In many Asian countries, poultry meat is a source of animal protein, prized for its distinctive flavor and aroma, which makes it a popular choice for preparing aromatic and savory broths (1). However, as laying hens age, their welfare deteriorates rapidly (e.g., lameness, contact dermatitis, and thermal discomfort), and muscle quality declines, leading to reduced consumer acceptance and economic viability in poultry production (2). This decline may be linked to a weakened antioxidant capacity in aged chickens (3). Therefore, improving the meat quality of aged hens after culling could enhance its market competitiveness.

Feed cost has long been a major concern in local poultry production. As poultry production costs continue to rise due to fluctuating prices of essential feedstuffs, such as soybean and corn, it is crucial to develop alternative feed sources. Utilizing agricultural by-products may help to achieve more sustainable resource utilization. Globally, more than 0.5 billion tons of by-products are produced annually from fruit processing, containing valuable nutrients that could serve as potential natural feed resources (4). As a by-product of strawberry juice processing, strawberry pomace contains high levels of dietary fiber, vitamins, minerals, polyphenols, anthocyanins, and ellagitannins (5). It also maintains stable antioxidant capacity (6). Therefore, incorporating strawberry pomace as a feed supplement for livestock and poultry not only helps utilize agricultural by-products but also provides inexpensive nutrients, lowering feed costs, and reducing overall production expenses.

However, strawberry pomace contains high-water content, which makes it prone to mold contamination and difficult to store, potentially leading to environmental pollution (5). Solid-state fermentation helps agricultural by-products last longer and become more nutritious (7). Recent studies have shown that microbial fermentation of agricultural by-products produces organic acids, heteropolysaccharides (e.g., xanthan and chitosan), bioethanol, enzymes, aroma compounds, antioxidants, and other nutrients (8). Consequently, microbial fermentation increases metabolite, enzyme, and probiotic bacteria content, reduces crude fiber, and enhances crude protein in the feed (9). Several studies have reported that fermented feed improves broiler production, nutrient utilization, and meat quality (10, 11). Additionally, a previous research has indicated that dietary supplementing fermented blueberry pomace improves production performance, egg composition, follicle development, and ovarian function in aged laying hens (12). Based on these potential benefits of fermented fruit pomace, we hypothesized that adding fermented strawberry pomace (FSP) to laying hen diets could enhance laying performance, slaughter outcomes, and meat quality by increasing antioxidant capacity. Therefore, the present study aimed to evaluate the effects of dietary FSP supplementation on carcass characteristics, meat quality, plasma biochemical parameters, and the antioxidant capacity in plasma and breast muscle in aged laying hens. Our findings provide a foundation for future studies exploring novel feeding resources.

The findings showed that FSP supplementation as a feed additive enhanced carcass characteristics, improved meat quality, and increased the antioxidant capacity of aged laying hens.

Carcass characteristics is an important metric for assessing the economic benefits of livestock production. In this study, 0.25% FSP supplementation increased the dressing percentage of aged laying hens compared to the control group. However, no statistically significant differences in dressing percentage were found among the different FSP supplementation levels, suggesting that a lower dose was sufficient to improve the dressing percentage. A previous study reported that 3% dried strawberry pomace improved the dressing percentage of broiler chickens (17). However, another study indicated that dietary treatments with 3 and 6% dried strawberry pomace did not alter dressing percentage (18). This difference might be explained by the fact that fermentation enhances the nutritional value of strawberry pomace. A decreasing trend in leg muscle percentage was observed as the FSP dose decreased, suggesting that high-dose FSP may not be beneficial for increasing leg muscle yield.

