Study on Application of Compound Essential Oil in Diet of Meat Rabbits

Su Xiangyu¹, He Jianbo¹, Guo Shenglan¹, Huang Mingya^2,3, Li Zhizhong^2,3, Lei Yan^2,3, Guo Chunhua*

1. College of Animal & Veterinary Sciences of Southwest Minzu University, Chengdu 610041;

2. DadHank (Chengdu) Biotech Corp., Chengdu 611130;

3. Sichuan Animal Feeding Regulation Engineering Technology Research Center, Chengdu 611130.

Abstract: To compare the effects of three kinds of compound essential oils on the health, growth performance and economic benefits of weaned rabbits, 240 healthy 33 days old IRA meat weaned rabbits with similar weight were selected and divided into four groups, each group had 15 replicates, and each replicates had 4 rabbits. Control group was fed(constituted) with the basic diet. Group Ⅰ, Ⅱ, and Ⅲ were fed with the test diet supplemented with different compound essential oils (300 mg/kg) in the basic diet, respectively, for 42 days. The results showed that: (1) The diarrhea rate (P=0.061) and mortality rate (P=0.002) of groups Ⅰ, Ⅱ, and Ⅲ were lower than those of control group; (2) Compared with control group, the daily gain of test groups Ⅰ, Ⅱ, and Ⅲ increased by 9.95%, 12.54% and 13.71% respectively (P=0.009), and the food intake increased by 9.98%, 11.85% and 3.12% respectively (P<0.001), but the difference among feed-gain ratio of each test group was not significant (P=0.187); (3) The economic benefit of test group Ⅰ, Ⅱ, and Ⅲ were 1.85, 3.81 and 1.83 times higher than that of control group respectively. In conclusion, adding compound essential oil to diet can enhance (improve) the health of weaned rabbits, reduce diarrhea rate and mortality, increase food intake and growth rate, and obtain better economic benefits. Among them, compound essential oil Ⅱ has the best effect, with an average gross profit of （CNY）11.99 yuan/rabbit.

Key words: Meat rabbit, Compound essential oil, Growth performance, Economic benefit

In the current production of meat rabbits, suckling young rabbits are generally weaned at 30-35 days old. However, due to the rapid growth and development of young rabbits before and after weaning, incomplete development of gastrointestinal function, insufficient secretion of endogenous enzymes, unsound nerve regulation function, and factors such as weaning stress and environmental changes (Zheng Jianting et al., 2020) ^[1], pathogenic microorganisms, such as Escherichia coli, breed in young rabbits, causing diarrhea, flatulence, depression, anepithymia, and will eventually lead to death, causing huge economic losses to farmers.

In the past, antibiotics and other drugs were added to diet or drinking water of young rabbits to treat bacterial diseases, but the resulting problems such as bacterial drug resistance and drug residues, were contrary to people's pursuit of green and healthy eating habits, leading to consumer panic and other problems. On July 1, 2020, China officially banned the addition of antibiotic growth promoting feed additives in diet, so it is urgent to find new green additives that can replace antibiotics.

The natural and residue free characteristics of plant essential oils in nature have been widely concerned by people. Plant essential oils have significant effects in bacteriostasis, antioxidation and improving the anti-stress ability of animals. Existing research shows(demonstrates) that adding plant essential oil to diet of young rabbits can effectively reduce the diarrhea occurrence of meat rabbits and increase the average daily gain of meat rabbits (Sun Haitao et al., 2018) ^[2].

Plant essential oil has strong liposolubility, can quickly pass through the cell membrane, change the permeability of cell membrane and mitochondrial membrane, leading to the loss of content (Burt, 2004) ^[3] and inhibit the respiration of microorganisms. Many plant essential oils can effectively reduce the growth and reproduction of gram-positive and gram-negative bacteria and inhibit or sterilize most animal and plant pathogens (Bajpai, 2009; He, 2007) ^[4-5]. Sun Haitao et al. (2018) reported that adding 5% oregano oil to diet of meat rabbits can significantly reduce the content of Escherichia coli and lactobacillus in the cecum of young rabbits ^[6]. Wang Gaiqin et al. (2014) found that carvacrol, cinnamaldehyde, thymol and eugenol can improve the intestinal flora, significantly reduce the number of harmful bacteria such as Escherichia coli, salmonella and staphylococcus aureus. Among them, cinnamaldehyde has the most obvious antibacterial effect ^[7]. Liu Yang et al. (2013) ^[8] added 200 mg/kg cinnamaldehyde to broiler diet can significantly reduce the number of Escherichia coli and increase the number of lactobacilli in broilers.

