Ruminants include cattle, sheep, goats, deer, and other cud-chewing cloven-hoofed mammals that are poly-gastric herbivorous with a unique gastrointestinal tract that allows them to digest plant materials and makes them an important part of the food chains all over the world (1, 2). Unlike monogastric animals, the ruminant’s digestive system has one stomach with four chambers. These chambers are the rumen, the reticulum, the omasum, and the abomasum. The energy requirements of ruminant animals are met predominantly through the production of volatile fatty acids (VFAs) by the microorganisms that live in the ruminant’s stomach, mostly in the rumen, in a symbiotic relationship with the ruminant animal (3). This symbiotic relationship is beneficial to ruminants as well as the microorganisms. On the one hand, the microorganisms benefit by having a warm, wet, nutrient-rich environment to reside in. In other words, the host animal provides an anaerobic fermentation chamber for the microbes to break down the ingested feed into microbial proteins and VFAs to supply high-quality nutrients for the ruminant animal. On the other hand, a major benefit that a ruminant animal gets from the symbiotic relationship is the ability of microorganisms to digest fibre in forage-based diets (4, 5).

The enteric fermentation that takes place in the rumen is adversely correlated to environmental sustainability since it results in greenhouse gas (GHG) emissions. Several studies have been conducted to reduce ruminant methane emissions since GHG profile of the cattle dairy sector is dominated by methane emissions that is produced during the feed energy utilisation process (6). Improving ruminant productivity and energy efficiency by increasing feed digestibility, for example, is the one of the most cost-effective and promising techniques for reducing ruminant methane gas emissions (6, 7).

The digestibility of plant cell-wall material such as cellulose, hemicellulose, pectin, and lignin, as the primary source of feed for ruminants, has a significant economic implication in both developed and developing countries. However, the rumen’s ability to digest fibre is not optimum, as evidenced by the fermentability of fibre recovered from faeces (5). Ruminant animals may not digest up to 70% of their diet that contains fibrous components (8). Therefore, researchers have attempted to enhance feed utilisation rate in the rumen by manipulation of ruminal fermentation and improving diet management (7).

Ruminants lack the enzymes required to digest fibrous materials. As such, they rely on microbes within their digestive system for producing digestive enzymes (9). Therefore, most of the approaches for enhancing feed utilisation in ruminants are based on manipulation of rumen fermentation genetically or via incorporation of fibrolytic microorganisms or enzymes in ruminant feed (5). The addition of highly fibrolytic ruminal microorganisms or their enzyme extract have the potential to increase fibre digestibility and feed utilisation in ruminants (10, 11). Several in vitro and animal studies have been conducted on the use of exogenous enzyme formulations to improve feed utilisation and productivity in ruminants (12, 13). Nevertheless, so far, the outcomes in terms of productivity improvement are inconsistent (12, 13). This has been attributed to the use of feed enzyme formulations that are not specifically formulated for the target application, the mode of delivery of the enzymes and its effect on their stability and activity (alone or mixed with the feed, the proportion of the feed in the mix), variation in the stability of exogenous enzyme formulations in the rumen environment, and limited understanding of the rumen microbiota and their enzymes that would have enabled better design of exogenous enzyme supplements for synergistic activity with the microbial enzymes in the rumen (13).

The stability and activity of enzymes is highly dependent on environmental factors such as pH, ionic strength, temperature, and the presence of proteases and other (bio)chemicals that enhance or inhibit their activity and/or cause denaturation. Studies indicate that exogenous enzymes that bind to the feed seem to be more effective possibly due to more resistance to degradation by microbial proteases in the rumen (13, 14). The rumen gastrointestinal (GI) tract is a highly complex and harsh environment comprising of the rumen with its microbiota and their enzymes as well as the very low pH environment of the abomasum, which can negatively affect the activity of exogenous enzymes. In this respect, technologies that protect enzymes against environmental stress are of great value. Microencapsulation is one such technology that enables protection of feed enzymes against the harsh environment in the rumen and abomasum and targeted release in the GI tract for effective enhancement of feed utilisation rate.

