Chinese herbal medicine (CHM) is the foundation of Chinese traditional veterinary medicine, in which more than 80% constituents of preparations are derived from plants. CHM is often used to maintain good health rather than to cure illness once it has developed, much in the same way that vitamin or mineral supplements are used in Western countries. Based on a belief that CHM is natural, safe, and of lower cost, consumers worldwide are spending more money on this form of therapy. In recent years, animal producer and veterinarian have begun to use the herbs to effectively improve the health and growth performance of pigs and poultry. Here we detail the current state of knowledge about the effects of CHMs on physiological and biochemical parameters and their uses as growth and health promoter, and the underlying mechanism, which including: regulating substance metabolizism, for example, decreasing the catabolism of amino acids by the small intestine, and increasing digestion and absorption of dietary amino acids. These new findings not only greatly advance the knowledge about the mechanisms for the action of the CHMs, but also provide a scientific and clinical basis for their use in enhancing the efficiency of animal production.

As an initial step to define the mechanisms responsible for the beneficial effects of typical Chinese herbs on health and growth performance of swine and poultry, researchers from the group of Livestock Ecology and Healthy Production determined contents of amino acids in seventeen Chinese herbs. The herbs included Polyporus, Radix glycyrrhizae, Radix angelicae sinensis, Radixginseng, Gold Theragran, Radix polygoni multiflori, Semen Allii Tuberosi, Radix paeoniae alba, Rhizoma atractylodis macrocephalae, Radix astragali, Radix codonopsis, Radix rehmanniae preparata, Rhizoma dioscoreae, Radix Salvia miltiorrhizae, Poria, Fructus crataegi and Acanthopanax senticosus. They found that the composition of amino acids in the Chinese herbs is largely similar to that in feeds of plant origin, which indicate that typical Chinese herbs are not unique in the composition of protein- precursor amino acids among plants. Other components in the herbs are likely major active components that beneficially regulate intestinal barrier integrity, nutrient metabolism, immune function, health, and growth in animals (Wu et al. J Anim Sci, 2007).

The first study was designed to determine the effect of ultra-fine Chinese herbal powder as a dietary additive on serum concentrations and apparent ileal digestibilities (AID) of amino acids (AA) in young pigs. The results showed that dietary supplementation with the herbal powder increased serum concentrations and AID of most AA by 10-50% and 10-16%, respectively. As an indicator of improved intestinal function, AID values of calcium were also enhanced in piglets supplemented with the herbal powder. These novel findings demonstrate that the herbal powder can enhance the digestibility of dietary protein and the intestinal absorption of AA into the systemic circulation in post-weaning pigs, therefore providing a new mechanism for its growth-promoting efficacy (Kong et al. Amino acids, 2009a).

The second study was conducted to determine the effects of acanthopanax senticosus (AS) extracts as a dietary additive on serum contents and AID of AA in weaned piglets. Data showed that the serum contents and AID of most AA in the AS extracts-supplemented group were gradually increased by 15.3 - 80.8% and 4.1 - 30.8%, respectively, as the experiment proceed in comparison with the colistin- additive group and/or control group. These findings indicated that the AS extracts could enhance the ability of digestion and absorption of AA, which may be a potential mechanism of its growth-promoting efficacy (Kong et al. Livest Sci, 2009b).

The third study was conducted to evaluate the effects of dietary supplementation with astragalus polysaccharide (APS) growth performance, AID of AA, and their serum concentrations in early-weaned piglets. The results showed that dietary APS did not affect ADFI, but enhanced ADG by 11% and 4.4%, and improved F/G by 5.6% and 8.4%, respectively, compared with the control and antibiotic groups. Addition of APS to the diet increased AID and serum concentrations of most nutritionally essential and nonessential AA (including arginine, proline, glutamate, lysine, methionine, tryptophan, and threonine) on days 14 and 28. Circulating levels of total AA were affected by the age of pigs and treatment × time interaction. Collectively, these findings indicate that APS may ameliorate the digestive and absorptive function and regulate AA metabolism to beneficially increase the entry of dietary AA into the systemic circulation, which provide a mechanism to explain the growth-promoting effect of APS in early-weaned piglets (Yin et al. Amino Acids, 2009).

Physiological levels of cortisol stimulate intestinal arginine synthesis in piglets. Interestingly, some herbal extracts contain GA (a pentacyclic triterpenoid derivative of the ？2-type amyrin), which has a chemical structure similar to cortisol. This study was conducted to test the hypothesis that dietary GA supplementation may increase arginine availability and growth performance in young pigs. Data showed that dietary supplementation with 0.02% GA increased feed intake by 27%, ADG by 47%, and the gain: feed ratio by 17%, while reducing scour frequency by 40%; and increased plasma arginine concentrations by 25%, compared with the control. These results suggest that GA enhances the endogenous provision of arginine and growth performance of milk-fed piglets (He et al. J Anim Sci, 2007).

In summary, dietary supplementation with the phytochemicals enhance the AID and absorption of dietary AA in weaned piglets. These findings aid in explaining the growth-promoting effect of the phytochemicals. Because the underlying mechanisms are likely to be complex and multifactorial, future studies are warranted to determine the effects of active components of the phytochemicals on the digestion and absorption of dietary nutrients.