Effect of chokeberry pomace as a feed additive for high-producing dairy goats on oxidative stress parameters and quality of milk

Phenolic compounds constitute the most important bioactive components of fruits with strong antioxidative properties (4). The black chokeberry (Aronia melanocarpa) contains an extraordinary number of polyphenolic compounds in high levels: dominant are proanthocyanidins and the second group by size are anthocyanins and phenolic acids, which have antioxidant properties. The strong antioxidative action of black chokeberry is known and was reported in studies in humans and some species of animals (13).

Poland is a leader in the production of chokeberry on a global scale. Annually, 1.5 million tonnes of fruit are processed in the domestic fruit industry, of which 30–40 thousand tonnes are chokeberries. The effective utilisation of chokeberry pomace remaining after the fruit is juiced by using it as animal feed fits the model of sustainable agriculture and has a positive impact on environmental conservation. In the available literature, data are lacking about the effect of chokeberry pomace on oxidative stress parameters in goat’s milk and on its quality. Oxidative stress is central to many diseases, reproductive disorders and reduced milk yield in ruminants (23). One of the approaches to minimising it is including chokeberry as a livestock feed ingredient to enrich and improve the quality of their milk. Another reason for implementing fodder modification is to increase the efficiency of breeding animals and maintain antioxidative/oxidative homeostasis.

Goat meat and milk are valued in modern society for their nutritional content and potential health benefits. Goat’s milk is regarded as a high-quality, valuable, healthy, tasty, and easily digestible nutritional product, diverse health benefits are ascribed to it, and it is rich in diverse macro- and micro-nutrients (16, 29). Moreover, it is more abundant in amino acids, vitamins, minerals, and its proteins and fats are digested more easily and faster than cow’s milk (29). One of the main characteristics of goat’s milk that has contributed to its appeal as an alternative to cow’s milk is its lower allergenicity (7). This explains why it is also becoming more and more popular among consumers. Milk from goats kept on large-herd farms, where the focus is mainly on volume production, and nutrition is from industrial feed products, cannot be guaranteed to have any health-promoting properties and nor will its consumption be certain to bring the expected results. Ameliorating industrial animal feed with plants including fruiting plants exploits an important source of diverse compounds with health-promoting bio-effects (4).

The aim of this study was to establish the impact of different amounts of chokeberry pomace addition to a diet for high-producing dairy goats on a range of parameters associated with oxidative stress, metabolic health and the quality of milk.

The results of the quantification of the physicochemical parameters of milk are presented in Table 1. The log SCC remained at a constant level in groups supplemented with chokeberry and changes were not observed, while in the control group a higher level was seen.

A lower fat level was recorded in the milk samples of both groups supplemented with chokeberry. However, it should be noted that the group given more chokeberry (A2 group) produced milk lower in fat content (P-value < 0.001) and density (P-value = 0.036). A significantly (P-value = 0.026) lower FP was found in the A1 group’s milk at the end of the experiment compared to the control group’s at the beginning of the experiment. A significant FP difference (P-value = 0.012) was noted over the course of the experiment between A1 group milk and A2 group milk.

Significant decrease in the NA of milk was observed; these were in the A1 group’s samples, between the control group’s and the A1 group’s samples and between the control group’s and the A2 group’s samples over the course of the experiment, as well as between the final control group milk samples and the final A2 group milk samples (P-values < 0.001–0.023). Moreover, a decrease was also found within the control group (P-value < 0.001), which might possibly be due to exogenous (environmental) factors that bore effect during the experimental period.

No statistically significant differences were observed in the levels of Cas, Lac, TS, SNF, urea, FFA or Cit acid content.

The results of aminopeptidase activity assessment are presented in Table 2. Significant differences (P-value < 0.001) were found in all tested aminopeptidase activity levels between the beginning and the end of chokeberry supplementation both within the supplemented groups and within the control group. A significant increase (P-value = 0.014) in LeuAP activity between the control group at the beginning of the experiment and A1 group at the end of supplementation was observed. There was also significant difference (P-value = 0.011) between the A1 and the A2 group at the end of the experiment for LeuAP activity, while for AlaAP and ArgAP there were no significant differences between the experimental groups after supplementation.

The results of lysosomal enzyme activity assessment are presented in Table 3. Chokeberry supplementation resulted in a significant increase in AcP activity in the A1 and A2 groups. The activity of this enzyme at the end of the experiment in the A2 group was significantly higher (P-value < 0.001) than in the control group. Acid phosphatase activity in the A1 group at the end of supplementation was significantly lower (P-value = 0.001) than its activity in the A2 group.

There was a significant (P-value < 0.001) increase in the activity of all tested glycoside enzymes in both supplemented groups between the beginning and the end of the experiment. Beta glucuronidase activity in the A1 and the A2 group increased significantly (P-value < 0.001) between the beginning and the end of supplementation. It should be noted that the increase in activity was much higher in the A2 group at the beginning of the experiment, and that it then increased further. Beta glucuronidase activity was also significantly higher in the A1 and A2 groups (P-value < 0.001) at the end of the experiment than it was in the control group before the start of supplementation. The differences in β-GRD activity in the final phase of the experiment between the A1 and the A2 group were also significant (P-value = 0.050).

