The major bioactive omega-3 (n-3) fatty acids (FA) are eicosapentaenoic acid (EPA; 20:5 n-3) and docosahexaenoic acid (DHA; 22:6 n-3). These 2 FA are derived from desaturation and elongation of the essential FA alpha-linolenic acid (ALA; C18:3 n-3). Low conversion rates of ALA into EPA and DHA indicate that dairy cows may benefit from direct supplementation of these conditionally essential FA, especially during periods of prolonged inflammation such as the transition period (Pawlosky et al., 2001; dos Santos Neto et al., 2024; Bradford et al., 2015). The first experiment in this thesis evaluated the effect of increasing abomasal infusion doses of DHA on milk and plasma FA as well as milk production responses. Correlations between DHA absorption and milk and plasma DHA were calculated to determine potential biomarkers of DHA absorption. Abomasal infusion of DHA linearly reduced milk somatic cell count (SCC) and increased DHA in milk fat as well as total plasma lipids, phospholipids (PL), triacylglycerols (TAG), and cholesterol esters (CE). DHA absorption was positively correlated with DHA in total plasma lipids, PL, TAG, and milk fat. The second experiment in this thesis evaluated the effect of feeding a calcium salt enriched in EPA and DHA to dairy cows during the 3 weeks before and 3 weeks after parturition on milk production, plasma metabolites, and milk FA during the first 3 weeks of lactation. Carryover effects of n-3 FA on milk production were also evaluated for 6 weeks post-supplementation. The diet containing EPA and DHA reduced milk fat yield for the first 5 weeks of lactation and tended to reduce yields of 3.5% fat-corrected milk (FCM) and energy-corrected milk (ECM). Supplementing EPA and DHA also reduced yields of de novo and mixed FA in milk. The results from our two studies will help to inform dairy farmers, nutritionists, and researchers on strategies to feed EPA and DHA and estimate absorption of these bioactive FA in dairy cows.
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