D. F. Jones
W. P. Weiss 1
The Ohio State University
Department of Animal Sciences
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
A study was conducted to test the effect on production when fish oil replaced a proportion of tallow in the diet of Holstein cows. Four mid-lactation Holstein cows were used in a 4x4 Latin square experiment. Cows were fed one of four diets consisting of 4.2% alfalfa hay, 35.1% alfalfa silage, 42.1% corn silage, and 18.6% pelleted concentrate. The diets contained 3% added fat (DM basis) as 100:0, 67:33, 50:50, or 33:67 tallow:fish oil. Each period consisted of 28 days, the first 21 days for diet adaptation and the last seven days for sampling milk, blood, and rumen fluid. Dry matter intake was not affected by treatment. Yields of milk, milk fat, milk protein, and milk protein percentage were not affected when fish oil replaced tallow in the diet. However, cows fed diets with fish oil tended to produce milk with lower milk fat percentage than cows not fed fish oil. Milk fatty acids 18:0 and cis 18:1 decreased; trans 18:1, 18:3 n-3, 20:4 n-6, and 20:5 n-3 increased; and 18:2 n-6 and 22:6 n-3 remained unchanged as fish oil was increased in the diet.
Fish oil may alter the fatty acid profile of milk specifically by the incorporation of 20:5 n-3 and 22:6 n-3 fatty acids. The resulting milk may have a fatty acid profile with potential human health benefits. When fish oil was fed to dairy cows, production was not affected greatly, but milk fat percentage usually was decreased (Nicholson and Sutton, 1971; Spain et al., 1995). The majority of studies evaluating fish oil used a control containing no supplemental fat.
Four diets were formulated to contain 66% forage, 31% concentrate, and 3% added fat. The source of supplemental fat in the four treatments were 100% tallow (3% of dietary DM), 67% tallow (2.25% of dietary DM) and 33% fish oil (0.75% of dietary DM), 50% tallow and 50% fish oil (each at 1.5% of dietary DM), and 33% tallow (0.75% of dietary DM) and 67% fish oil (2.25% of dietary DM).
Four multiparous Holstein cows at approximately 138 DIM (±11 DIM) were used in a 4x4 Latin square design consisting of 28-day periods. The first 21 days were used to adjust cows to dietary treatments and the last seven days were used for collection of blood, rumen fluid, and milk.
Rumen fluid was collected at 1,000 hours on the third day of the seven-day collection period and analyzed for volatile fatty acids. Milk was collected on the first three sample days (AM and PM), composited, and analyzed for fat, protein, and fatty acid profile.
No difference in DMI was observed among treatments (Table 1). Spain et al. (1995) reported no change in DMI when fish oil was infused in the rumen or duodenum of dairy cows. Doreau and Chilliard (1997) included treatments with 0, 1, or 2% of dietary DM as fish oil. The DMI decreased from 42.2 to 34.1 lb/day when 2% fish oil was added to the diet, but DMI was not reduced when 1% fish oil was fed.
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Table 1. Intake of DM and Major Fatty Acids by Cows Fed Varying Concentrations of Tallow and Fish Oil. | |||||
|---|---|---|---|---|---|
| Tallow:Fish Oil | |||||
| 100:0 | 67:33 | 50:50 | 33:67 | SE | |
| DMI, lb/day | 43.8 | 47.3 | 45.8 | 43.3 | 2.2 |
| Fatty acids, g/d | |||||
| 18:0a | 98 | 79 | 64 | 45 | 4 |
| cis 18:1a | 301 | 253 | 211 | 169 | 12 |
| 18:2 n-6a | 249 | 250 | 212 | 201 | 11 |
| 18:3 n-3 | 60 | 62 | 58 | 57 | 3 |
| 20:4 n-6a | 4 | 5 | 6 | 7 | 0 |
| 20:5 n-3a,b | 2 | 18 | 29 | 37 | 2 |
| Totala | 1,117 | 1,087 | 1,016 | 953 | 47 |
| a Linear effect (P <0.05). b Quadratic effect (P <0.10). | |||||
The consumption of 18:0, cis 18:1, and 18:2 n-6 linearly decreased while intake of 20:4 n-6 and 20:5 n-3 linearly increased as fish oil was increased in the diet (Table 1). Although fish oil contained twice as much 18:3 n-3 as tallow, the intake of this fatty acid was not different among treatments. This lack of difference is most likely due to the 18:3 n-3 supplied by the forage in the ration. Total fatty acid intake decreased linearly as fish oil was increased in the diet. This decrease occurred because the diets were balanced for crude fat and not fatty acids. Fatty acids are approximately 90% of tallow and 80 to 85% of fish oil (the remainder being glycerol and other nonfatty acid compounds); less fatty acid was added to the diet when fish oil was included.