A significant potentiation of β-GAL activity (P-value < 0.001) was evident in both groups supplemented with chokeberry. This was seen between the beginning and the end of supplementation.

There was a significant augmentation of β-GLU activity (P-value < 0.001) in both groups supplemented with chokeberry at the end of the experiment. The greatest significant difference between the initial activity level and the final activity level was in the group given 30 g chokeberry. Significantly higher β-GLU activity was demonstrated after supplementation and compared to the control group. A significant difference (P-value = 0.050) between the A1 and the A2 groups was noted at the end of supplementation.

After supplementation with chokeberry, both the A1 and A2 groups showed significant differences in HEX (P-value < 0.001), but the highest enzyme activity was observed in the A2 group. Significant difference between the three levels of chokeberry supplementation (P-value < 0.001) were also found.

As it did for the other glycoside enzymes, chokeberry supplementation resulted in a significant increase in α-GLU activity (P-value < 0.001). The highest increase in enzyme activity occurred in the A2 group after the end of supplementation.

Mannosidase activity increased significantly in both experimental groups after the addition of chokeberry to their feed. Interestingly, there were no significant differences in MAN activity in milk between the 15-g- and 30-g-supplemented groups.

Table 4 shows the results for non-enzymatic parameters. An increase in DPPH depending on the amount of chokeberry added in the feed, the highest level of DPPH (P-value < 0.001) was observed in the A2 group. However, no significant differences were found between the supplemented groups.

The addition of chokeberry did not significantly affect the level of Vit C in milk. Meanwhile, it had a positive effect on the oxidation-reduction potential of milk, which was manifested by an increase of GSH in the experimental groups. It was also shown that the level of GSH depends on the lactation period, which was manifested by an increased trend in GSH activity also in the control group.

It was shown that a higher level of chokeberry addition in the feed resulted in a significant increase in the total level of polyphenols in milk compared to the control group (P < 0.001). A significant relationship with the chokeberry dose was also found (P < 0.001).

Figure 1 correlates the milk physicochemical parameters with the activity of lysosomal enzymes and other tested non-enzymatic antioxidant parameters. There was a significant negative correlation between the fat level and the activity of other parameters except DDPH (r = -0.223). The acidity parameter correlated negatively with the activity of some lysosomal enzymes: β-GRD, MAN and GSH (Fig. 1). Natural acidity was also strong negatively correlated with AlaAP, LeuAP and ArgAP. A low positive correlation was also found between the level of FFA and DPPH activity, and between milk density and β-GLU and HEX activity.

Fig. 1.

Milk parameter correlation coefficients with the activity of lysosomal enzymes and other measured non-enzymatic antioxidant parameters AlaAP – aminopeptidase; LeuAP – leucyl aminopeptidase; ArgAP – arginyl aminopeptidase; AcP – acid phosphatase; β-GRD – β-glucuronidase; β-GAL – β-galactosidase; β-GLU – β-glucosidase; HEX – β-N-acetylhexosaminidase; α-GLU – α-galactosidase; MAN – mannosidase; DPPH – 1,1-diphenyl-2-picrylhydrazyl; Vit C – vitamin C; GSH – glutathione; Pol – polyphenol; Log SCC – logarithmic somatic cell count; Prot – protein; Cas – casein; Lac – lactose; TS – total solids; SNF – solids-non-fat; Cit acid – citric acid; FP – freezing-point; FFA – free fatty acid; D – density (of milk); NA – natural acidity

The total level of Pol in all experimental groups and also in the control group was slightly positively correlated with D (r = 0.283) and slightly negatively correlated with the level of fat in milk (r = -0.394). The remaining physicochemical parameters of milk did not show any correlation with the level of Pol.

The activity of all lysosomal enzymes was significantly and positively correlated with the total level of Pol in milk (Fig. 1.). The strongest correlation occurred for β-GRD activity (r = 0.838) and β-GAL (r = 0.831). A high correlation (r = 0.817) was also noted for GSH activity. For the remaining enzymes, the correlation ranged from 0.524 to 0.779.

The healthy food market is developing very dynamically. Consumers increasingly frequently look for food with high health benefits. Milk plays an important role in the human diet, and goat’s milk is an alternative for people allergic to cow’s milk protein. Using fruit pomace in animal feed conforms to the modern trend in sustainable agriculture and simultaneously may produce milk with beneficial properties desired by consumers.

The supplementation of the diet of high-production dairy goats with chokeberry pomace exhibits promising effects on oxidative stress parameters and the overall quality of milk, as demonstrated by our findings. This study contributes to the growing body of research evidence that underscores the potential health benefits of dietary polyphenol supplementation in livestock nutrition, particularly in the context of improving milk quality and animal welfare.

