1. Introduction
Northwest Mexico is characterized by a hot climate, mainly during the summer months, when temperatures range between 26 °C and 48 °C in the shade, with an average of 33 °C. The thermoneutral zone for growing-finishing pigs is between 18 °C and 25 °C [
1], and it is well known that temperatures above this thermoneutral zone induce heat stress [
2], which has negative effects on feed intake, weight gain, feed conversion, and carcass characteristics [
3,
4]. Some plant extracts were shown to be beneficial in heat-stress poultry [
5,
6]. Research in pigs indicates that the use of plant extracts (PE) can improve productive performance [
7,
8], and digestibility of dry matter and protein [
9,
10]. PE possess anti-inflammatory effects [
11], and antimicrobial effects for several pathogens [
12]. Together with the improvements in pig health, improvements in the parameters of meat quality such as the oxidative stability, smell, and taste have been reported [
13].
Some plant extracts individually induce positive effects on the animal. Celery (
Apium graveolens) contains analgesic, and anti-inflammatory components [
14], whereas garlic (
Allium sativum) improves digestibility [
15]. Aji et al. [
16] indicate that onions (
Allium cepa) can improve productive performance. Other extracts, like that of avocado (
Persea americana) and parsley (
Petroselinum crispun), have shown vasodilation [
17] and antimicrobial [
18] effects, respectively. Several plants extracts possess antioxidant properties including artichoke (
Cynara scolymus) [
19], oats (
Avena sativa) [
20], beet (
Beta vulgaris) [
14], and spinach (
Spinacea olearace) [
21].
Yang et al. [
22] and Krotkiewski and Janiak [
23] demonstrated that synergistic effects can be evoked when using mixtures of herbal components, both in vivo and in vitro. Currently, no information is available on the effect that the mixture of extracts of the aforementioned plants could have in supplementing pigs kept in commercial conditions during the summer. It is proposed that with the use of a mixture of different PE (celery, garlic, onion, avocado, parsley, artichoke, oat, beets, and spinach, contained in a commercial product, PROTORGAN
®, Tlaquepaque, Jalisco, Mexico), benefits for the pig can be inferred.
The objective of the present study was to assess the effect of adding plant extracts to the grower and finisher diets of pigs on growth performance, blood constituents, carcass characteristics, organ weight as a percentage of live weight (LW), meat quality, and sensory analysis of pork meat in the growing and finishing stage, produced under hot climate conditions categorized as heat stress.
2. Materials and Methods
All procedures involving animal handling were conducted under the approved Mexican official guidelines for domestic animal care [
24,
25,
26], and the study was approved by the University of Sonora Committee (Num.: USO313005360).
2.1. Animal and Housing Conditions
The study was performed in the porcine experimental unit of the Department of Agriculture and Livestock of the Universidad de Sonora. The study was performed in 60 pigs of commercial terminal crosses (Yorkshire × Landrace × Duroc), 30 males and 30 females, which were housed in an opened building similar to that used in commercial conditions in the growing to finishing periods, they were in individual pens, equipped with stainless steel feeders and nipple-type drinkers. Water and food were provided ad libitum. This study was performed in three phases of feeding: phase I (35 to 70 kg), phase II (70 to 95 kg) and phase III (95 to 120 kg live weight (LW). Pigs were individually identified with ear tags. Treatments were distributed based on weight and sex of the pigs, with 20 experimental units per treatment.
2.2. Source of the Plant Extracts (PE)
In this study, a commercial patented product (PROTORGAN®, from Guwlab, Tlaquepaque, Jalisco, Mexico) was used. The product contained extracts from the following plants: artichoke (Cynara sculymus), celery (Apium graveolens), beet (Beta vulgaris), onion (Allium cepa), garlic (Allium sativum), spinach (Spinacea olerace), avocado (Persea americana), oats (Avena sativa), and parsley (Petroselinum crispun).
2.3. Treatments
Pigs received one of three diets, provided as a meal: (1) control diet (CON), designed to satisfy the nutrients for high lean potential, high productivity, and used as a commercial ration in Hermosillo, Mexico during summer [
27]; (2) 0.1% PE, which was the control diet +0.1% (as fed) of plant extracts, PROTORGAN
®; and (3) 0.15% PE, which was the control diet +0.15% (as fed) of plant extracts, PROTORGAN
®. Diets were formulated to be isonitrogenous and isocaloric (
Table 1).
