Ann. Anim. Sci., Vol. 11, No. 1 (2011) 3–16

Factors inFluencing rumenic acid and vaccenic acid content in cow’s milk Fat* *

B a r b a r a N i w i ń s k a , K r z y s z t o f B i l i k , M a r c i n A n d r z e j e w s k i

Department of Animal Nutrition and Feed Science,National Research Institute of Animal Production, 32-080 Balice n. Kraków, Poland

abstractresults of studies with animal models, in tissue culture systems and in clinical research indicate that the functional health-related properties of milk fat appear to be linked to the presence of rumenic acid (ra) and vaccenic acid (va). milk fat provides 30% of fat consumed by humans and is the richest natural dietary source of those valuable fatty acids, but the mean intake is too low to exhibit a health protective effect. the concentration of ra and va in milk fat depends on intensity of ra and va synthesis by rumen bacteria related to the incomplete biohydrogenation of dietary unsaturated fatty acids and on ∆9-desaturase enzyme activity in the mammary gland. the strategies to enhance outflow from the rumen and mammary uptake of these fatty acids involve the manipulation of dietary factors which alter the biohydrogenation pathways in the rumen. By these means, several-fold increases in the content of ra and va in milk fat can be achieved. the activity of ∆9-desaturase enzyme in the mammary gland, responsible for the endogenous ra syn-thesis from va as a substrate, is modulated by mammary uptake of va and also by non-dietary factors such as enzyme genetic parameters, differences between cattle breeds, and lactation stage. the aim of this paper is an overview of the literature of the last decade on the possibility of enrich-ment of milk fat in ra and va.

key words: dairy cow, milk fat, rumenic acid, trans-vaccenic acid, functional food

The health and nutritional aspects of food composition have caused focus on the fatty acid composition of animal products. Milk fat provides 30% of fat consumed by humans and is the richest natural dietary source of conjugated linoleic acids (CLA) (Ritzenthaler et al., 2001). CLA, a family of positional and geometric isomers of oc-tadecadienoic acid with conjugated double bonds, was identified in the 1980s. Since then it has been intensively studied due to its various beneficial health effects such as antiinflammatory, antiatherogenic, anti-diabetic/obesity and anticarcinogenic (Ip et al., 1999; Wahle et al., 2004). The functional health-related properties appear to be linked to the presence of rumenic acid (Parodi, 2005; Lee, 2008). Rumenic acid

�Supported by the Ministry of Science and Higher Education, Grant No. 2 P06Z 049 30.

B. Niwińska et al.4

(RA) is a common name for the (9Z,11E)-octadeca-9,11-dienoic acid (the formal name by IUPAC Nomenclature of Organic Chemistry), the predominant isomer of CLA. Milk fat is the richest natural source of RA. This isomer typically represents from 66 to 92% of the total CLA in milk fat and from 78 to 84% of the total CLA in dairy products (Kramer et al., 1998; Harvatine et al., 2009). RA can be synthesized in the rumen as an intermediate in the biohydrogenation of linoleic and linolenic acids or by endogenous synthesis via ∆9 desaturation in mammalian tissues with the vaccenic acid as a substrate of reaction (Griinari et al., 2000; Piperova et al., 2002; Loor et al., 2005 a; Mosley et al., 2006 a). Vaccenic acid [VA, (E)-octadec-11-enoic acid], the major trans-monounsaturated fatty acid in milk fat (25 to 75% of total trans-C18:1) can be synthesized as an intermediate in the ruminal biohydrogenation of oleic, linoleic, and linolenic acids (Jenkins et al., 2008; Mendis et al., 2008). Previ-ously, VA was known only as a dietary precursor of RA, but recent results indicate that consumption of this trans fatty acid may increase health benefits beyond those associated with RA (Field et al., 2009). The human health effects associated with consumption of diets containing VA have been analysed in studies with animal mod-els, in tissue culture systems and in clinical research. The results demonstrate the po-tential anticancer and immunomodulatory properties of VA, as well as the significant ability to reduce the risk of development of disorders referred to as the metabolic syndrome (Kanwar et al., 2008; Reynolds et al., 2008; Bassett et al., 2010). The positive health effects are attributed to the VA itself or to the Δ9-desaturase enzyme activity in conversion of VA to RA resulted in alteration of cellular fatty acid profile and also to the increase in the concentration of endogenously synthesized RA (Field et al., 2009).

