Effects of supra-nutritional levels of vitamin E and vitamin C on growth performance and blood parameters of Japanese quails

Abstract

A study was conducted to evaluate growth performance and blood serum parameters of Japanese quails fed diets containing different supra-nutritional levels of vitamin E and C (600, 800 and 1000 mg/kg). A completely randomised design was adopted and main effects (vitamin E and C) were arranged in a 3 × 3 factorial approach. Throughout the study (1–42 d), the supplementation with 1000 mg/kg vitamin E and C resulted in the highest feed intake, weight gain, and final body weight (p < .01). Serum parameters showed that vitamin E and C at 1000 mg/kg determined the lowest serum concentrations of glucose, uric acid and creatinine (p ≤ 0.01) and the highest of high (HDL, p = .01) and low (LDL, p = .05) density lipoprotein cholesterol and albumin (p < .01). The administering of 1000 mg/kg vitamin E or C reduced triglycerides (p < .01), aspartate amino transferase (E, p < .01; C, p = .02) and alanine amino transferase (E, p < .01; C, p = .01) whereas increased total protein, calcium, phosphorous, thyroid stimulating hormone, red blood cells, mean corpuscular volume, mean corpuscular haemoglobin and mean corpuscular haemoglobin concentration (p < .01). Vitamin C at 800 or 1000 mg/kg level decreased serum total cholesterol (p < .01) whereas vitamin E achieved the lowest alkaline phosphatase and the highest haemoglobin serum concentration (p < .01). The findings showed that these vitamins, used together at 1000 mg/kg, can individually or synergistically act promoting quail health, feed intake and growth.

Highlights

• The use of vitamin E and C at high doses (1000 mg/kg) in quail diet can promote animal health.

• The vitamin E and C administration at high levels can be a good management practice in quail nutrition to promote feed intake and growth.

Keywords:

• Blood serum parameter
• growth performance
• Japanese quail
• vitamin C
• vitamin E

Introduction

Vitamins and minerals are crucial nutrients for metabolic and physiological processes, and thereby for animal productive and reproductive performance. Vitamins strengthen the immune status in animals and foster a normal metabolism helping to resist against disease and production stress. Vitamin E and C play a major role as antioxidants in biological systems breaking the chain of lipid peroxidation in cell membranes (Sahin and Kucuk 2001). Vitamin E is the primary chain-breaking antioxidant in lipid phases and acts as scavenger both of oxygen radicals attacking from outside the membrane and lipid peroxyl radicals generated within the membrane (Surai 2002). Vitamin C performs its antioxidant function in aqueous compartments by reacting with peroxyl radicals and by restoring the antioxidant properties of vitamin E (Cotelle et al. 2003).

There is also important evidence on the effects of vitamin E and C on the health and reproductive performance of livestock species (Wilkanowska and Kokoszyński 2015). Vitamin E is involved in the biosynthesis of several hormones associated with fertility and its deficiency exerts a suppressive effect on the gonadal function (Wilkanowska and Kokoszyński 2015). In poultry nutrition, dietary supplementation with vitamin C can improve the egg production and hatchability (Nowaczewski and Kontecka 2005). Moreover, studies have showed that feeding vitamin E and C, alone or in combination, can be a good management practice in poultry nutrition to alleviate the negative effects of heat stress and to promote growth performance (Sahin and Kucuk 2001; Ipek et al. 2007). Zaghari et al. (2013) observed a decrease in blood triglyceride concentration and a redistribution of cholesterol among the lipoproteins (favouring the high density lipoproteins [HDL]) by adding vitamin E to the diet of broiler breeder hens (400 mg/kg of diet). However, in poultry nutrition, additional research must be conducted to establish the optimal level of vitamin E and/or C in order to guarantee maximum growth performance.

The aim of the study was to evaluate the effects of different supra-nutritional levels of vitamin E and C on growth performance and blood serum parameters of Japanese quail.

Materials and methods

Birds and housing

The current study was conducted at a quail farm (Amol, Iran) during January–February 2016. All procedures were approved by the Animal Care and Welfare Committee of Islamic Azad University (Rasht Branch, Rasht, Iran).

