Introduction

Approximately 70% of the overall cost of production in the poultry sector is feed cost. Among different feed components, dietary protein is regarded as the most crucial component that affects the cost of commercial feed. Moreover, the world population is expected to reach 9.7 billion people (United Nations, Department of Economic and Social Affairs, Population Division 2019) and poultry population is expected to hit nearly 37.03 billion by 2050 (Rosegrant et al. 2009). With the expansion of the human and poultry population in the coming decades, there are great concerns on how to meet the protein needs of these broiler chickens. Among different protein sources, soybean is recognized as the most common plant protein source, and its production would have to double by 2050 to meet the requirements of monogastric animal feed supply. With the current crop productivity growth of 0.9%–1.6% per year (Ray et al. 2013), protein supply from soybean is expected to fall short. Therefore, we need appropriate strategies to close this “protein gap”, including lowering crude protein (CP) along with addition of medicinal plant extract, boosting amino acid digestibility, and utilizing alternate protein sources (Nuraini et al. 2014; Bryan et al. 2019; Pestana et al. 2020). Along with reduction of costs, lowered dietary protein may protect the environment by reducing nitrogen excretion (Saleh et al. 2021). Additionally, decreasing dietary protein levels in broilers' diets is an approach for reducing heat stress (Awad et al. 2019). A reduction of 4.5% CP in broiler diet can improve ileal amino acid digestibility coefficients (Awad et al. 2016). However, a low-protein diet impairs growth performance and gastrointestinal conditions in broilers (Dozier et al. 2000). It has been found that lowering CP in the diet has a negative impact on the performance of poultry (Mohammadigheisar and Kim 2018). Nuraini et al. (2014) reported that reducing dietary CP content while supplementing with antioxidant herbal extract may be an ideal technique for alleviating the detrimental impacts of low-CP (LCP) diet on the performance of broilers.

Achyranthes japonica is from the Amaranthaceae family. It is widely distributed in South Korea, Japan, and China (Jung et al. 2007). Various kinds of saponins, terpenoids, phytoecdysteroids, 20-hydroxyecdysone, and inokosterone can be found in the root of A. japonica extract (AJE) (He et al. 2017). Some of the previous research works indicated that AJE has a positive effect on growth, nutrient digestion, intestinal bacteria, and fecal gas emissions in broilers and pigs (Park and Kim 2020; Sun et al. 2020; Liu and Kim 2021). Park and Kim (2020) found linear improvement in growth performance, nutrient digestibility, and cecal microbial count when up to 0.10% AJE was supplied to broiler diet.

Until now, to the best of our knowledge the application of AJE in LCP broiler diet is still inadequate. We hypothesized that addition of AJE could positively improve the growth performance, nutrient utilization, cecal microbiota, and meat quality parameters in birds fed LCP diets. Therefore, the objective of this study was to determine whether supplementing AJE in LCP diets may improve broiler growth performance and reduce the detrimental effects of CP reduction on broiler chicks.

Materials and methods

Before the experiment was initiated, the protocol was reviewed and approved by the Institutional Animal Care and Use Committee at the University of Dankook. All animal procedures were approved by the Animal Care and Use Committee of Dankook University, Cheonan, South Korea (ethics approval number DK-1-1956).

Animals, experimental design, diets, and housing

A total of 450, day-old Ross 308 broiler chicks (42.22 ± 0.12g) were randomly distributed into five experimental treatment groups where each treatment had five replicates (18 birds per replicate). Total experimental period was 35 days (starter: days 1–7; grower: days 8–21; finisher: days 22–35). The experimental diets include standard CP (SCP) diet, low CP (LCP) diet, and LCP diet supplemented with 0.00%, 0.02%, 0.04%, and 0.06% AJE, respectively. The composition of the basal feed is shown in Table 1. AJE was incorporated into the diet by replacing the same quantity of corn. Dietary CP content in the LCP group was same as that in the SCP group in days 1–7, and the LCP diet was provided to the LCP treatment group during days 8–21 and 22–35. All of the experimental diets were prepared in accordance with the recommendations of the National Research Council (NRC 1994). All the birds were housed in steel cages (1.75 × 1.55m²) with three floors, and electric light was provided for 24h during the first 7days, and then for 22h until the end of the experiment. For the first 5days, the room temperature was maintained at 33°C, and then reduced to 22°C until day 35, and the relative humidity was around 60%. The birds were given access to ad libitum feed and water during the feeding trial. Water was supplied with nipple drinkers (5 nipples/pen) positioned at the side wall of the pen.

Table 1.

Feed composition of broilers (as-fed basis).

Results

The effects of AJE supplementation in different levels of protein diets on broilers’ growth performance are shown in Table 2. In this experiment, the LCP diet group tended to show lower (P < 0.10) total body weight gain (TBWG) compared with the SCP diet. At the same time, birds fed LCP diet with AJE showed linear improvement (P < 0.05) in TBWG compared with birds fed LCP diet without AJE supplementation. Feed intake and feed efficiency were not influenced by dietary protein levels and (or) AJE supplementation.

Table 2.

Effects of low crude protein diet supplemented with Achyranthes japonica extract on growth performance in broilers.

Table 3 shows the effects of graded levels of AJE supplementation to LCP diets on the apparent nutritional digestibility of broilers. In this study, protein levels and (or) AJE supplementation levels had no effect on ATTD of DM and nitrogen (P > 0.05). Energy digestibility tended to increase (P < 0.10) through the AJE supplementation in LCP diets compared with the LCP diet without AJE supplementation.

