The profile of tropical alfalfa in Indonesia: A review

Abstract

Alfalfa (Medicago sativa L.), or lucerne, is a subtropical plant popularly known as the “Queen of Forages”. It has a superior nutritional profile that includes high levels of crude protein, secondary metabolites, as well as macro and micro minerals, making it one of the best feed fodders in the world. Alfalfa is also highly adaptable to both warm and cold climates in addition to being highly nutritious. These features have led to the cultivation of alfalfa in tropical areas, such as Indonesia. Studies have been conducted on the vegetative and generative aspects of alfalfa cultivation in tropical regions to increase crop yield and sustainability. Progress in the cultivation and use of alfalfa in tropical regions has been encouraging and has led to the potential emergence of a new stock, namely tropical alfalfa, which is now a high-quality green forage source in tropical regions. Cultivation of tropical alfalfa provides breeders with a high-quality feed, leading to significant improvement in the condition and health of livestock and an increase in the production of meat, milk, and eggs. This review will be very important source of information not only for researchers but also for businessman who have a concern to develop alfalfa tropic either for feed or food (growth characteristic, function and nutrient content).

1. Introduction

Alfalfa (Medicago sativa L.), known as the “Queen of Forages”, is the oldest known wild plant found in the forests of Mediterranean mountainous areas southwest of Asia. The name ‘alfalfa’ comes from the Arabic word “Al-Fasfasa,” which means ‘father of all plants’ (Lacefield et al., 2014).

In 2007, the alfalfa plant was cultivated in Ciawi, Indonesia, as a collection forage crop, using imported seeds. However, the plant did not produce fertile seeds. Consequently, plant production has been limited by the low availability of fertile seeds (Sajimin and Purwantari, 2011). Tropical alfalfa needs to be cultivated so that livestock in the tropics can get good quality feed without having to import. A study by Suwignyo et al. (2017) reported the production of fertile alfalfa seeds, which confirmed that the plant had the potential to be cultivated in tropical areas. These plants have shown vegetative development with a high nutrient profile when compared to those from subtropical areas (Suwignyo et al., 2020a, Suwignyo et al., 2020b, Suwignyo et al., 2020c, Suwignyo et al., 2020d); this presents new hope for alfalfa cultivation in Indonesia and a potential categorization of the stock as a new strain/variety, namely tropical alfalfa (Suwignyo et al., 2021a, Suwignyo et al., 2021b). Tropical alfalfa already recognized by Ministry of Agriculture of the Republic of Indonesia (RI) as new variety with local name Kacang Ratu BW which Bambang Suwignyo as an inventor who developed alfalfa became tropical alfalfa with registered number 929/PVHP/2021 released by Center for Plant Variety Protection and Agricultural Licensing (PPVT) of the Ministry of Agriculture RI. This review paper focuses more on alfalfa research conducted in Indonesia (not the whole world), with comparisons of relevant papers from outside Indonesia. It should be noted that the development of alfalfa in Indonesia is still very limited both in number and in area distribution. Therefore, the existence of tropical alfalfa (Kacang Ratu BW) is a new hope for the development of alfalfa in the tropics, especially in Indonesia. The purpose of this review on tropical alfalfa is expected to increase public understanding of alfalfa and trigger the development of alfalfa in the tropics with nutrient values that are not different from alfalfa that is developed/ derived from subtropical areas.

2. Industrial production of alfalfa

Industrial production of alfalfa in tropical areas, especially in Indonesia, aims at supplying forage, food, and herbal supplements. For instance, Greenfields ltd, a dairy farm in Indonesia, already uses alfalfa as fodder, though the actual quantities being used remain unknown. Furthermore, on the Sariagri Farm alfalfa is used as the main forageforrabbits and has been proven to have a significant impact on their growth. Rabbits that are fed alfalfa showed increased growth when compared to those that were not given any. Furthermore, female rabbits fed on dry alfalfa during pregnancy produced litters that were more resistant to diseases and had a higher survival rate than those fed on other forage types. Alfalfa has also been used as forage for racehorses but, unfortunately, no data is available on its effects in Indonesia (Sajimin and Purwantari, 2011).

The alfalfa plant has also been used to produce herbal medicine. It is believed that alfalfa can serve as a cure for heart diseases in addition to being a complete source of vitamins and iron. Alfalfa extracts in the form of K-Liquid Chlorophyll are commercially available from K-Link Nusantara ltd (in 500-mL containers) and Alfalfa Herbal Bee® are manufactured by PT. BOS (in 500 mL containers).The government of Depok City cultivated alfalfa in February 2017 to produce herbal medicine. It was grown in the slaughter house areas of Tapos in Depok, Jawa Barat, by sowing seeds (500 g) in polybags.

