The effect of partial substitution of rapeseed meal and faba beans by Spirulina platensis microalgae on milk production, nitrogen utilization, and amino acid metabolism of lactating dairy cows.

Alternative protein sources such as microalgae and faba beans may have environmental benefits over rapeseed. We studied the effects of rapeseed meal (RSM) or faba beans (FB) as a sole protein feed or as protein feeds partially substituted with Spirulina platensis (spirulina) microalgae on milk production, N utilization, and AA metabolism of dairy cows. Eight multiparous Finnish Ayrshire cows (113 ± 36.3 d in milk; mean ± SD) were used in a balanced, replicated 4 × 4 Latin square with 2 × 2 factorial arrangement of treatments and 21-d periods. Four cows in one Latin square were rumen cannulated. Treatments were 2 isonitrogenously fed protein sources, RSM or rolled FB, or one of these sources with half of its crude protein substituted by spirulina (RSM-SPI and FB-SPI). Cows had ad libitum access to total mixed rations consisting of grass silage, barley, sugar beet pulp, minerals, and experimental protein feed. The substitution of RSM with FB did not affect dry matter intake (DMI) but decreased neutral detergent fiber intake and increased the digestibility of other nutrients. Spirulina in the diet decreased DMI and His intake. Spirulina had no effect on Met intake in cows on RSM diets but increased it in those on FB diets. Energy-corrected milk (ECM) and protein yields were decreased when RSM was substituted by FB. Milk and lactose yields were decreased in cows on the RSM-SPI diet compared with the RSM diet but increased in those on FB-SPI compared with FB. The opposite was true for milk fat and protein concentrations; thus, spirulina in the diet did not affect ECM. Feed conversion efficiency (ECM:DMI) increased in cows on FB diets with spirulina, whereas little effect was observed for those on RSM diets. The substitution of RSM by FB decreased arterial concentration of Met and essential AA. Spirulina in the diet increased milk urea N and ruminal NH ₄ -N and decreased the efficiency of N utilization in cows on RSM diets, whereas those on FB diets showed opposite results. Met likely limited milk production in cows on the FB diet as evidenced by the decrease in arterial Met concentration and milk protein yield when RSM was substituted by FB. The results suggest the potential to improve milk production response to faba beans with supplementation of Met-rich feeds such as spirulina. This study also confirmed spirulina had poorer palatability than RSM and FB despite total mixed ration feeding and lower milk production when spirulina partially replaced RSM.
(The Authors. Published by FASS Inc. and Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).)