A total of 360 1-d-old Japanese female quails (Coturnix coturnix Japonica) were randomly divided, according to their initial body weight (BW), into nine dietary treatment groups. Each group of birds was subdivided into four replicates (10 birds/replicate). Each replicate was housed in a ground cage (0.70 m × 0.50 m). Quails were reared throughout the experimental trial under the same environmental conditions. Temperature was maintained at: 37 °C in the first week of age, 33 °C in the second, 30 °C in the third, 27 °C in the fourth and 24 °C in the fifth and sixth. The relative humidity was 55%–65%. The lighting programme consisted of 23 h of light and 1 h of dark for the first week of age thereafter the hours of light were reduced by 1 h per week until the end of the trial (42 d). Water and experimental diets were offered ad libitum.

Dietary treatments

Quail responses to different dietary levels of vitamin E and C were evaluated from 1 to 42 d. Due to the particular environmental conditions of breeding, the standard diet, based on corn and soybean meal, was formulated according to a practical diet commercially and traditionally used for Japanese quails in Iran (Salary et al. 2015). Ingredients, chemical composition, and energy of the standard diet are shown in Table 1. The standard diet was supplemented with vitamin E (DL-α-tocopheryl acetate) and C (L-ascorbic acid) at three different levels (600, 800 and 1000 mg/kg of diet) in a 3 × 3 factorial design. All the experimental diets were iso-energetic and iso-nitrogenous.

Table 1. Ingredients, chemical composition, and energy of the experimental quail diet (from 1 to 42 d of age).

	Diet from 1 to 42 d
Ingredients, %
Corn	56.32
Soybean meal, 44% protein	33.32
Soybean oil	2.86
Salt	0.35
Limestone	5.35
Dicalcium phosphate	1.31
Vitamin and mineral premix^a	0.30
DL-methionine	0.14
Choline, 70%	0.05
Calculated analysis, % as fed
Metabolizable energy, kcal/kg	2900
Crude protein	20.00
Calcium	2.50
Available phosphorous	0.35
Methionine	0.45
Methionine + Cysteine	0.76
Lysine	1.07

^a Supplied the following per kilogram of diet: Cu, 8 mg; Fe, 50 mg; Mn, 70 mg; Zn 50 mg; I, 1.2 mg; Se, 0.2 mg; vitamin A, 14,000 U; vitamin D₃, 4000 U; vitamin E, 10 mg; vitamin K₃, 3.2 mg; vitamin B₂, 6 mg; vitamin B₁₂, 16 µg; niacin, 40 mg; pantothenic acid, 10 mg; antioxidant, 30 mg.

Growth performance and blood serum parameters

Body weight and feed intake were measured at d1, d21 and d42 by cage. The average daily feed intake (ADFI), average daily gain (ADG), and gain to feed ratio (G:F) were calculated for each replicate and for the growth periods 1–21 d, 22–42 d and 1–42 d.

At d42, blood samples were collected from 4 birds per treatment (1 bird/replicate group) by wing vein. Blood samples (1 mL/bird) were collected into EDTA tubes and centrifuged (3000 rpm ×10 min) at room temperature. Then, plasma was stored at −20 °C until analysis. Plasma was analysed for glucose, uric acid, triglycerides, total cholesterol, cholesterol linked to high density lipoproteins (HDL), cholesterol linked to low density lipoproteins (LDL), albumin, aspartate amino transferase (AST), alanine amino transferase (ALT), alkaline phosphatase (ALP), calcium, phosphorous, creatinine, thyroid stimulating hormone (TSH), red blood cell (RBC), haemoglobin, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC). Biochemical analyses were performed using standard protocols of commercial laboratory kits (Pars Azmoon Co., Tehran, Iran; Pourhossein et al. 2015; Golrokh et al. 2016).

Statistical analysis

Data were tested for normality with the Shapiro–Wilk test before statistical analysis. Then, data were analysed according to a completely randomised design using the GLM procedure of SAS (2003) according to the model reported below: $${\text{Y}}_{\text{ijk}}=\mu +{\text{VitE}}_{\text{i}}+{\text{VitC}}_{\text{j}}+{\left(\text{VitE x VitC}\right)}_{\text{ij}}+{\text{e}}_{\text{ijk}},$$ where, Y_ijk is the response variable, μ is the overall mean, Vit_i is the fixed effect of dietary level of VitE (i = 3), VitC_j is the fixed effect of dietary level of VitE (j = 3), (VitE × VitC)_ij is the first order interaction and e_ijk is the random residual error. The growth performance parameters were analysed both within experimental periods (i.e. 1–21 d and 22–42 d) and on whole period (i.e. 1–42 d). Post hoc least-squares means (LSMEANS) tests were performed with the LSMEANS option of SAS (2003), using the Tukey method for multiple testing correction. Significance was considered at p ≤ .05 and tendency was declared at .05 < p ≤ .10.

