Supplementation with antioxidants and phenolic compounds in ruminant feeding and its effect on dairy products: a systematic review

Abstract Milk and dairy products have great importance in human nutrition related to the presence of different nutrients, including protein, fatty acid profile and bioactive compounds. Dietary supplementation with foods containing these types of compounds may influence the chemical composition of milk and dairy products and hence, potentially, the consumer. Our objective was to summarize the evidence of the effect of supplementation with antioxidants and phenolic compounds in the diets of dairy animals and their effects on milk and dairy products. We conducted a systematic search in the MEDLINE/PubMed database for studies published up until July 2022 that reported on supplementation with antioxidants and phenolic compounds in diets that included plants, herbs, seeds, grains and isolated bioactive compounds of dairy animals such as cows, sheep and goats and their effects on milk and dairy products. Of the 94 studies identified in the search, only 15 met the inclusion criteria and were analyzed. The review revealed that supplementation with false flax cake, sweet grass, Acacia farnesiana, mushroom myceliated grains and sweet grass promoted an effect on the milk lipid profile, whereas supplementation with dried grape pomace and tannin extract promoted an effect on the milk and cheese lipid profiles. In six studies, the addition of Acacia farnesiana, hesperidin or naringin, durum wheat bran, mushroom myceliated grains, dried grape pomace and olive leaves increased the antioxidant activity of milk. In conclusion, supplementation with bioactive compounds had a positive impact which ranged from an increase in antioxidant capacity to a decrease in oxidative biomarkers such as malondialdehyde.

Milk is the sole and primary source of nutrition for newborns, and it has been demonstrated to be important for children's growth and adult health (Zhang et al., 2021).The beneficial effects are related to the presence of different nutrients, including protein, fat, lactose, essential minerals including calcium and magnesium, fat-soluble vitamins (A, D, E, and K) and bioactive compounds (Gil and Ortega, 2019;Scholz-Ahrens et al., 2020).Among these bioactive compounds are polyphenols, peptides and polyunsaturated fatty acids (PUFA), which are related to improved health.For children and adults, the main sources of milk and dairy products are dairy cattle, buffaloes, goats and sheep (Ferro et al., 2017).However, the chemical composition and presence of different bioactive compounds in the milk of these species can fluctuate due to several factors, such as animal breed, stage of lactation, season, management and nutrition.Many strategies have been implemented to enhance dairy ruminant product quality, one of which is to focus on the influence of dietary supplementation.
The enrichment of ruminant diets with agro-industrial by-products (for example, citrus pulp, grape pomace and pulp, molasses and olive leaves) that are rich in bioactive compounds such as polyphenols has been demonstrated to improve the nutritional and chemical composition of milk and dairy products (Křížová et al., 2021).Dietary supplementation has an important role regarding the presence of antioxidants in milk and dairy products.For example, supplementation with citrus pulp (9-18%) increased the polyphenol and flavonoid concentrations in Holstein milk (Santos et al., 2014).The identification of these types of compounds is important because they are thought to have health benefits, such as lowering blood pressure, stopping Gram-negative pathogens like Escherichia coli and Salmonella typhi (Murakami et al., 2004) and having anti-inflammatory and antioxidant effects (Marcone et al., 2017).
Fatty acids also play a significant role in the nutritional value of ruminant products and can be influenced by the enrichment of ruminant diets.The type and quantity of fatty acids in milk are influenced by the animal's breed, lactation stage, husbandry and diet (Tzamaloukas et al., 2021).Ianni et al., 2019 found that adding grape pomace to the diet of Friesian cows increased the concentration of polyphenols and linoleic (C18:3n-3), vaccenic (C18:1 trans 11) and rumenic (C18:2 cis 9, trans 11) acids in the cheese.It is known that polyunsaturated fatty acid (PUFA) content in milk plays an important role in consumer health (Chilliard and Ferlay, 2004).Thus, this review aimed to summarize evidence of the effects of dietary supplementation with antioxidants and phenolic compounds on the milk and dairy products of the main dairy animals.

Materials and methods
The present study was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines (Page et al., 2021).The study design required neither Institutional Review Board approval nor patient informed consent.

