D. F. Jones
W. P. Weiss 1
D. L. Palmquist
The Ohio State University
Department of Animal Sciences
T. C. Jenkins
Department of Animal, Dairy, and Veterinary Sciences
Clemson University
1 For more information, contact at: The Ohio State University, Ohio Agricultural Research and Development Center, 1680 Madison Avenue, Wooster, OH 44691; 330-263-3622; e-mail: weiss.6@osu.edu
Fat is a dense source of energy that can be used in place of carbohydrate. Fish oil may alter the fatty acid profile of milk by the incorporation of eicosapentaenoic acid (20:5 n-3) and docosahexaenoic acid (22:6 n-3). The resulting milk may have a fatty acid profile with perceived human health benefits such as reduced coronary vascular disease, reduced blood pressure, and reduced inflammatory and autoimmune disorders.
When fed to a dairy cow, biohydrogenation (the addition of hydrogen atoms to the fatty acid molecule) is a likely fate for the fatty acids entering the rumen. Biohydrogenation changes the fatty acid profile from what was fed, thus reducing any beneficial profile hoped to be gained in the milk.
A procedure, developed by Jenkins and co-workers at Clemson University, utilizes ethanolamine to protect long-chain polyunsaturated fatty acids from rumen biohydrogenation (Jenkins and Thies, 1997). This protection may prevent the beneficial long-chain polyunsaturated fatty acids (20:5 n-3 and 22:6 n-3) of fish oil from becoming altered in the rumen, allowing for maximum incorporation in the milk fat. Until now ethanolamine has not been tested with fish oil.
The objective of this study was to examine the incorporation of fish oil fatty acids, particularly the long-chain polyunsaturated fatty acids into milk fat with and without protection from ruminal biohydrogenation by ethanolamine.
Four diets were formulated to contain, on a DM basis, 22.7% alfalfa silage, 30.5% corn silage, and 46.8% pelleted concentrate. The diets contained 0 or 3% supplemental fat (tallow, fish oil, or fish oil protected from biohydrogenation with ethanolamine). Thirty-two Holstein cows, housed in tie stalls, were arranged in eight blocks. Cows were fed for 28 days with the first 21 days used to allow cows to adjust to the treatment diets and the last seven days for sample collection.
Rumen fluid was sampled, by means of a stomach tube, at 1,000 hours on the third day of the sample week and analyzed for volatile fatty acids. An AM and PM milk sample was collected on the fourth day of the collection period and analyzed for fat, protein, and fatty acid profile. Dry matter intake, fatty acid intake, and milk yield were monitored daily throughout the trial.
No biologically significant alteration of ruminal volatile fatty acids occurred. Dry matter intake was reduced by the addition of fat compared with the no fat control as well as by the addition of fish oil compared with tallow (Table 1). The decrease observed in milk, fat, and protein yields (Table 1) when fat was fed was most likely due to reduced dry matter intake. Similar reductions in milk, fat, and protein yields have been found in studies utilizing sources of long-chain fatty acids (Christensen et al., 1994). Milk fat and protein percentages were not affected by treatment. All cows in this trial had low milk fat, which may have compromised any potential effects of supplemental fat. The cause of reduced milk fat in these cows is unknown.
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Table 1. Dry Matter and Fatty Acid Intake, Milk Production, and Composition of Cows Fed Different Sources of Fat. | ||||||
|---|---|---|---|---|---|---|
| Treatment | ||||||
| No Fat | Tallow | Fish Oil | PrFO1 | SE | ||
| DMI, kg/da,b | 21.0 | 19.3 | 16.1 | 17.1 | 0.66 | |
| Fatty acid intake, g/da,b,c | 649 | 1,216 | 948 | 866 | 27.8 | |
| Production | ||||||
| Milk, kg/da | 29.4 | 24.6 | 23.3 | 24.2 | 1.38 | |
| Fat, kg/da | 0.8 | 0.6 | 0.6 | 0.5 | 0.06 | |
| Protein, kg/da | 1.0 | 0.8 | 0.8 | 0.8 | 0.04 | |
| Milk composition | ||||||
| Fat, % | 2.8 | 2.6 | 2.7 | 2.4 | 0.21 | |
| Protein, % | 3.2 | 3.2 | 3.4 | 3.3 | 0.08 | |
| 1 PrFO = Fish oil protected with ethanolamine. a The no fat treatment and the three fat treatments differed (P <0.05). b The tallow treatment and the two fish oil treatments differed (P <0.05). c The fish oil treatment and the protected fish oil treatment differed (P <0.05). | ||||||
Compared with the no fat control, the protected fish oil treatment decreased the proportion of short-chain fatty acids in the milk (Table 2). The reduction in the proportion of six to 14 carbon fatty acids and their replacement by increasing concentrations of long-chain polyunsaturated fatty acid in the milk (Table 2) has been shown by other researchers when fat is fed to the dairy cow (Banks et al., 1976). This reduction is caused by reduced synthesis of shorter chain fatty acids at the mammary gland and an increase in direct incorporation into milk fat of long-chain fatty acids coming from the diet.
