils of S. khuzistanica on average European broiler index in broiler chicks at 42 days of age.

Table 6. Effect of essential oils of S. khuzistanica on relative weight of duodenum and pancreas (at 21 and 42 days) and relative weight of liver and bile bladder (at 42 days) in broiler chickens.

		Essential oils of S. khuzistanica (mg/L)							Trends
	Control+	0	200	300	400	500	SEM	P value	Linear	Quadratic
g per 100 g body weight at 21 days
Duodenum	1.412	1.689	1.628	1.625	1.483	1.507	0.045	0.3120	0.2072	0.1176
Pancreas	0.549^ab	0.492^b	0.579^a	0.547^ab	0.528^ab	0.545^ab	0.012	0.0192	0.3519	0.0172
g per 100 g body weight at 42 days
Duodenum	1.180	1.218	1.269	1.356	1.223	1.178	0.023	0.1927	0.3451	0.2431
Pancreas	0.332^a	0.302^b	0.332^a	0.329^a	0.332^a	0.340^a	0.006	0.0121	0.0345	0.3391
Liver	3.783	3.639	3.831	3.566	3.583	3.500	0.065	0.6670	0.5100	0.4310
Gall bladder	0.094^ab	0.074^b	0.087^ab	0.104^a	0.083^ab	0.102^a	0.004	0.0146	0.0341	0.1021

Control+, the birds received drinking water supplemented with 500 mg/L polysorbate-80 throughout the trial; SEM, standard error of mean.

^a–eMeans within a column without a common superscript differ significantly (P < 0.05).

The mean duodenum weight in days 21 and 42 of age was not affected (P > 0.05) by SkEO-treated water (Table 6). Pancreas percentage was significantly (P < 0.05) increased for the birds receiving 200–500 mg/L SkEO at 21–42 days of age compared with the control− birds. Liver percentage (% of carcass weight) was not significantly differing among the treated and control birds at day 42 of age. The relative weight of gall bladder was 17.56%, 40.50%, 12.16% and 38.73% greater for the birds receiving 200, 300, 400 and 500 mg/L SkEO, respectively, compared with control− birds at day 42 of age (Table 6).

4. Discussion

In this study, SkEO exhibited no promising effects on DWG of the broiler chicken in days 1–28 of age when birds were maintained under normal production practices. During days 29–35, when the birds suffered from extreme heat stress, SkEO-added water decreased the DWG of the birds. The SkEO was determined as a natural product rich in carvacrol so that almost all its properties could be credited by carvacrol features. It has been shown that supplementation of drinking water with high doses of SkEO (ranging from 500 to 2500 mg/L) adversely affected production parameters in broilers from 1 to 28 days of age (Khosravinia et al. 2013). The same researchers found that by lowering the SkEO in water to 200, 300 or 400 mg/L, the treated birds with 500 mg/L SkEO during 1–28 days could effectively compensate their weight gain during 29–42 days of age. These findings are inconsistent with results of Lee et al. (2003) who reported 2% increase in average daily gain of broiler chicken by inclusion of 0.2 g/kg carvacrol in the diet. Addition of tymole, an isomer of carvacrol, at the same dose caused a 3% decrease in DWG. The same researchers did not report WI of the treated birds. However, the differences in the results could be endorsed by physiological status of the birds where in the current study birds were not raised in standard conditions. In agreement with the findings of the current study, Basmacioglu et al. (2004) reported that dietary oregano extract (a natural product rich in carvacrol) at 0.15 g/kg decreased DWG in broiler chicken by 2% compared to a control group. With doubling the dietary dose (0.3 g/kg), however, the same researchers observed a +2% difference in the same parameter compared to the control group.

The results on FI as well as FCR in this study were not such consistent that a dose-dependent or an age-associated response to SkEO could be pointed out. The unchanged FI for the treated birds was in agreement with the findings of Lee et al. (2003) but disagreed with the results reported by Basmacioglu et al. (2004). The latter researchers found that addition of 0.2 g/kg carvacrol and 0.15 g/kg oregano extract caused +2% and −6% difference in FI of treated birds compared with the relevant control groups. The results on FCR in the current study were disagreed with findings of almost all other reports. In this study, SkEO-treated water caused no change in FCR. These results are to some extent in discord with the findings of Lee et al. (2003) and Basmacioglu et al. (2004) who found decreased FCR for the carvacrol-received birds. The differences among the above-mentioned findings may be reasoned by differences in managerial practices applied in experimental flocks and by physiological state of the birds in each experiment.

