Introduction

The turkey (Meleagris gallopavo) was among the first animáis domesticated in México (^{Canul et al. 2011}), and its meat has been used as a source of protein, fat, sodium, iron and potassium (^{Laudadio et al. 2009}). However, the market now requires meat free of microorganisms and antibiotics from the animal production system to the final product. The use of plant extracts are currently being investigated as an alternative to antibiotics in poultry production systems, so there is interest in the use of essential oils derived from herbs and spices such as oregano (^{Kirkpinar et al. 2014}).

Oregano oil (OO) has antioxidant and antimi-crobial properties, so it offers an important benefit in the livestock sector. In general, OO is composed of volatile substances such as carvacrol, thymol, β-myrcene, α-terpinene, Υ-terpinene, p-cymene and cineole (^{Vazquez and Dunford 2005}, ^{Bakkali et al. 2008}, ^{Do et al. 2015}). These characteristics give OO its antioxidant, antibacterial and medicinal capacity, and its usefulness as a treatment of gastrointestinal disorders (^{Rivero-Cruz et al. 2011}). In particular, Mexican orégano (Lippia berlandieri Schauer) is a species characterized by a strong smell, biological activity and high yield of essential oils (^{Dunford and Vázquez 2005}, ^{Avila-Sosa et al. 2010}). The main compounds of the genus Lippia are carvacrol, thymol, cymene, pinene and linalool; these components confer its antibacterial, antioxidant, antiviral, anti-fungal and insecticidal proper- ties (^{Vázquez and Dunford 2005}, ^{Ortega-Nieblas et al. 2011}).

The use of orégano oil in turkey fattening has been little researched. Studies conducted so far have highlighted that OO could be used in the production of turkeys and that they delay lipid oxidation in the breast (^{Bampidis et al. 2005}, ^{Botsoglou et al. 2010}, ^{Giannenas et al. 2014}). Therefore, it would be interesting to provide more information on the influence of OO in turkey fattening. In this sense, although a few studies have been focused on assessing lipid oxidation in turkey breast and reducing the prevalence of pathogenic bacteria with OO of Origanum vulgare L., there is little information on the effect of Mexican orégano (Lippia berlandieri Schauer) oil on turkey meat performance. Therefore, the aim of this research was to evalúate the influence of Mexican orégano essential oil added to the diet on the slaughter quality of commercial turkeys.

Materials and methods

Research was conducted in the Faculty of Ani mal Science and Ecology at the Autonomous Univer- sity of Chihuahua, Chihuahua, México. Chihuahua City is located between 28° 05’ and 29° 48’ NL and 105° 41' and 106° 38’ WL at an elevation of 1 440 masl; it has a dry températe climate with an annual temperature range of 10-20 °C and rainfall of 200-600 mm (^{INEGI 2015}). Turkey fattening was carried out in the Turkey Fattening Area and the slaughter process in the Faculty Meat Unit.

Two treatments were evaluated: T0 control diet (Table 1) and TI the control diet + 400 mg kg^-1 of OO (Lippia berlandieri Schauer) with 60 % carvacrol. The OO was acquired from the Natural Solutions company, located in Ciudad Juárez, Chihuahua. OO composition was analyzed on a PerkinElmer^® Clarus 600 and SQ8 gas chromatograph. The oil was incorporated based on the weight of the diet, mixing it with the plant oil of the diets. Both treatments consisted of 700 day old American Orlopp médium genetic line turkeys. Flock fattening lasted 18 weeks, which was carried out in different 240 m² pens with a concrete floor and sawdust chips, 18 feeders (6 kg diet feeder^-1) and 16 waterers (8 L waterer^-1). The diets used were prepared based on the pre-initiation, initia- tion, growth, termination 1 and termination 2 stages (Table 1; ^{NRC 1994}). Feed and water were provided ad libitum throughout the fattening period. At the end of fattening the slaughter was performed to evalúate the slaughter variables, for which a completely randomized sampling of 45 unsexed turkeys was conducted per treatment, considering each turkey as an experimental unit.

Tabla 1: Formulation of the rations used. 

¹ingredients incorporated per kg of diet; ²diets were formulated according to the nutritional requirements for turkeys suggested by ^{NRC (1994)}; ³puriffed β-glucans, DL-α Tocopherols, zinc proteinates, selenium, vitamin A-acetate, protected vitamin C, vitamin D₃ intermediate metabolites

Turkey feeding was suspended 12 h before slaughter. The slaughter process was performed according to the method used by ^{Al-Kassie (2009}) and ^{NOM-033-ZOO (1995)}. Turkeys were placed on slaughter hooks, previously desensitized with an electric shock of 120 V 50 Hz for 5 s, then killed with a cut in the neck to bleed them for 3 min. Subse- quently, turkeys were scalded in water at 60 ± 1.0 °C for 90 s, and then plucked. The carcass was obtained by separating the head, drumsticks and viscera, which were then washed and placed in a cooling tub with water at 4.0 ±1.0 °C for 20 min. After this, the carcasses were removed, drained for 15 min and then stored at 4 ± 1.0 °C for 24 h.