2.4. Growth Performance
The total weight of the feed provided, and the feed rejected in each pen was recorded daily during the study period. At the end of each phase, the average daily feed intake (ADFI) was calculated. Pigs were weighed individually at the same frequency as feed intake was measured, and these data were used to calculate the average daily gain (ADG), and feed conversion ratio (F:G) per phase. The experiment was finished once the pigs reached an average of 120 kg LW, when they were sent for slaughter.
2.5. Blood Metabolites
At the end of the last two phases, blood samples were taken from the 10 pigs in each treatment (approximately 7 mL of blood was collected via jugular venipuncture) using two Vacutainer tubes (Becton, Dickinson and Company, Franklin Lakes, NJ, USA). One tube contained ethylenediaminetetraacetic acid (EDTA), and the other contained no additive.
Blood from tubes containing EDTA was used for the hemogram blood test. This included the determination of red blood cells, hemoglobin, hematocrit, leukocytes, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), lymphocytes, monocytes, and platelets. This was performed using an automated Coulter Electronics × 10 system. The blood from tubes containing no additive was centrifuged at 10,000 rpm for 10 min, and the serum was separated and stored at −20 °C until it was assayed for blood parameters (glucose, total protein, albumin, creatine kinase [CK] and cortisol). Glucose, total proteins, albumin, and creatine kinase (CK) were determined using the appropriate laboratory kits, following the manufacturer’s instructions (RANDOX® Manual). Cortisol was determined using ELISA methodology (Sigma-Aldrich®, St. Louis, MO, USA).
2.6. Slaughtering and Carcass Traits
Pigs were sent for slaughter at 120 kg LW. Pigs were slaughtered in the abattoir of the Departamento de Agricultura y Ganadería, of the Universidad de Sonora by trained personnel. Electrical stunning (head to head) using conventionally methods was applied before sticking and exsanguination, complying with the corresponding official Mexican standards [
24]. The carcasses were individually weighed to record the hot carcass weight (HCW, carcass weight included head, skin and legs, without viscera, internal organs, flare fat, kidneys, diaphragm, genitals and tail). Carcasses were then chilled for 24 h at 4 °C to obtain the cold carcass weight (CCW), carcass lengths, dressing percentage. Carcass shrinkage was determined (HCW–CCW as a percentage of original HCW), fat thickness, the longissimus thoracis muscle (LM) area, and marbling (24 h postmortem) was determined. Fat thickness and the LM area (cm
2) were measured at the 10th and 12th ribs. Marbling was also evaluated according to the guidelines of the United States Department of Agriculture. Finally, cooling loss and dressing values were calculated. The percentage of lean yield was calculated from equations as indicated in the corresponding Mexican Norm [
28].
2.7. Percentage Relation between the Weight of Organs and Live Weight
The liver, heart, lungs, stomach, spleen, and kidneys were extracted from each animal, and the weight was recorded to calculate the organ weight as a percentage of LW for each organ.
2.8. Dissection of the Longissimus Thoracis (LT) Muscle and Sampling
After evaluating the carcasses, the LT of the left side was extracted (4th to 12th intercostal space) from 10 pigs per treatment. The meat samples were marked for identification, vacuum packed, and transported under refrigeration to the facilities of the Centro de Investigación en Alimentación y Desarrollo (CIAD) in the city of Hermosillo, Sonora, for the corresponding analyses.
After arrival at the laboratory, the samples were kept frozen at −18 °C. Before analysis, samples were thawed for 24 h at 4 °C, and then sectioned to carry out chemical, physicochemical, and sensory measurements. Sectioning of the samples was consistently performed following the same protocol, and in the same order from the caudal end (the 12th-rib interface) to the cranial part of the LT muscle. The first cut (2.0 cm) was used to determine the contents of moisture, protein, and intramuscular fat. Four pairs of samples (2.54 cm each) were used for the Warner–Bratzler shear force (WBSF) test, cooking loss determination, and sensory analysis. A 2.5 cm slice was used to analyze color, pH, and water-holding capacity (WHC). All measurements were recorded immediately after the samples were sectioned.
