The effects of inclusion level of an extruded flaxseed-pea supplement on nitrogen balance and flow of amino and fatty acids in a dual-flow continuous culture system

n-3 Fatty acids (FA) have well-established benefits in human health, including anticarcinogenic and cardioprotective effects. This has prompted growing interest in enriching dairy products with n-3 FA through dietary manipulation in dairy cows. The objective of this study was to evaluate the effects of increasing dietary inclusion of linPRO-R (LIN), a proposed rumen-protected matrix of flaxseed and field pea proteins (21% fat, 24% CP, 10.07% n-3 FA; DM basis), on N metabolism, AA flow, and long-chain FA outflow using a dual-flow continuous culture system. Treatments consisted of 4 levels of LIN inclusion (0%, 2.5%, 5.0%, and 7.5% of diet DM) in a TMR, replacing portions of dried distillers grains and calcium salts of long-chain FA to maintain similar CP and ether extract levels across treatments. The study followed a replicated 4 × 4 Latin square design using 8 fermenters across four 10-d periods (7 d adaptation, 3 d sampling). Effluent samples were collected at 3, 6, 9, and 24 h after feeding and analyzed for AA, N balance, and long-chain FA concentrations. Data were analyzed using GLIMMIX procedure of SAS with fixed effects of treatment, period, and square, with fermenter nested within square as a random effect. Inclusion of LIN had no effect on AA flow, N flow, or calculations of RDP, RUP, or bacterial N efficiency. However, increasing dietary LIN reduced the outflow of SFA (notably C16:0) and increased the outflow of C18:3n3 (0.48%-3.47% of total FA), despite an increase in the biohydrogenation (93.4%-95.9%). These results suggest that LIN can enhance the delivery of n-3 FA postruminally, despite a large fraction of the FA being biohydrogenated, without impairing N metabolism or AA availability, supporting its use as a dietary strategy to increase the nutritive value of dairy products.