Introduction

Broiler meat is one of the largest sources of animal protein world wide. This industry is well developed in several areas, such as nutrition, genetics, and management (^{Chen et al., 2008}), with increasing focus on community health and the environment.

Additives are used in poultry feeding to increase yield, trying to ensure that their desired effects are held while harmful environmental and health effects are avoided (^{Ahmadi et al., 2019}). Several antibiotics have been used as growth promoters in poultry nutrition to improve performance by preventing growth of intestinal pathogens. Consumers are very concerned about the excessive use of antibiotics in poultry production due to increased bacterial resistance in humans (^{Abedi et al., 2008}). Europe has banned the use of growth promoting antibiotics in farm animals, thus the poultry industry needs to find suitable alternatives (^{Poorghasemi et al., 2018}).

Medicinal plants had been neglected in modern feeding of livestock and poultry due to the effectiveness of antimicrobial growth promoters. After the ban on antimicrobial growth promoters, several herbs have attracted the attention of researchers (^{Poorghasemi et al., 2014}). Medicinal plants contain phenols, polyphenols, terpenoids, volatile oils, alkaloids, and antimicrobial compounds that can stimulate digestion, decrease lipid and cholesterol levels, stimulate the immune system, increase antibody production, and promote growth (^{Soltan et al., 2008}). Many recent studies have focused on trying to find alternatives to growth-promoting antibiotics (^{Greathead, 2003}). Aditionally, research has shown that various herbs and essential oils can lower cholesterol (^{Adaszyńska- Skwirzyńska and Szczerbińska,2019}). Extracts from some plants, such as summer savory (Satureja hortensis L.), have also shown beneficial effects on performance, immune response, hematology, and microbiota of broilers (^{Movahhedkhah et al., 2019}).

Ferula gummosa boiss, commonly known as galbanum, is a medicinal plant of family Apiaceae or Umbelliferae, which has 275 genera and 2,850 species (^{Klaverand Van Der Meer, 1993}). Galbanum produces an oleo-gum resin that is mostly present in the root. This material contains 5 to 30% essential oil, 50 to 70% resin, 20 to 40% gummy material, and 1 to 10% moisture and minerals (^{Cross et al., 2007}). This resin has potent antibacterial effects against gram-negative bacteria (^{Dorman and Deans, 2000}).

The present study compared the effects of dietary addition of galbanum powder versus virginiamycin antibiotic on the performance, carcass characteristics, immune system, and blood factors of broiler chickens.

Materials and Methods

Results

Tables 2, 3 and 4 show the effect of experimental groups on the performance of broilers (body weight gain, feed intake, and feed conversion ratio). In the starter period, there was no significant difference in weight gain among treatments (p<0.05). During the grower period, weight gains in all treatments were different compared to the control (p<0.05). The treatment containing 10 g galbanum resulted in the highest weight gain. In the finisher period and during the whole period, the weight gain of the treatments containing 5 and 10 g galbanum increased compared to the control (p<0.05).

In the starter and finisher periods, feed intake was simmilar compared to the control (p>0.05). In the grower period, the differences in feed intake among treatments were significant compared to the control (p<0.05). Feed intake of broilers fed galbanum-containing diets was higher than the control and antibiotic-containing treatment. In the entire period, feed intake of treatments containing 5 or 10 g galbanum increased compared to the control (p<0.05). In contrast, feed intake of treatments containing 2.5 mg galbanum or antibiotic were lower than that of the control (p<0.05). In the grower period, the conversion ratio of treatments containing galbanum showed difference compared to the control (p<0.05). In the finisher period, the conversion of all treatments decreased compared to the control (p<0.05). In the whole period, the conversion of treatments containing 2.5 or 5 g galbanum and also the treatment containing antibiotic showed a significant decrease compared to the control (p<0.05).

Discussion

Acording to our results, adding galbanum powder to the diet of broiler chickens increased body weight gain and feed intake in the grower, finisher, and the overall period.