The major dietary sources of RA and VA in human diet are bovine products, but the mean daily intake of these valuable fatty acids is too low. In a light of Ritzenthal-er et al. (2001) study the mean intake of RA is around 193 mg/d for men and 140 mg/d for women. Based on the results of biomedical experiments authors suggest that daily intake should be 620 mg/d for men and 441 mg/d for women to exhibit a health protective effect. The results of recent studies have indicated, that the ad-ditional source of RA for human is the endogenous ∆9-desaturase synthesis with the VA as a substrate. This process is responsible for from 10 to 19% of RA in serum, cell membranes and milk lipids (Turpeinen et al., 2002; Mosley et al., 2006 a).

From the standpoint of human health, efforts to enrich the milk fat in both RA and VA seem reasonable. Results of research conducted over the past 25 years have indicated that the RA and VA content in milk fat is directly related and might be markedly enhanced through the use of diet formulation and nutritional management of dairy cows. Additionally, results of research conducted over the past 10 years have indicated that the endogenous synthesis of RA in cattle has been influenced by the non-dietary factors. The aim of this paper is an overview of the literature of the last decade on the possibility of enrichment of milk fat in RA and VA.

origin of ra and of va in milk fatThe view that the CLA content in dairy products depends only on the incomplete

biohydrogenation of dietary unsaturated fatty acids in the rumen has been generally

Enrichment of milk fat in rumenic acid and vaccenic acid 5

accepted until the last decade of the 20th century. In 1997 Griinari et al. (1997) found that content of RA in milk fat was not strictly dependent on production in the rumen. Authors formed the hypothesis that there is an additional route of synthesis de novo. This hypothesis has been confirmed within the last decade. Numerous studies have shown that synthesis de novo is responsible for from 71 to 100% of RA in milk fat and that the major site for endogenous synthesis are the epithelial cells of mammary gland (Griinari et al., 2000; Corl et al., 2001; Piperova et al., 2002; Loor et al., 2005 a; Mosley et al., 2006 b; Bharathan et al., 2008). The reaction of endogenous synthe-sis of RA is catalyzed by ∆9-desaturase enzyme, a membrane bound protein of the endoplasmic reticulum (EC 1.14.19.1; referred to as stearoyl-CoA 9-desaturase) that introduces a double bond in fatty acyl-coenzyme A at the delta 9 position in a large spectrum of fatty acids (Ntambi, 1999). The intensity of endogenous synthesis of RA in mammary gland is proportional to the quantity of VA delivered to the mammary gland in the blood and the ∆9-desaturase activity (Bharathan et al., 2008; Glasser et al., 2008). Therefore, the concentration of RA and VA in milk fat depends on VA and RA synthesis in the rumen and the ∆9-desaturase enzyme activity in the mam-mary gland.

Factors influencing ra and va synthesis in the rumenWhen dietary lipids enter the rumen, the initial step is the high (>85%) extent

hydrolysis of the ester linkages of triacylglycerides, phospholipids, and glycolipids, causing the release of free fatty acids. The second step is the isomerization (dou-ble-bond position or orientation changed) followed by hydrogenation of the dou-ble bonds catalyzed by different range of enzymes synthesized by rumen microbes, although the exact mechanisms are not well established (Harfoot and Hazlewood, 1988; Wallace et al., 2007). According to Kemp and Lander (1984), the popula-tion of rumen bacteria in the biohydrogenation processes is divided into two groups: A (including Butyrivibrio fibrisolvens) was able to hydrogenate linoleic (9Z,12Z-octadeca-9,12-dienoic acid, C18:2) acids and VA being their dominant end products; group B, bacteria (Fusocillus babrahamensis later named Clostridium proteoclasti-cum) which biohydrogenate VA to stearic acid (SA, 18:0, octadecanoic acid) being the principal end product.

