Determining the nutritional value of protein in two microalgae species Isochrysis galbana (I. galbana) and Nannochloropsis oculata (N. oculata) used in animal nutrition

Today, the nutritional value of microalgae is not hidden from anyone, and extensive research is being done to increase their production capacity and nutritional value. Due to the high cost of the protein portion of livestock diets, microalgae can be economically viable natural alternatives to protein supplements such as soybean meal in competitively priced diets. In all of the dietary amino acids, lysine and methionine are the first and second limiting amino acids. Most microalgae species contain relatively high levels of lysine. But they are somewhat deficient in sulfur-containing amino acids such as cysteine and methionine. The present experiment aimed to investigate the protein content and chemical composition of two species of microalgae, Isochrysis galbana (I. galbana) and Nannochloropsis oculata (N. oculata), the degree of nitrogen degradability (IVDN), and their different parts of the protein in the Cornell Net Carbohydrate and Protein )CNCPS( system.

For this purpose, after culturing and harvesting the two microalgae species in the laboratory and conducting experiments, the amount of dry matter (DM) composition, ash, crude protein (CP) and determination of amino acid pattern, evaluation of IVDN and determination of different parts of the protein of two species of microalgae I. galbana and N. oculata was made by CNCPS system. In this study, to estimate the IVDN, the ruminal fluid of three male Holeshtine castrated fistula calves with an average weight of 480 ± 40 kg and age 2 years was used.

The results showed that the two microalgae species were different in terms of CP%, fat %, and NSC % (P<0.05). The N. oculata 37% and I. galbana had 32% CP. The ratio of essential to non-essential amino acids was 18.79% in I. galbana and 28.8% in N. oculata (P <0.05). The percentage (IVDN) at 8, 12, and 24 h of incubation in I. galbana was 44%, 53%, and 48%, respectively, and in N. oculata was 35%, 40%, and 38% (P <0.05). The percentage of RUP at 8, 12, and 24 h of incubation was 56%, 47%, and 42% in I. galbana and 65%, 60%, and 62% in N. oculata, respectively. Sections A, B1, B2, and C in I. galbana 10.07, 8.85, 66.18, 7.56, and in N. oculata 15.16, 16.64, 54.98, and 8.8, respectively (P <0.05).

The results of the present study indicated that considering the amount of fat%, CP%, IVDN, and RUP in N. oculata and I. galbana, it seems that these microalgae are suitable for use in animal feed.