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Table 2. Fatty Acid Composition of Milk as a Percent of Total Fatty Acids in the Milk. | ||||||
|---|---|---|---|---|---|---|
| Treatment | ||||||
| No Fat | Tallow | Fish Oil | PrFO1 | SE | ||
| 4:0 to 14:0c | 29.7 | 18.9 | 24.0 | 24.6 | 1.07 | |
| 16:0b | 31.2 | 30.4 | 30.8 | 32.6 | 0.69 | |
| 16:1c | 2.3 | 2.9 | 3.8 | 3.3 | 0.23 | |
| 18:0b | 7.7 | 10.8 | 4.5 | 5.2 | 0.75 | |
| trans 18:1a,b,c | 3.3 | 5.0 | 10.6 | 7.9 | 0.92 | |
| cis 18:1b | 15.8 | 22.8 | 11.2 | 12.8 | 1.30 | |
| 18:2 | 3.6 | 2.8 | 3.8 | 3.2 | 0.23 | |
| 18:3 | 0.7 | 0.6 | 0.7 | 0.7 | 0.03 | |
| 20:1/CLA2,b,c | 0.8 | 0.9 | 2.6 | 2.8 | 0.25 | |
| 20:4 n-3b | 0.2 | 0.1 | 0.5 | 0.4 | 0.07 | |
| 20:4 n-6a,b,c | 0 | 0 | 0.9 | 0.3 | 0.08 | |
| 20:5 n-3a,b,c | 0 | 0 | 0.5 | 0.2 | 0.04 | |
| 22:5 n-3a,b,c | 0 | 0.1 | 0.5 | 0.2 | 0.04 | |
| 22:6 n-3b,c | 0 | 0 | 0.2 | 0.2 | 0.03 | |
| 1 PrFO = Fish oil protected from rumen biohydrogenation with ethanolamine. 2 CLA = Conjugated linoleic acid. a The treatment containing protected fish oil is significantly different than the treatment containing fish oil (P <0.05). b The treatment containing protected fish oil is significantly different than the treatment containing tallow (P <0.05). C The treatment containing no supplemental fat is significantly different than the three treatments containing supplemental fat (P <0.05).3 | ||||||
The reduction of trans 18:1, 20:4 n-6, 20:5 n-3, and 22:5 n-3 in milk with the protected fish oil treatment compared with the fish oil treatment reflects the reduced intake of protected fish oil fatty acids fed (1.91 vs. 2.09 lb/day, respectively). The reduction of these five fatty acids in milk also reflects incomplete protection of fish oil by ethanolamine, potentially allowing biohydrogenation to occur in the rumen. Minimal protection of fish oil by ethanolamine is apparent by the lack of difference in the major n-3 fatty acids, between the two fish oil treatments, secreted in the milk. Ethanolamine reacts with soybean oil (Jenkins and Thies, 1997), but the reaction may be less complete with fish oil limiting the protective effects from rumen biohydrogenation. Low DMI allows the protected fish oil to remain in the rumen longer, possibly giving rumen microbes more time to degrade the bond between fish oil and ethanolamine, also leading to reduced ability to protect fish oil from biohydrogenation in the rumen.
Reduced proportions of 18:0 and cis 18:1 and an increase in the proportion of trans 18:1 in milk (Table 2) with fish oil treatments compared with the no fat control treatment demonstrates incomplete biohydrogenation in the rumen (Jenkins and Thies, 1997). If biohydrogenation went to completion, 18:0 would increase (end product) and trans 18:1 would not increase because it is an intermediate in the pathway to produce 18:0. The higher long-chain n-3 fatty acids in the milk of cows receiving fish oil treatments is due to the increase in intake of these fatty acids when fish oil is fed.
The CLA, eicosapentaenoic acid (20:5 n-3), and docosahexaenoic acid (22:6 n-3) were significantly elevated in milk fat when fish oil was included in the diet (Table 2). Although the fish oil treatments increased the concentration of CLA (a proven anticarcinogenic fatty acid) in the milk, this must be viewed with caution because we could not separate CLA from the fatty acid 20:1.
Banks, W., J. L. Clapperton, and M. E. Ferrie. 1976. Effect of feeding fat to dairy cows receiving a fat deficient basal diet. II. Fatty acid composition of the milk fat. J. Dairy Res. 43:219-227.
Christensen, R. A., J. K. Drackley, D. W. LaCount, and J. H. Clark. 1994. Infusion of four long-chain fatty acid mixtures into the abomasum of the lactating dairy cow. J. Dairy Sci. 77:1052-1069.
Jenkins, T. C. and E. Thies. 1997. Plasma fatty acids in sheep fed hydroxyethylsoyamide, a fatty acyl amide that resists biohydrogenation. Lipids. 32:173-178.