Results

Growth performance

Growth performance of Japanese quails fed diets with different dietary levels of vitamin E and C are shown in Table 2.

Table 2. Growth performance of Japanese quails fed diets with different dietary levels of vitamin E and C.

Treatment
Vitamin E,	Vitamin C,	BW, g			ADFI, g			ADG, g			G:F
mg/kg	mg/kg	1 d	21 d	42 d	1–21 d	22–42 d	1–42 d	1–21 d	22–42 d	1–42 d	1–21 d	22–42 d	1–42 d
600	600	8.83	80.60^e	195.65^f	11.45^bc	24.06^bc	16.06^bc	3.42^d	5.48^cd	4.45^e	0.30^cd	0.23^b	0.28^c
600	800	9.05	81.45^e	196.75^ef	11.61^b	24.06^bc	16.10^bc	3.45^d	5.49^cd	4.47^de	0.30^d	0.23^b	0.28^c
600	1000	8.83	82.75^d	197.05^ef	11.61^b	23.95^bc	16.08^bc	3.52^c	5.44^de	4.48^de	0.30^bcd	0.23^b	0.28^bc
800	600	8.88	80.73^e	197.30^ef	11.45^bc	23.67^c	15.86^c	3.42^d	5.55^bc	4.48^de	0.30^cd	0.24^a	0.28^ab
800	800	8.98	85.53^b	198.23^de	11.30^c	24.05^bc	16.02^bc	3.65^b	5.37^e	4.51^cd	0.32^a	0.22^b	0.28^bc
800	1000	8.85	86.58^a	199.60^cd	11.51^bc	24.18^bc	16.19^b	3.70^a	5.38^e	4.54^bc	0.32^a	0.22^b	0.28^bc
1000	600	8.95	83.80^c	201.48^b	11.58^b	23.63^c	15.96^bc	3.56^c	5.60^ab	4.58^b	0.31^ab	0.24^a	0.29^a
1000	800	8.83	85.43^b	201.25^bc	11.50^bc	24.30^b	16.18^b	3.65^b	5.52^cd	4.58^b	0.32^a	0.23^b	0.28^ab
1000	1000	8.93	86.35^ab	205.48^a	12.08^a	25.19^a	16.70^a	3.69^ab	5.67^a	4.68^a	0.31^bc	0.23^b	0.28^bc
Main effect
Vitamin E
600		8.90	81.60	196.48	11.56	24.02	16.08	3.46	5.47	4.47	0.30	0.23	0.28
800		8.90	84.28	198.38	11.42	23.97	16.02	3.59	5.43	4.51	0.31	0.23	0.28
1000		8.90	85.19	202.73	11.72	24.37	16.28	3.63	5.60	4.62	0.31	0.23	0.28
Vitamin C
600		8.88	81.71	198.14	11.49	23.79	15.96	3.47	5.54	4.51	0.30	0.23	0.28
800		8.95	84.13	198.74	11.47	24.14	16.10	3.58	5.46	4.52	0.31	0.23	0.28
1000		8.87	85.23	200.71	11.73	24.44	16.32	3.64	5.50	4.57	0.31	0.23	0.28
SEM		0.10	0.21	0.37	0.06	0.12	0.06	0.01	0.02	0.01	<0.01	<0.01	<0.01
p values
Vitamin E		1.00	<.01	<.01	<.01	<.01	<.01	<.01	<.01	<.01	<.01	.02	<.01
Vitamin C		.57	<.01	<.01	<.01	<.01	<.01	<.01	<.01	<.01	<.01	<.01	.02
Vitamin E × C		.44	<.01	<.01	<.01	<.01	<.01	<.01	<.01	<.01	<.01	<.01	.01

BW: body weight; ADFI: average daily feed intake; ADG: average daily gain; G.F: gain to feed ratio.

