Effects of Adding Compound Essential Oils to Diets on Growth Performance, Blood Indicators and Economic Benefits of Weaned Lambs
Effects of Adding Compound Essential Oils to Diets on Growth Performance, Blood Indicators and Economic Benefits of Weaned Lambs
Dong Airong1, Chen Qian1, Yu Miao2,3, Huang Mingya2,3,
Zhang Zhengfan1 Guo Chunhua2*, Lyu Jirong2*,3
1 College of Life Science and Technology, Southwest Minzu University, Chengdu 610041
2 DadHank (Chengdu) Biotech Corp., Chengdu 611130
3 Sichuan Animal Feeding Regulation Engineering Technology Research Center, Chengdu 611130
Abstract: The purpose of this test was to study the effect of adding compound essential oils to diets with different concentrate-to-crude ratios on the growth performance, blood parameters and economic benefits of weaned lambs. The (1 + 2 × 2) factor test design was adopted, with the essential oil types (compound essential oil 1, compound essential oil 2) and diet with different concentrated-to-crude ratios (50:50 and 70:30) as the two factors of the test. The 60 weaned black goats (Lezhi type) with an average weight of (19.54 ± 2.23) kg at 2 months of age (same number of male and female) were selected. The test goats were divided into 5 groups (CT, L-EO1, L-EO2, H-EO1, H-EO2 groups), with 4 repeats in each group and 3 goats in each repeat. The control group (CT) was fed with a medium-level concentrated (60:40) pellet total mixed ration (TMR) without adding compound essential oils. The L-EO1, L-EO2, H-EO1 and H-EO2 groups were fed with low-level concentrated（concentrate） feed (50:50) + compound essential oil 1 (EO1), low-level concentrated（concentrate） feed (50:50) + compound essential oil 2（EO2）, high-level concentrated（concentrate） feed (70:30) + EO1 and high-level concentrated（concentrate） feed (70:30) + EO2 pellet TMR, respectively. The adding amount of essential oil was 100 g/t. The pre-feeding period was 10 days and the positive test period was 30 days. The results showed that: (1) Compared with the group CT, the addition of compound essential oils in(to) the diet highly significantly increased the average daily feed intake (ADFI) of goats (P=0.002), but no significant effect (P>0.05) on the average daily gain (ADG) and feed-gain ratio (F/G). The F/G of the high-level concentrated feed group (70:30) was significantly lower than that of the low-level concentrated feed group (50:50) (P=0.035). The concentrated-to-crude ratio had no significant effect on goat DMI and ADG (P>0.05). (2) Compared with the group CT, the addition of compound essential oil in the diet highly significantly increased the albumin (ALB) level in goat serum (P=0.005), while the serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), urea nitrogen (UN), total protein (TP), glucose (GLU), triglyceride (TG), total cholesterol (T-CHO), lactate dehydrogenase (LDH) level was not significantly affected (P>0.05). The TG levels of goat serum in the group EO1 (L-EO1 and H-EO1) were significantly lower than those in the group EO2 (L-EO2 and H-EO2) (P=0.038), while the levels of other biochemical indicators were not significantly different from the group EO2 (P＞0.05). The serum ALB level of goats in the high-level concentrated feed group was significantly higher than that in the low-level concentrated feed group (P=0.040), while the UN level was significantly lower than that i n the low-level concentrated feed group (P=0.045). The dietary concentrated-to-crude ratio had no significant effect on other biochemical indicators (P>0.05). (3) The IgA level(content) in goat serum of group L-EO1, L-EO2, H-EO1 and H-EO2 were 96.0%, 49.0%, 29.2% and 44.7% higher than that in group CT (P>0.05). The essential oil and concentrated-to-crude ratio of diet had no significant effect on serum IgA, IgG and IgM (P>0.05). (4) Compared with the group CT, the addition of compound essential oils in the diet significantly increased the total SOD activity in goat serum (P<0.001), but had no significant effect on MDA level(content), GSH-Px enzyme activity, CAT activity and T-AOC activity (P>0.05). The total SOD activity in goat serum of group EO2 was significantly higher than that in group EO1 (P=0.015). There were no significant effects on MDA level, GSH-Px enzyme activity, CAT activity and T-AOC activity in goat serum (P>0.05). (5) Compared with group CT, the gross profit of group L-EO1, H-EO1 and H-EO2 increased by 13.70%, 16.71% and 13.90% respectively, while the gross profit of group L-EO2 decreased by 9.57% compared with CT. The gross profit of group EO1 was 12.78% higher than that in group EO2. The gross profit of high-concentrated feed group is 12.98% higher than that of low- concentrated feed group. In summary, under the conditions of this test, adding compound essential oil to diet could increase the feed intake, immunity and antioxidant capacity of goats, and the compound essential oil 2 was more conducive to improving the antioxidant capacity of the body, but the economic effect of goats in group EO1 was better than that of group EO2. High-level concentrated feed reduced the goat feed-gain ratio, which was more conducive to improving goat protein utilization efficiency, immune and antioxidant capacity, and obtaining the best economic benefits.
