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Conjugated linoleic acids (CLA) and trans fatty acids in milk fat of dairy cows fed rapeseed or sunflower oil

G. Jahreis, F. Tischendorf, P. Mckel, F. Schne

Institute of Nutrition, University of Jena, Dornburger Str. 24, D-07743 Jena, Germany, e-Mail: b6jage@rz.uni-jena.de

Abstract

The effects of rapeseed or sunflower oil in combination with different amounts of a buffer-supplement (0, 100 or 200 g of a mixture containing NaHCO3 : MgO : CaCO3 = 9 : 3 : 1) were investigated in a three month lasting experiment with 30 lactating Holstein cows (first third of lactation). The two groups with 15 animals each received 400 g rapeseed oil (RO) or sunflower oil (SO) daily. There were no significant differences in total trans fatty acids content of milk fat between the treatments. The most interesting result was the high content of trans-10-octadecenoic acid in the unbuffered SO-groups (P< 0.05). The buffer supplements decreased the trans-10/trans-11-C18:1 ratio and milk fat content normalized. The trans-vaccenic acid percentage was not influenced by feed regimes. Both oil supplements caused high CLA content of milk fat (1.13 - 1.46 % FAME) in comparison with normal silage-based rations (about 0.5 %). It can be concluded that buffers modify the profiles of fatty acids in milk. The yield of the potent anticarcinogen CLA tended to be higher when buffer was added to SO. Especially in rations rich in polyunsaturated fatty acids (SO) buffer supplements prevent trans-10-C18:1 enrichment and milk fat depression.

KEYWORDS: Milk fat content, Trans-10-octadecenoic acid, Trans vaccenic acid, Rumenic acid,

As the percentage of concentrate in the diet of lactating cows increases, the percentage of milk fat decreases. The use of dietary buffers (alkalinizing compounds as NaHCO3, CaCO3) can help to prevent the pH decreasing and to maintain the fat concentration of milk (Thivierge et al. 1998). It seems that special trans fatty acids, mainly produced when oil supplemented diets were fed, directly inhibit mammary synthesis of milk fat. More substrate for the microbial fermentation in form of polyunsaturated fatty acids and unfavourable rumen environment (low fiber) results in an incomplete biohydrogenation. Especially, the intermediate, trans-10-octadecenoic acid, is associated with an inhibition of milk fat synthesis (Griinari et al. 1998). Other intermediates of partial biohydrogenation, like conjugated linoleic acids (CLA), are known to exert anticarcinogenic and other beneficial effects (Cook and Pariza, 1998). There is an interest in increasing the CLA content of milk fat.

This investigation was supported by a grant from the German Federal Ministry of Nutrition, Agriculture and Forestry, No 96HS062

The objective of the experiment was to examine the hypothesis that improved rumen conditions realized by buffer supplementation 1 decrease the formation of trans-10-octadecenoic acid and prevent milk fat depression. 2 guarantee a high CLA concentration of the milk fat.

Material and Methods

Animals: From a herd of 350 animals 30 lactating Holstein cows were selected in according to early lactation (1st trimenon) and a similarly high milk production. Randomized to two groups of 15 animals each, cows were fed a basal ration: 11.3 kg grass silage, 20.8 kg corn silage, 2.1 kg hay, the oil containing mixture (consisting of 400 g rapeseed oil [RO] or sunflower oil [SO], 2.1 kg ground barley, 1.1 kg soybean meal, 1.0 kg grass meal, 0.4 kg dried sugar beet pulp), 5.3 kg commercial dairy concentrate in dependence on milk yield, and 0.15 kg mineral/vitamin mixture together with different amounts of buffer (Table 1). The investigation period lasted three month.

Table 1: Groups, buffer supplementation and oils

Group

SO0

RO0

SO100

RO100

SO200

RO200

Cows (n)

5

5

5

5

5

5

Buffer* (g/d)

0

100

200

Rapeseed oil (g/d)

 

400

 

400

 

400

Sunflower oil (g/d)

400

 

400

 

400

 

* composition of buffer: 65 % NaHCO3, 18 % MgO, 7 % CaCO3, 10 % bran

Milk sampling: Milk yields were measured daily. Milk samples were taken at experimental days 0, 3, 12, 24, 36, 48, 64, 80 and 96 for fat, protein, lactose and somatic cell analyses of each cow. Aliquotes of the morning and evening milking yields were collected at days 0, 12, 48 and 96 for fatty acid analysis. Milk samples were freeze-dried and stored at -20C until analysis.

