Exploring Multiple Impacts of Dietary Tea Supplements on Ruminants: A Meta-Analysis

Ruminants such as cattle, sheep, and goats are crucial in the global food supply, providing significant sources of meat and milk. Enhancing productivity in these animals is a key objective for ruminant producers worldwide. For the past few years, products that are safe for to both people and the environment have become very popular. This popularity has led the use of plant-base compounds in animal feed. (Saeed et al., 2017; Kolling et al., 2022). Using natural additives in animal diets is good for health of ruminants, and matches the growing preference for more eco-friendly and health-farming practices. Plant extracts are being investigated due to the potential ability to act as natural feed additives with anthelmintic effects that improve boost productivity (Ramdani et al., 2023; Ramdani et al., 2017) while also supporting sustainability.

Tea, which comes from the Camellia sinensis plant, is well-known for having many different natural chemicals like polyphenols, catechins, and caffeine (Kolling et al., 2022; Ramdani et al., 2022; Li et al., 2019; Ma et al., 2021). These chemicals have been studied a lot for their antioxidant, anti-inflammatory, and metabolism-regulating effects in humans (Li et al., 2019). There is a great deal of interest in exploring plant bioactive compounds with beneficial effects on ruminants. A previous study stated that the application of green tea waste enhanced lactic acid fermentation of silage and affected performance in ruminants (Kondo et al., 2004a; b).

Several main components of tea include caffeine (15.2%), epigallocatechin gallate (49.8%), epigallocatechin (11.7%), epicatechin gallate (13.4%), theobromine (1.35%), rutin (1.11%), and other catechins namely catechin, gallocatechin gallate, and catechin gallate in lower amounts (Ramdani et al., 2018). These components influence the health of ruminants by regulating gut microbiota activity and nutrient absorption (Liu et al., 2019). Several forms of tea products are used as supplements, including leaf, extracts, and waste. Tea leaf was collected from Cammelia sinensis plant and then subjected to various processes such as withering, rolling, oxidation, and drying. Tea leaf, especially non-graded, has beneficial value due to the active ingredients, but does not have economic value, leading as ruminant dietary additive (Ramdani et al., 2020). Tea waste originates from beverage companies, which produce about 100.000 tons every year. The majority of the waste is burned, thrown into landfills, or turned into compost, resulting in economic and environmental problems (Kondo et al., 2004b; Nishida et al., 2006). Meanwhile, tea extract is produced from non-grade tea which has been subjected to an extraction process to identify the active ingredients and used as feed supplement for ruminants. Numerous studies have investigated the potential advantages of tea extract and waste supplementation in ruminants. However, the results varied, underscoring the need for a comprehensive synthesis of the available data to establish the overall effect of tea supplementation on productivity. A meta-analysis approach can consolidate published data to provide a comprehensive. Therefore, this meta-analysis aimed to determine the influence of tea supplementation on performance, digestibility, and blood parameters of ruminants.

All articles were selected in line with the standard inclusion criteria for a systematic review and meta-analysis, considering their quality and relevance. The initial step was to check the article databases from Science Direct and Scopus using keywords (“Tea” AND “Rumen” OR “Sheep” OR “Goat” OR “Cattle” OR “Cow”) in the reference manager software (Mendeley). The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA, Liberati et al., 2009) procedure was used for this review (Figure 1). Following the identification articles, a title review procedure was carried out. The criteria applied in the selection stage include article published in English as a full text, and belonging to reputable journal.

The appropriateness evaluation stage was completed by viewing the articles and selecting based on reasons-ableness for the point under study. This method provides good quality control for systematic reviews and minimizes the risk of error (Liberati et al., 2009). The review process showed that about 3,479 articles were not duplicated. The next step was to select articles based on the relevance of each title, performance, and blood analysis, comparison between control and experimental treatments, as well as the addition of tea. A total of 2,464 articles were deleted, and 15 were selected for meta-analysis.

