Dietary supplementation of pulverised Astragalus membranaceus improved performance, immunity and diarrhoea incidence in weaned piglets

Astragalus membranaceus root is widely produced in the north of China, it is an important component in Chinese herbal medicine (Wang et al., 2010). It is a leguminous plant from the two main varieties; A. membranaceus (Fisch.) Bunge variety mongholicus (Bunge.) Hsiao or A. membranaceus (Fisch.) Bunge (Wang et al., 2016). The dried roots of this leguminous plant contain chemical substances such as alkaloids, polysaccharides, glycosides, flavonoids, amino acids, saponins, trace minerals, which exhibits both medicinal and nutritional characteristics (Xi et al., 2014). This A. membranaceus plant roots were applied in Chinese traditional medicine for more than 2000 years (Shao et al., 2004), for its immune characteristics (Xi et al., 2014), circulatory functions, gut microbial wellness (Qin et al., 2012), and anti-(-inflammatory, -oxidant, -viral and -hyperglycemia) effects (Li et al., 2010) as discussed in Che et al., (2018). Early weaning is a usual husbandry practice in most commercial pig farms. Piglets during this period have immature digestive systems and adapting to the drastic change from the digestible watery milk to less digestible solid feed seems challenging (Chen et al., 2017). Furthermore, early weaning piglets are limited from immunological and other protections derived from the maternal milk, leading to a decrease in their susceptibility to diseases and infections by enteric bacteria like E. coli and Salmonella (Kick et al., 2012). We hypothesized that AMSLF may counteract the physiological and immunological stress conditions and improve growth performance during weaning. Thus, we investigate for the first time, the effects of fibres from A. membranaceus aerial parts on the diarrheal incidence, growth performance and immunity in early weaned piglets.

The A. membranaceus plant was collected at the plantation farm of the Department of Herbal plants and Chinese medicine, Jilin Agricultural University. The collected samples were dried overnight at 60°C and pulverized through a 5 mm sieve. The extract was stored in a closed vessel at room temperature before incorporation into the feed by hand mixing. A total of sixty crossbred (Landrace × Large white) piglets weaned at 28 days with an average body weight of 8.84±1.12 kg were randomly allocated to four groups, with each group comprising of three replicate pens (1.8 m × 1.2 m) containing five piglets each, and arranged in a completely randomized design. All pens were equipped with a feeder, and a nipple-type drinker to enable ad libitum access to feed and water. Fresh feed was offered twice daily and the residue was discarded the next day. The temperature and humidity in the pen were maintained at 24-26°C and 60-70% respectively. The pens were disinfected once in a month, cleaned with a broom every day to keep a healthy and hygienic condition and prevent disease infection among pigs. The basal diet was formulated according to the National Research Council requirements (National Research Council 1998). The feed was prepared with maize-soybean meals, without any antibacterial supplements, and supplied in a mash form (Table 1). The piglets in the control (G1; 0 g/kg AMSLF) were fed the basal diet, whereas in the treatment groups were fed the basal diets with the addition of 2.5, 5, and 7.5 g/kg pulverized AMSLF, denoted as G2, G3, and G4 respectively. The occurrence of diarrhoea (%) was estimated as described by Hu et al., (2014).



The average daily feed intake (ADFI) was measured by subtracting the residue from feed offered. Piglets were weighed early on the last day of the feeding trial on an empty stomach to obtain the final weight. The initial weight subtracted from the final weight and divided by the test period of 28 days for the average daily gain (ADG). The feed conversion ratio (FCR) was measured from the data. The serum IgA, IgG and IgM content were determined (Kuang et al., 2017). The data were analysed by one-way ANOVA using SPSS version 20.0 (SPSS Inc., Chicago, IL, USA). A statistical probability value of P<0.05 was considered significant.

Growth performanc
 
The supplementation of AMSLF in the diet of piglets increased (P<0.05) the growth performance in comparison with the control. Treatment G4 significantly increased (P<0.05) ADFI and ADG in piglets (Table 2). Similar growth-promoting effects were reported by Liu et al., (2006) and Kim et al., (2005), after feeding Fermented soybean meal as a protein source to weaned piglets. Also, the ADFI of day old broiler chicks increased at 10000 mg/kg A. membranaceus root powder (Wang et al., 2010). In addition, there was an increased in ADG after adding Astragalus polysaccharides (APS) in the drinking water of chickens (Li et al., 2004). Furthermore, Qiao et al., (2013) observed an increase in ADG, final body weight, and feed efficiency in Holstein diary heifers maintained on a higher fibre diet.  In contrast, fibre decreased ADFI and growth performance of piglets raised under good management practices (Wellock et al., 2008). We observed that G1 had the highest FCR in comparison with the control. Therefore, we deduced that the effectivity of AMSLF depends on the dietary composition, plant part used, types of animals, and the level of feeding adopted.

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Immune parameters
 
The stem and leaves of Astragalus contain the same active ingredients as the roots but the concentrations vary (Xi et al., 2014). The results of this experiment show that the addition of AMSLF in the diet, increased (P<0.05) the contents of IgG, IgA and IgM. This increased in immunoglobulins was as a result of the bioactive compounds present in AMSLF. Similarly, serum IgG, IgA, interferon-˜, and C-reactive proteins were higher on the 20th day of supplementing saponin to weaned piglets (Ilsley et al., 2005). Also, feeding Aspergillus oryzae fermented soybean meal increased serum IgM in broilers (Feng et al., 2007).
 
Diarrhoea
 
There was a decrease (P<0.05) in diarrhoea throughout the experimental period. The highest diarrhoea occurrences were registered in the G1 while the lowest diarrheal incidence was in the G4 (Table 3). Similarly, there was a reduction in diarrheal incidence and the diarrheal index in piglets fed Lactobacillus extract (Huang et al., 2004).  Also, there was a reduction in diarrheal incidence after feeding Atractylodes macrophala Koidz polysaccharides to early weaned piglets (Li et al., 2011). These implies that the addition of 2.5 g/kg to 7.5 g/kg of AMSLF in the feed of early weaned piglets, could decrease the diarrhoea occurrences, as piglet’s diarrhoea is a serious condition in commercial pig farms, and with the ban on antibiotic usage in most parts of the world has led to the massive increased in the cost of production and the loss of piglets. Therefore, the addition of AMSLF to the diet of piglet’s can improve the health of pigs as we earlier discussed in Che et al., (2018).

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In conclusion, AMSLF improved the growth performance of piglets, increased serum immunoglobulins and lowered the diarrhoea incidence in piglets. Further work is necessary to better explain the mechanisms of influence of the nutritional components in AMSLF on gut microbial composition and function in piglets.

Thanks to the national key research and development program of China (2017YFD0502104) and the scientific project of Jilin Province (20170309003NY and 20180101023JC) for providing financial support for publishing this article.