Search strategy
Two authors (AAN and IMV) performed the search strategy independently.The studies were identified through the online source MEDLINE/PubMed.The search was conducted for articles published until July 2022.We applied the description of the population, intervention, control and outcomes (PICO) strategy as described by Methley et al. (2014), where the population was dairy ruminants, the interventions were bioactive compounds and antioxidants in diets, a standard ruminant diet was the control and the outcomes were the fatty acid profile, bioactive compounds and antioxidant levels in the milk and dairy products of the population (online Supplementary Table S1).
Potential articles were searched using keywords by constructing blocks of descriptors in English.The Boolean operators AND (to add at least one word from each group) and OR (to list at least one word from each block), parentheses (to combine search terms by outcome categories) and quotation marks (to search for exact terms or expressions) were used.The groups of descriptors for the search strategy related to the outcome in dairy products were Ruminants AND bioactive compound AND dairy products NOT a review, Ruminants AND bioactive compound supplementation AND dairy product.

Selection of studies
After removing duplicates, the same authors (AAN and IMV) independently screened the titles and abstracts for eligibility evaluation based on the inclusion criteria.The title and abstract candidates to enter the review were evaluated in accordance with their eligibility criteria by all authors.Finally, data extraction of the full texts was carried out.Original studies were included if they met the following criteria: (1) performed on ruminants (for this review, the search only focused on dairy goats, cows and sheep) (2) reporting dietary interventions that included bioactive compounds and antioxidants in the diet of ruminants (3) a design with a standard diet as a comparator (4) reporting change or concentration of the fatty acid profile, bioactive compounds and antioxidants in milk and dairy products of the ruminants.
Exclusion criteria were: (1) in vitro studies (2) characterization of antioxidant concentrations in milk and dairy products without intervention studies (3) studies where the intervention was focused on comparing feeding by different types of grazing and did not supplement.

Data extraction
Data extraction for all selected articles was performed independently by all authors.This information included the ruminant species, the bioactive compound(s), the description of the intervention, the comparator, the follow-up time, the type of product studied, the main findings about dairy products and finally the first author's name and year of publication.The process of identification and extraction is given at online Supplementary Fig. S1 and the complete list of references is at online Supplementary Table S2.

Results
According to the search, 94 articles were identified, and when duplicates were excluded 81 records were evaluated with title and abstract.In accordance with the eligibility criteria 66 articles were excluded (online Supplementary Table S2).The principal reasons to exclude articles by title and abstract were: no-intervention (n = 17), no-intervention in ruminants (n = 14), food characterization study (n = 12), in vitro study (n = 8), intervention different from the stated objective (n = 6), study of supplementation food or food creation (n = 5), review study (n = 2) and interventions that did not involve bioactive compounds (n = 2).Finally, 15 articles were included in the review (online Supplementary Fig. S1).

Effects of supplementation on fatty acids profile of dairy products
Six studies investigated the impact of dietary intervention on the fat content of milk.et al., 2021).Due to its high phytochemical content, pomegranate has been widely studied for its health properties, and several products aimed at human health have been developed, causing an increase in agro-industrial residues (Varma et al., 2018).Pomegranate peel extract and pomegranate pulp improve in vitro dry matter digestibility and volatile fatty acid production (Jami et al., 2012;Shaani et al., 2016).Thus, the use of pomegranate residues in ruminant feed might have an important role in milk production.However, interventions with pomegranate seeds or pomegranate seed pulp did not show differences in milk fat (Safari et al., 2018).