A meta-analysis was performed using OpenMEE software (http://www.cebm.brown.edu/openmee/index.html) specifically designed for meta-analyses in the fields of biology and ecology (Wallace et al., 2017). The continuous outcome data for the averages of the experimental units (control vs. treatment) were set and organized in a comma-separated value (CSV) file, which was then input into the software. Hedges g was used to calculate the effect size for each outcome variable using a random-effects model. Generally, random effects models are applied when displaying the data as standardized mean differences (SMD) between the control and treatment groups. Hedges g accounts for the bias that can arise from small sample sizes in effect size estimation. When studies with different sample sizes are included in the meta-analysis, the correction improves the measure’s accuracy and dependability. Specifically, g≅d×(1-3/(4(n1+n2)-9)) was the formula used for this computation, where n is the sample size of the treatment and control groups (Higgins et al., 2003). Using a random-effects model with 95% confidence intervals (CIs), the output was produced. Due to the established analytical strength, particularly when working with small sample size, Hedge g was selected (Galkanda-Arachchige et al., 2020). When tea supplementation was given in this investigation, a positive value of Hedges g (P < 0.05) showed a significantly larger treatment effect when compared to the control group. Additionally, the DerSimonian and Laird test (Q-statistic) was used to compute the heterogeneity index (I2) at a significance threshold of P < 0.05. The degree of heterogeneity was categorized as follows no heterogeneity (0 < I2 ≤ 25%), low (25% < I2 ≤ 50%), moderate (50% < I2 ≤ 75%), and high (I2 > 75%) (Higgins et al., 2003).

The growing emphasis on animal welfare and human health has led to a rise in the usage of plant extracts as additives in animal feed (Maciej et al., 2016; Stivanin et al., 2019). Fruits, vegetables, tea, and nuts all contain polyphenols, a kind of naturally occurring plant chemical that is crucial for ruminant nutrition (Scalbert et al., 2005). In addition to providing color and flavor, these substances shield plants from environmental stressors and function as antioxidants. According to Vasta et al. (2010), polyphenols can neutralize free radicals and lessen oxidative stress, preventing cell damage. Numerous studies demonstrate the anti-inflammatory qualities of polyphenols, which enhance digestive health by reducing inflammation in ruminant digestive systems (Calsamiglia et al., 2007). Additionally, the chemicals have potent antioxidant and antibacterial qualities that aid in preventing harmful microbial activity and safeguard important food proteins in the rumen.

Vasta et al. (2007) found that dietary tannins might slow down the activity of ruminal microorganisms responsible for biohydrogenation. Several studies have shown that tannins can bind to proteins (Jones and Mangan, 1977; Vasta et al., 2010) and inhibit the growth of bacteria in ruminants (Min et al., 2003). Polyphenols from tea plants go through complex changes in the digestive system. This process starts when polyphenols are eaten and move through the digestive tract, encountering various enzymes (Kim et al., 2021). In the rumen, the main fermentation chamber of ruminants, microorganisms like bacteria and protozoa help break down the compounds through enzymatic actions, releasing metabolites (Kim et al., 2021). The metabolites then move to the lower digestive segments, where further changes occur. Absorption of these metabolites happens in the small intestine, allowing entry into the bloodstream.

The liver is essential for processing and modifying compounds before being distributed to various tissues. This complex series of metabolic events highlights the dynamic nature of how polyphenols are handled in ruminant systems. Additionally, the interaction between polyphenols and the microbial community in the rumen affects both the fate of these compounds and overall digestive efficiency. Understanding this interaction is crucial for grasping the broader effects on animal health and nutrition. The metabolic journey of polyphenols in ruminants is a key focus of ongoing research, offering insights into the complex dynamics of plant-derived compounds in animal physiology.