Microencapsulation protects bioactive compounds against biotic and abiotic stresses in their environment by enclosing them in a carrier matrix (15, 16). The technology not only helps to maintain biological activity of susceptible bioactive compounds during ingestion but also enable their release at a specific location (15). Desai and Jin Park (17) described microencapsulation as a technology that was invented about 65 years ago to encapsulate liquids, gases, or solids in sealed capsules and control the release of their content under certain conditions. Several methods have been developed for producing microcapsules. Chemical methods, physicochemical methods, and physical methods are the three broad categories of microcapsule formation technologies. The method used is determined by the size of microcapsules, both the core and the wall’s chemical/physical properties, the bioactive core’s applications, economics, core sensitivity, and mechanisms of release (18, 19). Microencapsulation technology is widely used in the pharmaceutical and the food industries (15). It is also used in the ruminant feed industry to a lesser extent, to protect active compounds from rumen degradation, allowing for increased bioavailability of these compounds in the lower gastrointestinal tract of ruminants (20). A number of studies investigated microencapsulation for the delivery of actives such as essential oils (21), polyunsaturated fatty acids (22) and vitamins (23, 24) to ruminants resulting in better outcomes compared to the same amount of non-encapsulated ingredients. Microencapsulated feed supplement such as essential oils, butyrate, and bacteria are already available in the market. However, limited information is available in the public domain on microencapsulation of enzymes for post-rumen delivery in ruminants. This review briefly discusses feed utilisation efficiency in ruminants and the use of exogenous fibrolytic enzymes for improving feed utilisation and the challenges to delivery of enzymes to the ruminant GI system post rumen followed by a discussion on the potential of microencapsulation technology to overcome these challenges.

Soluble carbohydrates as well as soluble cell wall carbohydrates such as sugars, starches, soluble fibres, pectins and β-glucans are rapidly digested in the rumen with very minimal amounts escaping to post-ruminal digestion. The majority of these soluble carbohydrates are degraded in both the small intestine and hindgut if they are not degraded in the rumen (25). However, insoluble cell wall carbohydrates, for example, neutral detergent fibre (NDF) are slowly degraded in the rumen. As a result, the retention time of the fibre in the rumen determines the extent of rumen digestion. For instance, grinding fibre into small particles may help it move through the rumen more quickly, however ruminal digestion of that fibre particle may be reduced as a result of the reduced surface area available for rumen microbes to attach and digest these fibrous materials (26). Huhtanen et al. (25) pointed out that there is no digestion of fibre in the small intestine since both soluble and insoluble fibre digestion is dependent on microbial fermentation. However, fibre that is not degraded by the rumen may be digested in the hindgut (27). However, much fewer efforts have been dedicated to understanding the digestion rate of fibre residues in the hindgut.

Factors limiting fibre digestion in the rumen involve microbial enzymes such as β 1–4 cellulase enzyme complex, allowing plant cell wall polysaccharides to be hydrolysed in the rumen. However, ruminants may not digest up to 70% of their diet, particularly the fibrous components, and only 10–35 percent of energy intake is received as net energy by the ruminant animal (8). Four main factors have been identified as limiting factors for fibre digestion in the rumen: (i) animal factors that boost the nutrient’s availability through salivation, digesta kinetics, and mastication (i.e., ruminant fibre intake and mastication alter the pace of passage through the digestive tract, with higher intakes resulting in decreased total fibre digestion), (ii) microbiological factors that affect adhesion to the hydrolytic enzyme complexes of microbes in the rumen, (iii) the population of the most common fibre-digesting microbes, (iv) the biodegradability and the chemical composition of plant material’s insoluble component (28). Rumen pH appears to be a major factor in fibre digestion. A moderate drop in pH to around 6.0 causes a slight reduction in fibre digestion, but the number of fibrolytic microorganisms is unaffected. Further reduction of pH to 5.5 or 5.0 results in slowed growth rate and fewer fibrolytic bacteria, and fibre digestion may be halted. The drop in pH is caused by inadequate fibre with a high level of starch in the diet or fibre that has been chopped finely, which adversely affects chewing periods and consequently saliva production (29). Other factors such the level of lignification of the feed, and cellulolytic enzyme inhibition may affect fibre digestion (30). Kung (29) noted that lignin acts as an intercellular cement, giving plants stiffness, but reducing fermentability. According to Allen and Mertens (31), the indigestible fraction of fibre is the most significant independent constraint on fibre digestion. This fraction makes up 1/3 to 1/2 of the total fibre fraction. The digestibility of various plant components in the rumen is illustrated in Figure 1.