There were seven instances of lipid profile being altered by supplementation.False flax cake increased the content of PUFA (by 1.5 times) and n-3 fatty acid levels (by 1.7 times) compared to the control group (Cais-Sokolińska et al., 2015).Intervention with sweet grass increased the concentration of monounsaturated fatty acids (MUFA) and PUFA by modest but significant amounts compared with rice straw (Mapato et al., 2021).It is important to increase the content of PUFA in dairy products because it has been established that PUFA, among other health benefits, regulates the inflammatory response (Bentsen, 2017).During this process, immune cells produce inflammatory mediators such as tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6, IL-12, interferon gamma, and IL-8.These mediators activate pro-inflammatory signaling cascades, including the nuclear factor-kB (NF-kB) signaling pathway, the Janus kinase/signal transducer and activator of transcription signaling pathway and the mitogen-activated protein kinase signaling pathway (Kahkhaie et al., 2019).It has been demonstrated that PUFA, specifically n-3 PUFA, inhibits the synthesis of IL-1, IL-2, and IL-6 and the NF-kB signaling pathway (Oppedisano et al., 2020).Thus, the increase in PUFA concentration observed in the evaluated supplementations indicates that it is possible to enhance the nutritional value of milk and, therefore, might improve the consumer health.It must be cautioned that there is no direct evidence for this, nevertheless, it is an exciting prospect.
Among the PUFA compounds that showed the most change through interventions were linolenic acid, linoleic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).Intervention with Acacia farnesiana at 30% significantly increased the concentration in milk of linoleic acid and DHA compared with control (Delgadillo-Puga et al., 2019).Similarly, dietary supplementation with dried grape pomace promoted an increase in the percentage of linoleic acid and linolenic acid (Ianni et al., 2019).One of these studies showed that EPA was only detected in the milk of groups fed mushroom myceliated grains (MMG), but this intervention did not show an effect on other PUFA such as linoleic (C18:2 n-6), rumenic (CLA, C18:2 c9 t11), α-linolenic (C18:3 n-3) and arachidonic (C20:4 n-6) acids (Bonanno et al., 2019b).Also, sweet grass increased the proportion of C18:1 cis-9, C18:2, C18:2 cis-9, trans-11 and C18:3 (Mapato et al., 2021).PUFA have an important role as active dietary compounds, particularly CLA has shown different beneficial effects, such as antihypertensive and anti-carcinogenic activities (Koba and Yanagita, 2014).In this aspect, when compared to women who consumed 1 serving/d, those who consumed >4 servings of high-fat dairy foods and CLA per day (including whole milk, full-fat cultured milk, cheese, cream, sour cream and butter) had a tendency to decrease the incidence of colorectal cancer (rate ratio = 0.59 [95% CI: 0.44, 0.79; P for trend = 0.002]), and the increment of 2 servings of high-fat dairy foods/d decreased by 13% risk of colorectal cancer (multivariate rate ratio: 0.87, 95% CI: 0.78, 0.96).Thus, consuming high-fat dairy products rich in CLA may lower the risk of developing colorectal cancer (Larsson et al., 2005).Once again, a caveat is needed since these effects are small and have not been confirmed in bigger studies.
A further note of caution is needed.Supplementation not only showed an effect on these potentially beneficial fatty acids but also promoted an effect on saturated fatty acids.Supplementation with MMG increased the amounts of saturated fatty acids (80.3 vs. 77.94g/100g of fatty acid, P < 0.01: Bonanno et al., 2019a).For several years, the consumption of saturated fatty acids was associated with the prevalence of cardiovascular disease (Siri-Tarino et al., 2010) and metabolic diseases such as metabolic syndrome and type 2 diabetes (Warensjö et al., 2005), however, recent evidence indicates that there is a clear difference between dietary and circulating saturated fatty acids, and multiple studies indicate that there is no association between the consumption of saturated fatty acids and the risk of chronic disease (Astrup et al., 2020).It is important to note that milk and dairy products are food matrix foods rich in saturated fatty acids and beneficial compounds such as PUFA, and their consumption should not be associated with an increase in cardiovascular and metabolic risk.
Four studies showed the effect of the intervention on the fat composition of cheese.Supplementation with grape pomace resulted in a significant increase in the concentration of oleic acid, linoleic acid and rumenic acid (all P < 0.01) compared with the control group (Ianni et al., 2019) and intervention with tannin extract during the dry season increased the concentration of conjugated linoleic acid (Menci et al., 2021).However, durum wheat bran and MGG supplementation did not modify the chemical composition of the cheeses (Bonanno et al., 2019a(Bonanno et al., , 2019b) ) despite the latter's effect on milk composition.