This increase was higher than that of the virginiamycin-containing treatment. Also, feed conversion ratio improved by galbanum addition to the diet, and this improvement was higher compared with the antibiotic-containing treatment. These results are inconsistent with the report by ^{Hernandez et al. (2004)} who observed that medicinal plants and their extracts did not affect feed intake. They stated that the addition of mint leaves to the diet did not have a significant effect on poultry performance. ^{Cross et al. (2007)} reported that feeding medicinal plants at concentrations of 1 and 0.1% increased body weight and feed intake, and improved feed conversion ratio compared to the control, which was probably due to the antibacterial and antifungal effects of mint. The positive effects on body weight using essential oils in the diet have also been observed in other studies (^{Abudabos et al., 2017}). The use of herbal medicines in the diet increased the body weight of broiler chickens by 3% at 42 days of age (^{Tiihonen et al., 2010}). The effect of herbal ingredients may be due to increased nutrient utilization that improve poultry growth. Also, the increase of appetite, stimulation of digestive secretions and antibacterial effects are among the mechanisms that can be responsible for performance improvement (^{Tiihonen et al., 2010}). Using a mixture of effective oils from several wild medicinal plants for broiler chickens resulted in improved conversion ratio compared to the control and the antibiotic-containing treatment (^{Alçiçek et al., 2003}). It has been suggested that herbal ingredients can improve feed conversion through better nutrient utilization due to increased digestive enzymes and improved ileal digestibility (^{Isabel and Santos, 2009}). According to our results, feed conversion for the whole period in the antibiotic-containing treatment was lower than the control and the other treatments due to a reduced feed intake. It has been reported that the antibiotic effect on broiler performance is due to decreased feed intake per unit of weight gain, resulting in improved feed conversion ratio (^{Alhidary et al., 2016}).

According to our results, the percentage of carcass, breast, thigh, and gizzard in galbanum- containing treatments was not different compared to the control, though it was numerically higher compared to the antibiotic-containing treatment. The compounds in medicinal herbs have a microbicidal effect and, by decreasing the microbial population in the digestive tract, prevent amino acid degradation, increase their absorption and improve carcass traits (^{Nobakht et al., 2015}). The presence of high levels of microbial mass in the digestive system results in protein and amino acid degradation through deamination, thus significant amounts of amino acids and proteins are not decomposed and not absorbed (^{Lee et al., 2003}). Additionaly, when harmful microbial populations are reduced, the conditions for growth and proliferation of beneficial microbes are provided and the health of the chickens improves, leading to optimized digestion and absorption and improved carcass traits (^{Lee et al., 2003}). The lack of difference in carcass, breast, and thigh percentage in the present study may be due to the fact that proper sanitary breeding conditions were provided, thus the activity of harmful microbes was not up to a limit as to allow galbanum and antibiotic to considerably affect carcass components in comparison with the control.

Based on our results, while the relative weight of the liver increased by increasing galbanum levels, the liver percentage in the 5 and 10 g galbanum treatments decreased compared to the control, which is consistent with the report of Nasiri et al. (2011). It has been reported that 0.5% herbal addition to the diet not only result in increased liver size but also reduce its size relative to the control diet (^{Galiband Al- kassie, 2010}). The liver is the target organ for toxins, which can cause liver toxicity and affect its weight (^{Galiband Al-kassie, 2010}). Since galbanum has toxic effects due to its alpha- thujene compound, it can increase liver size by hypertrophy of the smooth endoplastic reticulum in the hepatocyte (^{Sayyah et al., 2001}). While the long term use of high doses of herbal drugs can have deleterious effects on the liver, the use of low doses result in low toxicity and improves organ function due to its antioxidant properties (^{Ocak et al., 2008}), which could explain the decrease in liver percentage compared to the control in the present study.

Heart weight decreased significantly in galbanum-containing treatments compared to the other treatments, which is consistent with the results of ^{Cross et al. (2007)}. Thymol and phenolic compounds present in medicinal plants have antimicrobial and antifungal activity and are considered antioxidants and growth stimulants (^{Cross et al., 2007}).

Regarding the theory that lipid peroxidation may cause heart tissue damage and blood pressure syndrome, the role of medicinal plants with antioxidant properties has been widely investigated. ^{Ciftci et al.(2010)} found that adding 5 g of medicinal herbs with antioxidant properties per kilogram of diet reduces the thickness of the outer wall of arteries, which subsequently decreases the resistance to blood flow, thus reducing the size of the heart. Furthermore, ^{Ruiz-Feria (2009)} reported that 5 ml of lemon balm essential oil in the diet of broilers significantly reduced heart weight. Increasing the antioxidant capacity, especially in tissues involved with ascites such as myocardium cells, can create an antioxidant protective effect, stop peroxidation of the capillary membrane lipid tissue, and prevent the hypertrophy of heart ventricles. It is possible that galbanum antioxidant could prevent cellular peroxidation in the heart tissue and inhibit its growth (^{Geng et al., 2004b}).

It has been reported that the addition of medicinal plants to the diet of broilers results in decreased abdominal fat due to increased secretion of pancreatic enzymes (^{Jamroz et al., 2005}). This effect has also been attributed to inhibition of liver enzymes involved in lipogenesis or lipoprotein lipase present in the fat tissue (^{Gavanji et al., 2014}).

