Effect of a monounsaturated fatty acid-enriched fat infusion on fatty acid composition in various lipid fractions of plasma and follicular fluid of 46-day versus 67-day postpartum dairy cows

Abstract

The composition of fatty acids (FA) in follicular fluid (FF) can be influenced by both dietary FA and endogenous lipid mobilization. Since the latter predominantly occurs during early lactation, we compared the impact of dietary lipid supplementation on the FA composition in FF lipid classes at two distinct time points in lactation. Furthermore, we investigated how the correlations between plasma and FF FA were affected by lipid supplementation and postcalving time. Twenty Holstein multiparous cows were randomly assigned to 200 g/d of prilled saturated fat in the rumen (n = 10) or sea buckthorn oil (SBT) in the abomasum (n = 10); specially, prilled saturated fat supplements enriched in palmitic acid (82 % 16:0; PA treatment) while SBT treatment included 27 % 16:1n-7, 28 % 16:0, 7.8 % 18:1n-7, 22 % 18:1n-9 and 11 % 18:2n-6. The treatment period ranged from 20 ± 5 d precalving to 67 ± 2 d (mean ± standard deviation) postcalving. Plasma and FF samples were collected from 2 sequential sessions of ovum pick-up (OPU-1 and OPU-2) at 46 and 67 ± 2 d postcalving. Except for 18:1n-9, proportions of the main unsaturated FA, supplied by SBT (i.e. 16:1n-7, 18:1n-7, and 18:2n-6) were increased (P_fat < 0.05) in most lipid fractions of plasma and FF as compared with PA group. Nevertheless, - particularly for 16:1n-7 - the response depended on the sampling time (P_{fat x time} < 0.10) was of lower magnitude at OPU-1. Despite the 18:1n-9 supply to the SBT group, proportions of this FA in the phospholipid (PL) and cholesterol esters (CHE) fractions of plasma and FF were lower as compared with the PA group (P_fat < 0.001). However, in the plasma PL fraction the difference between fat sources was greater at OPU-1 than at OPU-2 (P_{fat x time} < 0.05). Additionally, the ratio of 18:1n-9–18:0 decreased in the plasma non-esterified FA (NEFA) and PL fractions from OPU-1 to OPU-2 (P_time < 0. 10), while the ratio increased in FF NEFA and CHE (P_time < 0.05), irrespective of the fat source (P_{fat x time} > 0.05 except for plasma PL). Differences between lactation stages, either or not dependent on fat supplementation, were hypothesized to be related to the (need for) alleviation of lipotoxicity through endogenous desaturation. Furthermore, except for 16:1n-7, plasma and FF NEFA were uncorrelated, while esterified plasma and FF FA showed higher correlations at OPU-2 than OPU-1. As such, (dietary) interventions with MUFA-enriched supplements potentially are less effective earlier after calving.