Identification of bioactive compounds in dairy products altered by supplementation
One of the most important aspects of interventions with bioactive compounds in the feeding of dairy animals is that these compounds need to be bioavailable in the products obtained.Among the studies included, five reported the presence of bioactive compounds in milk (Delgadillo-Puga et al., 2019;Ianni et al., 2019Ianni et al., , 2021;;Bonanno et al., 2019aBonanno et al., , 2019b) ) and three in the composition of cheese (Ianni et al., 2019;Bonanno et al., 2019aBonanno et al., , 2019b)).The inclusion of Acacia farnesiana at 20 and 30% in the diet of goats significantly increased the total phenolic content in the milk and bioactive compounds such as gallic, chlorogenic, ferulic acids and catechin were only detected in milk from supplemented goats (Delgadillo-Puga et al., 2019).The same group tested the impact of consuming goat milk supplemented with 30% Acacia farnesiana in conjunction with a highfat diet to assess metabolic alterations in a mouse model, and decreased body weight and body fat mass, improved glucose tolerance, and prevention of hypertrophy of adipose tissue and hepatic steatosis.The effect of supplementation on body weight and body fat mass could be explained because a higher energy expenditure was documented, evidenced by a higher oxygen consumption in indirect calorimetry.Additionally, it has been documented that a lower amount of lipids in brown adipose tissue is related to an increased abundance of uncoupling protein 1.The effects demonstrated in this study might indicate that the consumption of goat's milk supplemented with Acacia farnesiana would be a dietary strategy to improve the metabolic alterations induced by the high-fat diet.However, human studies are required before any definitive conclusions can be drawn.According to the body surface area normalization method (FDA, 2005), the mouse dosage would equate to an equivalent daily human intake of 1.4-2.8cups (250 ml per cup/d) of fresh goat's milk for a 60 kg adult, so this dose could be the reference to show its effectiveness in clinical studies.
Supplementation with grape pomace caused an increase in the total phenolic compounds in milk in comparison with the non-supplemented group (Ianni et al., 2019).Grape pomace is a product with prebiotic activity because it contains up to 75% dietary fiber (Yu and Ahmedna, 2013), however, the prebiotic effect in addition to the fiber could be given by the phenolic compounds, as they also have a significant effect on the composition and activity of the intestinal microbiota by stimulating or inhibiting specific bacterial groups (Seo et al., 2017).Phenolic compounds are poorly absorbed in the small intestine and do, therefore, reach the colon, where they are metabolized by the resident microbiota into biologically active metabolites (Ozdal et al., 2016).This results in the appearance of a wide range of phenolic metabolites (phenylacetic acids, phenylpropionic acids, valeric acids, cinnamic acids, benzoic acids, and phenols, among others: Mena et al., 2019).Grape derivatives, such as phenolic compounds, can promote the growth of probiotic bacteria, including Bifidobacterium teenageris, Bifidobacterium bifidum, Lactobacillus acidophilus, and Lactobacillus rhamnosus (Parkar et al., 2008;Gwiazdowska et al., 2015).This modulation in the intestinal microbiota has a positive effect on the health of the host because experimental studies have shown effects in decreasing weight, waist circumference and fat mass and also in decreasing insulin resistance after probiotic treatments, mainly Lactobacillus and Bifidobacterium (Ejtahed et al., 2019).
Unfortunately, phenolic compounds are not particularly stable in refrigerated milk.Dairy products that were enriched with polyphenolic compounds showed a decrease in the phenolic content after 28 d of refrigerated storage, which was attributed to their oxidation (Deolindo et al., 2019).One option to prevent oxidation would be the encapsulation of polyphenols, since encapsulation can protect the bioactive compounds from oxidation.However, encapsulation is more favorable for the enrichment of the dairy product than for the interventions to the diets of the ruminants.