3. Academic development of alfalfa

Research on alfalfa has been conducted for agriculture, animal husbandry, healthcare, and food industries. In the fields of agriculture and animal husbandry, research has been conducted using various developmental models at the laboratory scale (Suwignyo et al., 2017, Suwignyo et al., 2020a, Suwignyo et al., 2020b, Suwignyo et al., 2020c, Suwignyo et al., 2020d, Suwignyo et al., 2021a, Suwignyo et al., 2021b, Suwignyo et al., 2021c, Suwignyo et al., 2022, Suwignyo and Sasongko, 2019). In animal husbandry, alfalfa is used as highly nutritious forage for both ruminant and non-ruminant animals to increase livestock production and improve the nutrient content of the meat, eggs, and milk produced. Further, a study by Sirait et al. (2011) on meat goats in Sungai Putih, North Sumatra, showed that alfalfa grown in the wet climate of the Karo district highlands can potentially be used as goat forage because it grows well in that district, has a high production rate and a higher nutrient value than natural grass, and represents a rich protein source with high palatability (Sinar Tani Edisi 15–21 February, No. 3444 of the year XLII).

The research on tropical alfalfa by Bambang Suwignyo has progressed significantly since 2010 (e.g., Suwignyo et al., 2020a, Suwignyo et al., 2020b, Suwignyo et al., 2020c, Suwignyo et al., 2020d, Suwignyo et al., 2021a, Suwignyo et al., 2021b, Suwignyo et al., 2021c, Suwignyo et al., 2021d, Suwignyo et al., 2022, Suwignyo and Sasongko, 2019, Suwignyo et al., 2017). Some alfalfa varieties/species have been used as study materials for cross-breeding studies using specific treatments such asthe use of dolomit fertilizer, and by varying the duration and wavelength of lightduring cultivation. From 2019 onwards, the progeny that possessed distinct characteristics from their parental stock, was referred to as tropical alfalfa (Suwignyo et al., 2021b). Notably, tropical alfalfa is better than subtropical alfalfa, given the following attributes:

• 1.Subtropical alfalfa can be harvested approximately every-two months (five–six times a year), whereas tropical alfalfa grows faster and can be harvested approximately every month (11–12 times a year).
• 2.The yield of freshly harvested subtropical alfalfa is in the range of 20–35 tons per hectare (every-two months), while that of tropical alfalfa is 8–13.75 tons per hectare per month. Cumulatively, the annual production of fresh tropical alfalfa is comparable to that of subtropical alfalfa.
• 3.Generative characteristics (flower and seed) can emerge in fertile tropical alfalfa seed, with the results of initial and current viability tests being 82 %. Thus, it may potentially result in alfalfa seed self-sufficiency. Conversely, Cupic et al. (2005) stated that the viability test of alfalfa in subtropical countries such as Croatia was 92 %.
• 4.The crude protein content of tropical alfalfa is in the range of 20–32 %, which is significantly influenced by harvesting age.
• 5.Optimal growth of subtropical alfalfa occurs at approximately 20 °C, while tropical alfalfa can grow well even in temperatures reaching up to 48 °C (Suwignyo and Sasongko, 2019).
• 6.Average growth rate after defoliation is approximately 1.4–1.6 cm per day, and in the first to second week after defoliation, the rate can reach 2–5 cm per day (Suwignyo et al., 2021a, Suwignyo et al., 2021b).

4. Vegetative growth of tropical alfalfa

Growth is the irreversible increase in size, volume, and cell number of living organisms (Harahap, 2012). Plant growth can be classified into vegetative and generative growth. Vegetative growth refers to the increase in volume, number, and size as well as change in form of vegetative organs such as leaves, stems, and roots. It begins with the formation of leaves and continues until the initiation of generative organs. Generative growth is the growth of generative organs, beginning with the formation of flower primordia and culminating in the formation of ripe fruits (Solikin, 2013).

The comparison growth of alfalfa tropic (Kacang Ratu BW) vs subtropic from seed to flower, as illustrated in Table 1, lasts for 30 days. The hypocotyl (precursor stem) appears within the first 10 days after seeding and the roots start to develop. Thereafter, the epicotyl (shoot precursor) emerges at 10–15 days with the formation of the first leaf (cotyledon). Once the cotyledon has emerged, the first unifoliate leaf (single leaf) emerges. At 15–30 days, the trifoliate leaf begins to emerge, and other plant parts such as the leaves, shoots, and stem develop. This is followed by further elongation of the roots. Once the vegetative growth phase has reached its peak, alfalfa starts flowering owing to the optimum nutrient levels in the plant. A study by Wahyuni and Kamaliyah (2010) reported that when the plant is 60 days of age it is harvested and at that time its average height is 44.78 cm, while at the cutting age of 80 days of age, the average height is 50.63 cm. The increase in plant height is rapid during the cutting age of 20–70 days; thereafter, it starts to decrease between 70 and 90 days of age. Suwignyo et al. (2020c) reported that in the first week after cutting, the mean height/growth rate of the alfalfa plant increases by2–5 cm per day, after which it gradually declines during the third and fourth weeks as the plant begins to flower.