Table 3.

Effects of low crude protein diet supplemented with Achyranthes japonica extract on nutrient digestibility in broilers.

Table 4 shows the effect of standard versus low-protein diets and LCP diets with and without AJE supplementation on the bacterial count in the excreta of broilers. The counts of Escherichia coli, Lactobacillus, and Salmonella did not alter as a result of AJE supplementation or change in dietary protein intake.

Table 4.

Effects of low crude protein diet supplemented with Achyranthes japonica extract on cecal microflora in broilers.

Breast muscle weight tended to increase (P < 0.10) linearly in broiler chicks fed the LCP diet supplemented with increasing levels of A. japonica Nakai (AJN) root extract (Table 5). Other meat quality parameters remained unchanged as a result of AJE supplementation or changes in dietary protein intake.

Table 5.

Effects of low crude protein diet supplemented with Achyranthes japonica extract on meat quality in broilers.

Discussion

BWG was lower in broilers fed a low-protein diet compared with broilers on an SCP diet. The findings of this investigation were consistent with the findings of earlier research, which revealed that feeding broiler chickens LCP diets resulted in a negative influence on growth performance in the birds. Mohammadi Gheisar and Kim (2018) showed that broiler chicks' BWG was affected when 1% LCP diet was fed to them. Several researchers, such as Namroud et al. (2008) and Bregendahl et al. (2002), have demonstrated that reducing CP in diets from 23% to 18% while supplementing necessary amino acid results in a reduction in final BWs and BWG. In contrast, Harn et al. (2019) found that the CP content of grower and finisher diets can be lowered by 2.2%–2.3% without having any adverse effects on growth performance of broilers. They noted that the wet litter in the control group may have contributed to this phenomenon, which may also have caused some thermal discomfort in the birds, which may have negatively impacted their growth performance. Growth retardation can be induced by a deficiency of either a single or a combination of limiting amino acids such as lysine, methionine, valine, threonine, isoleucine, and tryptophan in broilers (Corzo et al. 2009; Kumar et al. 2016). The addition of AJE to a low-protein diet results in a linear improvement in body weight growth. In agreement with our findings, Nuraini et al. (2014) discovered that broiler chicks fed a low-protein diet supplemented with 9g/kg antioxidant herbal extract (Sauropus androgynus leaves) have equal growth performance to those on a standard protein diet. Park and Kim (2020) and Sun et al. (2020) found that broilers fed a diet supplemented with 0.025%, 0.050%, or 0.10% AJN root extract had higher BWG and lower FCR than those fed a diet containing no AJN root extract. Moreover, Long et al. (2020) found that broiler chicks that were fed a diet with antioxidant herbal extract Forsythia suspensa gained weight, which was connected to an increase in feed intake and a decrease in feed efficiency, which implied that their body weight increased. The increased growth performance of broilers observed in this study could be attributed to improved nutrient usage. Additionally, other research conducted on other animals discovered that Azardirachta indica extracts possessed antioxidative, antibacterial, and immunostimulatory capabilities, which may have a beneficial effect on nutrient absorption and growth performance (Tahiliani and Kar 2000; Chen et al. 2009). Improved growth performance observed with AJE supplementation in this study could therefore be attributed to the stimulation of both digestion and absorption of nutrients.

There was a tendency toward greater digestibility of energy in the AJE supplemented group, which indicates that increased digestibility is connected to an increasing amount of AJE in broiler diet. According to previous research, herbs and their extracts stimulate digestive secretions, such as bile and mucus, and it enhances enzyme activity in the gastrointestinal tract (Windisch et al. 2008). Inclusion of a plant extract mixture in the diet increased the activities of pancreatic trypsin and α-amylase in the gastrointestinal tract (Jang et al. 2007). It is possible that these adjustments will aid in improving the digestibility of broilers.

Microbial count in broilers fed a low-protein diet did not show any difference among different treatments. A previous study by Mohammadi Gheisar and Kim (2018) found no changes in E. coli count between a low-protein diet and a standard protein diet. Additionally, Nyachoti et al. (2006) claimed that the reduction of 23%–17% CP did not affect the microbial counts in both beneficial and pathogenic bacteria in ileal digesta.

There are few reports on the impact of herbs and their extracts on broiler carcass metrics, and the results differ. Erener et al. (2011) found that the addition of green tea extract increased the carcass weight of broilers. However, some other research shows that herbal extracts do not have an effect on the carcass parameters of chicken (Garcia et al. 2007; Koreleski and Swiatkiewicz 2007). However, the exact way that AJN extracts affect meat quality is not clear. This may be because AJN extracts have antioxidative properties, which could be why the breast meat percentage increased (Frankic et al. 2009). However still, it was thought that herb extracts used in animal nutrition could help animals digest their food better, which could help them use more nutrients and grow faster. This could be another reason for increased breast meat percentage. It could be said that the addition of AJN extract did not have a big detrimental impact on meat quality parameters.

Conclusion

Reduced CP in broiler diet reduces the growth performance, which can be improved by addition of AJE up to 0.06%. Supplementation of AJE to LCP diet alleviates the negative effects caused by dietary CP reduction on the performance of broilers. Therefore, inclusion of 0.06% AJE as a feed supplement may be appropriate for minimizing the negative impact of reduced CP (−3%) diet on the growth performance of broilers.