Improving fibre digestion in ruminants has been a focus of research in rumen microbiology for several decades. Ruminants rely on the microbial population within their rumen to produce the necessary enzymes for fibre digestion, as they lack the required endogenous enzymes themselves (9). The supplementation of highly fibrolytic ruminal microorganisms or their enzyme extracts has been found to increase fibre degradability in ruminants (10). However, the effects on growth traits and feed efficiency ratio were not constant, and the impact may vary depending on breeds and dosages used. Further research may be required to assess the optimal dosage and specific benefits of exogenous fibrolytic enzymes supplementation in ruminants’ nutrition.

Other factors such as diet composition, feed processing methods, environmental stress and rumen microbial populations can also influence fibre digestion and feed utilisation in ruminants. For instance, diets containing high levels of readily fermentable carbohydrates may impede the efficacy of enzymes in fibre digestion (32). Therefore, a comprehensive understanding of the interactions between enzymes, microorganisms, and the rumen environment is necessary to optimise the use of enzymes for enhancing feed utilisation.

In various industrial sectors where enzymes play a pivotal role, the issue of enzyme stability emerges as a crucial obstacle in optimising their efficacy. Despite the potential benefits of exogenous enzyme supplementation in improving fibre digestibility and nutrient absorption, the practical application of these enzymes is frequently impeded by challenges pertaining to their stability (39, 41, 48). Roy Choudhury (55) stated that enzymes are most effective when the pH and temperature are maintained within a limited range. Based on that, the shape of the active site of an enzyme can be altered by heating or changing the pH of the enzyme’s surroundings, rendering it inactive. Factors such as extreme pH and temperature variations, exposure to proteolytic enzymes, and interactions with dietary components can lead to enzyme denaturation, degradation, or loss of activity before reaching their intended targets (56–59). Thus, there is a critical need for research and development efforts aimed at enhancing enzyme stability across various environments. Addressing these stability issues is paramount to unlocking the full potential of enzyme supplementation. Thus, microencapsulating these enzymes is a viable option for improving their application in commercial products and industrial processes (60).

Microencapsulation is a versatile technique that has been widely utilised for the encapsulation of various compounds, including water-soluble substances like enzymes. This process involves the coating or surrounding of individual particles, referred to as core or active materials, with a protective wall material, resulting in the formation of microcapsules or microspheres (61, 62). Microcapsules consist of an inner core containing the enzyme and a polymer membrane that encapsulates it, while microspheres are composed of a polymer matrix with the enzyme uniformly dispersed or dissolved within it as shown in Figure 3 (64, 65). Microencapsulation has emerged as a promising technique for the protected delivery of enzymes to the gastrointestinal (GI) tracts of both humans and animals, including poultry (62, 66). This innovative approach involves encapsulating enzymes within protective coatings, allowing for controlled release and targeted delivery within the GI environment (67).

The primary objective of microencapsulation is to protect the encapsulated enzyme from harsh environmental conditions, such as pH, temperature, and oxidative stress, thereby enhancing its stability and prolonging its shelf life (54). The encapsulation process creates a barrier between the enzyme and its surroundings, preventing degradation and maintaining its activity during storage or when exposed to unfavourable conditions. Table 2 shows a summary of studies on microencapsulation techniques for enzyme protection against environmental stress.