Oxidative stress is a common problem in animal production. Because young rabbits can not adapt to the changes in formula diets and new environments in time after weaning, it is easy to cause oxidative stress in young rabbits, increase the production of free radicals or reduce the ability to remove free radicals, cause disorders in the body oxidation system and antioxidant system, lead to the process of oxidative damage caused by the accumulation of free radicals in the body (Wen Pengfei, 2017) ^[9], and cause intestinal inflammation in young rabbits, anorexia and the increase of diarrhea incidence, which will eventually lead to the death of young rabbits and cause huge economic losses, if they can not be treated in time. Wang Dongde et al. (2013) ^[10] found that adding 100 mg/kg oregano oil to diet of meat rabbits can significantly increase the activities of SOD, GXH-Px and CAT in the liver of meat rabbits, and improve the antioxidant capacity of meat rabbits. Wang Lan et al. (2019) ^[11] found that adding 200 mg/kg of mixed plant essential oil, the main components of which are thymol, carvacrol and cinnamaldehyde, to broiler diet can significantly increase the activity of total superoxide dismutase and the content of immunoglobulin in the blood of broilers, and significantly improve the antioxidant capacity of broilers.

Before and after weaning, because the growth and development of young rabbits are immature and the development of immune system is not perfect, in addition, the house environment is semi-open or fully open. In case of severe external temperature changes, it is very easy to cause cold, diarrhea, anorexia and reduce productivity. Tian Mei et al. (2019) ^[12] found that adding 100 mg/kg thymol to diet of meat rabbits can significantly improve the growth performance of meat rabbits under high temperature environment, promote rabbit meat production, reduce the fat content around the rabbit kidney and scapula, and improve the oxidation stability of rabbit meat. Sun Haitao (2018) ^[6] found that adding 5% oregano oil to diet of meat rabbits can increase the content of IgG in the serum of meat rabbits and improve the immunity of meat rabbits. Adding 500 g/t thyme essential oil to diet can increase the IgA content in small intestine, especially in duodenum, enhance the intestinal barrier function, maintain the integrity of intestine, reduce the content of malondialdehyde in kidney (Zhu Xiaolei, 2013) ^[13], and adjust the intestinal flora to alleviate intestinal inflammation and reduce the incidence of diarrhea (Xu et al., 2018; He et al., 2017) ^[14-15]. 

Zheng Jianting et al. (2019) ^[16] found that the addition of apple pomace in the diet of meat rabbits had no significant impact on the slaughter performance, meat quality and chemical composition of muscle. Yuan Kang (2007) ^[17] found that adding 8% beet pomace in the diet of meat rabbits can significantly improve the slaughter performance of meat rabbits, and the addition of thymol in the high-temperature environment can improve the water holding capacity, muscle color and oxidation stability of rabbit meat ^[12]. It has also been found that essential oil can protect muscle from lipid peroxidation, reduce dripping loss and enhance antioxidant activity ^[18].

The purpose of this test to study the effects of three kinds of compound essential oils on the performance, health status and economic benefits of weaned meat rabbits, so as to provide experimental basis for the non-resistant feeding meat rabbits.

1 Materials and Methods

1.1 Test materials

This experiment was conducted in a rabbit farm in Jintang County, Sichuan Province from July 6 to August 17, 2020. The experimental meat rabbit was IRA rabbit.

The main components of compound essential oil Ⅰ are 10.0% of cinnamaldehyde, 3.0% of thymol, 1.5% of eugenol and 6.0% of carvacrol, the main components of compound essential oil Ⅱ are 12.0% of cinnamaldehyde, 6.0% of carvacrol and 3.0% of natural essential oil extract, and the main components of compound essential oil Ⅲ are 10% of thymol, 9.0% of carvacrol and 2.5% of butyric acid. Three kinds of compound essential oil products are provided by DadHank (Chengdu) Biotech Corp. 

1.2 Test design

This experiment set up four groups, that was one control group and three test groups, and three different compound essential oils (300 g/t) were added to the basic diet as the diets for test groups. There were 15 replicates in each test group, four rabbits in each replicate, a total of 240 test rabbits. From 60 litters of 33-day-old weaned IRA meat rabbits, four healthy rabbits with a weight close to (0.798±0.083kg) were selected from each litter and randomly divided into four test groups by litter (Table 1). The test period is 42 days.