In the present study, SkEO brought about a pronounced decrease in WI in all the treated birds. Such effect has already been attributed to water flavour (Khosravinia et al. 2013). The bitter and pungent taste of carvacrol and possibly other principles in SkEO caused a significant drop in WI. Water is involved in every aspect of broiler metabolism, playing important roles in regulating body temperature, digesting food and eliminating body wastes. At normal temperatures, poultry consumes at least twice as much water as feed. When heat stress occurs, WI will increase. It seems that the caustic taste of water did not allow the treated birds to increase their WI as it demonstrated by dose-response decrease observed in mean FI:WI ratio for all the treated birds (Figure 1). Some researchers verified that the bitter-tasting essential oils adversely affect WI in broiler flocks (Lee et al., 2004a, 2004b). In many other studies the quality of drinking water, but not with special reference to additives, has been considered (Barton 1996; Grizzle et al. 1997). Unfortunately, effects of flavours on chickens performance have not been investigated since based on early indications most researchers believe that broilers may not actually respond to flavour when compared to mammals (Moran 1982). In concord with the conclusion made by Lee et al. (2004a) and Windisch et al. (2008) finding of the present study confirm that assumption that phytogenic extracts improve the palatability of feed does not seem to be justified in general. The great attention currently focused on administration of essential oils and other phytogenic products to poultry urges further investigation on response of avian species to flavours in water and feed. The disability of the treated birds in demonstrating anticipated growth could be attributed to lowered WI imposing a great conflict to the birds as they needed more WI to overcome their disturbed homeothermic state.

Mortality always represents a major economic loss in broiler flocks. It is usually greater in broiler flocks exposed to hot environmental temperatures compared to those maintained in normal conditions. Water intake is an important determinant in mortality rate in heat stressed birds (Belay et al. 1993). Water intake increases in heat stressed birds in order to maintain thermoregulatory balance (Bruno & Macari 2002), as heat stress induces high water loss through the respiratory tract as a means to achieve efficient thermoregulation through evaporative cooling. In the current study it was anticipated that the decreased WI due to pungent taste of carvacrol may result in greater mortality rate in treated birds. Such expectations have realised when 300 and 500 mg/L SkEO increased mortality rate of the birds mainly in days 21–42 of age when the birds were suffering from extreme ambient temperature.

No single production indication can perfectly reveal the economic output of a broiler flock. Researchers have tried to pool the fractional influence of many production parameters in an index to compare performance of different flocks. The EBI (Euribrid 1994) is calculated based on final body weight, FCR and mortality. The calculated index for the treated birds with 400 mg/L of SkEO through drinking water was greater compared to the other groups. The diminutive advantages of water treated with 400 mg/L SkEO in DWG, improved FCR in 1–42 days of age and lower mortality rate especially during 22–42 days of age accumulates in the index and suggests that 400 mg/L as the recommended dose for addition of SkEO into drinking water of broiler chickens.

In the current study CW and CY were not influenced by treatments in both male or female birds. These results are expected as carcass weight is mainly associated with pre-slaughter weight but carcass yield is correlated with body composition among many other factors. However, it was anticipated that SkEO exerted considerable impact on AF percentage. It was reported that dietary carvacrol affected fat metabolism in chicken as shown by decreased AF in broiler chicken (Case et al. 1995). In broiler chicken, lipids and triglycerides in particular are stored in the abdominal cavity (Saadoun & Leclercq 1987). There is an apparently general postulation that almost all the fat built up in broiler adipose tissue including AF is synthesised in the liver or derived from the diet (Griffin et al. 1992; Hermier 1997). The results on AF disagree with the findings of Khosravinia et al. (2013) who reported that supplementation of drinking water with SkEO (500–2500 mg/L) significantly reduced AF in both male and female birds raised in normal conditions.

There are suggestions that dietary administration of phytogenic products may improve digestion processes in avian species (Mellor 2000a, 2000b). In a number of experiments the positive effect of essential oils on feed digestion has been attributed to increased bile salt secretion (Sambaiah & Srinivasan 1991) and stimulation of digestive enzymes activity of intestinal mucosa and of pancreas (Platel & Srinivasan 2000). The latter effect was mainly reasoned by pungent principles in essential oils. In the current study, increased pancreas and gall bladder weight at days 21 and 42 of age verified that SkEO stimulates pancreatic enzymes activities and bile salts secretion.

5. Conclusion

In conclusion, the present study revealed that administration of SkEO at 400 mg/L through drinking water to heat stressed broiler chickens possibly improves economic efficiency if broiler flocks. Such beneficial effects are due to accumulation of minute advantages of SkEO in greater DWG and improved FCR over days 1–42 of age and lowered mortality rate.

Acknowledgment

The author wishes to thank Dr. Ali Salehnia for his encouragement and many useful supports in this study.

Disclosure statement

There is no conflict of interest in this paper.

Notes

1. The plant was already identified by the Department of Botany of the Research Institute of Forests and Rangelands (TARI), Tehran. A voucher specimen (No. 58416) has been deposited at the Herbarium of TARI.