Antibiotics are secondary metabolites produced by bacteria, molds or other microorganisms or artificially synthesized substances that have a specific ability to kill microorganisms. The antibiotics applied in livestock and poultry production can be divided into two types: one is feed antibiotics, which are added to feed through certain technical means to play a role in disease prevention and growth promotion in production; The other is therapeutic antibiotics, which are administered by stockmen(feeding managers) to treat livestock and poultry through mixing in feed, injection and perfusion [1]. Due to the abuse of feed antibiotics, a series of problems such as drug residues, the emergence of resistant strains, and environmental pollution, have been caused, posing a potential threat to human health. In March 2019, the Ministry of Agriculture and Rural affair proposed the “Withdrawal Plan for Pharmaceutical Feed Additives”, requiring that the production of commercial feed containing antibiotic additives be banned from July 1, 2020. Therefore, safe, efficient and pollution-free alternatives to feed antibiotics have been widely used in feeding production in recent years. Currently, the commonly used substitutes for feed antibiotics include Chinese herbal medicine, enzyme preparations, microecological preparations, antimicrobial peptides, plant essential oils, acidifiers, oligosaccharides, etc. [2-3]. Plant essential oil is a secondary metabolite in plants, mainly distributed in flowers, branches, leaves, roots, barks, and fruits of plants [4]. Its composition is relatively complex, with a variety of active substances, mostly liquid at room temperature, and generally has a special volatile odor. As one of the effective substitutes for antibiotics, plant essential oils have been studied by many scholars due to their antibacterial properties [4], antioxidant properties [5] and immune activities [6]. Adding plant essential oil to diet of ruminants can inhibit the growth of harmful bacteria in some degrees, such as methanogens in the rumen, and can also promote the growth of dominant bacteria, such as Ruminococcus flavefaciens, Ruminococcus albus, and Fibrobacter succinogenes, improve rumen environment, enhance metabolism of protein in rumen and increase feed utilization efficiency [7-9].
The dietary concentrate-to-forage ratio in diet refers to the ratio of dry matter level of concentrated(concentrates) feed to roughage in diet formulation, and is an important factor in regulating the rumen internal environment. Appropriate dietary concentrate-to-forage ratio can not only improve digestive enzyme activity in the gastrointestinal tract, but also regulate rumen microflora, thereby improving the production performance and feed digestibility of ruminants [10]. It has been reported that low-level concentrated feed can cause metabolic diseases such as diarrhea, fatty liver and rumen flatulence in ruminants. Diets with high-level concentrated feed can lead to rumen acidosis, laminitis and ketosis in ruminants. Both are not conducive to the growth of ruminants, seriously affecting their production performance [11].
Currently, most studies on the effects of plant essential oils on ruminants have been conducted on the basis of in vitro culture, while only a few studies have verified the effects of plant essential oils on(in) non-ruminants. This test studied the effects of adding compound essential oils to diets with different concentrate-to-forage ratios on growth performance, serum biochemistry, immunity, and antioxidant capacity of weaned lambs, so as to provide test data for the application of plant essential oils in goat diets and the selection of diets with suitable concentrate-to-forage ratios for fattening lambs.