^a,b,c,d,e,f Means within a column with different superscript letters differ (p < .05).

With the exception of initial BW (1 d), a vitamin E × C interaction effect (p ≤ .01) was observed on all growth performance parameters. In the three periods of observation (i.e. 1–21 d, 22–42 d and 1–42 d), the highest ADFI were obtained when quails received the highest levels of vitamin E and C (i.e. 1000 mg/kg of diet). After 21 d of trial, the highest ADG and BW were achieved with 800 and 1000 mg/kg of vitamin E and C as well as 1000 mg/kg of both vitamin E and C. From 22 to 42 d and throughout the study (i.e. 1 to 42 d), the highest ADG (i.e. 5.67 g and 4.68 g, respectively) were obtained by administering 1000 mg/kg of both vitamin E and C and consequently, the highest final BW (i.e. 42 d) was achieved at these levels of vitamins.

In the first 21 d of trial, the highest G:F ratios (i.e. 0.323, 0.322 and 0.317) were observed when quails received 800 mg/kg of vitamin E and 800 or 1000 mg/kg of vitamin C or 1000 mg/kg of vitamin E and 800 mg/kg of vitamin C. From 22 to 42 d of trial, the highest G:F ratios were obtained with 800 or 1000 mg/kg of vitamin E and 600 mg/kg of vitamin C. Throughout the study, 800 mg/kg of vitamin E and 600 mg/kg of vitamin C or 1000 mg/kg of vitamin E and 600 or 800 mg/kg of vitamin C achieved the highest G:F ratios.

Blood serum parameters

Blood serum parameters of Japanese quails fed diets with different dietary levels of vitamin E and C are shown in Table 3.

Table 3. Blood serum parameters of Japanese quails fed diets with different dietary levels of vitamin E and C.

