Optimizing early lactation performance in dairy cows through co-supplementation of rumen-protected methionine and n-3-enriched calcium salts

Supplementing rumen-protected Met (RP-Met) during the transition period has been shown to improve DMI and increase milk production in dairy cows. The n-3 fatty acids (FA), particularly eicosapentaenoic acid (EPA; C20:5) and docosahexaenoic acid (DHA; C22:6), are known to support immune function in nonruminants, but their effects in dairy cows remain less defined. We aimed to investigate the combined effects of RP-Met and calcium salts (CS) of FA enriched with EPA and DHA on lactation performance in periparturient Holstein cows. Seventy-nine multiparous cows were enrolled in a randomized complete block design and assigned to 1 of 4 dietary treatments (n = 18 to 19 per treatment) from 3 wk before (-21 ± 3 d) to 3 wk after calving as follows: (1) no RP-Met and CS without n-3 FA (-Met/-n3FA; CS contained 56.0% saturated FA, 35.2% oleic acid, and 8.10% linoleic acid), (2) RP-Met with CS without n-3 FA (+Met/-n3FA), (3) no RP-Met with CS enriched in n-3 FA (-Met/+n3FA; CS contained 64.5% SFA, 25.4% oleic acid, 5.10% linoleic acid, 0.60% linolenic acid, 2.60% EPA and 1.40% DHA), or 4) RP-Met and CS enriched in n-3 FA (+Met/+n3FA). All cows were fed a corn silage-based TMR pre- and postpartum. Diets were formulated to provide either ≤0.96 g Met/Mcal of ME (-Met) or ≥1.13 g Met/Mcal of ME (+Met). Calcium salts were included at 1.5% of dietary DM across all diets. Prepartum DMI, BW, and BCS were unaffected by treatment. The main effect of treatment (supplemental Met and n-3 FA) increased postpartum DMI, Met (25.2 vs. 20.1 g/d Met prepartum and 59.9 vs. 35.9 g/d Met postpartum for +Met and -Met diets, respectively) and n-3 FA intakes (1.36 vs. 0 g/d EPA and DHA prepartum and 6.61 vs. 0 g/d EPA and DHA postpartum for +n3FA and -n3FA diets, respectively). Co-supplementation increased ECM, and FCM yields, and milk fat and true protein yields, and tended to increase milk yield, relative to diets containing only RP-Met or only n-3 FA. Cows co-supplemented with RP-Met and CS enriched in n-3 FA had marginally higher plasma glucose and lower plasma triglyceride concentrations at calving, and reduced plasma total and nonessential AA concentrations during lactation. Nutrient-specific responses included increased plasma Met in cows fed +Met diets and elevated milk lactose contents and yields, along with higher n-3 FA and PUFA contents and yields in cows fed CS enriched in n-3 FA. The additive effects of co-supplementation suggest potential synergy when cows are fed Met, EPA, and DHA. Although the underlying mechanisms were not fully elucidated, the observed improvements may be linked to enhanced mammary de novo FA synthesis, altered AA utilization, and increased hepatic gluconeogenesis, collectively supporting improved metabolic function and lactation performance in early lactation dairy cows.