1.2 Test design
Adapting (1+2×2) factor test design, 60 2-month-old weaned black goats(60 weaned black goats at 2 months of age) (Lezhi type) with an average weight of 19.54 ± 2.23 kg (same number of male and female) were selected. According to a randomized block design, the test goats were divided into 5 groups, with 4 replicates in each group and 3 goats in each replicate. The control group (CT) was fed a total mixed pellet diet with concentrate-to-forage ratio of 60:40, without adding compound essential oils; Four test groups, L-EO1, L-EO2, H-EO1 and H-EO2 were fed a total mixed pellet diet consisting of low-level concentrated feed (50:50) + compound essential oil 1, low-level concentrated feed (50:50) + compound essential oil 2, high-level concentrated feed (70:30) + compound essential oil 1, and high-level concentrated feed (70:30) + compound essential oil 2, respectively, and the adding amount of compound essential oil was 100 g/t (see Table 1). The pre-feeding period was 10 days, and the trial period was 30 days.
1.5.2 Blood parameters
After the test, six goats (three males and three females) were randomly selected from each group. When fasting, 10 mL blood was taken from each goat's jugular vein, placed in two 5 mL blood collection tubes, kept still at 4℃ for 2 to 4 hours, centrifuged at 3500 r/min for 10 minutes, collected upper serum samples, divided it into three 2 mL EP tubes, and stored at -20℃.
1.6 Data analysis
Summarize the test data using Excel 2010 and perform variance analysis using SPSS 18.0 software. (1) Using the single df contrast to compare the differences between the control group and the four test groups; (2) After removing the control group, the four test groups were subjected to a two-factor analysis of variance (two-way ANOVA), with a mathematical model of diet effect + essential oil effect + interaction effect. The results were expressed as mean ± standard deviation, with P<0.05 indicating significant differences, 0.05<P<0.10 indicating a trend, and P>0.05 indicating insignificant differences.
3 Discussion
3.1 Effect of adding compound essential oils to diets on growth performance of weaned lambs
The dietary concentrate-to-forage ratio can improve the level of concentrated feed in diet by adjusting the structure and nutritional level of diet. An appropriate dietary concentrate-to-forage ratio can regulate the rumen microbial community and the activity of digestive enzymes in the gastrointestinal tract, thus improving the production performance and feed utilization of ruminants. Hao Haizhi et al. [10] studied the effect of different concentrate-to-forage ratio (40:60, 50:50, 60:40) in corn and straw-based total mixed rations on the production performance of meat sheep. The results showed that the average daily gain and daily feed intake of the 60:40 group were higher than those of the 40:60 and 50:50 groups, while the feed-gain ratio was the lowest. In this test, the feed-gain ratio of the 70:30 group was significantly lower than that of the 50:50 group, which was similar to the results of previous studies. Gao Linqing et al. [12] found that the average daily gain of the 70:30 group was significantly higher than that of the 50:50 and 40:60 groups. Xu Xiangting et al. [13] found that with an increase in the concentrate-to-forage ratio in diet, the average daily gain showed an increasing trend, while the average daily feed intake and feed-gain ratio showed a gradual decrease. Similar results were obtained by Yin Fuquan et al. [14]. In this test, the control group had a concentrate-to-forage ratio of 60:40, the low-level concentrated feed group had a concentrate-to-forage ratio of 50:50, and the high-level concentrated feed group had a concentrate-to-forage ratio of 70:30. Both the high and low-level concentrated feed groups had higher daily gain and feed intake than the control group, which was inconsistent with previous research results, which may be related to the addition of compound essential oils in both low and high-level concentrated feed groups. Adding plant essential oils to diet can inhibit mold growth, maintain the freshness of feed, and the essential oils also had a special volatile aroma that induces animals to increase feed intake. A large number of studies had shown that adding plant essential oils to diets of ruminants can regulate rumen nitrogen metabolism, improve rumen fermentation patterns and improve feed utilization efficiency [9, 15-16]. Yao Xixi et al. [17] found that adding oregano oil to diet of Holstein dairy cows can effectively lower the diet temperature, improve palatability, increase dry matter intake and increase milk production. Jiang Hui et al. [18] also found that compared with the control group, adding oregano oil can significantly improve the average daily gain of Hexi Cashmere goats. The main reason may be that oregano oil had a special volatile aroma, which had an appetizing effect and promotes feed intake, while also improving the growth of rumen microorganisms, enhancing enzyme activity, which was beneficial for feed digestion and can promote animal growth. In this test, the addition of the compound essential oil significantly increased the goats' feed intake and daily gain. Among them, the groups added essential oil 1 showed better results than the groups added essential oil 2. This may be related to the main active ingredients of the two compound essential oils and further research needs to be done.