Table 1.

Growth characteristic Tropical and Subtropic Alfalfa.

Day	Growth characteristic
	Alfalfa Tropic	Alfalfa Subtropic
1st – 3rd	Hypocotyl	Hypocotyl
4th – 7th	Epicotyl	Hypocotyl
8th – 10th	Cotyledon	Epicotyl
10th – 15th	First leaf unifoliate	Cotyledon
16th – 20th	Second leaf trifoliate	First leaf unifoliate
21th – 25th	Many trifoliate leaf with branches	Second leaf trifoliate
26th – 30th	Many trifoliate leaf with many branches	Many trifoliate leaf with branches
	Source: Suwignyo, B. 2021. Characteristic of Medicago sativa cv Kacang Ratu BW.	Source: Dodds and Meyer, Nort Dakota State University, 1984.

Radovićet al. (2009) (9)suggest that alfalfa has been widely cultivated in temperate countries, and its fresh and dry matter yields can reach 80 and 20 tons/ha, respectively. The major factors influencing the fresh weight of a plant are its water content and metabolic activity, and the nutrient content of the soil. Lahadassy (2007) stated that a plant continually requires large amounts of energy and nutrients to achieve optimal fresh weight. The plant uses the energy and the nutrients to increase the number and size of cells, which in turn leads to an increase in optimal water content required for the growth and sustenance of the plant. The characteristics of alfalfa cultivated in temperate areas are: high production capacity (40–150 tons of fresh matter/ha/year), high quality green forage (CP:18–24 %), high growth capability, which is influenced by seasonal stress, resistance to leaf and root diseases, rapid growth rate after cutting, and high-quality seed production (Smith, 1962).

5. Generative growth of tropical alfalfa

Alfalfa is a herb with deep and ramifying roots that form rhizomes. It has horizontal and upright creeping stems which grow up to 30–120 cm in length and are woody in the lower part. Each stalk has three leaves (trifoliate), 5–15 mm in length and with hairy lower parts (Mannetje and Jones, 2000). Tropical alfalfa in Taiwan is produced by breeding subtropical alfalfa to enable it to adapt to the tropical areas of Taiwan and grow as a green forage. Seeds from this stock produce plants that breed naturally. The major constraint in alfalfa cultivated in Indonesia is that it does not produce fertile seeds (Sajimin and Purwantari, 2011). However, Bambang Suwignyo has grown generative alfalfa capable of bearing flowers and seeds from fertile tropical alfalfa seeds (Kacang Ratu BW). The plant had an initial viability of 67 %, which has now increased to 82 % (Suwignyo et al., 2021a, Suwignyo et al., 2021b).

The reproductive phase of alfalfa is divided into several stages, namely, the last vegetative stage, marked by the absence of flower buds with a plant height of more than 30 cm (from the ground), the flower bud stage, the first flowering stage, all flowering stage, and the last flowering stage (Bagg, 2003). The ideal time for alfalfa to flower and produce seeds is the dry season. Dense bunches of 10–35 flowers are formed and they have purple or blue crowns; rarely white crowns are also formed (Mannetje and Jones, 2000). The plant keeps flowering for three weeks, however the seeds ripen only after several weeks (Shroyer et al., 1987). The flowers produce seed pods containing seeds that ripen within 3 to 5 weeks. However, whenunder high insect pressure, some pods do not produce any viable seeds (Caddel et al., 2001).

Flowering during the generative growth phase of alfalfa can be induced by treatment with different amounts of dolomite and photoperiod length. The first flower emerges at 48 days or approximately 7 weeks after planting (WAP) following treatments with 12 t/ha dolomite under a 16/14 h photoperiod. Seed pods are produced at 77 days or 11 WAP; a longer photoperiod influences podding time. Therefore, the podding time has a significantly close correlation with flowering time. The interval from flowering to podding was 7–14 days. Moreover, the percentage of flowering plants is also influenced by photoperiod. Suwignyo et al. (2017) found that the highest mean percentage of flowering and podding alfalfa plants under a 16 h photoperiod was 77.8 % and 50 %, respectively. Furthermore, alfalfa plants exposed to 16 h photoperiods and treated with 12 t/ha dolomite produced the highest number of pods (252.25) at 14 WAP. Meanwhile, the same amount of dolomite but different photoperiod produced 78.75 pods at 14 h photoperiods and 4.50 pods at 12 h photoperiods. The weight of seeds per plant under 16 h and 14 h photoperiods was 4.48 g and 2.89 g, respectively. The F1 alfalfa seed viability test showed that when the plants were grown under normal sunlight (12 h), the viability was 67 % (8 days after planting). These results confirm that the alfalfa seeds produced in the study by Suwignyo et al. (2017) can be categorized as fertile seeds