1.6 Data treatment and statistics

Sort the test data by Excel (Experimental data were compiled using Excel), and use one-way ANOVA to analyze the production performance indicators (weight gain, feed intake, feed-gain ratio) by SPSS statistical software and diarrhea rate and mortality by Chi-square test, where P<0.05 indicates significant difference and P<0.10 indicates there is a trend.

2 Test results and analysis

2.1 Effects of different treatments on health of growing rabbits after weaning (0-42 days)

The diarrhea rate and mortality of the weaned rabbits in each test group were shown in Table 1 and Figure 1.

During the test, the diarrhea rate in each test group was 1.05%-2.16%. And the diarrhea rate in test group Ⅰ, Ⅱ and Ⅲ was lower than that in control group, but the difference was not significant (P=0.061). The results were similar to those of Sun Haitao (2018), Xu (2018) and He (2017).

The overall diarrhea rate of rabbits in this test was generally low, and diarrhea mainly occurs in the week 2-3 after weaning. It should be noted that the number of diarrhea rabbits that may be observed was less than the actual number of diarrhea because the test rabbits were raised on the A-shaped double-row rabbit cage with three layers, and the rabbit hair（rabbits' fur） was thick, which is difficult to observe. This result was only for reference.

The mortality of rabbits in each test group was significantly(quite) different (P=0.002). The mortality of rabbit in test group was lower than that in control group. Among them, the mortality of rabbit in test group Ⅱ was the lowest (1.67%) and that in control group was the highest (26.27%).

The results showed that all three different kinds of compound essential oils had positive effects on improving the health of newborn rabbits and reducing diarrhea rate and mortality, and the effect of compound essential oil Ⅱ was better.

2.2 Effects of different treatments on production performance of growing rabbits after weaning (0-42 days)

Daily gain, feed intake and feed-gain ratio after weaning were shown in Table 2. During the whole test (Day 1-42), the daily gain of rabbits in test groups Ⅰ, Ⅱ and Ⅲ was highly significantly higher than that in control group (P=0.009) by 9.95%, 12.54% and 13.71% respectively; The feed intake of test group Ⅰ and Ⅱ was highly significantly higher than that of control group (P<0.001). The feed intake of test group I, II and Ⅲ was 9.98%, 11.85% and 3.12% higher than that of control group, respectively; However, there was no significant difference in the feed weight ratio among test groups (P=0.187).

The results showed that the three compound essential oils all had positive effects on improving food intake and daily gain, which was consistent with the conclusion that the essential oil groups could enhance the health of young rabbits.

3.3 Effect on economic benefits of growing rabbits after weaning (Day 0-42)

The gross profit was the total income of the meat rabbits sold in each treatment group after deducting the total feed input during the test period and the results were shown in Table 3. It can be seen from Table 3 that the economic benefit of the essential oil groups was better than that in control group. The economic benefit of the test group Ⅰ, Ⅱ and Ⅲ was 1.85, 3.81 and 1.83 times of that in control group respectively. Among them, the economic benefit of the test group Ⅱ was the highest, with a gross profit of （CNY）719.44 yuan, and an average gross profit of （CNY）11.99 yuan per animal. The gross profit of the test group Ⅰ and the test group Ⅲ were similar, with （CNY）426.53 yuan and （CNY）424.49 yuan respectively, while too more rabbits in control group died, only （CNY）149.50 yuan of gross profit was obtained.

3 Conclusion

Under the conditions of this test, compared with the control group, the three compound essential oil groups significantly reduced the diarrhea rate and mortality of growing rabbits after weaning, increased the feed intake and daily weight gain, and achieved better economic benefits. In general, the compound essential oil Ⅱ was the best, with an average gross profit of 11.99 yuan per rabbit. The effect of compound essential oil Ⅰ and Ⅲ was similar, but both results were better than control group.

注意！！！ 所有references的journal名字斜体。

[1] Zheng Jianting, Feng Guoliang, Cao Liang, et al. Effects of citric acid on growth performance, apparent digestibility of nutrients, serum antioxidant index and meat quality of growing meat rabbits [J]. Chinese Journal Animal Nutrition, 2020, 32(05): 2282-2289.

[2] Sun Haitao, Xie Hongmei, Jiang Wenxue, et al. Effects of a compound Chinese medicine on growth and development, serum biochemical indexes and intestinal development of meat rabbits from weaning to 2-month-old [J]. Feed Research, 2018, (04): 58-61+67.