2.9. Meat Quality
2.9.1. Chemical Composition
The moisture, intramuscular fat, and protein content of the meat was determined following AOAC methods [
29] for moisture (method 950.46), fat (method 920.39), and protein (method 955.04). The results are expressed as a percentage of fresh weight.
2.9.2. Physical Analysis
To measure the color parameters in the meat cuts, a Hunter Lab colorimeter was used. Color determination included the parameters L *, a *, b *, hue angle (HUE) using the formula tan
−1 (b/a), and chroma (color saturation) using the formula Chroma = (a * + b *)
½. For measurements, the illuminator D65 with 10° was used in the colorimeter. Color determinations were performed on the surface of the cold samples (4–6 °C) in five sites on the surface of the muscle [
30].
The pH was determined in cold meat samples at 4–6 °C, using a portable digital HANNA (Hanna Instruments, Woonsocket, RI, USA) potentiometer with a penetrating electrode provided with a HANNA HI 99163 thermometer. Measurements were performed in triplicate.
Water Holding Capacity (WHC) was determined following the methodology of Sutton et al. [
31]. The sample was placed in micro-nylon fabric, and introduced into a 50 mL propylene tube. The sample was centrifuged at 2800
g for 5 min at 4 °C. The WHC percentage was calculated according to the difference in weight of the sample before and after the centrifugation.
Texture (WBSF) measurements were made with a Texture Analyzer TAXT-Plus (Texture Technologies Corp., Scarsdale, NY, USA). To measure the cutting effort (CE) of the meat, 2.54 cm thick slices were cut, and then cooked in an electric fryer (Cook Master Ester, Model 3222-3) until reaching an internal temperature of 71 °C. Once cooked, samples were cooled to room temperature (25–30 °C) and then refrigerated at 4 °C for 24 h. To measure the cutting effort, the cooked sample was cut in pieces of 1 cm2 by 3 cm length along the direction of muscle fibers (10 times per cut). The CE was measured perpendicularly to the muscle fibers, using the Warner–Bratzler accessory cutter mounted on the TAXT-Plus texture meter. The WBSF values was expressed in kilogram-force.
Cooking loss was determined by calculating the difference in weight of the sample before and after cooking it at an internal temperature of 71 °C in an electric fryer (Cook Master Ester, Model 3222-3), following the AMSA [
32] technique.
2.10. Sensory Analysis
Sensory assessment was performed by a trained panel of 10 members [
33]. The training of the assessment panel was achieved using the AMSA [
32] methodology. One day before performing the sensory analysis, the meat cuts were removed from the freezer, and thawed at 4 °C for 24 h. The meat cuts were cooked using the same procedure described for the assessment of texture (WBSF). Each portion of meat was cut to a thickness of 1.27 × 1.27 cm. The trained panel (using a dim red light) assessed the cooked samples in terms of odor intensity, taste intensity, fatty sensation, tenderness, juiciness, and amount of connective tissue, using a structured linear scale of 10 cm. The value anchored to the left (0 cm) of the linear scale refers to a descriptive term that represents the lowest intensity of odor, taste, fat, tenderness, juiciness, and amount of connective tissue. The right end (10 cm) refers to the highest degree for each sensory characteristic. Two characteristics were assessed visually (total color and total appearance) on raw samples, under white light and using the same type of scale.
2.11. Statistical Analysis
Each pig was considered as an experimental unit. All data were explored prior to statistical analysis to discard any possible outliers. For the analysis of variance (ANOVA) of growth performance, analysis of blood metabolites and carcass characteristics, a random complete blocks design was used [
34], with initial weight as a blocking factor. Data of the quality and sensory analysis of the meat were analyzed by ANOVA with a completely randomized design, data normality was performed using the Shapiro–Wilk test. The experimental diet was included in the model as the main factor. When statistical differences (
p < 0.05) were observed among treatments, then means were compared using Tukey’s multiple rank test. Effects were accepted as different at
p < 0.05, and tended to be significant at
p < 0.10. All data were processed with SAS (ver. 9.1. SAS Inst. Inc., Cary, NC, USA) statistical software [
35].