Meat quality is critical because it affects shelf life, taste, flavor, and consumer preferences (19). Previous research has demonstrated that lipid and protein oxidation reduce water-holding capacity (WHC) in meat by altering membrane structures and compositions, and by affecting protein fragmentation and aggregation (20, 21). Drip loss, as an indicator of meat WHC, plays a vital role in both the meat industry and consumer evaluation of meat quality. In this study, dietary FSP supplementation reduced the 24-h and 48-h drip loss of the breast muscle; the 24-h drip loss of leg muscle tended to decrease in the 0.25–1% FSP groups, and the 48-h drip loss decreased in the 0.25% FSP group compared to the control and 1% FSP groups. These results suggest that dietary FSP improves WHC in both breast and leg muscles. These findings align with a previous study (17), which reported that strawberry pomace reduces drip loss in breast and leg muscles. Antioxidants serve as protective agents by neutralizing reactive oxygen species, thereby safeguarding organelles, cells, and tissues from oxidative damage (22, 23). Therefore, the decline in drip loss can be due to the high content of diverse antioxidants present in strawberry pomace, including vitamins, polyphenols, and anthocyanins, which protect against oxidative cell damage.

After slaughter, lactic acid production in muscle from glycolysis causes pH reduction, and this pH decrease is positively linked to meat quality traits like tenderness, WHC, color, juiciness, and shelf life. A higher pH indicates improved WHC, reduced cooking loss, and darker muscle color (24). Several previous studies have found that strawberry pomace supplementation did not affect pH values (18, 25). However, in our study, dietary FSP (0.25–1%) supplementation decreased the pH at 48 h in the breast muscle. In addition, the pH at 45 min in the leg muscle was increased in the 0.5% FSP group compared with the control and 0.25% FSP groups, while the pH at 48 h in the leg muscle was higher in the 0.25 and 0.5% FSP groups compared with the control and 1% FSP groups, indicating that dietary FSP can improve leg meat quality. Furthermore, 0.5% FSP supplementation increased the breast muscle cooking loss compared with the control group, which might be attributed to the decreased pH in the breast muscle. Moreover, the leg muscle cooking loss was significantly reduced with 0.25–1% FSP supplementation compared to the control group, possibly due to the increased pH, suggesting a beneficial effect on leg muscle quality.

To further understand the changes in meat quality, the myofiber profiles in the breast muscle were examined. However, there were no significant differences between the control and all treated groups. In the process of postmortem glycolysis, skeletal muscle converts stored glycogen into ATP, lactate, and ultimately hydrogen ions. The formation of hydrogen ions results in a drop in muscle pH (26). FSP may have altered the glycogen content in different skeletal muscles by influencing plasma glucose level, thereby affecting muscle pH. However, the specific mechanisms require further investigation.

Meat color reflects freshness and quality (27). Strawberry pomace is rich in natural bioactive components, such as carotenoids and anthocyanins, which may influence meat color (28). In the present study, 0.5% FSP supplementation increased the L* value in the leg muscle compared to the 0.25% FSP group. Moreover, dietary 0.25 and 1% FSP decreased the a* value in the leg muscle compared to the control group. However, Colombino et al. (18) indicated that the addition of 3 and 6% strawberry pomace to broilers’ diets did not affect meat color. Similarly, Juśkiewicz et al. (25) reported that supplementing 5% dried strawberry pomace in the diet had no effect on the color parameters of turkeys. However, Sosnówka-Czajka et al. (17) found that 3% strawberry pomace supplementation tended to decrease the a* value in the breast muscle of broiler chickens. These findings suggest that a higher dose of strawberry pomace may decrease the color quality of leg muscle. The discrepancy between these findings and our results may result from differences in chicken breeds and the doses used. Further investigation is warranted to elucidate the specific reasons.

