**1. Introduction**

3

Chicken meat is the most accessible protein source for humans in most countries. However, the poultry sector may be limited by a series of problems, including high or low environmental temperature, high stocking density, etc. Heat stress is one of the main problems encountered within the poultry sector [1,2]. Heat stress affects nutritional quality, resulting in a lower protein content and higher fat deposition, etc. [3], and sensorial quality such as low water-holding capacity, higher brightness, and lower redness of meat, etc. [4]. In recent years, much attention has been paid to the inclusion of phytochemicals (vitamins, minerals, phytogenic feed additives) with antioxidant properties in the feed mixture, which would overcome the effects of heat stress on poultry health and on the quality of the meat they produce [5]. Some authors have stated that dietary Cr supplementation had a positive effect on meat quality by decreasing the fat content of the carcass, [6] and on carcass traits of broiler chicks in natural [7,8] or heat stress conditions [9]. Moreover, it has been suggested that combinations between Cr and other antioxidants (Zn, vitamin C) might have a synergistic action [2,10].

Vitamin C is a renowned water-soluble vitamin, with undeniable antioxidant activity. In heat-stressed broilers, dietary vitamin C supplementations have improved performance and humoral immunity [11].

Zinc is one of the most important components of the poultry diet, being a cofactor for enzymes with implication in the antioxidant defense system [12]. It was reported

**Citation:** Saracila, M.; Panaite, T.D.; Mironeasa, S.; Untea, A.E. Dietary Supplementation of Some Antioxidants as Attenuators of Heat Stress on Chicken Meat Characteristics. *Agriculture* **2021**, *11*, 638. https://doi.org/10.3390/ agriculture11070638

Academic Editors: Lubomira Gresakova and Emilio Sabia

Received: 28 May 2021 Accepted: 7 July 2021 Published: 8 July 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. 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/).

that dietary Zn supplementation in broiler chickens improved broiler carcass quality by reducing the percentage of abdominal fat, suppressing lipid peroxidation of chicken meat [13].

Creeping wood sorrel (*Oxalis corniculata*) is a little-known plant, which contains an important amount of vitamin C [14] and phenolic compounds with strong free radical scavenging activity [15]. Previous studies demonstrated that including creeping wood sorrel in chicken diet (1%) and Cr picolinate (0.2 mg/kg diet) could counteract the effects of heat stress, resulting in unaffecting growth performance, improving lactobacilli populations and reducing pathogenic bacteria [14].

However, dietary supplementation with Cr together with other minerals such as Zn, vitamins (C, E), or phytogenic feed additives may potentate the antioxidant effect. Therefore, the objective of this study was to assess the effect of dietary inclusion of chromium and vitamin C, Zinc, and sorrel wood powder supplements on chicken health and nutritional, textural, and sensorial quality of chicken meat.

#### **2. Materials and Methods**

#### *2.1. Birds, Diets, and Treatments*

A 6 week feeding trial (0–42 d) was conducted on 120 unsexed Cobb 500 chickens (1 day of age), weighed and randomly divided into four homogenous groups (C, E1, E2, and E3) with 30 chickens/group. Each group consisted of 6 replicates, with 5 chickens per replicate (1 replicate/chickens/cage). The feeding trial was conducted in an experimental hall of the National Institute for Animal Nutrition (Ilfov, Romania) according to experimental protocol approved (case no. 4775/02.08.2019) by the Ethics Commission of the Institute (Ethical Committee no. 52/30.07.2014). The chicks were housed in three-tiered digestibility cages (cage dimensions 65 × 75 × 45 cm, one cage per replicate) During the experimental period, the chickens were reared under controlled environmental conditions and monitored by a Viper Touch computer (temperature 32 ± 0.5 ◦C, humidity 36 ± 1.4%, with 0.38 ± 0.01% ventilation/broiler, and 899 ± 0.2 ppm CO2 emission). The light regimen was 23 h light/1 h darkness. Compared with the control diet (C group), the experimental diets (E1, E2, and E3 group) included 200 μg/kg diet chromium picolinate, CrPic (Table 1). Additionally, the experimental diets contained 0.25 g vitamin C (VC)/kg diet (E1), 0.025 g Zn/kg diet (E2), and 10 g creeping wood sorrel powder (CWS)/kg diet (E3). The chickens had free access to feed and water. Creeping wood sorrel was analyzed, and the data was published previously by Saracila et al. [14]. The analysis revealed a concentration of 15.44% CP, 2.83% EE, 4.96 mg/g GAE total polyphenols, 31.60 mmol ascorbic acid equivalent antioxidant capacity and 11.77 mg/100 g vitamin C.

#### *2.2. Sample Collection and Analysis*

At the end of experiment (42 days), from each group with homogenous weights, 6 chickens/group were randomly selected (1 chicken/replicate). From each group selected, blood samples were collected aseptically from the sub-axial region into heparinized test tubes. The blood samples were centrifuged (775× *g* for 25 min at 4 ◦C), and the serum obtained was analyzed using an automatic BS-130 chemistry analyzer (Bio-Medical Electronics Co., Ltd., Shenzhen, China) in order to determine the biochemical parameters (serum glucose, cholesterol, triglycerides, phosphorus, calcium, iron, alanine aminotransferase, and aspartate aminotransferase).