One of the significant advantages of microencapsulation is its ability to improve the stability of enzymes. Studies have shown a significant increase in the thermal stability of encapsulated enzymes compared to their free counterparts. For example, microencapsulation of phytase by alginate beads was reported to significant increase the stability of the enzyme from 20 to 79% (73). In Another study conducted by Zhao et al. (74), lipase encapsulation resulted in the preservation of 87.5% of its activity following exposure to a thermal treatment at 70°C for 2 h, whereas the unencapsulated enzyme experienced a substantial loss of 99.5% activity under identical conditions. Similarly, Yang et al. (70) noted that lipase encapsulated within a matrix retained higher activity at elevated temperatures (50°C and 60°C) for an extended period compared to the free form. This enhanced thermal stability is attributed to the protective effect of the encapsulating material, which acts as a shield against heat-induced denaturation and degradation. Furthermore, microencapsulation provides a buffer against pH variations, maintaining enzyme activity over a broader pH range. Zhang et al. (59) found that encapsulated protease retained approximately 40% of its activity under varying pH conditions, indicating improved stability compared to the free enzyme. This stability is crucial for applications in diverse pH environments, such as industrial processes or gastrointestinal delivery. Additionally, Free enzymes are susceptible to proteolytic degradation, limiting their functionality in biological systems. However, encapsulation offers protection against proteases, as observed by Sari et al. (69) and Simone et al. (58). These studies reported significant enzyme activity retention even after exposure to proteolytic conditions, highlighting the potential of encapsulation in enhancing enzyme stability in biological fluids or environments rich in proteases.

In addition to improving stability, microencapsulation offers several other benefits for enzymes. It allows controlled release of the encapsulated enzyme, enabling targeted delivery to specific sites or controlled release over a prolonged period (75, 76). This controlled release is particularly advantageous in applications where a sustained enzyme activity is required, such as in drug delivery systems or in biotechnology industries. The key parameters influencing release rates are interactions between the wall material and the core, core’s volatility, the ratio of the core to the wall material, and the wall material’s viscosity grade (77). The primary mechanisms involved in core release are shown in Table 3. More than one mechanism is used in practice (17).

Furthermore, microencapsulation provides a means to enhance the loading capacity of enzymes. The encapsulating material can accommodate a high concentration of enzymes, maximising their content within the microcapsules or microspheres. This high enzyme loading capacity ensures that a significant amount of active enzyme is available for the desired application. For example, the successful encapsulation of Flavourzyme^® into a cross-linked chitosan matrix enabled improved loading capacity of Flavourzyme^® in chitosan-TPP microparticles and could be a promising option for utilising commercial proteases in food processing (78). Thomas et al. (79) and Anjani (80) highlighted the efficacy of a microcapsule system in facilitating the efficient loading of enzymes while ensuring extended shelf life and sustained activity. Moreover, Weng et al. (73) successfully optimised the overall efficiency of phytase encapsulation by employing a three-fluid nozzle spray drying technique, resulting in a substantial enzyme loading capacity of 48 wt%. These findings collectively highlight the potential of different encapsulation strategies in enhancing enzyme loading and preserving their activity for diverse applications in various fields.

Overall, microencapsulation has emerged as a promising approach for the effective delivery and protection of water-soluble compounds, including enzymes. The technique offers improved stability, controlled release, and enhanced loading capacity, making it a valuable tool in various fields such as pharmaceuticals, biotechnology, food, and cosmetics. Further research and development in microencapsulation methods and materials hold great potential for advancing the application of enzymes in diverse industries.

In animal nutrition, microencapsulation can be utilised for a variety of applications. It can be used to deliver substances to a specific location of the gastrointestinal (GI) tract (i.e., targeting a particular site of the intestinal tract as a dietary component of the feed), to mask the flavour of products with undesirable flavour, to ensure product stability during long periods of storage, or to increase the bioavailability of a product to improve animal performance (84). Several studies have contributed to refining methods for preserving nutrient integrity during ruminal passage. Yoshimaru et al. (51) demonstrated the successful transit of spray-dried microcapsules of protease through the rumen with minimal degradation, releasing their content in the abomasum. Similarly, studies by Yoshimaru et al. (85) highlighted the potential of spray-dried L-lysine with zein to resist ruminal damage and pass through the rumen with minimal degradation. Recent investigations, such as (86), have explored microencapsulation with ethyl cellulose and carbomer to protect L-carnitine in the rumen, showcasing improved antioxidant capacity compared to unprotected supplementation. Likewise, encapsulation of soybean meal with zein or wheat gluten demonstrated enhanced ruminal protection compared to unprotected soybean meal (52).

