Hot topic: Enhancing omega-3 fatty acids in milk fat of dairy cows by using stearidonic acid-enriched soybean oil from genetically modified soybeans

Very long chain n-3 fatty acids such as eicosapentaenoic acid (EPA; 20: 5n-3) are important in human cardiac health and the prevention of chronic diseases, but food sources are limited. Stearidonic acid (SDA; 18: 4n-3) is an n-3 fatty acid that humans are able to convert to EPA. In utilizing SDA-enhanced soybean oil (SBO) derived from genetically modified soybeans, our objectives were to examine the potential to increase the n-3 fatty acid content of milk fat and to determine the efficiency of SDA uptake from the digestive tract and transfer to milk fat. Three multiparous, rumen-fistulated Holstein cows were assigned randomly in a 3 x 3 Latin square design to the following treatments: 1) control (no oil infusion); 2) abomasal infusion of SDA-enhanced SBO (SDA-abo); and 3) ruminal infusion of SDA-enhanced SBO (SDA-rum). The SDA-enhanced SBO contained 27.1% SDA, 10.4% alpha-linolenic acid, and 7.2% gamma-linolenic acid. Oil infusions provided 57 g/d of SDA with equal amounts of oil infused into either the rumen or abomasum at 6-h intervals over a 7-d infusion period. Cow numbers were limited and no treatment differences were detected for DMI or milk production (22.9 +/- 0.5 kg/d and 32.3 +/- 0.9 kg/d, respectively; least squares means +/- SE), milk protein percentage and yield (3.24 +/- 0.04% and 1.03 +/- 0.02 kg/d), or lactose percentage and yield (4.88 +/- 0.05% and 1.55 +/- 0.05 kg/d). Treatment also had no effect on milk fat yield (1.36 +/- 0.03 kg/d), but milk fat percentage was lower for the SDA-rum treatment (4.04 +/- 0.04% vs. 4.30 +/- 0.04% for control and 4.41 +/- 0.05% for SDA-abo). The SDA-abo treatment increased n-3 fatty acids to 3.9% of total milk fatty acids, a value more than 5-fold greater than that for the control. Expressed as a percentage of total milk fatty acids, values (least squares means +/- SE) for the SDA-abo treatment were 1.55 +/- 0.03% for alpha-linolenic acid (18: 3n-3), 1.86 +/- 0.02 for SDA, 0.23 +/- <0.01 for eicosatetraenoic acid (20: 4n-3), and 0.18 +/- 0.01 for EPA. Transfer efficiency of SDA to milk fat represented 39.3% (range = 36.8 to 41.9%) of the abomasally infused SDA and 47.3% (range = 45.0 to 49.6%) when the n-3 fatty acids downstream from SDA were included. In contrast, transfer of ruminally infused SDA to milk fat averaged only 1.7% (range = 1.3 to 2.1%), indicating extensive rumen biohydrogenation. Overall, results demonstrate the potential to use SDA-enhanced SBO from genetically modified soybeans combined with proper ruminal protection to achieve impressive increases in the milk fat content of SDA and other n-3 fatty acids that are beneficial for human health.