Analysis of the generative characteristics of the second regrowth phase (after first cutting) of alfalfa upon treatment with dolomite and light exposure revealed that the highest percentage of flowering plants (83.33 %) occurred when exposed to the 16 h photoperiod. In the regrowth phase, the mean time required for alfalfa to produce pods was 5 days after flowering. The highest mean percentage of podding plants under a 16 h photoperiod was 80.55 %, greater than that reported in a previous study (ref). This difference could be attributed to the fact that the study by Suwignyo et al., 2021a, Suwignyo et al., 2021b analyzed the second regrowth phase, whereas their previous study (Suwignyo et al., 2017) analyzed the initial growth phase from seeds. The results showed a positive correlation between the percentage of flowering plants, percentage of podding plants, and percentage of pods n each individual plant. The study by Suwignyo et al. (2021a) showed that the purity of alfalfa seeds was 61.63 %. The total seed weight was 1.4446 g, of which 0.0674 g was foreign materials, and 0.4868 g was the actual weight of the seed. Approximately 33.69 % of the samples had damaged seeds. Seed damage was caused during harvesting and storage. The results of the viability test showed that the viability percentage was 13.33 %, meaning that number of alfalfa seeds that had the ability to germinate was low (Suwignyo et al., 2021a).

6. Alfalfa as food and forage

Alfalfa has a high nutrient content that includes Ca, chlorophyll, carotene, and vitamin K (Griffiths, 1949, Suwignyo et al., 2020b), and contains several bioactive materials such as saponins, sterols, flavonoids, cumarins, alkaloids, vitamins, amino acids, sugars, proteins, and minerals. Additionally, alfalfa contains large quantities of dietary fiber, which could help to lower cholesterol levels. The use of tropical alfalfa (Kacang Ratu BW) in ducks (35 days) from 3% up to a level of 10 % did not affect the production performance of ducks, but reduced FCR (Suwignyo et al., 2020a, Suwignyo et al., 2020b, Suwignyo et al., 2020c, Suwignyo et al., 2020d, Suwignyo et al., 2021c, Suwignyo et al., 2021d) reduced cholesterol from 66.5 to 34.8 mg/100 g (Samur et al., 2020) from 177.7 to 116.2 mg/100g (in the liver), 162.9 to 134 mg/100 (in the blood) and reduced LDL from 83.70 to 68.0 mg/dL but increased HDL from 54.6 to 71.96 mg/dL (Suwignyo et al., 2022). The use of 2 % tropical alfalfa in laying hens (hyline 50 weeks old) produced eggs with higher levels of Fe, Zn, beta carotene, vitamin A and antioxidants than controls, respectively 5.6 vs 4.9 mg/100 g, 3.4 vs 1 mg/100 g, 1818.1 vs 1512.7 µg/100 g, 4934.9 vs 4382.9 µg/100 g, 4.9 vs 15.8 %, making it good for nutritional intervention for stunting eradication programs, that are still high in several developing countries, including Indonesia (Suwignyo and Indartono, 2022).

7. The nutrient content of alfalfa

The protein content of alfalfa can reach up to29%; further, the proximate composition of alfalfa is as follows: dry content (DC), 19 %; organic matter, (OM), 88 %; crude fat (EE), 10 %; and crude fiber (CF), 31 % (Hermanto et al., 2017). Research has been carried out on three varieties of alfalfa, namely Multiking 1, Vernal, and Common. The highest crude fat content was observed in the Common varietal (2.49 %), whereas the lowest crude fiber content was observed in the Vernal varietal (26.22 %), which also had the highest ash content (12.46 %). The highest water content was observed in the Multiking 1 varietal (69.62 %). The crude protein (CP) content found in the Common varietal was 20.61 % (Subantoro, 2013). The nutrient content of alfalfa during the first regrowth under different photoperiods with respect to the control (100 % soil) was as follows: DM (18.55 %), OM (87.95 %), CP (28.5 %), and CF (8.5 %) (Suwignyo, et al., 2020c). The nutrient content of alfalfa in the second regrowth under different photoperiods was as follows: DM (17.31 %) and OM (87.41 %) (Suwignyo et al., 2020c). Alfalfa is considered a good forage crop owing to its high adaptability, production potential, and quality as feed fodder (Dale, 1994). Furthermore, it is high in protein, Ca, and fiber. The average values of the various nutrients found in alfalfa (summarized from several sources) are shown in Table 2. and Table 3

Table 2.

Nutrient Content of Tropical Alfalfa.

Nutrient	Average value (%)
Dry matter (DM)	17.7–21.2
Organic matter (OM)	87.72 + 3.55
Crude protein	15.3–32.27
Crude fiber	25.47 + 4.01
Extract ether	8.21 + 1.54
Nitrogen free extract	39.18 + 1.43
Total Digestible Nutrient	56.27 + 1.90
DM In vitro digestibility	68.78 + 5.97
DM In vitro digestibility	67.30 + 5.09
DM In vitro (HCL) digestibility	21.61 + 0.54
DM In vitro (HCL) digestibility	26.43 + 0.40
l-Lysine	0.52–0.58
l-Leucine	1.02–1.29
l-Isoleucine	0.82–0.91
l-Methionine	0.09–0.14
l-Glycine	0.66–0.87
l-Valine	0.96–1.08

Table 3.