Plasma biochemical parameters directly indicate animal health and metabolic status. Nordestgaard and Varbo (29) indicated that increased TG content is associated with several diseases, such as cardiovascular disease, acute pancreatitis, and atherosclerosis. In the present study, 1% FSP supplementation showed a decreasing trend in plasma TG content, suggesting that dietary FSP might improve lipid metabolism and benefit overall health. Additionally, 1% FSP supplementation was found to be most effective for increasing GLU content, which may imply that a higher dose of FSP could aid in carbohydrate digestion and absorption (30). Plasma FFA level is elevated in conditions such as obesity, non-alcoholic fatty liver disease, insulin resistance, cardiovascular disease, and type 2 diabetes (31). In the present study, plasma FFA levels decreased in all treated groups, indicating positive effects on metabolic status. However, several previous studies have reported no impacts of tomato pomace, grape pomace, or papaya pomace on plasma GLU, FFA, or TG levels (32–34). These findings suggest that strawberry pomace exhibits greater antioxidant activity than other fruit pomaces, likely due to its unique nutritional composition (35).

Oxidative rancidity is a common cause of quality deterioration in food, primarily due to the oxidative deterioration of lipids. This process not only produces unpleasant odors but also leads to changes in flavor, texture, consistency, appearance, and nutritional value in meat (36). Antioxidant enzymes are crucial for maintaining the redox balance in the body and supporting normal organ function. Increasing the activity of these enzymes is an effective strategy to reduce oxidative stress and delay oxidation processes, thereby maintaining optimal quality and extending shelf life (37). Strawberry pomace has demonstrated beneficial antioxidant activity, enhancing the nutritional value and health advantages of animal products for consumers (38, 39). In the present study, plasma T-AOC level increased in the 1% FSP group, consistent with the findings of the Qin et al. (12). These results suggest that antioxidants in FSP, such as vitamin C and anthocyanins, may modulate the enzymatic system in plasma by increasing T-AOC level. However, plasma GSH-PX level decreased in the 0.5 and 1% FSP groups, possibly due to increased oxidative stress in certain tissues, which led to excessive consumption or damage of GSH-PX in those regions. Despite this, the overall antioxidant capacity increased due to enhanced antioxidant status in other areas. MDA is a widely accepted biomarker of oxidative stress, particularly lipid peroxidation (40). In the present study, MDA level in breast muscle was significantly reduced in the 0.25% FSP group compared to the 1% FSP group, suggesting that low-dose FSP may alleviate lipid peroxidation and improve meat quality.

SOD is commonly recognized as an enzyme that scavenges free radicals, playing a critical role in antioxidant defense through driving the conversion of superoxide anions to hydrogen peroxide during cellular antioxidant processes (41). The Cu and Zn-containing enzymes (Cu-SOD and Zn-SOD), known as SOD1, is located in the cytosol, intermembrane space of mitochondria, and nucleus (42). In the present study, 0.5% FSP supplementation significantly up-regulated SOD1 expression in the breast muscle compared to the control and 0.25% FSP groups, indicating an enhancement in the breast muscle’s antioxidant capacity.

Increasing the proportion of slow fibers in muscle can enhance the color and water retention capacity of fresh meat. MYH1B interacts with lncRNA-FKBP1C to stabilize muscle protein, promoting the conversion from fast to slow muscle fibers (43). In the present study, FSP supplementation up-regulated MYH1B expression in the breast muscle, indicating a reduction in drip loss, which is consistent with earlier findings in this study.

Dietary FSP supplementation improves carcass characteristics, meat quality, plasma lipid profiles, and plasma antioxidant capacity in aged laying hens by enhancing muscle antioxidant capacity and muscle fiber type. Notably, low-dose FSP synergistically enhanced production efficiency and meat quality, with 0.25% improving dressing percentage, reducing oxidative damage (lower MDA), and minimizing drip loss, while 0.5% upregulating antioxidant (SOD1) and myogenic (MYH1B) genes, suggesting optimal bioactive compound utilization. In contrast, 1% FSP paradoxically compromised muscle yield (leg muscle decline) and disrupted redox balance (elevated T-AOC but suppressed GSH-PX), indicating potential metabolic overload. Further research is needed to determine the optimal dosage of FSP for maximizing benefits while minimizing adverse effects. These findings offer a valuable reference for the cost-effective use of dietary FSP in poultry rearing and the utilization of fruit-processing by-products.