As shown in Table 1, various studies have examined three forms of tea, namely leaf, extracts, and waste. These studies, in general, show that tea can significantly improve Dry Matter Intake (DMI) and digestibility compared to controls. However, some studies did not find significant changes. Different forms of tea can have varying effects on the observed parameters, likely due to the bioactive content of tea, such as polyphenols and catechins (Figure 2), which can affect gut microbiota and boost digestive efficiency. The increased DMI might also be due to tea’s high palatability, leading to greater feed consumption. However, not all studies reported significant results, presumably due to differences in the type of tea used, dosage, environmental conditions, and subjects. Some studies also found that certain forms of tea can significantly lower blood glucose and urea levels. This blood glucose-lowering effect is presumably due to the presence of compounds such as epigallocatechin gallate (EGCG) in tea, which has been shown to increase insulin sensitivity and reduce resistance. The decrease in blood urea levels may be related to the increased efficiency of protein metabolism and the reduced protein catabolism due to tea consumption. However, similar to DMI and digestibility,

Table 1: Articles selected for metaanalysis and its general effect.

not all studies reported significant reductions. This suggests that the physiological response to tea may vary depending on factors such as the type of tea, dose, duration of administration, and health status of the subject before the study.

The meta-analysis results in Table 2 showed that there was almost no significant influence from various types of tea sources on AWG, DMI, body condition score, dry matter, crude protein, acid detergent fiber, and neutral detergent fiber digestibility (P > 0.05), except for blood glucose levels (P = 0.069) and blood urea content (P = 0.006). However, when analyzed using subgroup analysis, the administration of various forms of tea such as extract, leaf, and waste showed different effects (Table 3). Tea waste supplementation had a significant effect on DMI (P = 0.004) and acid detergent fiber digestibility (P = 0.032). Tea extract supplementation also had a significant effect on blood glucose (P < 0.001) and blood urea (P < 0.001). In contrast, untreated tea did not show any significant effects on AWG, DMI, as well as dry matter, crude protein, acid detergent fiber, and neutral detergent fiber digestibility.

Po et al. (2012) reported that tannin supplementation in ruminant diets led to decreased feed intake, attributed to the bitter taste. Similarly, Méndez-Ortiz et al. (2018) concluded that tannin intake did not have a significant impact on DMI and AWG in sheep. Various studies (Kolling et al., 2022; Stivanin et al., 2019; Vizzotto et al., 2021) also showed that there was no significant difference between the control and treatment groups regarding DMI.

Diets supplemented with polyphenols may affect nutritional profiles that not only influence DMI but also have a positive effect on the efficiency of using certain nutrients (Makkar, 2003). Polyphenols can modulate metabolic processes in sheep, including the effects on the absorption and use of nutrients. This may lead to differences in the AWG, even though the DMI is relatively stable (Makkar et al., 2007). Green tea, which is abundant in tannins, can diminish the solubility and rumen degradability of numerous leaf proteins due to the protein-binding properties (Huang et al., 2010; Bodas et al., 2012). However, the results in Table 3 showed that giving various types of tea did not affect digestibility, including dry matter, protein, acid detergent fiber, or neutral detergent fiber. The subgroup analysis showed that the administration of tea waste had a significant effect on acid detergent fiber digestibility.

Nutrient balance in the diet plays an important role in the psychological well-being of ruminants by ensuring ade

Table 2: Meta-analysis the effect tea supplementations on AWG (Kg/head/day), DMI (g/head/day), MEI (MJ/day), TDNI (kg/day), NDFI (kg/day), CPI (kg/day) Daily time spent in activity (Min), Diurnal time spent standing up (Min), Diurnal time spent lying down (Min), DMD (%), CPD (%), ADFD (%), NDFD (%), Blood Glucose (mg/dl) and Blood Urea (mg/dl) in ruminants.

AWG: average weight gain; DMI: dry matter intake; MEI: metabolizable energy intake; TDNI: total digestible nutrient intake; NDFI: neutral detergent fiber intake; CPI: crude protein intake; DMD: dry matter digestibility; CPD: crude protein digestibility; ADFD: acid detergent fiber digestibility; NDFD: neutral detergent fiber digestibility.

quate nutrition that supports brain function and hormonal balance (Mertens, 1994). Polyphenols reportedly have the potential to support brain function through antioxidant activity and the ability to protect neurons from oxidative stress (Spencer, 2009). According to several studies, these compounds can influence hormonal balance by interacting with the endocrine system, including modulating the activity of hormones such as insulin and estrogen (Williams et al., 2009).

