As a kind of natural green feed additive, plant extract has bactericidal, antiviral, immunity enhancement and intestinal health improvement, so it has broad application prospect in livestock and poultry breeding. As an effective substitute for antibiotics, plant extracts have attracted more and more attention under the background of prohibition of adding antibiotics. According to the existing research results, whether in vitro antibacterial test or clinical application, plant extracts have achieved good results in the prevention and treatment of diarrhea in young animals and improve intestinal health, and the therapeutic effect is superior to antibiotics. However, the digestive tract of young ruminants is very different from that of piglets and chicks in the stage of rapid rumen development. The research on preventing diarrhea and promoting intestinal health of young animals with plant extract as feed additive is still at the primary level and has not been widely promoted. In future study, therefore, need according to the characteristics of the ruminant animal digestive tract development, purposefully screening plant extracts, establish the calf, lamb precision feeding mode, combined with the feature of the body's physiological and biological basic rule, promote intestinal health, reduce diarrhea rate, improve feed utilization, improve animal health, thus improve the farming economy benefit.
Factors affecting anti-diarrhea effect of plant extracts：
1. Species of animals
The anti-diarrhea effect of plant extracts was affected by animal species and body weight. For example, APS can effectively reduce the incidence of diarrhea in calves and piglets, but diarrhea rates are different. Deng Shaoji and Li Chunsheng injected 3 mL and 4 mL APS injection into the neck of weaned piglets and calves, respectively, for 3 consecutive days, and fed them with 20 g APS powder in 100 kg basal diet for 7 consecutive days. The results showed that under the same treatment conditions, the diarrhea rate of calves and piglets was 5.5% and 8.6%, respectively, and the diarrhea rate of calves was 36% lower than that of piglets.
2. Types of plant extracts
Different plant extracts have different inhibitory effects on diarrhea of animals. Lu et al added 1 kg/t of compound natural plant extract to the basic diet of weaned piglets in compound groups ⅰ to ⅲ, which was made up of flos lonicerae, Astragalus membranaceus, forsythia suspensa, cornus officinalis, coptis chinensis and Astragalus membranaceus in different proportions. It was found that the diarrhea rate of piglets fed with different compound diets varied from 1.96% to 2.26%, among which compound ⅱ group had the most significant effect on reducing diarrhea rate and diarrhea score of piglets. Feeding garlic vegetable oil, turmeric oil resin and chili oil resin to weaned piglets can effectively reduce diarrhea rate, and feeding garlic vegetable oil and turmeric oil resin to weaned piglets can inhibit diarrhea better than chili oil resin.
3. The content of active ingredients in plants
The content of effective components in plants will directly affect the effect of animal diarrhea control, which is affected by the factors of plant origin, growth environment, sampling site and harvest date. For example, the content of APS in Astragalus membranaceus from Shanxi and Heilongjiang provinces was different, and the content of APS in Astragalus membranaceus from Shanxi Province was significantly higher than that from Heilongjiang Province. The contents of total triterpenoids were affected by altitude, air temperature, precipitation and frost-free period, and there was a significant correlation between the contents of total triterpenoids in leaves. The contents of total triterpenoids in leaves were the highest, followed by branches, pericarp and seeds. The total flavonoids content in blueberry leaves collected from August to September was significantly higher than that collected from May to June, and the total flavonoids content was the highest in September.
4. The amount of plant extracts added
Plant extracts can effectively reduce the average diarrhea rate of young animals. Within a certain range of supplemental level, the diarrhea frequency decreased gradually with the increase of supplemental level of plant extracts. For example, Li Tongzhou et al. found that adding 0.02%, 0.05% and 0.1% APS in the basal diet of weaned piglets reduced the diarrhea rate of piglets by 12.50%, 18.75% and 31.25%, respectively. Oral administration of 50~400 mg/kg of c. aureus bark extract can effectively reduce diarrhea rate in mice, and 400 mg/kg of oral administration has the most significant diarrhea inhibition effect.
