Feeding cows flaxseed rich in polyunsaturated fatty acids has been shown to decrease the proportion of saturated fatty acids and increase the proportion of n-3 polyunsaturated fatty acids (PUFAs) in milk. Consuming products enriched in n-3 PUFAs have beneficial effects to human health; thus, feeding cows flaxseed could potentially increase the nutrient and economical value of milk. However, nearly all dietary n-3 PUFAs are hydrogenated in the rumen. To prevent ruminal biohydrogenation of dietary PUFAs, various processing methods of oilseeds have been tested with limited or varying success. In this study, a novel method to “rumen-protect” flaxseed is proposed, which encapsulates ground flaxseed using a proprietary method (12BT40; N3Feed® LLC; Tualatin, OR). The objective of this study was to determine if rumen-bypass processing of flaxseed can increase the concentrations of n-3 PUFAs in serum and milk fat above what can be achieved with its ground ingredients, without adversely affecting production characteristics. Using a double 3 x 3 Latin square design, 6 Holstein cows (1 block each for primiparous and multiparous cows) were fed in a random order for 2 weeks each no flaxseed (Control), 3 kg/d of rumen-bypass flaxseed (Bypass Flaxseed), and 3 kg/d of the ground ingredients of bypass flaxseed (Ground Flaxseed) as top-dressing. In addition to measuring feed intake, milk yield, and body condition score, at the end of each 2-week feeding period, milk and serum samples were collected and analyzed for fatty acid composition. Data were analyzed using PROC MIXED in SAS version 9.3. Fixed effects were treatment, period, and parity. Repeated measures within cows were modeled with the random statement. Bypass flaxseed increased concentrations of n-3 polyunsaturated fatty acids in serum (Control: 304 ± 51 μg/mL; Ground Flaxseed: 456 ± 51 μg/mL; Bypass Flaxseed: 614 ± 51 μg/mL) and in milk fat (Control: 1.21 ± 0.26 wt%; Ground Flaxseed: 1.70 ± 0.26 wt%; Bypass Flaxseed: 2.55 ± 0.26 wt%) beyond what could be achieved
with its ground ingredients. Both flaxseed supplements increased milk yield (Control: 27.3 ± 1.5 kg/d; Ground Flaxseed: 30.6 ± 1.5 kg/d; Bypass Flaxseed: 30.3 ± 1.5 kg/d) and bypass flaxseed also decreased serum BHBA concentrations (Control: 0.98 ± 0.05 mmol/L; Ground Flaxseed: 0.83 ± 0.05 mmol/L; Bypass Flaxseed: 0.74 ± 0.05 mmol/L). In conclusion, supplementing pregnant, mid- to late lactation dairy cows with 3 kg/d of rumen-bypass flaxseed increases energy status, milk yield, and the transfer of dietary n-3 PUFAs from flaxseed into serum and milk fat. Thus, feeding rumen-bypass flaxseed is a potential management tool to improve the nutritional value of milk and dairy products, while at the same time increasing milk yield.