Animals : an Open Access Journal from MDPI · 4 authors, 3 centres
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This study found that feeding lambs an EPA-rich microalga for 21 days did not increase brain EPA levels, but did increase retinal EPA by 4.6-fold in freeze-dried microalgae-fed lambs compared to controls. Retinal tissues were highly responsive to short-term n-3 PUFA supplementation, while brain EPA remained unchanged. These findings suggest that retinal tissue is a sensitive target for evaluating dietary n-3 LC-PUFA absorption in ruminants.
**Background:** Omega-3 polyunsaturated fatty acids (n-3 PUFAs), particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are crucial for brain and retinal function, influencing neurogenesis, neurotransmission, and inflammation. Ruminants can selectively accumulate n-3 LC-PUFAs in brain and retina despite extensive rumen biohydrogenation. This study aimed to evaluate the fatty acid (FA) profile of lamb brain and retinal tissues after short-term dietary supplementation with an EPA-rich microalga (Nannochloropsis sp.) in different formats (oil, spray-dried, freeze-dried), hypothesizing that processing method would affect EPA bioavailability and tissue deposition.
**Methods:** Twenty-eight 60-day-old Merino Branco ram lambs were randomly assigned to four groups (n=7 each): control diet (C), or control diet supplemented with Nannochloropsis sp. as free oil (O diet, 12 g/kg), spray-dried biomass (SD diet, 123 g/kg), or freeze-dried biomass (FD diet, 92 g/kg), all providing ~3 g EPA/kg diet DM. After 21 days, lambs were slaughtered; brain (grey matter, white matter, hippocampus, prefrontal cortex) and retina with tapetum lucidum (RTL) were collected, lyophilized, and analyzed for fatty acid methyl esters (FAMEs) and dimethyl acetals (DMAs) via GC-FID and GC-MS. Data were analyzed using SAS MIXED procedure (p<0.05 significant).
**Key Results:** Total FA+DMA content did not differ among treatments in any brain region (grey matter: ~191 mg/g DM; white matter: ~227 mg/g DM; hippocampus: ~199 mg/g DM; prefrontal cortex: ~208 mg/g DM) or RTL (~53 mg/g DM). In brain, EPA proportions were low (~0.6%) and unchanged across treatments. However, in hippocampus and prefrontal cortex, n-3 docosapentaenoic acid (DPA, 22:5n-3) was significantly higher in FD-fed lambs compared to C (p<0.05), with intermediate values in O and SD. DHA did not differ. In RTL, EPA was 4.6-fold higher in FD-fed lambs (0.82% TFA+DMA) vs C (0.18%), and DPA was 2-fold higher (p<0.05). DHA averaged 6.4% and did not differ. The AA/EPA ratio was significantly higher in C vs all supplemented groups (p<0.001). sPLSDA analysis showed clear separation of C from supplemented lambs based on RTL FA composition, but not brain regions.
**Clinical Implications:** This study demonstrates that short-term (21-day) dietary EPA supplementation in lambs does not increase brain EPA levels, likely due to rapid β-oxidation, elongation to DPA, or slow turnover. However, retinal tissues are highly responsive, with a 4.6-fold increase in EPA, suggesting the retina is a sensitive biomarker for n-3 LC-PUFA absorption in ruminants. The lack of DHA increase in both brain and retina may reflect homeostatic maintenance from liver stores. These findings have implications for optimizing n-3 PUFA delivery in animal feed to enhance retinal health, and potentially for translational research on retinal function in humans. The study also highlights that freeze-dried microalgae biomass is more effective than oil for EPA enrichment in retina, likely due to better protection from rumen biohydrogenation.