However, as techniques of identification and classification of microorganisms and also identification of FA isomers expanded it has been recognized that in the pathways of biohydrogenation much more species related to Butyrivibrio fibrisol-vens represented bacteria metabolized linoleic acid and Clostridium proteoclasticum, Butyrivibrio hungatei and Eubacterium ruminantium represented stearate producers (Maia at al., 2007). Additionally, in the rumen contents there were found a multitude of trans octadecenoic acid isomers, conjugated isomers and intermediates as prod-ucts of unsaturated FA transformation by various microbial species (Jenkins et al., 2008). Under certain dietary conditions the pathways of rumen biohydrogenation are altered to produce RA and VA. The dietary factors affecting biohydrogenation path-ways have been included in two main categories: that modifying the microbial activ-ity (forage/concentrate ratio, type of forage, plant-derived chemicals, marine oils) and that providing lipid precursors in the rumen (dietary forage, vegetable oils).

B. Niwińska et al.6

Forage/concentrate ratioThe dietary forage/concentrate ratio (F/C) affects the extent of ruminal lipolysis

and biohydrogenation of unsaturated FA. The effects of F/C and ruminal pH inter-action on effluent FA composition were analysed in continuous flow ruminal fer-menters (Fuentes et al., 2009). Authors demonstrated that under a constant ruminal pH (6.4) the increase from 30 to 70% of concentrate in diet resulted in about 40% reduction of RA and VA concentration in effluent and that at a constant concentrate level the reduction of pH value from 6.4 to 5.6 resulted in decrease of concentration of these fatty acids in effluent (an average of 80%). The results of bacterial nucleic acid analysis showed that low pH inhibited cellulolytic bacteria involved in biohy-drogenation processes and these effects were more clear when high concentrate diet was used.

F/C ratio effects on RA and VA concentration in milk fat are not conclusive. The reduction of RA (from 0.53 to 0.33 g/d) and VA (from 33.61 to 20.76 g/d) duodenal flows as a consequence of increasing content of concentrates (from 25 to 60% in diet DM) were observed by Piperova et al. (2002) in a study with dairy cows. On the other hand, Loor et al. (2004) found that the yield of these FA remained stable (8.1 and 4.7 g/d; respectively) although the content of concentrates in diet DM increased from 35 to 65%. Similar results have been presented by Nielsen et al. (2006), who observed that the increase of concentrate from 27 to 47% in ration DM did not reduce RA and VA in milk fat when grass silage was a base forage, but the significant re-ductions of RA concentration (from 2.80 to 1.5% of milk FA) and VA (from 1.61 to 1.17%) were noted when maize silage was substituted by grass silage. The maize si-lage is higher in starch (nearly 40% of DM) compared with grass silage (below 1%). Authors concluded that the starch/fibre ratio in the diet impaired the rate of lipolysis of dietary lipids and it is a factor controlling the formation of individual biohydro-genation intermediates in the rumen. The important role of starch participation in the ration on rumen metabolism of dietary lipids was confirmed by Boeckaert et al. (2008 a). Rumen pH and also RA and VA contents in milk fat remained constant in cows receiving diets differing in starch content by no more than 10%. Additionally, the current results indicated the role of type of starch on milk FA profile. Moham-med et al. (2010) found the higher concentration of RA (1.46 vs. 0.89% FA) and of VA (2.6 vs. 1.7% FA) in milk from cows receiving barley starch compared with that found in milk of cows receiving corn starch. In summary, the effects of F/C on milk FA composition indicated that the starch/fibre ratio influenced the concentration of RA and VA in milk fat, and also indicated the role of type of starch included in the diet of dairy cows.

Type of forageConcentration of RA and VA in milk FA has been affected by type of forage.