Olive leaf supplementation is another intervention that significantly increases the concentration of phenolic compounds in milk.The main compounds detected in this milk were cinnamic acid, chlorogenic acid and tyrosol (Ianni et al., 2021).An interesting finding in the profile of bioactive compounds in milk was the content of chlorogenic acids (CGAs), since these are among the most common bioactive compounds in plant foods such as coffee, apples, tea and berries, as well as in beverages such as wine (Zanotti et al., 2015).These compounds are esters that are made when quinic acid and trans-cinnamic acids join together.They are usually partially absorbed in the small intestine and partially absorbed in the large intestine after being broken down by bacteria (Olthof et al., 2001(Olthof et al., , 2003)).The concentration of CGAs in milk is relevant because, according to the literature, their consumption could have an important impact on the improvement of glucose and lipid metabolism.Various mechanisms have been proposed, including that they are involved in the inhibition of α-amylase, an enzyme responsible for the decomposition of starch present in saliva that inhibits the absorption of sugar from diet (Narita and Inouye, 2009).In addition, they could modulate gastrointestinal peptides such as gastric inhibitory polypeptide and glucagon-like peptide 1 (Johnston et al., 2003) as well as stimulating glucose transporter 4, thereby increasing glucose uptake by peripheral tissues (Song et al., 2014).All these mechanisms result in a significant reduction in blood glucose levels (Van Dam, 2006).On the other hand, for lipid metabolism it has been shown that CGAs could down-regulate sterol regulatory elementbinding protein 1C (Murase et al., 2011) which is the main genetic switch that controls lipogenesis.Both CGA and caffeic acid stimulate the peroxisome expression of nuclear transcription receptor proliferator-activated receptor alpha in obese mice induced by a high-fat diet.This receptor, when activated, acts as a sensor of lipids, and regulates lipid metabolism.The liver is its main target tissue, and its key genes are enzymes involved in the β-oxidation of fatty acids (Cho et al., 2010).Although highly speculative, all of this together may result in improvements in lipid metabolism.However, not all supplementations have positive effects.Intervention with durum wheat bran (20%) only showed a tendency in phenolic compounds in milk with respect to the control group (Bonanno et al., 2019b), and none of the cheese studies yielded positive changes on total phenolic compounds.

Antioxidant compounds in dairy products affected by supplementation
An outcome of interest from supplementation is the antioxidant effect generated by dairy products.Of the fifteen selected studies, six of these reported an antioxidant effect in milk after the intervention of Acacia farnesiana (Delgadillo-Puga et al., 2019), hesperidin or naringin (Simitzis et al., 2019), durum wheat bran (Bonanno et al., 2019b), MMG (Bonanno et al., 2019a), grape pomace (Ianni et al., 2019), and olive leaves (Ianni et al., 2021).
Intervention with Acacia farnesiana at different concentrations significantly increased antioxidant activity determined both by oxygen radical absorbance capacity assay and ferric reducing antioxidant power assay compared with conventional diet (Delgadillo-Puga et al., 2019).Similarly, supplementation with MMG at 20% showed a significant increase in total equivalent antioxidant capacity with respect to the control without interventions (Bonanno et al., 2019a), antioxidant activity in milk from animals that were fed grape pomace (Ianni et al., 2019) or olive leaf (Ianni et al., 2021) increased significantly compared with the control groups and 14 d of hesperidin, naringin or α-tocopheryl acetate dietary supplementation achieved the same effect (Simitzis et al., 2019).
The role of antioxidants is relevant because they can contribute to the reduction of reactive oxygen species (ROS).Where there is an abundance of ROS and a deficiency of antioxidants, oxidative stress is generated, which in turn causes oxidative damage to biomolecules such as DNA, proteins and lipids (Aranda-Rivera et al., 2022).Since lipid oxidation, also known as lipid peroxidation, produces oxidative biomarkers such as malondialdehyde (MDA) and oxidized LDL (ox-LDL), an increase in these biomarkers has been associated with metabolic alterations and cardiovascular complications (Lee et al., 2012).
Scientific evidence to support the use of antioxidants from food, such as dairy products, as a strategy to prevent pathologies and/or complications related to oxidative stress would be of considerable value, but simply showing their presence in the raw product is only a part of the solution.There are only a few studies that demonstrate the antioxidant effect of dairy products.One of these studies in a healthy population showed that after 21 d of consumption of goats' milk there was a small but significant increase in the percentage of total antioxidant activity and a decrease in the relationship of levels of the endogenous antioxidant glutathione (oxidized glutathione:reduced glutathione: Kullisaar et al., 2003).A second asked participants to consume, for 4 weeks, an experimental cheese that was made from the milk of cows fed a diet containing 5% linseed oil.In this case, serum ox-LDL decreased significantly (Intorre et al., 2011).
