Chinese herbal medicines are rich in nutrients and biologically active substances (Hossain et al., 2012). In addition to disease prevention, treatment, and enhancing the body's immunity, they can also improve feed conversion efficiency and promote animal growth and development (Qiao et al., 2016). Zhong et al. (2012) found that the addition of Astragalus polysaccharides to the diet increased the daily feed intake of lambs. Also, Qiao et al. (2016) found that the addition of Chinese herbal medicine increased the average daily gain, final body weight and feed conversion efficiency of Holstein dairy cows. The results of an experiment on the various levels of a Chinese herbal medicine complex on the growth performance of simulated Taiwan country chickens showed that the complex at 0.3% increased both average daily weight gain and feed conversion ratio (Li et al., 2012). In contrast to the above experiments, the results of the present experiment indicated that dietary supplementation of 10% TGR did not affect the growth performance of sheep. However, 15% TGR supplementation decreased the average daily gain and increased the feed conversion ratio of sheep. This may have been related to the effect of puerarin, an active ingredient in Tongmai Granule, on weight loss and regulation of fat metabolism (Wang et al., 2017). However, its related mechanism needs further study.
Digestibility is a major indicator of the absorption and utilization of feed nutrients in animals, and is influenced by factors such as feed quality and animal feeding (Lin et al., 2006; Eiras et al., 2014). At present, there is little research on the effect of TGR on the apparent digestibility in ruminants. However, studies have shown that Chinese herbal medicine has the effect of enhancing animal body metabolism and improving nutrient digestibility and utilization. For example, the apparent digestibility of organic matter, crude protein and acid detergent fiber increased when heat stressed beef cattle diet was supplemented with a traditional Chinese medicine prescription (Song et al., 2014). In the present study, the digestibility of dietary CP, ADF and NDF decreased with an increase in TGR addition. Conversely, the digestibility of NDF in the 15% TGR group was significantly lower than that in the control group. This result is inconsistent with that of Kim et al. (2002) who reported that the addition of dried Wormwood (Artemisia sp.; a traditional Chinese medicine) increased the feed intake and apparent digestibility of dry matter, total digestible nutrients, crude protein and crude fibre in sheep. The decreased digestibility in the present study may be due to the fact that Tongmai granules contain more fibrous substances. In this experiment, the addition of TGR increased the apparent digestibility of organic matter and crude fat. This agrees with findings by Qiao et al. (2012) who found that the addition of Fructus Ligustri Lucidi extract to sheep diet increased the digestibility of dry matter and organic matter and had no effect on CP, ADF, and NDF digestibility in sheep. This suggests that TGR can stimulate rumen degradation of non-structural carbohydrates in sheep.
Blood biochemical parameters usually reflect the health of an animal. These parameters are vital indicators of the physiological and nutritional status of animals (Alagawany and EI-Hack, 2015). Blood glucose level is a direct response of animals’ body to sugar absorption, transport, and metabolic homeostasis. In the current study, dietary inclusion of TGR had no significant effect on serum TC, TG and GLU concentrations. The results indicate that TGR supplementation has no adverse effects on the heart and liver, as well as the occurrence of hyperlipidemia in sheep, because TC and TG concentrations in the blood are strongly associated with cardiovascular diseases (Chanjula and Cherdthong, 2018). However, the serum GLU concentrations had a downward trend in the present study, which may be related to the activity of Pueraria, the main medicinal ingredient in TGR, in lowering blood glucose (Xie and Du, 2011).
The levels of serum LDL-C and HDL-C are important indicators that reflect the lipometabolic status in animals. HDL-C has a protective effect on blood vessels, which is generally considered to be good cholesterol and resistant to atherosclerosis, whereas LDL-C is prone to arteriosclerosis when it appears at high levels (Chen et al., 2016). The results of this study indicate that there was no significant difference in serum LDL-C content from day 15 to day 60 of the experimental period. On day 15, the 10% and 15% TGR groups significantly increased the HDL-C content, and on day 60, the 15% TGR group significantly increased the HDL-C content, suggesting that dietary TGR addition could improve the cardiovascular system of sheep. This may be due to TGR’s ability to activate blood circulation and treat diseases such as coronary heart disease and atherosclerosis.