Treatment
Vitamin E, mg/kg	Vitamin C, mg/kg	Glucose, mg/dL	Uric acid, mg/dL	Total cholesterol, mg/dL	Triglycerides, mg/dL	HDL cholesterol, mg/dL	LDL cholesterol, mg/dL	LDL/HDL	AST, U/L	ALT, U/L	ALP, U/L	Total protein, g/dL	Albumin, g/dL
600	600	228.50^a	5.90^a	183.00	293.00	150.25^d	25.50^d	0.16^d	150.25	36.75	155.00	9.73	2.41^e
600	800	225.00^a	5.42^bc	174.00	281.50	178.75^b	60.75^b	0.34^ab	149.25	34.25	150.25	9.82	2.45^de
600	1000	225.25^a	5.41^bc	172.00	273.75	183.00^a	62.25^ab	0.34^a	146.50	36.00	155.00	9.87	2.46^de
800	600	228.75^a	5.71^ab	179.50	288.75	157.25^cd	35.00^cd	0.22^cd	143.50	32.25	146.50	9.73	2.49^d
800	800	219.50^ab	5.31^c	170.50	273.50	163.25^cd	47.00^bc	0.28^cd	137.75	28.50	148.00	9.89	2.65^ab
800	1000	189.75^c	4.80^de	165.50	257.00	179.00^ab	64.50^ab	0.35^ab	133.75	26.75	147.75	9.91	2.58^bc
1000	600	226.75^a	5.63a^bc	178.25	288.25	155.25^cd	34.25^cd	0.22^cd	139.75	33.00	142.75	9.78	2.57^c
1000	800	208.00^b	4.89^d	173.75	261.00	167.00^bc	45.00b^cd	0.27^bc	132.25	29.00	149.00	9.90	2.63a^bc
1000	1000	185.25^c	4.45^e	164.50	253.50	182.50^a	68.25^a	0.37^a	133.00	25.75	141.25	9.96	2.66^a
Main effect
Vitamin E
600		226.25	5.58	176.33	282.75^a	170.67	49.50	0.28	148.67^a	35.67^a	153.42^a	9.81^c	2.44
800		212.67	5.27	171.83	273.08^b	166.50	48.83	0.28	138.33^b	29.17^b	147.42^b	9.84^b	2.57
1000		206.67	4.99	172.17	267.58^b	168.25	49.17	0.28	135.00^b	29.25^b	144.33^b	9.88^a	2.62
Vitamin C
600		228.00	5.75	180.25^a	290.00^a	154.25	31.58	0.20^c	144.50^a	34.00^a	148.08	9.75^c	2.49
800		217.50	5.21	172.75^b	272.00^b	169.67	50.92	0.29^b	139.75^b	30.58^ab	149.08	9.87^b	2.58
1000		200.08	4.89	167.33^b	261.42^c	181.50	65.00	0.35^a	137.75^b	29.50^b	148.00	9.91^a	2.57
SEM		2.65	0.08	3.49	3.61	2.95	4.45	0.02	2.75	1.70	2.59	0.01	0.02
p values
Vitamin E		<.01	<.01	.23	<.01	.24	.98	.95	<.01	<.01	<.01	<.01	<.01
Vitamin C		<.01	<.01	<.01	<.01	<.01	<.01	<.01	.02	.01	.85	<.01	<.01
Vitamin E × C		<.01	<.01	.87	.11	.01	.05	.09	.68	.40	.16	.11	<.01
Treatment
Vitamin E, mg/kg	Vitamin C, mg/kg	Calcium, mg/dL	Phosphorous, mg/dL	Creatinine, mg/dL	TSH, mU/mL	RBC, 10^6/mL	Hemoglobin, g/dL	MCV, fL	MCH, pg	MCHC, g/dL
600	600	14.30	8.70	1.96^a	1.07	5.22^d	15.25	146.98	49.67	40.27
600	800	15.33	9.45	1.52^bc	1.09	5.21^d	15.35	147.44	50.05	40.56
600	1000	15.35	9.50	1.44^cd	1.17	5.44^cd	15.40	148.37	50.42	41.00
800	600	14.50	8.85	1.90^a	1.21	5.41^cd	15.78	148.38	50.76	41.30
800	800	15.48	9.70	1.55^bc	1.26	5.70a^bc	16.20	149.98	51.43	42.11
800	1000	15.73	9.83	1.31^cd	1.31	5.91^ab	16.25	150.26	51.76	42.10
1000	600	14.78	9.28	1.92^a	1.26	5.46b^cd	15.88	149.11	51.04	41.67
1000	800	15.73	9.75	1.76^ab	1.35	5.99^a	16.08	150.07	51.75	42.40
1000	1000	15.83	9.88	1.21^d	1.37	6.13^a	16.28	150.63	51.85	42.47
Main effect
Vitamin E
600		14.99^b	9.22^b	1.64	1.11^c	5.29^b	15.33^b	147.60^b	50.04^b	40.61^b
800		15.23^ab	9.46^a	1.58	1.26^b	5.67^a	16.08^a	149.54^a	51.32^a	41.83^a
1000		15.44^a	9.63^a	1.63	1.33^a	5.86^a	16.08^a	149.94^a	51.55^a	42.18^a
Vitamin C
600		14.53^b	8.94^b	1.92	1.18^b	5.37^b	15.63	148.16^b	50.49^b	41.08^b
800		15.51^a	9.63^a	1.61	1.24^ab	5.63^a	15.88	149.17^ab	51.08^a	41.69^a
1000		15.63^a	9.73^a	1.32	1.28^a	5.82^a	15.98	149.75^a	51.34^a	41.86^a
SEM		0.14	0.11	0.06	0.03	0.10	0.21	0.52	0.17	0.23
p values
Vitamin E		<.01	<.01	.48	<.01	<.01	<.01	<.01	<.01	<.01
Vitamin C		<.01	<.01	<.01	<.01	<.01	.14	<.01	<.01	<.01
Vitamin E × C		.92	.41	.01	.82	.09	.91	.88	.78	.78

HDL: cholesterol linked to high density lipoproteins; LDL: cholesterol linked to low density lipoproteins; AST: aspartate amino transferase; ALT: alanine amino transferase; ALP: alkaline phosphatase; TSH: thyroid stimulating hormone; RBC: red blood cells; MCV: mean corpuscular volume; MCH: mean corpuscular haemoglobin; MCHC: mean corpuscular haemoglobin concentration.

^a,b,c,d,e Means within a column with different superscript letters differ (p < .05).

