INTRODUCTION

Emissions of greenhouse gases (GHGs), particularly carbon dioxide (CO2) and methane (CH4), from livestock production are major contributors to global warming. Increasing demand for livestock products further exacerbates the accumulation of GHGs in the atmosphere. Reducing enteric CH4 production in ruminants is therefore an important strategy for improving environmental sustainability and feed utilization efficiency. However, the high cost and limited availability of concentrate feeds remain major constraints for animal production systems, prompting nutritionists to explore affordable and sustainable alternatives. Numerous plant species contain nutrients and bioactive compounds that enhance animal health, and several plant-derived compounds have shown considerable promise as natural feed additives [1]. In tropical regions, leguminous plants are widely utilized to improve the availability and nutritional quality of ruminant diets. Forages, shrubs, legumes, cereals, and grains are rich sources of phytogenic compounds, particularly condensed tannins (CT) and saponins (SP), which have attracted considerable attention as natural rumen modifiers capable of improving feed efficiency and reducing CH4 emissions [2]. Depending on their concentration, tannins may exert either antinutritional or beneficial effects, contributing to improved animal productivity and reduced CH4 formation. Moreover, the leaves of leguminous trees and shrubs represent inexpensive and readily available sources of dietary protein.

Leucaena leucocephala, commonly known as leucaena, has attracted considerable interest as a ruminant feed because of its high crude protein (CP) content, rapid ruminal degradability, and capacity to enhance rumen microbial activity [3]. Recent evaluations have demonstrated favorable in vitro rumen fermentation kinetics, indicating that the leaves and stems of Leucaena are highly suitable protein supplements for ruminants [4]. Furthermore, several Leucaena species have been reported to positively modify fermentation pathways and increase post-ruminal protein supply without adversely affecting total gas production [5]. Leucaena contains approximately 31.1% CP, 5.6% crude fat, 94.8% dry matter (DM), 13.2% crude fiber, 4.5% ash, and 1.89% CT [6]. Variations among subspecies and cultivars influence CT concentration, underscoring Leucaena's value as a fodder legume for its high palatability and abundance of protein, amino acids, minerals, and fiber. The ability of Leucaena to reduce enteric CH4 production is largely attributed to CT, which forms complexes with proteins and polysaccharides, thereby decreasing nutrient degradation in the rumen. In addition, Leucaena leaves provide substantial amounts of essential amino acids such as isoleucine and leucine, as well as limiting amino acids such as lysine and methionine, compared with other multipurpose tree species [7]. According to Montoya-Flores_ et al._ [8], supplementation with dried L. leucocephala leaves at levels up to 12% DM improved digestible CP and reduced daily CH4 emissions without negatively affecting DM intake, fermentation characteristics, or rumen microbial populations in crossbred heifers. Similarly, Aoetpah et al. [9] reported that Timor Bali cattle fed a Cipelang grass-based diet containing 56% leucaena leaf meal exhibited improved DM intake, nutrient digestibility, and average daily gain. Consequently, natural feed additives have attracted increasing attention as a strategy for enhancing feed utilization and animal performance.

Medicinal plants containing bioactive secondary metabolites with antimicrobial properties have been widely used to improve productivity in pigs, poultry, ruminants, and aquaculture species. Among these, ginger (Zingiber officinale) has recently emerged as a potent modulator of the rumen ecosystem and has demonstrated a significant capacity for CH4 mitigation under in vitro conditions [10]. These findings are consistent with the broader use of phytogenic additives to alter rumen fermentation patterns and reduce GHG emissions [2]. Ginger powder contains approximately 60%–70% carbohydrates, 9% protein, 3%–8% fiber, 2%–6% proteases, 3%–6% lipids, and 1%–3% volatile compounds, including gingerol, zingiberene, zingiberol, shogaol, terpenes, oleoresin, and zingerone, in addition to vitamins A, C, and B3, phenols, and flavonoids [11]. Phytobiotics and phytochemicals derived from ginger enhance nutrient digestibility, growth rate, feed conversion efficiency, and feed palatability. Moreover, ginger promotes animal growth through its antimicrobial activity against pathogenic microorganisms, thereby improving digestive efficiency [12]. Increased salivary secretion and stimulation of digestive enzymes induced by ginger also promote the proliferation of cellulolytic bacteria. Al-Dain and Jarjeis [13] observed that supplementation with 75 or 150 g of ginger root powder/head/day improved feed intake and milk production in dairy cows. Thus, ginger has been extensively investigated as a phytogenic feed additive because of its beneficial effects on animal health and productivity.

Although numerous studies have documented the individual effects of L. leucocephala and ginger, a critical knowledge gap remains. Previous studies have primarily focused on the use of Leucaena as a source of CT to reduce CH4 emissions and enhance bypass protein, whereas the effects of ginger have largely been investigated independently due to its antimicrobial and fermentation-modulating properties. Moreover, most studies evaluating ginger have been conducted in vitro, whereas in vivo studies assessing its effects in ruminants remain limited. To date, no study has strategically integrated these two phytogenic resources into a practical pelleted formulation intended for beef cattle. Consequently, the potential synergistic interactions among CT from Leucaena, flavonoids, and essential oils from ginger on nutrient utilization, rumen fermentation, microbial population dynamics, microbial protein synthesis, and CH4 mitigation have not been comprehensively investigated. In addition, information regarding the efficacy of such a combination in animals maintained on low-quality rice straw-based diets is lacking. Despite the excellent nutritional profile of L. leucocephala, its utilization is constrained by the presence of mimosine, a toxic non-protein amino acid that may constitute 2%–10% of leaf DM and can adversely affect growth and thyroid function at excessive intake levels. Nevertheless, previous evidence suggests that appropriate processing methods, including drying and pelleting, together with controlled inclusion levels, can effectively minimize these risks.

Considering the complementary biological activities of L. leucocephala and ginger, this study hypothesized that co-pelleting Leucaena leaves and ginger powder at a 75:15 ratio would generate synergistic effects that improve nutrient degradability, suppress protozoal populations, enhance microbial efficiency, and mitigate enteric CH4 production without compromising animal health. To ensure safety, the maximum supplementation level was limited to 150 g/head/day, corresponding to approximately 112.5 g of Leucaena leaves, thereby allowing the formulation to function as a phytogenic modulator rather than a major protein source. Therefore, the objective of this study was to develop and evaluate a novel Leucaena-ginger phytogenic pellet (LGP) and to determine its effects on nutrient utilization, rumen fermentation characteristics, microbial protein synthesis, microbial populations, and enteric CH4 production in Thai native beef cattle. Furthermore, the study aimed to assess the feasibility of this phytogenic formulation as a practical and environmentally sustainable feed additive for tropical beef production systems.