Chilliard and Ferlay (2004) suggested that milk RA response varied among forages, and identified the following sequence: fresh grass > hay > grass silage. Results of Couvreur et al. (2006) and Ferlay et al. (2006) studies documented that young grass given to cows enriched milk in RA and VA. Couvreur et al. (2006) reported that increase of fresh cut grass content in cows’ diet (from 0 to 30, 60, and 100% of DM

Enrichment of milk fat in rumenic acid and vaccenic acid 7

of forage) resulted in the linear increase in milk RA content (from 0.48, to 0.54, 1.21, and 1.65% of total FA, respectively) and in milk VA content (from 0.58, to 1.45, 3.12, and 4.70% of total FA, respectively). Effects were mostly linear when the proportion of fresh grass in the forage (82% of forage DM in diet DM) was between 30 and 60% of DM. Similar effects were observed in a study of Ferlay et al. (2006). The concentrations of RA (1.72%) and VA (3.69% of FA) in milk from cows receiv-ing mountain natural pasture (100% of DM intake) were 3 times higher than in milk FA from cows receiving mountain natural grassland hay (87% of DM intake). In the same study the effects of including hay (ryegrass or mountain natural grassland) in the diet (over 86% of DM intake) vs. silage (corn or ryegrass) vs. diet rich in concen-trate (65% of concentrate and 35% of hay) were analysed. The concentration of RA ranged from 0.87% to 0.39 and VA from 1.83% to 0.62 in milk FA according to the following sequence: ryegrass hay > mountain natural grassland hay > corn silage > ryegrass silage > diet rich in concentrate.

There were also differences between types of silage. The effects of replacing grass silage with maize silage were observed by Kliem et al. (2008) in cows fed a total mixed ration (54% of silage on diet DM basis). The lower (0.48%) concentra-tion of RA was noted in milk FA from cows fed grass silage compared with those found in cows fed maize silage (0.54%), but the concentration of VA did not differ (0.90%). Similarly, the lower RA and VA content in milk FA was noted in cows re-ceiving ad libitum ryegrass silage (0.37 and 1.16%; respectively) compared with FA from cows fed silages prepared from alfalfa, white clover or red clover (Dewhurst et al., 2003). The highest concentration of RA and VA was found in milk FA of cows receiving red clover silage (0.42 and 1.31%, respectively). Dewhurst et al. (2003) suggested that the increase in RA content in milk with inclusion of pasture was pri-marily associated with a higher intake of linolenic acid. The fresh grass is the richest source of linolenic acid. It contains 1–3% FA and about 55–65% of FA is linolenic acid (Chilliard et al., 2007).

In summary, the highest concentration of RA and VA in milk can be achieved by inclusion of pasture or fresh cut grass in cows’ diet. The less efficient feeds in modulation of RA and VA concentration in milk fat are preserved forages, which, however, show differences because red clover and maize silages are more effective compared with ryegrass silage.

Production methodsThe effect of feeding strategies on milk FA composition was studied by Slots et

al. (2009). Authors analysed the effects of conventional (62:38 F/C, based on feed-ing of grass silage, cereals and commercial concentrate mix) and organic (69:31 F/C; according the Council Regulation CR no. 2092/91) and extensive production sys-tems (94:6 F/C; based on pasture). There were found greater concentrations of VA (2 times) and RA (2.5 times) in milk from extensively fed cows compared with those found in the milk from cows fed in organic and conventional systems. The results indicated that the extensive production strategy with a high level of pasture could be recommended for production of milk high in VA and RA.