A vitamin E × C interaction effect was observed on serum concentrations of glucose (p < .01), uric acid (p < .01), HDL (p = .01) and LDL (p = .05) cholesterol, LDL/HDL (tendency, p = .09), albumin (p < .01) and creatinine (p = .01). The serum concentration of glucose was the lowest when vitamin E and C were supplied at high levels (800 or 1000 mg/kg of vitamin E and 1000 mg/kg of vitamin C). The administration of vitamin E and C at the highest level (1000 mg/kg) determined also the lowest concentration of uric acid (i.e. 4.45 mg/dL) and creatinine (i.e. 1.21 mg/dL), and the highest of albumin (i.e. 2.66 g/dL). When vitamin C was used at the highest dose (1000 mg/kg) in combination with 600, 800 or 1000 mg/kg of vitamin E, serum HDL and LDL cholesterol and LDL/HDL ratio increased.

A vitamin E and C effect was observed on serum concentration of triglycerides, AST, ALT, total protein, calcium, phosphorous, TSH, RBC, MCV, MCH and MCHC. In particular, vitamin E and C administered at the lowest level (600 mg/kg) determined the highest serum concentrations of triglycerides (vitamin E and C, p < .01), AST (vitamin E, p < .01; vitamin C, p = .02), and ALT (vitamin E, p < .01; vitamin C, p = .01) and the lowest serum concentrations of total protein, calcium, phosphorous, TSH, RBC, MCV, MCH and MCHC (vitamin E and C, p < .01).

The lowest serum concentration of total cholesterol were obtained with 800 or 1000 mg/kg of vitamin C (p < .01). The integration of the quail diet with high levels of vitamin E (800 or 1000 mg/kg, p < .01) achieved the lowest ALP and the highest haemoglobin serum concentration.

Discussion

Growth performance

Our growth performance results showed that throughout the study (i.e. 1–42 d) the quails receiving the diet supplemented with the highest doses of both vitamin E and C (1000 mg/kg) grew faster and therefore, achieved the highest final weight compared with the quails receiving the other experimental diets. This result seems to be due to higher feed intake rather than better feed efficiency. In fact, throughout the study, the addition of both vitamin E and C at other different level combinations increased feed efficiency without improving the quail growth. Previous studies showed that the supplementation of quail diet with vitamin E and C can positively affect growth performance under heat stress conditions (Sahin and Kucuk 2001; Ipek et al. 2007). Vitamin E and C act synergistically such that vitamin E explicates its antioxidant function in lipid phases and the oxidising free radical chain reactions are terminated in aqueous compartments with vitamin C as terminal reductant (Kurutas 2016). Thus, these vitamins play an important role in responding to stress thanks to their antioxidant properties and to the ability of vitamin C to increase the use of corticosteroids released during stress (Phoprasit et al. 2014). Moreover, animal requirements for vitamin E and C under stress can increase (Sahin et al. 2002) because the stress condition increases mineral and vitamin mobilisation from tissues and their excretion (Haq et al. 2016). However, there is growing evidence that the interaction between the two major antioxidant vitamins (i.e. E and C) is also of pathophysiological importance (Subasree 2014). Our findings would suggest that, under thermoneutral condition, vitamin E and C added together at high doses (1000 mg/kg) to quail diet interact promoting a general animals’ welfare which results in raised growth.

Blood serum parameters

In birds, blood components are important indicators of the welfare condition because they reflect the physiological responses of birds to exogenous factors such as animal diet. In agreement with that observed on the growth performance, blood serum parameters showed that vitamin E and C, when used in quail diet both at 1000 mg/kg level, interplay with positive effects on glycaemia, protein anabolism and renal and liver functionality promoting the animals’ health. In fact, at these levels of vitamins, the lowest serum concentrations of glucose, uric acid and creatinine and the highest of albumin were measured. Stress factors affect serum concentration of glucose. In particular, glucocorticoids, produced under stress conditions, stimulate gluconeogenesis from muscle tissue proteins (Tawfeek et al. 2014) determining an increase in glucose serum level (Borges et al. 2007). In birds, the uric acid, being the major end product of nitrogen catabolism (Hosseintabar et al. 2015), represents a useful indicator of nitrogen utilisation (Donsbough et al. 2010). Generally, a decreased serum level of uric acid is related to an increased amino acid incorporation into tissue muscle proteins (Donsbough et al. 2010) whereas an increased concentration to renal failure (Lierz 2003). In avian species, creatine is mostly excreted in urine before it is converted to creatinine so levels of plasma creatinine are low (Lierz 2003). Creatinine is excreted by glomerular filtration and reabsorbed in the tubules and both this mechanisms maintain constant plasma concentration (Lumeij and Remple 1991; Lierz 2003). An raised plasma level of creatinine occurs as an result of severe muscle damage or renal injury (Lierz 2003; Scholtz et al. 2009). Albumin is a plasma protein synthesised by the liver and its serum concentration indicates body defence mechanism (Kabir 2013). In avian species, serum total protein consists mainly of albumin and globulin (Scholtz et al. 2009). Thus, elevated concentrations of total protein are accompanied by increased levels of serum albumin and globulin. In fact, in the current study, when vitamin E or C were administered at 1000 mg/kg, the highest concentrations of total protein were also observed. In agreement with our findings, Imik et al. (2009) reported that the supplementation of quail diet with vitamin E and C, to prevent stress oxidative, raises protein and total protein concentration in blood serum.