3.2 Effects of adding compound essential oils to diets on serum biochemical indicators of weaned lambs
Changes in serum biochemical indicators reflect the health, nutritional status and metabolic state of an animal. GLU is the main energy source required for animal metabolism, growth and development and its level is an important indicator of energy metabolism in the body. In ruminants, 85% of GLU is produced through gluconeogenesis, while the remaining 15% is from energy absorbed and utilized by the digestive tract [19]. Studies have shown that the concentration of GLU in animal blood should not exceed 6.1 mmol/L, and the GLU level in high-yielding animals is higher than that in low-yielding animals within the normal blood glucose concentration range [20-21]. In this test, the GLU level in each group was within the normal range, and there was no significant difference between the groups. The four treatment groups that were administered with a compound essential oil had higher GLU level in goat serum compared to CT group, which may be related to their feed intake. The feed intake of the group that received the compound essential oil was significantly higher than that of CT group. An increase in feed intake leads to an increase in energy intake of the animals, thus causing an increase in blood sugar concentration. LDH is an important enzyme substance involved in glycolysis and gluconeogenesis processes and its main function is to catalyze the oxidation-reduction reaction between lactate and pyruvate. LDH is present in the cytoplasm of all tissues and cells in the body, with the kidneys having a higher level. In this test, essential oil and concentrate-to-forage ratio had no significant effect on LDH level in serum. The level of TP and ALB reflects the absorption and metabolism of protein in the body, and an increase in these levels is beneficial for improving metabolic levels and immune function. ALB is secreted by liver cells, and when liver function is impaired, the liver's ability to eliminate pathogens in the body will decrease, resulting in a decrease in ALB synthesis. AST and ALT are also indicators of liver function, and their concentrations will increase when the level of protein metabolism in the animal body increases or when liver cells are damaged due to inflammation, toxicity, etc. [22-23] In this test, the ALB level in the serum of four treatment groups that received the compound essential oil was significantly higher than that of CT group, indicating that the addition of compound essential oil was beneficial for promoting animal liver function and improving immune function. However, there was no significant difference in serum ALB level between the two types of compound essential oils, and the essential oils had no significant effect on TP, AST and ALT in serum. A study by Lin Bo et al. [23] found that adding 0.5 g/d of plant essential oil active ingredients to diet of Hu sheep reduced the AST level, which was inconsistent with the results of this test, and may be related to the main active ingredients of the essential oil. The serum ALB level in the high-level concentrated feed groups were significantly higher than that in the low-level concentrated feed groups, but concentrate-to-forage ratio had no significant effect on TP, AS and ALT level in serum, which is similar to the results of a study by Cheng Guangmin et al. [24]. UN is a product of protein metabolism, and its level is an important balance indicator between protein and amino acids. Good protein metabolism in body leads to a decrease in UN level in serum, and when impaired renal excretion function or problems in protein conversion can lead to an increase in UN level in the serum [25]. In this test, the high-level concentrated feed groups had significantly higher serum UN level than the low-level concentrated feed groups, which was inconsistent with the results of Xu Xiangting et al. [13] and may be related to the composition of diet and test animals. TG and T-CHO are components of blood lipids, and their levels can reflect the absorption and metabolism of lipids [26]. In this test, the concentrate-to-forage ratio had no significant effect on the TG and T-CHO level in blood, which was inconsistent with the results reported by Guo Wanzheng et al. [27] and Zhou Rong et al. [28], and may be related to the different composition of diet. Liu Lishan et al. [29] found that adding oregano oil to diet can significantly reduce the TG level in Holstein bulls' blood, which may be because adding essential oil can improve the rumen microbial environment, increase feed conversion rate, increase protein intake and enhance protein metabolism. In this test, the TG level in the essential oil 1 groups was significantly lower than that in the essential oil 2 groups, indicating that there are differences in the metabolism of lipid substances in the body of goats between the compound essential oil 1 and essential oil 2, which may be related to their main components. ALP is mainly synthesized and secreted by osteoblasts and liver, and it is an important indicator reflecting bone metabolism and plays a positive role in the process of bone mineralization. Guo Wanzheng et al. [27] studied the feeding Hu sheep with diets different concentrate-to-forage ratios (5:5, 4:6 and 3:7) of total mixed pellet diet, and the results showed that the biochemical indicators of Hu sheep were within the normal range, and there was no significant difference in ALP level among the groups. Song Shuzhen et al. [30] found that the extract of Echinacea purpurea could significantly increased the serum ALP of fattening sheep. The above research results are inconsistent, and it is speculated that it may be related to the types of essential oils and their main active ingredients.