Macro-Micro Nutrient others Concern of Tropical Alfalfa.

Macro-Micro Nutrient	Average value
DPPH	9.19–11.98 %
Ca	0.46–0.9 %
P	0.19–0.33 %
Na	0.07–0.12 %
Fe	309.46–426.2 mg kg−1
Zn	22.9–68.0 mg kg−1
K	2.85 %
Total Flavonoids	1.99 %
Saponins	5.1 %
Tannins	4.28 %
Total Fenol	3.9 %
Chlorofil	0.81–1.00 mg g−1
Mature Leaf color	RHS Green group N 137 A
Young Leaf color	RHS Green group N 138 A
Flower color	RHS Purple Violet Group N 81 A
Young podd color	RHS Yellow green group 144C
Mature podd color	RHS Grey Brown group N 199 D

Alfalfa has higher crude fiber content than other leguminous plants; this has a significant impact on the digestibility of feed by livestock. The nutrient contents of alfalfa ranged from 16.0 to 29.1 % (CP), 40.45–44.9 % (NDF), and 16.2–25.4 % (ADF), respectively (Sajimin and Purwantari, 2011). It was found that the type of growth media does not significantly affect the quality of CP and CF, or the digestibility of dry and organic matter obtained during the first harvest of green alfalfa (Widyawati et al., 2009).

The leaves of alfalfa have high protein and fiber contents and can be used as green forage and supplements for ruminant livestock, as well as for non-ruminants, including poultry (Suwignyo et al., 2020b). Suwignyo and Sasongko (2019) showed that supplementation with fresh and hay alfalfa in the diet of hybrid ducks has a significant impact on feed consumption, feed conversion ratio (FCR), and body weight (BW). When compared to the control diet (basal diet without alfalfa supplementation), supplementation with 6 % fresh alfalfa increased the feed consumption of hybrid ducks in weeks 2, 3, and 4 more than when they were supplemented with hay alfalfa; this might be due to increased palatability of the fresh alfalfa feed. Bodyweight and FCR significantly increased in the second, third, and fourth weeks 4th, respectively. These increases in body weight and FCR of hybrid ducks occurred due to increased feed intake following supplementation with 6 % fresh alfalfa.

Furthermore, the same study found that supplementation with fresh and hay alfalfa also had a significant impact on meat quality (Suwignyo et al., 2020a, 2020b, 2020c, 2020d). The isoenergy and isoprotein rations do did not have any significant impact on the live and carcass weights of hybrid ducks. Additionally, supplementation with fresh and hay alfalfa could reduce the cost of feed. Higher income was generated from the ducks (live and carcass) supplemented exclusively with 6 % alfalfa, followed by those supplemented with both 6 % fresh alfalfa and the control diet. The study by Samur et al.(2020) on the supplementation with alfalfa in different basal rations showed that by supplementing commercial and alternative feeds with 10 % fresh alfalfa had a significant impact on feed consumption, BW, and FCR. The commercial feed supplemented with 10 % alfalfa resulted in the highest feed consumption, BW, and FCR. Furthermore, Addini et al. (2020) reported that supplementation with 5 % alfalfa in commercial rations resulted in the best physical and chemical meat quality.

7.1. Secondary metabolites in alfalfa

Alfalfa contains various secondary metabolites such as polysaccharides, saponins, leaf protein concentrates, and flavonoids, and alarge amount of tocopherol, primarily in the alpha form. It also contains several phytochemicals such as carotene, chlorophyll, cumarin, beta-sitosterol, isofavon, cryptoxanthin, daidzein, genistin, limonene, lutein, and zeaxanthin (Rahmayanti and Sitanggang, 2006). Several studies have shown that alfalfa could improve growth and feed efficiency (Kass et al., 1980, Xiangyang et al., 2006), meat quality (Ponte et al., 2004), and anti-oxidizing action (Yujing et al., 2006), and decrease cholesterol levels in serum, yolk, and meat(Wang et al., 2005). Conversely, the production performance, meat quality, and gene expression of broilers were also found to decrease owing to the effect of total flavonoids in alfalfa (Dong et al., 2011).