It is not only important to consider that antioxidant activity increases, but also that it is able to decrease levels of ROS.Excessive ROS oxidizes cell components, which produce alterations in their structure, causing interruption of signaling pathways or even generating dysfunction of metabolic pathways.Thus, the importance of antioxidants showing this effect on health is to promote benefits in populations with pathologies associated with oxidative stress such as obesity, type 2 diabetes, dyslipidemia and cardiovascular disease (Forrester et al., 2018).A study that included patients with a diagnosis of metabolic syndrome and a 12-week intervention with several serves of dairy per day (adequate dairy) or less than one (low dairy) showed that adequate dairy consumption significantly decreased levels of MDA and ox-LDL (Stancliffe et al., 2011).The decrease in these markers is potentially of great importance, however, it is an isolated example and more evidence about the consumption of dairy products in different types of populations is needed to demonstrate the antioxidant effect it may generate.

Discussion
In recent years, bioactive compounds and agro-industrial residues have been used as feed for dairy animals because they may have positive effects on animal production, such as regulating ruminal fermentation, stopping methane production and protein breakdown, boosting the immune response, and increasing antioxidant activities in animal tissues (Niderkorn and Jayanegara, 2021).There are a great variety of bioactive compounds that can be used in the nutrition of dairy animals.In this review, 19 different types of supplements were used.Only one of them, biotin, is an approved additive according to the EU Register on Nutrition Health Claims; pomegranate seed, alfalfa hay, hesperidin, naringin, mushroom myceliated grains, and tannins are not approved.Meanwhile, the remaining interventions do not appear on any list as authorized or non-authorized.To ensure food safety and animal welfare, it is essential to regulate the feeding of dairy animals with bioactive substances and agro-industrial residues.
Milk and milk products are important foods for human nutrition, constituting 25-30% of the diet.Their nutritional value is, in part, associated with the lipid content due to the inclusion of fatty acids, vitamins and minerals (Visioli and Strata, 2014).Epidemiological data have shown associations between health effects and dairy product intake (Givens, 2020).On the other hand, many other studies have linked the consumption of dairy products with the risk of developing pathologies, mainly because of their lipid content (Fontecha and Juárez, 2017).Thus, health policies have suggested the consumption of fat-free milk and milk-derived products to prevent the risk of cardiometabolic pathologies (You, 2015).More recent analysis employing systematic review has shown inconclusive or contradictory results about the health effects of dairy product consumption (Nieman et al., 2021).Epidemiological studies have shown an inverse association between the intake of dairy products and hypertension, stroke, and colorectal cancer, but there is no evidence of an association between the consumption of dairy products and breast cancer.There is some weak evidence of the protective capacity of dairy products for bone health (Alvarez-León et al., 2006).A meta-analysis showed that milk and total dairy products, but not cheese or other dairy products, are associated with a reduction in colorectal cancer risk.Inverse associations were observed in both men and women but were restricted to colon cancer, where there was evidence of a significant nonlinear association between milk and total dairy products and colorectal cancer risk, and the inverse associations appeared to be the strongest at the higher range of intake (Aune et al., 2012).The nutritional benefits of milk and dairy products are undeniable, but the intricacies of specific health or disease consequences are very difficult to establish.
Dairy products may contain antioxidants such as vitamins A and E, which may provide health benefits due to their ability to reduce oxidative stress and inflammation, but note the term 'may'.Depending on factors such as animal diet, breed and production methods, the antioxidant content of dairy products can vary.Some studies indicate that feeding dairy animal diets rich in antioxidants, such as those containing high levels of vitamin E or plant-based compounds, can increase the antioxidant content of their milk (Delgadillo-Puga et al., 2019, 2020), which is encouraging but we are far from understanding whether such increases actually achieve health benefits.Nevertheless, we can say that improving the diet of dairy animals could potentially increase the nutritional value of the milk they produce.