Plant additives can increase the relative weight of the spleen (^{Moorthy et al., 2009}), which is consistent with this study. Medicinal plants are rich in flavonoids and terpenes, which indirectly enhance and stimulate the immune system with their antibacterial effects. When the immune system is stimulated, the spleen size and protein synthesis increases, leading to refining and activation of the immune system in response to the disease (^{Nasiroleslami and Torki, 2010}). Regarding the high titer of antibodies against Newcastle Virus and SRBC in galbanum-containing treatments in the present study, the plant effectively boosted the immune system compared to the antibiotic, which is consistent with ^{Feizi and Nazari (2011)} and ^{Ghalamkari et al. (2011)}. The response rate of the immune system varies based on genetic variation (^{Webster et al., 2006}). In addition to genetic factors, non-genetic factors such as diet supplements that affect growth, can change or modify the expression of the genes responsible for immune sensitivity by altering antibody production and immune maturation. Herbal medicines eliminate harmful bacteria in the intestines, help the digestive system to better absorb dietary nutrients and cause further growth of cells, which consequently increases the production of immunization compounds (^{Okoro et al., 2016}). Various compounds in medicinal plants can stimulate lymphoid organs due to their nutritional and antioxidant effects. They can contribute to amplification and proliferation of chicken embryonic fibroblast cells that play a role in the development of the immune system and bone marrow (^{Mahanta et al., 2017}). Regarding the effects of medicinal plants on broiler immunity, they can increase the percentage of lymphocytes and heterophile, indicating their beneficial effects on immunity (^{Al-Jaff, 2011}; ^{Nacimento et al., 2020}). Additionally, free radicals is an important mechanism of cell damage (^{Kumar et al., 2003}).

The high level of total protein, albumin, and globulin in the 10 g galbanum treatment can be attributed to the increased nutrient absorption such as protein and its presence in blood serum. It has been reported that galbanum powder reduces the harmful gastrointestinal microbial populations and, therefore, the degradation of protein and amino acids. As a result, absorption increases, improving nutrient digestibility and serum concentration of total protein, albumin, and globulin (^{Lee et al., 2003}; ^{Ghazvinian et al., 2018}).

A decrease in total cholesterol, triglyceride and LDL levels, as well as a significant increase in HDL in the treatments containing galbanum compared to the control and antibiotic-containing treatment demonstrates the effectiveness of the plant in modifying blood lipids. ^{Abdel-Hafez et al. (2017)} stated that the decrease in abdominal fat is due to increased populations of beneficial bacteria such as Bacillus subtilis. These bacteria further reduce the activity of acetyl coenzyme A carboxylase by excreting bile acids, thereby reducing the synthesis of fatty acids and their availability for esterification reactions and production of triglycerides for storage in the adipose tissue.

The role of medicinal plants in reducing cholesterol and triglycerides (^{Hosseini et al., 2013}) is consistent with our results. Supplementation can be effective in lowering cholesterol levels due to the activity of lactic acid bacteria by producing bile-degrading enzymes and their deconjugation, as well as by decreasing the pH of the intestinal tract (^{Jahromi et al., 2016}). Solubility of unconjugated bile acids decreases at low pH, resulting in less intestinal absorption and more excretion in the stools (^{Jahromi et al., 2016}). As a result, the liver converts more cholesterol into bile to rebuild the cycle of bile acids, hence decreasing the concentration of cholesterol in tissues and blood (^{Ali et al., 2007}). Herbal ingredients inhibit the activity of 3-hydroxyl 3-methylglutaryl-coenzyme A (HMG-COA) liver reductase (^{Souri et al., 2015}). This is a key enzyme in the regulation of cholesterol synthesis. As it has been reported, there is a link between the activity of HMG-COA reductase, serum cholesterol and lipoproteins in broilers (^{Iqbal et al., 2018}). 5% HMG-COA reductase inhibitory activity can reduce serum cholesterol, triglyceride and LDL of poultry by 1% and also increase HDL (^{Safa and Al-Beitawi, 2009}). ^{Jeong and Kim (2015)} tested the hypothesis that a medicinal herb used in the diet could restrain the biosynthesis of isopentenyl pyrophosphate, a precursor to cholesterol synthesis. ^{Ajuwon (2016)} reported that poultry diets containing medicinal plants increased the microbial population of lactobacilli in the intestine and these lactobacilli can metabolize and absorb cholesterol in the small intestine and also reduce its absorption to the bloodstream.

^{Rostami et al. (2020)} investigated the effects of Thymus vulgaris extract in comparison with some common feed additives on performance, blood biochemical parameters and antibody response of broiler chickens under heat stress. They suggested that thyme extract at 500 mg/ kg of diet can be an alternative to common feed additives to improve growth performance and health benefits of heat-stressed broilers.

The present study shows that dietary inclusion of galbanum powder is effective in improving performance and carcass characteristics of broilers, increasing the immune response without adverse effects on blood parameters.