BUN is an indicator of protein metabolism and dietary amino acid balance in animals. An increase in BUN levels reflects the impaired renal function/glomerular function (Blome et al., 2003; Tong et al., 2008). Our results indicated that serum BUN content was not affected by TGR addition except on day 30 of the experiment where the BUN content in the 15% TGR group significantly reduced.. This shows that TGR has no negative effects on renal function. TP is composed of GLB and ALB. It has been found that serum TP content is an indicator for assessing the nutritional and metabolic status of an organism, and can reflect the health and immune levels in the organism. TP measurements are based on dietary protein content, liver metabolism and even protein loss caused by some lesions (Wang et al., 2011; Ortuno et al., 2001; Chen et al., 2016). In the present study, dietary addition of TGR had no significant effect on the total protein, albumin, and globulin content throughout the feeding period.
Immunoglobulin molecules (IgA, IgG and IgM) which are associated with humoral immunity are produced by the differentiation and proliferation of B lymphocytes. They are a class of globulins with antibody activity or chemical structure similar to antibody molecules, which can specifically bind to antigens and play an important role in regulating immune responses. The level of its content can reflect the status of the body's immune function (Li et al., 2016; Li et al., 2018). In this study, Dietary TGR supplementation increased the content of serum IgM, IgA and IgG in sheep. This indicates that TGR can increase the number of lymphocytes and improve the rate of lymphocyte transformation. Furthermore, the increase in immunoglobulin content reflects the enhancement of humoral immune function in sheep.
Ruminal pH is an important indicator that reflects the level of rumen fermentation, and mainly affected by factors such as the type of diet and the amount of saliva secreted (Anantasook et al., 2013). Low ruminal pH has been shown to have a negative effect on fibre digestion and attachment of bacteria to plant cell walls (Cheng et al., 1984). In the present study, ruminal pH was significantly increased with the addition of 15% TGR and ranged from 5.83 to 6.31. These values were optimal for rumen fermentation (Dalley et al., 1997). The increase of pH may be due to the decrease in rumen TVFA. This indicates that dietary addition of TGR has the potential to regulate the efficiency of nutrient digestion and the rumen fermentation pattern.
NH3-N is the main source of N in the process of microbial protein synthesis in the rumen, and plays a vital role in efficient microbial fermentation of feed. The level of ruminal NH3-N represents a balance between microbial protein synthesis and rumen protein degradation (Erdman et al., 1986; Cherdthong and Wanapat, 2013; Wang et al., 2016). Previous studies indicated that the optimal concentration of NH3-N in the rumen is 0.35–29 mg/dL (Owens and Bergen, 1983). In the current study, the rumen NH3-N concentration in each group was within the normal range, which can meet the needs of rumen microbial growth. However, dietary inclusion of 15% TGR significantly increased the concentration of ruminal NH3-N. These findings indicate that supplementation of high levels of TGR may result in an increased NH3-N concentration, which in turn may affect microbial fermentation of feed in the rumen.
Volatile fatty acids are the main products of carbohydrate fermentation by various microorganisms in the rumen. They play the role of maintaining the rumen environment and providing energy for the animals’ body. In the present study, dietary inclusion of 10% TGR did not affect the concentration of TVFA but they had an increasing tendency. It shows that adding a suitable amount of TGR can help rumen microorganisms to produce more VFA, which can provide more energy for animals. There are some studies on the effects of herbal medicines on ruminal VFA formation. Qiao et al. (2012) observed higher concentrations of TVFA and propionate in sheep supplemented with Fructus Ligustri Lucidi extract at 300 or 500 mg/kg DM. Furthermore, Zhong et al. (2012) reported higher propionic acid concentration and lower acetic acid to propionic ratios in ruminal fluid when Astragalus polysaccharide and Astragalus membranaceus root was fed to weaned lambs. Also, Jin et al. (2018) found no changes in TVFA, propionate concentration and acetate: propionate proportion, but higher acetate and lower butyrate concentrations in growing lambs when diet was supplemented with 500 g/kg Urtica cannabina. In contrast, results of the current study indicate that dietary inclusion of 15% TGR significantly decreased the concentration of acetic acid, propionic acid, butyric acid and TVFA, which may be related to the type, dosage and form of the residue. This indicates that excessive addition of TGR may adversely affect rumen microorganisms, and then reduce rumen fermentation function.
This study demonstrated that dietary supplementation of TGR can improve the apparent digestibility of crude fat and organic matter, and improve the anti-atherosclerosis ability and immune function of Doper x Small Tail Han hybrid female lambs. However, dietary supplementation of TGR up to 15% may have adverse effects on growth performance, slaughter performance, and digestibility of NDF, as well as rumen fermentation patterns. Therefore, under the conditions of the current experiment, it can be concluded that the addition of TGR up to 10% yielded the best results in improving performance in sheep. Further studies should be conducted to validate the effects of supplementing TGR to the diet and to determine the optimal feeding amounts in sheep.