Efforts have been made to maximize the potential health benefits of dairy products and increase their clinical relevance.Studies have demonstrated that improved chemical composition or enrichment with bioactive compounds such as PUFA, peptides and antioxidants can contribute to the enhancement of the quality of these products by promoting positive effects.Recent evidence suggests that benefits from dairy products on health include regulation of carbohydrate and lipid metabolism through effects on abundance and composition of gut microbiota, cardiovascular diseases, type 2 diabetes, modulation of the immune response and decreased risk of different types of cancer (Tong et al., 2011;Sharafedtinov et al., 2013;Nilsen et al., 2015;Brassard et al., 2017;Santurino et al., 2020).
Changes in these types of products brought about by the presence of bioactive compounds can also have positive outcomes for the production animal.For example, the increase in milk fat concentration due to plant bioactive lipid compounds and biotin can be explained by the prevention of postpartum weight loss and an increase in back fat thickness (Hausmann et al., 2018).Fumaric acid had a negative impact on total fat content.The authors theorized that this was due to the decreased proportion of precursors for the de novo synthesis of milk fatty acids, such as butyrate and the acetate-to-propionate ratio (Li et al., 2021).The higher production of fat in milk when sweet grass was supplemented was accompanied by an increase in digestibility and feed intake, thereby increasing the nutrients available for the rumen microbes and enhancing rumen fermentation, total milk production and milk composition (Mapato et al., 2021).Also, sweet grass increases the concentration of MUFA in milk because fresh grass increases milk fatty acids that are ruminal biohydrogenation intermediates (C18:1, C18:2, C18:3).It has been demonstrated that MUFA can improve glycemic control and prevent the development of metabolic syndrome and its complications (Sheashea et al., 2021).Similar results are shown in the intervention with Acacia farmesiana, dried grape pomace, and MMG that increased the long-chain fatty acids, like linoleic and alpha-linolenic acids.This effect can probably be related to ruminal kinetic modifications due to the rich bioactive compounds found in supplements (Delgadillo-Puga et al., 2019).Enrichment in the content of PUFA in this study has an important role in consumer health because PUFA are associated with preservation of insulin sensitivity, regulation of blood pressure, adequate coagulation and enhanced endothelial function (Julibert et al., 2019).
The use of tannin extract in the diet, by contrast, had a negative effect on C18:1 trans-10, which may affect the pathway of microbial conversion of C18:3 cis-9, cis-12, and cis-15 to C18:1 trans-10 in the rumen.However, these effects were not reflected on cheese-making parameters (Menci et al., 2021).Mapato et al. (2021) found that adding bamboo grass with bioactive compounds like condensed tannins improved the rumen microbiome, which had a positive effect on total volatile fatty acids and propionic acid.The increment of saturated fatty acids due to the inclusion of MMG in the diet was explained by an increment in palmitic acid (C16:0) (Bonanno et al., 2019a).
Variation in milk composition may also be accompanied by the presence of bioactive compounds such as phenols and ferulic acid in milk, with a subsequent presence in processed products.A positive effect on oxidative damage was observed in cheese, which was less prone to proteolysis during ripening without any changes in sensory characteristics (Ianni et al., 2019).Another example of the antioxidant capacity was also described in cheeses induced by MMG in the diet due to the presence of phenolic acids, flavonoids, polysaccharides, carotenoids, ascorbic-acids, and tocopherols.
In conclusion, consumption of products with antioxidants and an adequate lipid profile can be considered a strategy to prevent the damage caused by oxidative stress (Rani et al., 2016).This systematic review compiles scientific studies about supplementation with bioactive compounds to improve the nutrition profile and composition of milk and dairy products.It was observed that supplementation with bioactive compounds in the diet of dairy animals had a positive impact on dairy products, which ranged from an increase in antioxidant capacity to a decrease in metabolites such as malondialdehyde.Future studies should focus on exploring the impact of consuming these products on human health.
Supplementary material.The supplementary material for this article can be found at https://doi.org/10.1017/S0022029923000511

Table 1 .
Bioactive compounds and nutritional interventions used in dairy cattle and its effect on milk and dairy products ↑ T-AOC ↑ SOD FUM ↓ Milk fat content ↓ (trend) daily far yield ↓ MDA ↑ T-AOC