3.3 Effects of adding compound essential oils to diets on serum immune indicators of weaned lambs
Immunoglobulin is a specific protein produced by B lymphocytes. IgA, IgG and IgM are immunoglobulins involved in humoral immune response in the body(organism), and they are an important part of the immune system. IgM is the primary antibody involved in the initial immune response, while IgG is the primary antibody involved in humoral immunity. Immunoglobulins have antimicrobial and antiviral properties, and a decrease in their levels indicates a decrease in the body's immune function. Numerous studies have shown that plant essential oils have the ability to enhance immune function in the body. The immune properties of plant essential oils are mainly achieved by enhancing the body's antioxidant function and relieving various inflammatory reactions, thereby improving immunity. [6] Zhang Qiang et al. [32] found that adding 0.025% of plant essential oils to low-energy feed significantly increased the serum levels of ALB, IgA and IgG in piglets. Similar results were reported by Liu Meng [33], Wang Shunan [34], Zhou Xuanwu [35] et al. In this test, the ratio of essential oil to dietary concentrated-to-forage ratio had no significant effect on serum immune indicators, and the addition of essential oils did not cause significant differences in IgA, IgG, and IgM levels, compared to the control group. This result was inconsistent with the aforementioned studies, and it was speculated that the differences may be related to the active ingredients of the essential oils and the test animals used.
3.4 Effect of adding compound essential oil to diet on serum antioxidant indicators of weaned lambs
Antioxidant capacity refers to the body's ability to fight against oxidative free radicals. When animals are exposed to certain environmental factors, the body produces a large number of free radicals, which can lead to the occurrence of diseases [36]. Under normal physiological conditions, the nutritional status of the body maintains a dynamic balance with the content of free radicals. Once this balance is disrupted, the production of free radicals will increase, causing oxidative damage to the body's cells [37]. MDA is a lipid peroxide product in the body [38], while GSH-Px and SOD are two important enzymes that resist lipid peroxidation in the body. They can effectively remove and prevent the chain reaction of free radicals, thus protecting the structure and function of cell membranes [39]. CAT is a type of antioxidant enzyme widely distributed in biological organisms that promotes the decomposition of hydrogen peroxide (H₂O₂) and protects cells from free radical damage [40]. T-AOC is a comprehensive indicator of body's antioxidant system status, reflecting the combined effects of various antioxidant enzymes in the body [41]. Studies have found that most plant essential oils contain antioxidant active ingredients, which can be classified into direct or indirect antioxidant activities based on their antioxidant mechanisms [5]. Wang Xinwei et al. [42] found that oregano oil, carvacrol, citral and cinnamaldehyde had good antioxidant properties, and their antioxidant index increased with their concentration. Chen Huiliang et al. [38] added 10% oregano oil to diet of dairy cows, and the serum SOD and GSH-Px activities increased by 6.97% and 10.86%, respectively, while the serum MDA level decreased by 7.94%. Song Junshuai et al. [43] found that adding 200 mg/kg of compound plant essential oil to diet can significantly improve the ADG, SOD activity and T-AOC of piglets, as well as significantly increase the IgG level in piglet serum. In this test, the total SOD activity in serum of four treatment groups that added compound essential oil was significantly higher than that of CT group without essential oil. Among the two compound essential oils, the total SOD activity in goat serum in the essential oil 2 groups was significantly higher than that of the essential oil 1 groups. Essential oil had no significant effect on the MDA level and GSH-Px, CAT and T-AOC activity in serum, indicating that adding compound essential oil to goat diet can improve the animal's