B. Niwińska et al.8

Marine oils The marine oils are rich in eicosapentaenoic [EPA, (5Z,8Z,11Z,14Z,17Z)-eicos-

apentenoic acid, C20:5] and docosahexaenoic [DHA, (4Z,7Z,10Z,13Z,16Z,19Z)-do-cosahexaenoic acid, C22:6] acids. Marine oils (from fish, mammals, plankton or algae) are well known as modifiers of rumen biohydrogenation processes. DHA and EPA were found to be the active compounds in the inhibition of reduction of trans-C18:1 to SA in the rumen. In continuous flow ruminal fermenters in a study of AbuGhazaleh and Jenkins (2004), addition of DHA or EPA increased accumulation of trans-C18:1 isomers and decreased SA concentration compared with control. The inhibition of rumen biohydrogenation of unsaturated FA increased the accumulation of various hydrogenation intermediates, predominantly VA. In an in vitro experiment Boeck-aert et al. (2007) demonstrated the DHA dose-dependent VA accumulation. These results were confirmed in in vivo studies. In the experiment performed with rumen-fistulated dairy cows receiving a concentrate containing algae (0.85 g/kg of diet DM) it was shown that the diet supplementation with algae resulting in increased VA concentrations from 0.92 to 6.38 mg/g ruminal digesta and at the same time the numbers of Butyrivibrio species decreased numerically (Boeckaert et al., 2008 b). It was also shown that supplementation of marine oils was associated with changes in the structure of rumen bacterial community.

Ionophores and plant secondary metabolites Ionophores inhibited lipolysis and subsequently reduced the formation of free

carboxyl groups necessary for the hydrogenation of double bonds and, consequently, lowered rumen biohydrogenation of unsaturated FA to SA, leading to the accumula-tion of hydrogenation intermediates (Jenkins et al., 2003). The high concentrations of trans-C18:1 and RA in continuous cultures of ruminal bacteria has resulted from ad-dition of different ionophores including monensin, nigercin and tetronasin (Fellner et al., 1997) and from addition of a combination of monensin with soybean oil (Jenkins et al., 2003). Results of in vitro study were confirmed in studies with dairy cows. The monensin interacted with safflower oil to increase 10 times the concentration of RA (Bell et al., 2006), and with soybean oil to increase 3 times the concentration of VA and RA (AlZahal et al., 2008). Plant secondary metabolites have been sug-gested as a potential means to manipulate bacterial populations involved in ruminal biohydrogenation. Results of a batch culture incubation study showed that extracts and essential oils from plants inhibited the growth of pure cultures of C. proteoclas-ticum (Durmic et al., 2008) and that the condensed tannins inhibited the growth of B. fibrisolvens (Kronberg et al., 2007). Such concentrations of plant secondary me-tabolites in in vitro experiments are higher than likely to occur in vivo and would cor-respond to impractical feeding rates. Results of a study with dairy cows presented by Benchaar and Chouinard (2009) show a low potential of cinnamaldehyde (1 g/d), condensed tannins (100 g/d), and saponins (6 g/d) used at practical feeding rates in dairy cow diets to modify the fatty acid profile of milk fat. These considera-tions suggest that conclusions drawn from in vitro studies should be interpreted with caution.

Enrichment of milk fat in rumenic acid and vaccenic acid 9

Lipid precursors in the rumen The fatty acid composition of milk fat can be enriched in RA and VA by utiliza-

tion of diets with greater unsaturated fatty acids content (Palmquist et al., 2005). The pathway of oleic acid biohydrogenation described previously, indicates that

oleic acid is saturated directly to SA without the formation of intermediates in the rumen. More recently, AbuGhazaleh et al. (2005) found that conversion of oleic acid to VA depends on pH conditions in the rumen. Using 13C-labelled oleic acid in ruminal batch cultures it was found that in 24-h effluent at pH 5.5 the VA was not detected but at pH 6.5 the concentration of VA was found to be around 1.4% of FA. Thus pH near 6.5 is favourable for converting oleic acid to a wide variety of trans-C18:1 positional isomers, including VA.

The classical pathway of linoleic acid includes isomerization to RA followed by subsequent hydrogenation to a mixture of trans-18:1 intermediates and SA as final products (Chilliard and Ferlay, 2004). The latest results indicated that the synthesis of RA from linoleic acid by ruminal bacteria occurs via diverse biochemical mecha-nisms. According to the results of Wallace et al. (2007), the hydrogenation process occurs simultaneously and does not involve isomerization.