A beneficial role of vitamin E supplementation in redistributing cholesterol among the lipoproteins, from LDL to HDL, has been reported (Zaghari et al. 2013). Studies on animals and humans have also demonstrated the ability of vitamin E and C in decreasing plasma total cholesterol level (Zaghari et al. 2013; Sahin et al. 2003; Ashor et al. 2016). In our study, vitamin C at the highest level (1000 mg/kg) interacted with vitamin E raising HDL cholesterol as well as LDL cholesterol and LDL to HDL ratio (tendency). However, when vitamin C was used at high doses (800 or 1000 mg/kg) serum concentration of total cholesterol decreased.

Moreover, the results obtained on blood serum suggested that vitamin E and C, when added to quail diet at high levels (800 or 1000 mg/kg), can individually act with positive effects on protein anabolism, lipid metabolism, thyroid and liver functionality, and animal health. In particular, the administering of 1000 mg/kg vitamin E or C reduced simultaneously triglycerides, AST and ALT whereas increased total protein, TSH, RBC, MCV, MCH and MCHC values. The increase in calcium level agreed with the raised serum level of calcium bound plasmatic protein as discussed above (Ali et al. 2012). Moreover, it is known that birds under stress condition reduce feed intake and compensate their need to energy by lipolysis of body lipid which in turn increases blood serum triglycerides (Rashidi et al. 2010). Serum concentrations of transaminase enzymes (i.e. AST and ALT), are commonly used as an index of liver disease so that increased AST and ALT levels are associated to hepatic damage (Scholtz et al. 2009). In agreement with our serum TSH results, Sahin et al. (2003) found increased plasma concentration of thyroid hormones (triiodothyronine and thyroxine) in birds receiving supplemental vitamin C. It is also suggested that thyroid size and activity are affected by stress factors such as environmental temperature (Yahav et al. 1997; Sahin et al. 2003). A positive linear correlation has been reported between plasma triiodothyronine concentration and feed intake and weight gain in birds reared at a constant ambient temperature (Yahav et al. 1997; Sahin et al. 2003). In disagree with Ipek et al. (2007), in the current study, the supplementation of quail diet with vitamin E and C increased serum RBC concentration and relative corpuscular indices (i.e. MCV, MCH and MCHC) suggesting an improvement in the birds’ health condition. Moreover, vitamin E used alone at high doses (800 or 1000 mg/kg) raised serum haemoglobin which is good for overall disease resistance (Kabir 2013) and decreased plasma ALP; as AST and ALT, ALP is an index of liver health status (Arslan et al. 2004). Moreover, ALP plays an important role in bone mineralisation. In agreement with our serum phosphorous results, it was observed that serum ALP activity is inversely proportional to serum phosphorous concentration, suggesting that the synthesis of this protein is dependent on phosphorous levels (Bilal et al. 2015).

Conclusions

Current findings showed that feeding vitamin E and C at supra-nutritional levels can be a good management practice in poultry nutrition to promote growth performance under thermoneutral condition. In particular, when these vitamins are added together at 1000 mg/kg to quail diet, they can individually or synergistically act with positive effects on protein and lipid metabolism, glycaemia and functionality of thyroid, kidneys and liver promoting the animal health which in turn can result in increased animal AFDI and growth.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Rasht Branch, Islamic Azad University under Grant number 4.5830.