Production of milk, 4% FCM, milk protein, and milk fat was not affected by treatment (Table 2). Although no difference in milk fat percentage was found among treatments, a trend for fish oil to suppress milk fat percentage was observed. No difference in ruminal VFA profile was found among treatments. These data suggest that treatment had little effect on ruminal fermentation.
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Table 2. Milk Yield and Composition From Cows Fed Varying Concentrations of Tallow and Fish Oil.1 | |||||
|---|---|---|---|---|---|
| Tallow:Fish Oil | |||||
| 100:0 | 67:33 | 50:50 | 33:67 | SE | |
| Milk, lb/day | 66.7 | 73.5 | 73.7 | 69.5 | 3.3 |
| Milk protein, lb/day | 2.20 | 2.42 | 2.20 | 2.20 | 0.22 |
| Milk protein, % | 3.2 | 3.2 | 3.3 | 3.2 | 0.1 |
| Milk fat, lb/day | 1.76 | 1.76 | 1.76 | 1.54 | 0.22 |
| Milk fat, % | 2.7 | 2.2 | 2.5 | 2.3 | 0.2 |
| 4% FCM, lb/day | 53.2 | 53.9 | 53.2 | 51.0 | 2.6 |
| 1 No differences were found among treatments. | |||||
The fatty acids 18:0 and cis 18:1 in milk linearly decreased while trans 18:1 and 18:3 n-3 linearly increased as fish oil was increased in the diet (Table 3). The decrease in 18:0 and the increase in trans 18:1 in milk suggest ruminal biohydrogenation was less able to go to completion as more fish oil was included in the diet. Increased concentrations of 20:4 n-6 and 20:5 n-3 in milk (Table 3) is the result of increased intake of these fatty acids as fish oil was increased in the diet. Low uptake of 20:5 n-3 and 22:6 n-3 by the mammary gland (Mansbridge and Blake, 1997) and biohydrogenation of these two fatty acids (Doreau and Chilliard, 1997) may be factors related to the low concentration of these fatty acids in the milk. Ashes et al. (1992), however, reported that 20:5 n-3 and 22:6 n-3 are not biohydrogenated in the rumen.
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Table 3. Fatty Acid Profile of Milk Produced by Cows Fed Differing Concentrations of Tallow and Fish Oil. | |||||
|---|---|---|---|---|---|
| Tallow:Fish Oil | |||||
| 100:0 | 67:33 | 50:50 | 33:67 | SE | |
| % of Total Fatty Acids | |||||
| 4:0 to 16:0 | 49.2 | 49.7 | 51.8 | 52.5 | 0.3 |
| 16:1a | 2.6 | 3.4 | 3.6 | 3.6 | 0.3 |
| 18:0a | 10.5 | 8.4 | 7.8 | 6.4 | 0.7 |
| trans18:1a | 5.3 | 8.1 | 7.7 | 9.8 | 1.1 |
| cis18:1a | 24.1 | 20.4 | 18.1 | 14.8 | 0.8 |
| 18:2 n-6 | 2.3 | 2.8 | 2.9 | 2.8 | 0.3 |
| 18:3 n-3a | 0.5 | 0.6 | 0.6 | 0.6 | 0.0 |
| 20:1/CLA1,a | 1.1 | 1.8 | 1.9 | 2.2 | 0.2 |
| 20:4 n-6a | 0.0 | 0.1 | 0.2 | 0.5 | 0.2 |
| 20:5 n-3b | 0.0 | 0.1 | 0.1 | 0.3 | 0.1 |
| 22:5 n-3a | 0.0 | 0.0 | 0.1 | 0.2 | 0.1 |
| 22:6 n-3 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| a Linear effect (P <0.05). b Linear effect (P <0.10). 1 CLA = Conjugated linoleic acid. | |||||
Ashes, J. R., B. D. Siebert, S. K. Gulati, A. Z. Cuhetson, and T. W. Scott. 1992. Incorporation of n-3 fatty acids of fish oil into tissue and serum lipids of ruminants. Lipids. Doreau, M. and Y. Chilliard. 1997. Effects of post ruminal fish oil supplementation on intake and digestion in dairy cows. Reprod. Nutr. Dev. 37:113-124.
Doreau, M. and Y. Chilliard. 1997. Effects of ruminal or post ruminal fish oil supplementation on intake and digestion in dairy cows. Reprod. Nutr. Dev. 37:113-124.
Mansbridge, R. J., and J. S. Blake. 1997. Nutritional factors affecting the fatty acid composition of bovine milk. Br. J. Nutr. 78:S37-S47.
Nicholson, J. W. G. and J. D. Sutton. 1971. Some effects of unsaturated oils given to dairy cows with rations of different roughage content. J. Dairy Res. 38:363-372.
Spain, J. N., C. E. Poland, and B. A. Watkins. 1995. Evaluating effects of fish meal on milk fat yield of dairy cows. J. Dairy Sci. 78:1142-1153.