Ohio State University Extension Bulletin

Research and Reviews: Dairy

Special Circular 163-99

Dietary Fish Oil for Dairy Cows: 2. Effects on Neutrophil Function and Digestibility

D. F. Jones
W. P. Weiss 1

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


This experiment was designed to determine the effects of fat source on blood neutrophil (PMN) function, digestibility, and production. Four diets (23% alfalfa silage, 31% corn silage, and 46% concentrate) with either 0 or 3% of the DM as tallow, fish oil, or fish oil treated with ethanolamine to prevent rumen biohydrogenation were formulated. Based on milk fatty acid data, protection of fish oil with ethanolamine was not complete. Thirty-two Holstein cows in late lactation were arranged in eight blocks and fed diets for 28 days. Digestibility was determined by total collection. Viability of PMN was not different for any of the four treatments. Phagocytic index (the ability of PMN to phagocytize Staphylococcus aureus) was significantly higher for cows fed fish oil compared with cows fed the other three treatments. The survival index (S. Aureus surviving within the PMN) was not different among treatments. The apparent digestibility of DM, NDF, and fatty acids was not different among the three sources of fat. These results indicate fish oil may improve the ability of PMN to phagocytize S. aureus. The treatment of fish oil with ethanolamine did not affect the digestibility of fish oil; however, protection was low.


Using supplementary fat in the dairy cow ration increases the energy density of the ration. Fish oil may alter the fatty acid profile of the milk to a profile perceived to be beneficial to human health. However, studies with rats show that fatty acids in fish oil (20:5 n-3 and 22:6 n-3) may compromise immune functions. Some of these adverse effects include increased super-oxide and hydrogen peroxide production, reduced PMN chemotaxis, reduced macrophage cytotoxic index, inhibition of T-cell proliferation, and reduced antigen presentation.

Biohydrogenation of long-chain polyunsaturated fatty acids in the rumen may alter the fatty acid profile of fish oil enough to prevent adverse effects on the immune cells of the dairy cow. Biohydrogenation would reduce the amounts of 20:5 n-3 and 22:6 n-3 leaving the rumen.

A procedure, developed by Jenkins and coworkers at Clemson University, utilizes ethanolamine to protect long-chain polyunsaturated fatty acids from rumen biohydrogenation (Jenkins and Thies, 1997). This protection may protect the long-chain polyunsaturated fatty acids of fish oil from biohydrogenation, therefore allowing larger amounts of 20:5 n-3 and 22:6 n-3 to leave the rumen. Ethanolamine has not been tested with fish oil, so the digestibility of ethanolamine-protected fish oil is unknown.

Materials and Methods

Four diets were formulated to contain, on a DM basis, 22.7% alfalfa silage, 30.5% corn silage, 46.8% pelleted concentrate. Diets contained 0 or 3% supplemental fat (tallow, fish oil, or fish oil protected from biohydrogenation with ethanolamine). 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.

Blood was collected by means of jugular puncture for the isolation of PMN. Fat-supplemented cows from four blocks were used in the digestion trial (control cows not receiving supplemental fat were not used). Total collection of feces and urine was performed and digestibilities were determined for DM, organic matter (OM), NDF, nitrogen, and fatty acids.

Results and Discussion

No differences occurred among the three fat supplements for the intake of DM, OM, NDF, and nitrogen during the collection period (Table 1). The intake of fatty acids on the protected fish oil treatment was lower than that for the tallow treatment (Table 1). This occurred because the fatty acid content of the protected fish oil diet was lower than the tallow diet. Apparent digestibilities were not different among the three fat-supplemented treatments for DM, OM, NDF, and fatty acids (Table 1). However, nitrogen digestibility was lower for the tallow supplemented cows than for the cows supplemented with protected fish oil (Table 1). The pelleted concentrate containing tallow was unexpectedly low in nitrogen (CP), which may have caused the lower nitrogen digestibility of this treatment.

Table 1. Intakes During Collection Period
and Apparent Digestibilities of Nutrients
for Cows Fed Diets Containing
Supplemental Fat.
TallowFish OilPrFO1SE
Intake, kg/d
Fatty acida1.
Digestibility, %
Na 60.367.265.31.35
Fatty acid84.086.590.94.67
1 PrFO = Fish oil protected with ethanolamine.
A The tallow treatment and the PrFO treatment are different (P <0.05).

The viability of PMN for the four treatments was not different (Table 2). The phagocytic index (the ability of PMN to phagocytize S. aureus) was higher for the fish oil treatment compared with the protected fish oil treatment (Table 2). This result may have been skewed by an outlying value for the fish oil treatment. If the protected fish oil treatment had more 20:5 n-3 and 22:6 n-3 passing through the rumen, this may affect PMN phagocytosis, causing the lower index for this treatment. However, work is scarce with PMN and work with macrophages shows no effect of 20:5 n-3 and 22:6 n-3 on phagocytosis (Halvorsen et al., 1997). The survival index (the ability of PMN to kill S. aureus) was not different among the four treatments (Table 2). This means the same numbers of S. aureus were surviving within the PMN for all treatments. The fish oil treatment tended to have the lowest survival index, which suggests that PMN on this treatment not only phagocytized better, but tended to kill S. aureus better. The limited difference for these indexes among treatments (Table 2) may have occurred because not enough fat was fed.

Table 2. PMN Response of Cows Fed
Supplemental Fat.
Viability, %93.292.592.192.90.01
Phagocytic index2,a13.612.420.815.31.85
Survival index36.
1 PrFO = Fish oil protected with ethanolamine.
2 A higher number represents better phagocytosis of S. aureus
by the PMN.
3 A lower number represents less S. aureus surviving within
the PMN (better killing ability by the PMN).
a The fish oil treatment and PrFO treatment are different
(P <0.05).


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.

Halvorsen, D. S., J. B. Hansen, S. Grimsgaard, K. H. Bønaa, P. Kierulf, and A. Nordøy. 1997. The effect of highly purified eicosapentaenoic and docosahexaenoic acids on monocyte phagocytosis in man. Lipids. 32(9):935-941.

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.

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