Supplementation of rumen-protected microalgae high in docosahexaenoic acid to lactating dairy cows: Dynamics of lactation performance, milk and plasma fatty acids, and transfer rate of docosahexaenoic acid to milk

This study evaluated the effects of rumen-protected Schizochytrium powder (SP) on dynamics of lactation performance, plasma and milk fatty acids (FA) profiles, and transfer rate of DHA to milk in dairy cows. A total of 30 Holstein cows (181 ± 32 DIM; 29.0 ± 3.1 kg milk yield) were divided into 2 blocks based on milk yield and were then randomly assigned to 1 of 3 groups (n = 10 cows per group): a control group (CON), an uncoated SP group (USP), and a coated SP group (CSP). The experiment comprised a 14-d adaptation phase, 21-d treatment phase, and 7-d washout period. The SP supplementation did not affect milk yield but showed a significant treatment × time interaction for milk fat concentration. The CSP showed reduced milk fat concentration on d 7 and 14 compared with CON and USP, but recovered to comparable levels by d 21. Based on principal coordinate analysis, significant variations in plasma FA profiles were identified among the 3 groups. A treatment × time interaction was detected for plasma docosahexaenoic acid (DHA) and n-3 PUFA concentrations. On d 14, CSP exhibited elevated plasma DHA and n-3 PUFA levels compared with CON and USP. On d 21, plasma DHA levels were higher in CSP than in USP, and higher in USP than in CON. Furthermore, on d 21, plasma n-3 PUFA levels in both CSP and USP were higher than those in CON. A treatment × time interaction was observed for milk DHA concentration, DHA excretion via milk, and DHA transfer rate. From d 1 to 7, CSP showed higher DHA concentration and DHA excretion via milk compared with USP. From d 14 to 28, CSP consistently maintained higher DHA concentration and excretion via milk than USP, which in turn exceeded the levels observed in CON. Following the cessation of supplementation, DHA levels exhibited a gradual decline over a 7-d period; however, CSP group retained comparatively high levels. Throughout the 0- to 21-d feeding interval, the milk DHA transfer rate demonstrated a continuous increase in both CSP and USP, with CSP consistently outperforming USP. On d 21, both DHA concentration and transfer rate attained their maximum values in cows supplemented with CSP and USP, with DHA transfer rate recorded at 11.82% and 2.36%, respectively. In summary, SP can be effectively used as a dietary supplement in dairy cows to optimize the milk FA profile and increase DHA content, with CSP exhibiting superior efficacy relative to USP.