In the same context, the administration of tea, containing polyphenols, has been recognized for the potential impact on physiological parameters. Previous studies reported a connection between polyphenol-rich tea and blood chemistry, specifically in terms of urea and blood glucose levels. Kondo et al. (2004b) observed a significant reduction in serum cholesterol levels in lactating cows fed ensiled green tea waste. According to Kasahara and Kato (1993), green tea contains polyphenols (catechins), tannins, caffeine, and pyrroloquinoline quinone. Some components of these compounds can enhance both basal and insulin-stimulated glucose uptake in adipocytes (Wu et al., 2004). Additionally, these components have demonstrated the ability to hinder intestinal glucose uptake by targeting sodium-dependent glucose transporters in intestinal epithelial cells, as reported by Kobayashi et al. (2000). The subgroup analysis showed that among the various types of tea sources, the extract had a significant influence on glucose levels in the blood.

The results also showed that tea extract had a significant influence on blood urea levels. Ruminants and other mammals produce urea through a process known as urea synthesis. This physiological mechanism plays a significant role in preventing the accumulation of excess nitrogen, thereby preventing potential toxicity. The rate and amount of ammonia production reflect the solubility and fermentation ability of food and the endogenous N source (Huntington and Archibeque, 1999). Previous studies (Vizotto et al., 2021; Kondo et al., 2004b; Ahmed et al., 2015) have shown that tea waste and extract reduced glucose content in the blood.

In conclusion, many tea varieties have an impact on ruminant health, particularly on factors like blood chemistry, digestibility, average weight gain (AWG), and dry matter intake (DMI). While the overall effects of tea supplementation on AWG and DMI were not statistically significant, certain subgroups exhibited significant outcomes. For instance, tea extract dramatically reduced blood glucose and urea levels, while tea waste considerably increased the digestion of acid-detergent fiber. Overall, the absence of meaningful outcomes was a result of the disparities between trials, which included differences in tea type, dose, animal breed, and experimental circumstances. To create dietary plans for the future, it is essential to comprehend the intricate metabolism of polyphenols in ruminants, which influences metabolic consequences and the effectiveness of the digestive system.

Table 3: Sub-group effect of different type of tea on AWG (Kg/head/day), DMI (g/head/day), DMD (%), CPD (%), ADFD (%), NDFD (%) Blood Glucose (mg/dl) and Blood Urea (mg/dl) in ruminants.

AWG: average weight gain; DMI: dry matter intake; MEI: metabolizable energy intake; TDNI: total digestible nutrient intake; NDFI: neutral detergent fiber intake; CPI: crude protein intake; DMD: dry matter digestibility; CPD, crude protein digestibility; ADFD,:acid detergent fiber digestibility; NDFD: neutral detergent fiber digestibility.

Ririn S. Rahmatillah received a master’s degree scholarship from the Indonesia Endowment Fund for Education Agency (LPDP). This research was jointly supported by an LPDP grant (Number: KET-583/LPDP.4/2023).

Meta-analysis reveals that while various tea supplements can significantly affect certain physiological parameters such as blood glucose levels, their overall impact on ruminant health and productivity is variable, highlighting the potential but variable benefits of tea as a natural feed additive in small-scale farming

Ririn Siti Rahmatillah: Conceptualization, Formal Analysis, Writing Original Draft, Writing review and editing.

Diky Ramdani: Conceptualization, Methodology, Supervision, Validation, Writing review and editing.

Iman Hernaman: Conceptualization, Methodology, Supervision, Validation.

Anuraga Jayanegara: Conceptualization, Methodology, Supervision, Validation.

Yulianri Rizki Yanza: Methodology, Writing review and editing.

The authors do not have any conflict of interest.