Abomasal infusions of linoleic and linolenic acid in lactating dairy cows differentially alter the fatty acid composition of plasma lipid fractions and immune cells

The balance of n-3 and n-6 fatty acids (FA) in immune system tissues can influence the degree of inflammatory responses in dairy cattle. Linoleic acid (C18:2 n-6) and linolenic acid (C18:3 n-3) are the most abundant n-6 and n-3 FA in lactating dairy cow rations, and are associated with pro-inflammatory and anti-inflammatory responses, respectively. Our objective was to evaluate the incorporation of these FA, and their downstream oxidized FA (oxylipids), into plasma and white blood cells (WBC) following supplementation. Six mid-lactation dairy cows were abomasally infused 4x/d for 7-d treatment periods with 7-d washout intervals in a replicated balanced Latin square design with 3 treatments: 1) CON = ethanol carrier, 2) LA = 45 g/d C18:2 n-6, and 3) LNA = 45 g/d C18:3 n-3. Blood was collected on d 7 of the treatment periods and analyzed for WBC and plasma lipid fraction FA and plasma oxylipid composition. Yields of milk and milk components were calculated for d 6 and d 7 of the treatment periods. Statistical analysis was performed using linear mixed models. Dry matter intake was not affected by treatment (P = 0.68). LA treatment increased the yield of milk and milk protein compared to CON and LNA (P ≤ 0.05). LNA treatment increased milk fat concentration compared to CON and LA (P ≤ 0.05). The concentration of C18:3 n-3 in WBC was increased by LNA (0.86 g/100 g FA; P ≤ 0.05), compared to LA (0.39 g/100 g FA) and CON (0.34 g/100 g FA), but C18:2 n-6 was unaffected by treatment (P = 0.15). LNA increased C18:3 n-3 (3.17 g/100 g FA) and C20:5 n-3 (0.43 g/100 g FA) in the phospholipid fraction of plasma, compared to CON and LA (P ≤ 0.01), while LA increased C18:2 n-6 (38.7 g/100 g FA), compared to the other treatments (P < 0.01). Plasma phospholipid C20:4 n-6 concentration was not altered by treatment (P = 0.65). LNA decreased C20:4 n-6-derived 8,9-DiHETrE (P < 0.01) and tended to decrease C18:2 n-6-derived 12,13 EpOME in plasma (P = 0.09). When C18:3 n-3 and C18:2 n-6 were abomasally infused at the same dose, C18:3 n-3 had a greater influence on the profile of plasma FA and oxylipids and the FA composition of WBC. These changes have the potential to mediate inflammatory responses in cattle at risk of infection.