One of the primary components of alfalfa is saponin. Alfalfa saponin extracts can decrease cholesterol levels and low-density lipoproteins (LDLs) but increasehigh-density lipoprotein (HDL) levels. Further, these extracts inhibit the activity of cholesterol synthesis-related enzymes, such as HMG-CoA reductase and Acyl-CoAcholesterol-acyltransferase 2(ACAT-2), that play an important role in atherogenic lipoprotein synthesis by increasing cholesterol excretion through the increase in cholesterol 7alpha-hydroxylase(CYP₇A₁) activity. CYP₇A₁ plays an important role in the breakdown of serum cholesterol in the liver, and increases the activity of LDL receptors (Shi et al., 2014). Kocaoğlu et al. (2004) reported that alfalfa saponins could prevent the reabsorption of bile acids, which then get diverted from the enterohepatic cycle and excreted in the feces. Deng et al. (2012) also reported that liquid alfalfa extracts did not significantly decrease the production performance and egg quality of layer hens.

Alfalfa extracts contain high levels of polyphenol compounds that serve as antioxidants (Rana et al., 2010). Antioxidants play an important role in influencing the reaction chain by removing the intermediate product of free radicals and inhibiting other oxidation agents. Flavonoids serve as antioxidants by donating hydrogen ions to catch free radicals (like OH) so that they are no longer reactive; hence, they inhibit free radical activity. Furthermore, flavonoids also remove an O molecule in nitric peroxide (ONOO⁻), which is formed when nitric oxide (NO) and superoxide (O2^–) react, both of which have the characteristics of free radicals (Valcheva-Kuzmanova et al., 2007). Flavonoids can prevent injury caused by free radicals in various ways, one of which is through direct scavenging of free radicals. Flavonoids are oxidized by radicals, resulting in a more stable, less-reactive radical. In other words, flavonoids react with the radical’s reactive compound and stabilize the reactive oxygen species. Owing to the high reactivity of the hydroxyl group of flavonoids, radicals become inactive (Korkina and Afanas’ Ev, 1996).

The activity of lipoprotein lipase can be accelerated by flavonoids, which influence the serum triglyceride content (Ling et al., 2001). Increased lipoprotein lipase activities subsequently increase very low-density lipoproteins (VLDL), which are converted to fatty acid and glycerol by hydrolysis. The fatty acid produced is absorbed by the musculature tissue and other tissues via oxidation and is stored as energy. In contrast, in adipose tissue, it is stored as an energy reserve (Marks et al., 2019). Flavonoids are also known to inhibit the activity of fatty acid synthase (FAS), an important enzyme in fat metabolism. The inhibition of FAS leads to a direct decrease in the formation of fatty acids, leading to a reduction in the formation of triglycerides (Tian et al., 2011).

Flavonoids exhibit various biological activities such as antioxidant, antitumor, and immune regulation (Georgiev et al., 2014). In animals, they promote growth, enhance reproduction, and improve immune functions (Surai, 2014). Galati and O’Brien (2004) demonstrated that alfalfa is rich in flavonoids and has many bio functions. It was found that supplementation with alfalfa flavonoids (AF) improved the growth performance of chickens when compared to the control group (no AF supplementation), especially at the supplementation level of 15 mg/kg diet. This was supported by Ouyang et al.(2013)who found that the growth performance of Chongren chickens was improved when their feed was supplemented with alfalfa flavones. Xie et al. (2002) also stated that flavonoid supplementation increased growth performance of chickens, and Zhu et al. (2008) reported that alfalfa isoflavone increased the mean daily body and stomach weight gain of mice. The causal factor responsible for the increased growth rate is that the combination of growth hormone and hepatic growth hormone receptor is upregulated by isoflavone. Thereafter, it leads to an increase in the concentration ofinsulin-like growth factor-1, which promotes the growth of the animal. Additionally, isoflavone can promote protein synthesis in the muscles leading to an increase in growth (Kamboh and Zhu, 2013).

Polysavone is a natural extract obtained from alfalfa and contains polysaccharides (18.63 %), triterpenoid saponins (5.58 %), and flavonoids (5.89 %). Plant polysaccharides have several immune-modulating effects. Furthermore, they regulate the neuroendocrine-immune network (Liang et al., 2002, Kong et al., 2006). Previous studies have reported that polysavones can suppress abdominal fat deposition and positively influence broiler chicken growth (Tong et al., 2004).

7.2. Mineral content of alfalfa

Minerals contribute a small proportion of the animal diet. However, they play an essential role in the health, growth, and production of animals (Lemus, 2013). Macro and micro mineral levels should be optimal to obtain good quality and quantity in plant and animal production (Arslan, 2017). Mineral concentrations in forage show significantly more variations than protein and energy concentrations (Lemus, 2013). Crop yield and forage quality are the primary and secondary determinant factors of forage value per land unit, respectively (Orloff, 2007). The quality of hay alfalfa is closely related to its protein and mineral content (Tongel & Ayan, 2010), with the latter being influenced by several factors such as harvesting time, physiological stage of the plant, loss of leaves during hay production, climate, soil conditions, diseases and pests, weeds, cultivar, moisture content during storage, water supply, and fertilizers (Khan et al., 2006, Orloff, 2007, Tongel and Ayan, 2010).