Analysis: For fatty acid analysis freeze-dried samples were extracted with a mixture of hexane and isopropanol (3:2, vol/vol). Fatty acids analysis was performed immediately after methylation with Na-methylate on a gas-liquid chromatograph (Shimadzu GC-17A) fitted with a flame ionization detector and equipped with an automatic injector (AOC-20i). Each sample was run two times (Table 2). First, the total fatty acid profile was determined using a temperature gradient program (80 to 240C). Second, after argentation thin layer chromatography the oven was operated isothermically at 173C to separate the trans- and cis-octadecenoic acids. Fatty acid profile was expressed as a weight percentage of total fatty acid methyl esters (FAME). Weight percentage of the single trans-octadecenoic acids was calculated as a proportion of total C18:1 area (trans-4-C18:1 through trans-16-C18:1). Fatty acids were identified by comparison of the retention times with standard FAME. The standards and the CLA mixture were purchased from Sigma (Deisenhofen, Germany), the individual CLA references (cis-9,trans-11, trans-9,trans-11; cis-9,cis-11; trans-10,cis-12) were obtained from Matreya (Pleasent Gap, PA, USA).

Results

Dry matter and energy intake were not significantly affected by rapeseed or sunflower oil feeding and different buffer additives. The overall daily intake during the 3-month investigation period averaged: 21.95 kg DM, 149.7 MJ NEL and 3807 g crude protein per cow and day. In spite of milk yield-dependent supply with the commercial dairy concentrate (transponder feeding) there was also no significant influence on the roughage/concentrate ratio (mean: 57.9 : 42.1 %). Effects of type of oil and amount of buffer added were significant for milk yield, fat yield and FCM (Table 3).

Table 2: Separation of fatty acid methyl esters by capillary gas liquid chromatography

Separation of C4 through C24 Column: DB-Wax 30m x 0.25, dr= 0.20m

TINIT: 80C TimeINIT: 5 min

TFINAL: 240C Time FINAL: 8min Rate PROG: 5.5C/min

TINJ: 250C TDET: 260C Column flow: 2.2 ml/min

Split RATIO: 100:1 Carrier gas: H2 Volumen INJ : 1 l

 

Separation of trans-C18:1 isomers by combined argentation TLC and GLC

Column: SP 2560, 100 m x 0.25 mm, df = 0.20 m

TCOL: 173C – isotherm TINJ: 250C TDET: 260C V = 0.53 ml/min

Split RATIO: 100:1 Carrier gas: H2 Volumen INJ : 0.5 l

Table 3: Effect of type of fat and amount of buffer added on performance

Group

SO0

RO0

SO100

RO100

SO200

RO200

Milk yield, kg/d

30.0 a

29.0 a

29.3 a

31.8 b

31.8 b

31.9 b

Milk fat, %

3.12 c

3.75 ab

3.88 a

3.70 ab

3.73 ab

3.22 bc

Milk fat, g/d

936 a

1092 ab

1152 b

1151 b

1174 b

1008 ab

Milk protein, %

3.07 bc

3.28 a

3.22 ab

3.20 ab

3.15 abc

3.01 c

Milk protein, g/d

937

961

957

1011

998

952

Milk lactose, %

4.81

4.80

4.88

4.75

4.85

4.80

FCM *, kg/d

26.3 a

28.1 ab

29.2 ab

30.0 ab

30.2 b

27.8 ab

* Fat-corrected milk

a,b,c Different superscripts indicate significant differences (P < 0.05)

Feeding the oil-rich diets without buffer (SO0, RO0) and the sunflower-oil diet with 100g buffer (SO100) resulted in significantly reduced milk yield (Table 3) and in the case of unbuffered PUFA-rich sunflower-diet (SO0) in a milk fat depression (MFD). There is also a decrease of milk fat and protein percentage of RO200-cows. Because of the high milk yield in this group the fat and protein yield is not significantly different (P > 0.05) from the other buffer-supplemented groups. An important result is the increasing milk fat content with the buffer addition to the sunflower diet (Table 3).

The supplementation of both oils with different parts of PUFA (rapeseed oil: 20.4 % linoleic acid and 11.6 % linolenic acid; sunflower oil: 61.0 and 0.3 % resp.) resulted in similar milk fatty acid composition caused by biohydrogenation (Table 4). In comparison with normal diets, the addition of both oils decreased the content of fatty acids resulting mainly from de novo synthesis (C4 to C16), whereas the parts of stearic acid (from biohydrogenation of C18 MUFA and PUFA), octadecenoic acids and CLA increased. Thus, the ratio of C16:0/C18:1 is about 1, that means a good spreadability of butter fat.