The linolenic acid in the rumen is transformed by ruminal microorganisms ini-tially to a large number of isomers which were identified in duodenal flow (Loor et al., 2004). According to Destaillats et al. (2005) only cis-9, trans-11, cis-15-18:3 and the cis-9, trans-13, cis-15-18:3 isomers are reduced to conjugated dienes including RA. The addition of linseed oil (at 3% of DM) to low concentrate diets (≤35% of diet DM) increased the duodenal flow of VA from 40 to 113 g/d and of RA from 0.52 to 0.86 g/d (Loor et al., 2005 b).

The case of stearidonic acid [SDA; (6Z,9Z,12Z,15Z)-octadecatetraenoic acid; 18:4n-3] derived from genetically modified soybeans (27.1% of FA) is interesting be-cause SDA is able to change the rumen biohydrogenation pathways. Bernal-San-tos et al. (2010) found that the ruminal infusion of SDA provided 57 g/d increased trans-18:1 isomers concentration in the rumen content and significantly increased VA (from 1.1 to 1.9%) and RA (from 0.4 to 0.7%) concentration in milk FA.

Dietary unsaturated fatty acidsThe possibility of increasing the content of RA and VA in the milk fat by feeding

dairy cows with basal diet supplemented with plant oils as a source of unsaturated fatty acids has been the leading subject of research during the last decade. The results indicated that the effects were differentiated by type of unsaturated fatty acids and also by type of forage introduced in the diet. The higher content of RA (2.73-fold) and VA (3.18-fold) were found in milk from cows receiving soybean oil supple-ment (4% on DM basis; 59/41 F/C; 50.3% of linoleic acid in FA) compared with those found in milk from cows fed diet without oil supplement (0.64% and 1.48% of FA, respectively; Bu et al., 2007). The effects of supplementation (0.5 kg/d) with rapeseed oil (61.2% of oleic acid in FA) or sunflower oil (64.9% of linoleic acid) or linseed oil (56.7% of linolenic acid) of cows, which had 20-h access to pasture on FA profile of milk fat were presented by Rego et al. (2009). The concentration of VA in milk FA was higher in cows received linolenic acid (1.4 times) or linoleic

B. Niwińska et al.10

acid (1.3 times) and the concentration of RA was higher in milk from cows receiving both types of FA (1.3 times) than in milk fat FA from cows receiving a diet not sup-plemented with oils. The oleic acid treatment resulted in moderate increases.

The effects of marine oils as modifiers of rumen microbial fermentation were confirmed in milk FA composition. The concentration of VA and RA can be en-hanced by combining marine oils with plant oils or oilseeds rich in linoleic acid, which has been found by AbuGhazaleh et al. (2009) with dairy cows grazing pasture and receiving experimental concentrate supplemented with soybean oil and fish oil or algae. The concentration of VA and RA in milk increased 1.3-fold. Authors con-cluded that DHA was the active component that caused the inhibition of biohydro-genation of VA to SA in the rumen and its activity increased the amount of substrate in the mammary glands for endogenous synthesis of RA. However, the combined use of fish and plant oils is an effective strategy for increasing milk fat RA content. This effect is time and dose dependent. Shingfield et al. (2006) examined milk FA compo-sition responses to fish and sunflower oils (fish oil/sunflower oil ratio 1:2; 45 g/kg of diet DM) in the silage-based rations (60/40 F/C) over a 28-day period. The high level of enrichment in VA (10-fold) and in RA (9-fold) within the first week decreased over the time but remained 5-fold higher than the control. Authors suggested that the time-dependent modifications in the rumen biohydrogenation processes resulted in the formation of other trans-18:1 isomers than VA.

