Microalgae are suitable protein feeds for lactating dairy cows

The potential of non-defatted microalgae as protein feeds for dairy cows was evaluated in a series of four Latin square experiments conducted with 4-8 lactating cows on grass-silage based diets. In the experiments: (1) mixture of Chlorella vulgaris and Spirulina platensis; or (2) S. platensis were compared to rapeseed meal (RSM); (3) S. platensis, C. vulgaris and mixture of C. vulgaris and Nannochloropsis gaditana to soya bean meal (SBM); and (4) S. platensis to RSM and faba beans (FB). Microalgae replaced the conventional protein feeds partially [50% of crude protein (CP)] in Exp. 1, 2 and 4, or completely (100% of CP) in Exp. 1-3. Data was analysed by analysis of variance. In this abstract, the main results with significance (P<0.05) or tendency towards significance (0.05<P≤0.10) are summarised. The CP concentration was on average 690, 597 and 385 g/kg dry matter (DM) for S. platensis, C. vulgaris and N. gaditana, respectively. Cows showed reduced palatability of microalgae in three experiments. When forage and concentrates were fed separately, cows compensated the decreased intake of microalgae containing concentrates by increasing silage intake, leading to unaffected DM intake (DMI). When fed as total mixed ration, DMI was decreased on average 0.65 kg/d with microalgae. The slight inferiority of microalgae to RSM was demonstrated in one out of three experiments by lower milk yield, and in two experiments by lower N use efficiency (NUE) and human-edible protein efficiency (HEPE), as well as tendency towards lower protein yield on microalgae than RSM diets. Microalgae seemed to be suitable substitute for grain legumes. Microalgae resulted in similar milk and protein yields and NUE as SBM, and tended to increase HEPE in comparison to SBM. Compared to FB, microalgae increased milk yield and NUE, tended to increase protein yield, and did not affect HEPE. In conclusion, the results showed no biological or physiological constraints for protein feed use of microalgae. The greatest challenge limiting the feed use of microalgae for lactating cows is the poorer palatability relative to conventional feeds.