One of the factors that affects the macro and micro mineral content of the plant is its stage of maturity. Based on research done by Karayilanli and Veysel (2016), the highest average P and Zn content of alfalfa (0.25 % and 16.32 ppm, respectively) occurs in the germination period. The highest averages of Ca, Cu, and Mn were 1.08 %, 17.13 %, and 57.26 ppm during seed formation, full flowering, and early flowering, respectively. The lowest average values of P and Ca were 0.21 % at seed setting and 0.88 % at the beginning of flowering, respectively, whereas the highest values were 0.25 % in the grafting period and 1.08 % in the seed setting period for the same minerals, respectively.

P content is affected by harvest timing. By studying different plant species, Yolcu et al. (2008) found that the P content of alfalfa decreased as maturity increased. At the beginning of the vegetation period, plants had a high mineral content owing to a high water content in this period (Aydemir and Ince, 1988).

Radović et al. (2009) conducted a study consisting of cutting alfalfa at three different growth stages. The first, second, and third stages involved cutting after 22 (full boot stage), 29 (approximately 40 % flowering stage), and 36 (full flowering stage) days of vegetation, respectively. The stage of plant maturity affects the mineral content levels; the decrease in nitrogen content coincided with plant aging in leaf, stem, and whole plants. The highest nitrogen content was found in alfalfa leaves in the first stage of development (54.76 g kg⁻¹ DM). The highest macro element content was in the first stage of growth, except for P and Ca. Levels of P and K decreased significantly with increasing maturity, whereas those of Ca did not change much at the maturity stage. The highest Fe, Zn, and Cu (309.46, 40.62, and 18.12 g kg⁻¹ DM, respectively) contents were recorded in leaves at the first stage of plant development. The highest concentration of Mn (74.76 g kg⁻¹ DM) was found in the leaves at the third development stage.

Collins and Taylor (1980) found that temperature affected the yield and chemical composition of alfalfa, whereby the P content of the plant varied from 0.24 % to 0.34 % as temperature increased/decreased. Tongel and Ayan (2010) demonstrated that the K content of alfalfa varied from 2.96 % to 5.83 %, while Ca content ranged from 1.08 % to 2.33 %.. Scholtz et al.(2009) reported that the K content in 168 South African hay alfalfa samples varied from 10.6 to 42.7 g kg⁻¹. The difference in the K content were attributed to the differences in genotype, vegetative parts of the plant, maturity stage of the plant, level of Cu available in the soil, and soil pH (Khan et al., 2006). Another study found that the concentration of Ca in cool/warm regimes and cool regimes ranged from 1.55 % to 1.89 %, respectively (Smith, 1969).

The Na content of alfalfa ranged from 0.9 to 1.0 g kg⁻¹ (Pirhofer et al., 2011). Animals need Na to transport glucose and amino acid, retain body fluids, and maintain an acid-base balance (Lemus, 2013). The Mn content of hay alfalfa ranged from 15.4 to 54.3 mg kg⁻¹, with a mean Mn content of 34.60 mg kg⁻¹ (Özköse, 2018), Similar results were reported by Pirhofer‐Walzl et al. (2011) (43.5 to 47.7 mg kg⁻¹), Turan et al.(2010) (8.0 to 33.0 mg kg⁻¹), and Tongel and Ayan (2010) (13.10–39.54 mg kg⁻¹).

The Fe content of hay alfalfa ranged from 44.3 to 92.7 mg kg⁻¹, with a mean Fe content of 69.7 mg kg⁻¹ (Özköse, 2018). These values were consistent with those found by Pirhofer et al. (2011), who reported that the Fe content of hay alfalfa ranged from 63.1 to 69.8 mg kg⁻¹. However, Turan et al. (2010) found a much larger range of Fe contents in alfalfa, 62 to 188 mg kg⁻¹. Furthermore, higher values of Fe content were reported by Tongel and Ayan (2010) (209.3–343.1 mg kg⁻¹), and by Scholtz et al (2009) (149 to 3,138 mg kg⁻¹). According to Kacar (1972), soil pH is the most important factor influencing Fe uptake. A low availability of insoluble oxides and phosphates is caused by an Fe deficiency; therefore, it most likely affects plants grown in calcareous soils. Several researchers state that differences in Fe content could be partially attributed to variations in the soil Fe content and spatial variation in climatic conditions (Khan et al., 2006).

The Zn content of various alfalfa cultivars were reported by Tongel and Ayan (2010) (24.89–83.01 mg kg⁻¹), Turan et al.(2010) (25–85 mg kg⁻¹), and Scholtz et al. (Scholtz et al., 2009) (23–75 mg kg⁻¹). However, Pirhofer et al. (2011) found that the Zn content of alfalfa varied from 22.9 to 25.0 mg kg⁻¹ and the B values were 18.8–19.6 mg kg⁻¹, which were different from those reported by Smith (1969) (30–52 mg kg⁻¹) and Caldwell et al.(1969) (7–52 mg kg⁻¹). The Mo content of hay alfalfa ranged from 0.50 to 6.13 mg kg⁻¹ with a mean Mo content of 1.94 mg kg⁻¹ (Özköse, 2018).