A stable contents of VA (4% of milk FA) and RA (2%) were achieved by sup-plementing cows with a diet with 3% sunflower oil in the presence of 0.5% fish oil in diet DM (Cruz-Hernandez et al., 2007). The diet was composed of forage that consisted of barley silage (20.3% of diet DM), alfalfa silage (19.86%) and alfalfa hay (7.91%) and concentrate contained corn grain (30%) and barley grain (11%). The diet was characterized by 50/50 F/C ratio. The effects of supplementing basal diet (44% forage in diet DM) with ruminally inert Ca salts of palm and fish oil (2.7% DM basis; 34.59% of oleic acid and 0.08% of DHA and 0.08% of EPA in FA) alone or in combination with 5% extruded full-fat soybeans or 0.75% soybean oil were investigated by Allred et al. (2006). The concentrations of VA were estimated at 3.29 (basal diet), 4.66, 6.34, 7.81 and RA 0.56 (basal diet), 1.20, 1.36, 1.74% of milk FA, respectively. The highest effectiveness was found for the supplement composed of oleic (23%), linoleic (32%), linolenic (4%), EPA (5%) and DPA (5%) Ca salts. For efficient protection of Ca-salts against hydrogenation keeping the pH above 6.3 has been necessary (Van Nevel and Demeyer, 1996). The objectives of Mohammed et al. (2009) study were to investigate the underlying mechanisms for the elevation in milk RA concentration associated with grazing vs. receiving grass vs. receiving grass silage in cows, and all cows received 90 g of soybean oil in concentrate. Au-thors estimated that approximately 75% of the variability in milk RA yield could be explained by the variation in total unsaturated fatty acids intake. According to the authors’ interpretation the rest of the variability was influenced by the factors regulating ruminal VA production and its supply to the mammary tissue. The fac-tors of ruminal VA production include differences in DM intake, rumen fill, rumen pH, rumen bacterial populations, intake characteristics (e.g., pattern of chewing, ru-mination, saliva production), and digesta kinetics favouring increased ruminal VA

Enrichment of milk fat in rumenic acid and vaccenic acid 11

production or biohydrogenation inhibition and differences in assimilation and flow of biohydrogenation intermediates to the mammary tissue.

non dietary factors influencing ra synthesis in mammary glandThe RA endogenous synthesis catalyzed by ∆9-desaturase enzyme in the epithe-

lial cells of mammary gland has been shown to play a significant role in modulation of VA and RA concentration in milk fat. The current state of knowledge about the influences of breeds, stage of lactation, type of tissues, enzyme gene polymorphisms and interactions with other genes, nutrients and hormones at tissue level on the en-dogenous synthesis of RA in cattle was presented by Niwińska (2010). The purpose of this part of the article is a brief characterization of non-dietary factors influencing VA and RA content in milk fat.

Enzyme genetic parameters The ∆9-desaturase-1 locus (GenBank accession no. AY241932) has been mapped

on the bovine chromosome 26 (Chung et al., 2000; Lengi and Corl, 2007). In 2004, Taniguchi et al. (2004) found that the nucleotide polymorphism with 2 alleles (A and V) in the fifth exon of this gene has been related to the content of monounsaturated fatty acids in milk fatty acids. This relationship has been confirmed by Mele et al. (2009) in Italian Holstein Friesian cows. The AA genotype was characterized by the higher content of total monounsaturated fatty acids (nearly 10%), the higher content of VA and RA, and the higher value of RA-desaturation index when compared with VV genotype; however, the differences did not reach the level of significance.

Breed The higher activity of ∆9-desaturase enzyme was observed in Holstein cows in

comparison with Jersey (Beaulieu and Palmquist, 1995) and with Brown Swiss cows (Kelsey et al., 2003). The significantly higher activity was found in the Holstein breed compared with activity characteristic of the dual-purpose Belgian Blue, Jersey, Montbeliarde, non-Holstein Meuse-Rhine-Yssel type Red White breeds (Soyeurt et al., 2006, 2008).