Live weight at slaughter (LWS), weight of blood, feathers, drumsticks, head, neck, viscera and hot carcass weight were evaluated at slaughter, and then the percentage valúes were determined according to LWS (^{Kirkpinar et al. 2011}). Hot carcass yield (HCY) was calculated with LWS and hot carcass weight, while coid carcass weight was obtained at 24 h post mortem to determine coid carcass yield (CCY).

The data of the measured variables were subjected to analysis of variance via the PROC GLM procedure (^{SAS 2002}), based on the statistical model: y_ij = µ + T_i + e _ij ;where: y _ij = response variable for the effect of the i-th treatment; µ = overall mean; T_i = effect of the i-th treatment (T0 and T1); e _ij = the residual error normally distributed with zero mean and variance σ² [ε_ij ˜ N (O, σ²)]. Differences between treatments were determined at a significance level of 0.05.

Results and discussion

Chromatographic analysis of the orégano oil indicated that the composition was 60.02 % carvacrol, 3.96 % thymol, 23.63 % cineole, 9.57 % p-cymene, 0.11 % gamma-terpinene and 2.70 % other compounds. Essential oils have been recognized for their antimicrobial activity and influence on birds’ productive performance (^{Lee et al. 2004}). But few studies have evaluated the effect of OO on turkey characteristics at slaughter. In this study, the LWS of turkeys was different between treatments (p < 0.05), TI being 890.0 g heavier than T0, which differs from ^{Papageorgiou et al. (2003}) and ^{Bampidis et al. (2005}), who found no effect on turkey live weight, in addition to indicating that the constituents of OO can stimulate feed in take and improve nutrient assimilation. In this regard, studies in chickens made with OO in the feed found improved chicken weight. This result can be attributed to the thymol and carvacrol, which stimulate digestibility and increase nutrient absorption (^{Symeon et al. 2009}, ^{Roofchaee et al. 2011}, ^{Alali et al. 2013}, ^{Kücükyilmaz et al. 2014}, ^{Méndez-Zamora et al. 2015}). Therefore, the increase in turkey LWS could be due to the OO in T1.

The influence of essential oils depends on the concentrations used in the diet (^{Marcinčák et al. 2011}), so some of their components may have an effect on the metabolism of the birds and weight of the organs (^{Simsek et al. 2007}). In this study the blood, viscera, head and neck showed no statistical differences between treatments (Table 2), since pos- sibly the effect of 400 mg kg^-1 of orégano oil added to the diet had no effect on the evaluated variables. Similar results were reported in studies by ^{Bampidis et al. (2005}) and ^{Kücükyilmaz et al. (2014}), who found no statistical differences in turkey and chicken viscera, while studies in chickens suggested that essential oils can modify hemoglobin and cholesterol, but not bird slaughter variables (^{Toghyani et al. 2011}, ^{Issa and Abo 2012}, ^{Kücükyilmaz et al. 2014}).

Tabla 2: Inffuence of oregano oil incorporated into the diet on turkey slaughter quality. 

¹LWS = Live weight at slaughter; HCY = Hot carcass yield; CCY = Cold carcass yield; ²T0 = control diet; T1 = control diet + 400 mg kg^-1 oregano oil (Lippia berlandieri Schauer; 60 % Carvacrol); Means (± Standard error) and F value in the same row are significantly different if p < 0.05 (n=45).

Few studies have reported the effect of OO on turkey slaughter variables. The weight of feathers and drumsticks was different between treatments (p < 0.05). This may be due to the weight of the turkeys, with TI presenting the highest LWS valúes. This evidence indicates a possible effect of OO on some turkey slaughter variables.

Turkey carcass characteristics depend on the capacity for lean tissue deposition (^{Firman 2004}). In the evaluated treatments no statistical differences in HCY and CCY were detected (Table 2). In this regard, ^{Lee et al. (2004}) indícate that some OO components in diets can be deposited in the flesh of the carcass through improved digestive efficiency while research with chickens found no effect on carcass yield with 28.8 mg kg^-1 of carvacrol and 300 mg kg^-1 et al. 2014). On the other hand, with 1600 mg kg^-1 of orégano (Lippia berlandieri Schauer) oil an effect was found on hot and coid chicken carcass (^{Méndez-Zamora et al. 2015}). With 400 mg kg^-1 of orégano oil there was a response in turkey live weight at slaughter, without affecting hot and coid carcass yields. Therefore, further research should be carried out with higher levels of OO (Lippia berlandieri Schauer) and emphasis should be placed on studying meat quality variables such as nutrients, lipid oxidation, antimicrobial eect and preservation of food of animal origin.