The field has seen diverse approaches, including studies comparing microencapsulation methods and wall materials for nutrient protection. Chauhan and Gautam (87) assessed pan coating and fluidized bed coating methods, determining that choline chloride granules coated with cellulose-based polymer and hydrogenated vegetable oils using fluidized bed coating exhibited high rumen bypass potency. Conversely, Pretorius (88) found that evaluated wall materials like zein and kafirin displayed consistent release curves during ruminal transit, with protein coatings failing to provide complete protection. Chiang et al. (89) and Cao et al. (90) delved into the stability of protected amino acids and the controlled release of L-carnitine, emphasising the importance of coating composition and levels. Other authors have also highlighted the coating levels influenced the efficacy of active ingredients release at the desired location (86, 91–93). Notably, Ibrahim and Hassen (67) employed the solid-in-oil-in-water (S/O/W) technique to encapsulate Mimosa tannin, achieving smaller diameters, lower density, and high encapsulation efficiency. The study demonstrated controlled release dynamics, with a fraction released in the stimulated rumen, and specific percentages in the abomasum and small intestine.

Furthermore, Carrillo-Díaz et al. (94) stated that understanding the efficacy of encapsulated materials necessitates a consideration of various factors, including enzyme type and dose, forage composition, and the forage-to-concentrate ratio. In vitro results may not perfectly align with in vivo effects, highlighting the intricate interplay of exogenous fibrolytic enzymes (EFEs), ruminal fluid, and animal-specific conditions. In conclusion, numerous studies underscore the potential of microencapsulation in delivering various compounds to distinct regions of the ruminant GI tract. Despite the complexities involved, these endeavours collectively contribute to advancing our understanding of microencapsulation’s feasibility and efficacy in optimising nutrient delivery for improved animal nutrition and well-being.

Low feed utilisation efficiency is still a major problem in livestock production with forage as the main feedstock. Various approaches such as breeding and genetic approaches for breeds with higher feed utilisation efficiency and supplementing the feed with exogenous microorganisms and fibre-digesting enzymes have been evaluated for improving feed utilisation efficiency with different degree of success. The use of exogenous enzymes in particular has significant potential for enhancing fibre digestibility in rumen and post-rumen. However, better enzyme formulations to synergistically work with rumen microbial enzymes and delivery systems that protect exogenous enzymes during delivery to the rumen and beyond in the GI tract of ruminants are required in order to fully benefit from enzyme supplementation. In this regard, the use of microencapsulation for protected and targeted delivery of enzymes has a huge potential. Improving feed utilisation rate in ruminants, will result in increasing production of milk and meat for human consumption and improving the efficiency of livestock production in a more cost-effective manner as well as reducing environmental footprint. Although many studies and reviews on the delivery of encapsulated active compounds in ruminants have been undertaken, it is still unknown if the delivery of encapsulated enzymes in active form to the rumen and the hindgut of ruminants would be successful. Therefore, further studies are needed to develop microencapsulation approaches that enable the delivery of enzymes at specific targets in the GI tract of ruminants. Additionally, studies evaluating the stability of encapsulated enzymes under simulated gastrointestinal conditions, such as variations in pH, temperature, and enzymatic activity are needed. Assessing the bioavailability and efficacy of encapsulated enzymes in vivo is essential to determine their impact on fibre digestion and feed utilisation efficiency in ruminants. Investigating the long-term effects of microencapsulated enzyme supplementation on animal health, productivity, and performance is also critical for ensuring safety and sustainability. These studies will help refine microencapsulation approaches for enzyme delivery in ruminants, ultimately enhancing fibre digestion, feed utilisation efficiency, and livestock productivity in a sustainable manner.

NA: Visualization, Conceptualization, Investigation, Writing – original draft, Writing – review & editing. FT: Funding acquisition, Resources, Supervision, Writing – review & editing. NT: Conceptualization, Funding acquisition, Resources, Supervision, Writing – review & editing.