Figure 1: Trans-10/trans-11 ratio of octadecenoic acid in the milk fat of the sunflower oil

supplemented groups in dependence on the buffer supplementation

Table 4: Effect of type of fat and amount of buffer added on fatty acid composition of milk

(% of FAME of the samples at 48 and 96 experimental days)

Fatty acid

SO0

RO0

SO100

RO100

SO200

RO200

C4 to C14

19.46

21.30

20.25

23.32

21.49

20.51

C16:0

23.50

23.13

24.10

28.16

27.3

25.71

C18:0

12.27

12.27

13.04

11.07

10.46

9.74

C18:1

23.67

22.95

23.64

19.80

21.38

23.96

C18:2 cis-9/cis-12

2.85

2.52

2.40

2.14

2.58

2.45

C18:3 α 9,12,15

0.38

0.41

0.34

0.34

0.37

0.40

Σ TFA*

8.71

8.00

7.18

6.60

7.37

7.48

C16:0/C18:1

1.02

1.04

1.03

1.44

1.31

1.12

trans-10/trans-11

0.61

0.41

0.31

0.30

0.28

0.40

* Trans fatty acids

Some of the most pronounced changes occured in the fraction of trans-octadecenoic acids (Table 4, Fig. 1). Generally, the unbuffered oil supplementation leads to an increase of trans fatty acids, especially of the trans-10-C18:1. At the beginning of the experimental period the trans-10 content of the SO0 milk exceeded those of trans-11. With increasing buffer amount and with the duration of the experimental period the trans-10/trans-11 ratio decreased towards 0.5 (Fig.1)

Table 5: Effect of type of fat and amount of buffer added on trans-10-C18:1 and CLA yield

Group

SO0

RO0

SO100

RO100

SO200

RO200

trans-10-C18:1, % FAME

1.30

0.92

0.60

0.54

0.59

0.75

trans-10-C18:1, g/d

10.6

7.9

5.6

5.6

6.7

6.8

Σ CLA, % FAME

1.30

1.41

1.24

1.12

1.41

1.46

Σ CLA, g/d

9.8 b

12.0 ab

11.5 ab

12.0 ab

15.7 a

13.5 ab

The MFD that occured with sunflower oil diet without buffer involved a significant reduction in the CLA yield (9.8 g/d) in comparison with the buffered diets (SO100: 11.5 g/d; SO200: 15.7 g/d). On the other hand, the yield of trans-10-C18:1 decreased with the buffer addition (Table 5).

Conclusions:

1. Different oils and buffer supplementation influenced the ruminal biohydrogenation and had significant effects on milk performance, milk fat percentage and fat yield. Buffer supplementation diminished the negative effects of unsaturated fat. When sunflower oil in combination with buffer was fed, milk fat percentage and yield were increased by 20 % and more compared with the unbuffered diet.

2. The milk fat depression caused by intake of polyunsaturated fat was correlated with an higher percentage of trans fatty acids, especially an increase of trans-10-octadecenoic acid.

3. The daily addition of 100 or 200 g buffer mixture (alkalinizing agents and MgO) reduced the formation of trans-10-C18:1.

4. The CLA percentage in milk fat of the different groups was relativeley high (1.12 up to 1.46 % of FAME) in comparison with usual diets without fat supplements (about 0.3 to 0.6% of FAME). The CLA yield varied between 9.8 and 15.7 g/d with the significantly lowest amount in cows fed the unbuffered sunflower diet. The buffer supplementation to the RO diet was without an effect on CLA yield.

References:

1. Cook, M. E. and Pariza, M. 1998: The role of conjugated linoleic acid (CLA) in health. Int. Dairy Journal 8, 459-462

2. Griinari, J. M., Dwyer, D. A., McGuire, M. A., Bauman, D. E., Palmquist, D. L. and Numela, K. V. V. 1998: Trans-octadecenoic acids and milk fat depression in lactating dairy cows. J. Dairy Sci. 81, 1265-1261

3. Thivierge, M. C., Chouinard, P. Y., Lvesque, J., Girard, V., Seoane, J. R. and Brisson, G. J. 1998: Effects of buffer on milk fatty acids and mammary arteriovenous differences in dairy cows fed Ca salts on fatty acids. J. Dairy Sci. 81, 2001-2010

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