While chokeberry and chokeberry-derived by-products (such as pomace) are broadly studied as health-promoting nutraceuticals (11), the putative effects of chokeberry supplementation on the milk quality of livestock animals remained unexplored up to now. Chokeberry is known to be rich in polyphenolic compounds (11), and the supplementation with chokeberry pomace significantly enhanced the antioxidative capacity parameters (DPPH, GSH and total Pol level) of goat’s milk (Table 4). The better antioxidative capacity of milk resulted in the stabilisation of log SCC, which remained materially unchanged through the chokeberry supplementation, while rising in the control group as is typical in the course of lactation (28). Therefore chokeberry pomace also improved the cytological quality of goat milk. These results align with the growing body of findings from previous studies which have highlighted the role of dietary polyphenols in boosting antioxidant defence mechanisms in dairy animals (9, 24).

Relatedly, our study noted significant improvements in the levels of non-enzymatic antioxidants such as GSH and Pol. The elevation in GSH level is particularly noteworthy, since GSH is a key antioxidant that plays a major role in neutralising free radicals and protecting mammalian cells from oxidative stress (2, 20). This finding is consistent with previous works that reported that dietary antioxidant supplementation could modulate reduced GSH levels in ruminants, leading to better stress resilience and health- and productivity-related outcomes (6, 18, 22). Moreover, our work also aligns particularly well with previous research involving dietary chokeberry pomace supplementation, which demonstrated an increase in reduced GSH blood levels in Polish Merino and Wrzosówka lambs (13).

In this investigation the synthesis of basic ingredients such as protein and lactose was at a constant level, while fat anabolism was less efficient. The fat content in milk decreased in chokeberry-supplemented goats and the larger chokeberry mass supplement had a significant impact on reducing the fat content. Interestingly, this research showed a negative correlation between the activity of the tested enzymes and the percentage of fat content in goat’s milk. It can be assumed that the reduction of fat content brought about by chokeberry supplementation may be caused by the increased activity of lysosomal enzymes originating from mammary gland cells and bacteria present in the milk. In respect to milk fat content, the observed reduction associated with chokeberry supplementation (Table 1) raises important considerations regarding the nutritional and sensory qualities of milk. A reduced fat content can influence these qualities and the caloric value of milk, which are critical factors for consumer acceptance. However, from a health perspective, lower-fat milk may be preferable in diets aiming at an overall health improvement, weight loss and reduced fat intake (17, 30).

Interestingly, despite the increased activity of aminopeptidases, the experimental animals maintained their metabolic balance, and the protein level in their milk was not raised by the chokeberry pomace supplementation. Higher aminopeptidase activity is typical during lactation, and the similar increased in activity of aminopeptidases in the control group may have been due to the increase in log SCC. On the other hand, the significant correlation between the content of polyphenols and the activity of aminopeptidases may indicate that chokeberry accelerates protein degradation processes, but may also be the cause of increased protein synthesis, as no changes in milk protein content were seen. A further interesting observation in the present work is the increased activities of aminopeptidases, AcP and carbohydrate-metabolising enzymes (Tables 2 and 3) in the milk samples of chokeberry-supplemented goats. Importantly, some of the boosted enzymes, particularly β-GRD, are crucial not just for metabolic processes but also for cellular detoxification (27). Of particular importance could also be the chokeberry pomace-induced increase in the enzymatic activity of β-GAL and α-GAL, which are involved in the degradation of the lactose that is frequently not tolerated by milk and dairy-product consumers (14, 25). On the other hand, reduction of lactose content did not occur. Therefore, potentiated activity of glycoside enzymes not only improves the physicochemical parameters of milk, but also its quality and nutritional value.

In respect of the conducted correlation study (Fig. 1), it was notable that overall, increased enzyme activities in the milk correlated positively with polyphenol content and negatively with fat content, which established potential causal links between these parameters, but also suggested a coordinated anabolism–catabolism programme shift in the studied population.

From a clinical perspective, the enhanced antioxidative properties of milk could be indicative of the improved health status of the dairy goats, with potential implications for the reduction of the incidence of diseases linked to oxidative stress, such as mastitis (8). A dietary supplementation approach using chokeberry pomace could possibly lower a farm’s veterinary costs and reduce its use of antibiotics, aligning well with the goals of sustainable and ethical animal farming practices.

With respect to farming sustainability and environmental protection, the use of chokeberry pomace, a by-product of chokeberry juice production, as a feed additive is also contributory because it utilises agricultural waste. Such a dietary supplementation practice thus might not only provide health benefits to livestock animals but also build out the circular economy in agriculture, reducing waste and the environmental footprint of goat farming.

While the current study provides valuable insights into the benefits of chokeberry pomace in dairy goat nutrition, future research should explore the longer-term effects of such dietary modifications on animal health and milk production. It would also be beneficial to assess consumer acceptance of milk with altered fat content and antioxidative properties such as chokeberry-supplemented goats produce, as these factors play key roles in the commercial success of dairy products.

The supplementation of high-producing dairy goat diets with chokeberry pomace enhances the antioxidative properties of milk and improves various quality parameters (including reduction of fat content and enhancement of metabolic enzyme activities). These changes reflect the potential of chokeberry pomace as a natural antioxidant in improving animal health and milk quality, offering a promising strategy for sustainable dairy goat farming. The findings also suggest that chokeberry pomace could be a valuable feed additive in the context of precision livestock farming, where diet formulations induce specific metabolic patterns that could be optimised for health and productivity outcomes.