antioxidant capacity to a certain extent, which was similar to the results of previous studies, and the effect of adding compound essential oil 2 was better than essential oil 1. The dietary concentrate-to-forage ratio is an important indicator for measuring the nutritional characteristics of ruminant diets. An appropriate dietary concentrate-to-forage ratio can improve the body's antioxidant capacity and promote animal health. Hou Zhigao et al. [44] studied the effects of nine different levels of concentrated feed in diet on the rumen environment and serum antioxidant capacity of cows, and found that the SOD activity in rumen was significantly higher in group with 55% concentrated feed, the MDA level was significantly lower than that in other groups, the T-AOC activity, as well as the SOD and T-AOC activity in the serum, were significantly higher than in other groups with different levels of concentrated feed. Research conducted by Shi Liguang et al. [45] investigated the effects of different concentrate-to-forage ratios (50:50, 20:80 and 80:20) in diet on the antioxidant capability of Hainan black goats. The results showed that goats fed diets with a concentrate-to-forage ratio of 20:80 and 80:20 had lower T-AOC, ACT and GSH-Px activities compared to the control group (50:50), while MDA levels were significantly higher. In this test, the total SOD activity in the serum of goats in the high-level concentrated feed group was significantly higher than that in the low-level concentrated feed group. However, the concentrate-to-forage ratio had no significant effect on the MDA level and GSH-Px, CAT and T-AOC activities in the serum, which differed from previous studies. This difference may be due to the design of the concentrate-to-forage ratio in diet, as well as differences in test animals used [11].
3.5 Effect of adding compound essential oil to diet on economic benefits of weaned lambs
The main factors that determine the economic benefits in animal production include average daily gain, market price and feed cost. The nutrients in diet are digested and absorbed to form body deposits, so the average daily gain reflects the changing patterns between the comprehensive nutritional value of the diet and feed intake, feed conversion rate. From the economic benefit table, it can be seen that after adding compound essential oils, the feed intake of both the high-level concentrated feed groups and low-level concentrated feed groups was higher than that of control group, while the feed intake of high-level concentrated feed groups was lower than that of low-level concentrated feed groups. The total feed expenditure of high-level concentrated feed groups was higher than that of low-level concentrated feed groups, but the weight gain of the high-level concentrated feed groups was higher than that of low-level concentrated feed groups. Therefore, the profit of high-level concentrated feed groups was higher than that of low-level concentrated feed groups. Xu Xiangting et al. [13] and Wang Xiaoguang et al. [47] all believed that the level of concentrated feed and daily gain were key factors affecting economic benefits, which was consistent with the results of this study. In this study, L-EO1 and L-EO2 were both low-level concentrated feed group, while H-EO1 and H-EO2 were high-level concentrated feed group. The economic benefit of L-EO1 was 25.73% higher than that of L-EO2, and the economic benefit of H-EO1 was 2.47% higher than that of H-EO2, indicating that the economic benefit of essential oil 1 was superior to that of essential oil 2.
Fund Project: National Key Research and Development Program—"Research and Development of Comprehensive Technology for Prevention and Control of Major Animal Diseases and Efficient and Safe Feeding" (2018YFD0502002); 2019 Chengdu Innovative Research and Development Project—"Research and Development of New Drug and Food Homologous Attractant" (2019-YF-05-01028-SN)
Author Profile: Dong Airong (1994-), female, Tujia people, from Youyang, Chongqing, is studying for a master's degree in animal nutrition and feed science. Email: 1427255635@qq.com
* Corresponding author.
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