Lactation stage Bionaz and Loor (2008) found that the concentration of ∆9-desaturase mRNA in

mammary tissue in Holstein cows increased over 40-fold during 60 days postpartum, and subsequently decreased during the next 180 days. These results were confirmed by Kgwatalala et al. (2009). The concentration of RA in milk from Canadian Jersey cows in early lactation (before 100 days) increased significantly and at a later stage remained at a constant level (above 200 days). Cited results indicated changes of the ∆9-desaturase activity throughout lactation.

In summary it may be stated that the ∆9-desaturase enzyme activity in the mam-mary gland has been affected by enzyme genetic parameters, breed and stage of lac-tation differences. This could be a start of other studies looking into the interaction between the dietary and non-dietary factors in modulation of RA and VA content in milk fat.

B. Niwińska et al.12

conclusionThe recent studies have presented various beneficial health effects of RA and VA

in human. The concentration of RA and VA in milk fat depends on their synthesis in the rumen and on the endogenous synthesis of RA with VA as a substrate via ∆9-desaturase enzyme activity in the mammary gland.

The concentrations of RA and VA in milk fat can be significantly altered through dietary factors. The development of chromatographic identification of fatty acid iso-mers leads to more precise identification and description of biohydrogenation path-ways in the rumen metabolism. The results of current research confirmed the role of quality and quantity of unsaturated fatty acids included in the diet and additionally have indicated the positive role of starch/fibre ratio, participation of pasture or fresh cut grass and application of marine oils in the diet as modifiers of rumen microbial fermentation. As a result of utilization of dietary factors the increase of rumenic acid (9-fold) and vaccenic acid (10-fold) contents in milk fat is obtained in experimental conditions. But the question remains how these achievements could be repeated in practice.

The current knowledge confirms also the existence of non-dietary factors af-fecting the ∆9-desaturase enzyme activity in the mammary gland such as enzyme genetic parameters, breed and stage of lactation differences, but precise assessment and utilization of these factors is a matter of future.

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Accepted for printing 15 II 2011

BARBARA NIWIńSKA, KRZYSZTOF BILIK, MARCIN ANDRZEJEWSKI

Czynniki wpływające na zawartość kwasu żwaczowego i wakcenowego w tłuszczu mleka krowiego

STRESZCZENIE

Wyniki badań prowadzonych na modelach zwierzęcych, w kulturach tkankowych i w warunkach klinicznych wskazują, że funkcjonalne, zdrowotne właściwości tłuszczu mleka związane są z obecnością kwasu żwaczowego i wakcenowego. Tłuszcz mleka, stanowiący 30% tłuszczu spożywanego przez ludzi, jest najbogatszym naturalnym źródłem tych cennych kwasów tłuszczowych w diecie, jednak średnie jego spożycie jest zbyt małe, by wpływało na ochronę zdrowia.

Stężenie kwasu żwaczowego i wakcenowego w tłuszczu mleka zależy od intensywności ich syntezy przez bakterie żwacza, związanej z niepełnym biouwodornieniem nienasyconych kwasów tłuszczowych oraz od aktywności enzymu ∆9-desaturazy w gruczole mlekowym. Metody zwiększania wypływu ze żwacza i wychwytu tych kwasów tłuszczowych przez gruczoł mlekowy polegają na regulacji czyn-ników żywieniowych zmieniających szlaki biouwodornienia w żwaczu. W ten sposób można uzyskać kilkakrotny wzrost zawartości kwasu żwaczowego i wakcenowego w tłuszczu mleka. Aktywność ∆9-de-saturazy w gruczole mlekowym, enzymu odpowiedzialnego za endogenną syntezę kwasu żwaczowego z kwasu wakcenowgo jako substratu, modulowana jest przez wychwyt kwasu wakcenowego przez gruczoł mlekowy oraz przez czynniki pozażywieniowe, takie jak parametry genetyczne enzymu, różnice pomiędzy rasami bydła i stadium laktacji.

Celem niniejszej pracy jest przegląd literatury z ostatnich dziesięciu lat dotyczącej możliwości wzbogacania tłuszczu mleka w kwas żwaczowy i wakcenowy.