The Cu content of hay alfalfa ranged from 3.13 to 4.17 mg kg⁻¹ with a mean Cu content of 3.83 mg kg⁻¹ (Özköse, 2018). Smith (1969)reported the Cu content of vernal alfalfa herbage grown under cool (18 °C at day time and 10 °C at nith time) and warm (32 °C at day time and 24 °C at night time) temperature regimes and harvested at the first flower stage varied from 3.0 to 4.0 mg kg⁻¹. However, previous studies showed conflicting results. Higher values were obtained by Turan et al.(2010) (5–20 mg kg⁻¹) and Tongel and Ayan (2010) (3.08 to 15.69 mg kg⁻¹). Furthermore, Pirhofer et al. (2011) reported that Cu contents ranged from 5.8 to 7.4 mg kg⁻¹. The variation among Cu values could be partly explained by genotypic differences, vegetative parts used, maturity stage, levels of available Cu in the soil, and soil pH (Khan et al., 2006).

The Cr content of hay alfalfa ranged from 0.93 to 2.40 mg kg⁻¹ with a mean Cr content of 1.19 mg kg⁻¹ (Özköse, 2018). Pirhofer et al. (2011) showed that the Cr content of alfalfa was 0.2 mg kg⁻¹. The Se content of hay alfalfa ranged from 0.77 to 1.03 mg kg⁻¹ with a mean of 0.70 mg kg⁻¹ (Özköse, 2018). Se plays an important role in animal nutrition because even trace amounts can prevent muscular dystrophy; however, higher levels of Se can cause blind staggers or alkali disease (Kacar, 1972). The Al content of alfalfa hay ranged from 31.2 to 57.8 mg kg⁻¹, with the mean content of 42.2 mg kg⁻¹ (Özköse, 2018). This result is consistent with thoseof a prior study by Smith (1969), who reported that the Al content in alfalfa ranged from 41 to 49 mg kg⁻¹.

7.3. Amino acid content of alfalfa

Alfalfa contains several amino acids, including lysine (0.69 %) and methionine (0.24 %) (Shahsavari, 2015, Tkáčová et al., 2011). Alfalfa may serve as a potential feed ingredient for poultry since it has a complete amino acid profile, same as that of corn (containing lysine and tryptophan), fish meal (containing methionine and lysine), and soybean meal (containingmethionine, cysteine, lysine, and tryptophan). It has been reported that poultry requires lysine at concentrations ranging from 0.45 % to 0.85 %, while the methionine requirement ranges from 0.10 % to 0.32 % (Parkhurst & Mountney, 2012). Sitompul (2004) stated that lysine and methionine are limiting amino acids in feed; hence it is necessary to consider them while formulating poultry mixtures. Alfalfa is not only high in protein content (22–32 %), twice as high ascorn (between 8 % and 11 %), but also containslysine(0.54 % – 0.58 %) at levels 11 times higher than that of corn (0.05 %) (Suwignyo et al., 2020b, Suarni and Widowati, 2005). However, lysine and methionine contents in alfalfa (0.58 % and 0.1 %) arelower than that in fish meal (2.71 % and 0.99 %) orsoybean meal (1.17 % and 0.7 %), respectively (Sitompul, 2004).Based on the findings of the study of alfalfa, it is predicted that alfalfa will meet the nutritional needs of poultry (Suwignyo et al., 2020b).

8. Conclusions

Alfalfa is popularly known as the “Queen of Forages” towing to its high forage yield and nutrient quality content. The alfalfa plant is native to the Mediterranean mountainous areas and was brought to other countries, such as Indonesia, for cultivation. Tropical alfalfa is cultivated in tropical areas for its superior nutrient and crude protein content, secondary metabolic content, amino acid content, and macro and micro mineral content. The plant can be used as forage to increase the production of meat, milk, and eggs. Additionally, the cultivation of tropical alfalfa provides breeders with high-quality feed, leading to a significant improvement in livestock production.

Alfalfa thrives in subtropical regions because the climate, temperature, and humidity of the region support its growth; however, the plant has not thrived well in tropical areas. The cultivation of the plant in the tropics is difficult because the variations in climate, temperature, and humidity have a significant impact on the development of the plant. Additionally, it takes relatively longer for the plant to yield fertile seeds that can be sown for further crops.

Availability of data and materials

Data were collected from journal, proceeding, news and some legal source then analyzed it with analitical dercription.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors' contributions

BS: Designed, guided the study, and reviewed the manuscript. EAR: Collected and analyzed the data. SH: Reviewed the manuscript prior to be submitted. All authors read and approved the final manuscript.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.