Effects of supplementing fish oil in the drinking water of dairy cows on production performance and milk fatty acid composition.

The objective of this study was to determine the effects of supplementing fish oil (FO) in the drinking water of dairy cows on production performance and milk fatty acid composition. Sixteen multiparous Holstein dairy cows (741 +/- 84 kg of BW; 60 +/- 2.3 d in milk, mean +/- SD) housed in a tie-stall facility were used in the study. The study was conducted as a completely randomized design with repeated measurements. The cows were blocked by days in milk and allocated to 1 of 2 treatments: 10 g of menhaden FO/kg of DM top-dressed on the total mixed ration (FOT), and 2 g of menhaden FO/L delivered in the drinking water (FOW). The trial lasted for 5 wk: a 1-wk pretreatment adjustment period and 4 wk of treatment. The animals were fed and milked twice daily (feeding at 0830 and 1300; milking at 0500 and 1500) and had unlimited access to water. Dry matter intake (21.3 kg/d for FOT vs. 22.7 +/- 0.74 kg/d for FOW), milk yield (38.2 kg/d for FOT vs. 39.5 +/- 1.9 kg/d for FOW), and water intake (101 L/d for FOT vs. 107 +/- 4.4 L/d for FOW) were not affected by treatment. The mode of delivery of FO had no effect on milk fat percentage, but milk fat percentage declined linearly with time. The fatty acid contents of 7:0; 8:0; 9:0; 10:0; 12:0 in the milk of FOT cows were lower than for FOW cows, whereas 18:1 trans-12; 18:1 trans-13 and 14; 18:1 trans-16; and trans-9, trans-11 plus trans-10, trans-12 CLA were greater for FOT than for FOW. The contents of 24:1 in the milk of FOW cows were 48% greater than for FOT cows, although the concentrations were low in both groups. There was a tendency for the contents of 14:0 and 22:5n-6 to be greater in FOW cows than FOT cows and for the contents of iso-18:0 to be lower for FOW cows than for FOT cows. Although it appears that the amount of FO added in the study did not bypass the rumen as hypothesized, these results suggest that drinking water can be an alternative for supplementing FO to dairy cows without decreasing feed or water intake relative to cows fed FO in the diet.