The study on the crude protein content and amino acid composition in Brassica napus feed

To evaluate the differences in the nutritional quality of Brassica napus feed at different growth periods, a randomized block design was conducted with two factors, i.e., varieties and mowing periods. Three varieties (Shengsi No.1, Shengsi No.2, and Youyan 50) and four mowing periods bolting stage (BS), early flowering stage (EFS), full bloom stage (FBS) and one week after the final flowering stage (FFS) were set as factor levels in this experiment. The results showed that 1) biological yield was significantly different between different varieties (P < 0.05), and there were highly significant differences between different mowing periods (P < 0.01); however, the interaction between varieties and mowing period did not show differences (P > 0.05). Among the treatments, the highest biological yield was determined in ‘Shengsi No.2’ at FFS. 2) The crude protein (CP) content (dry base) of the three varieties decreased from 26.88%, 27.05%, and 25.66% to 15.22%, 16.06%, and 15.45% from BS to FFS for ‘Shengsi No.1’, ‘Shengsi No.2’, and ‘Youyan 50’, respectively. Additionally, the CP contents differed significantly between the mowing periods (P < 0.05). The CP yield trends were FBS > FFS > EFS > BS in ‘Shengsi No.2’ and ‘Youyan 50’, and FBS > EFS > FFS > BS in ‘Shengsi No.1’. The highest yield (1 855.55 kg·ha⁻¹) was determined in ‘Shengsi No.2’ at FBS, followed by ‘Shengsi No.1’ (1 645.85 kg·ha⁻¹) at the same mowing period. 3) All varieties contained seven essential amino acids (E) and ten non-essential amino acids (N). The amino acids (A), total amino acids (T), E, N, medical amino acids (M), sweet amino acids (S), fresh amino acids (F), and bitter amino acids (B) were significantly different between treatments. Except for Met, the essential amino acid content trend was BS > EFS > FBS > FFS. The E/T of the other essential amino acids was higher than the recommended amino acid pattern by the Food and Agriculture Organization/World Health Organization (FAO/WHO), and the ratio coefficient of amino acid (RC) was close to 1, except for Met + Cys. The score of ratio coefficient of amino acid (SRC) in each treatment ranged from 56.81～71.34, among which the highest SRC value of 71.34 was determined in ‘Shengsi No.2’ at FFS. 4) Using Sanjiang cattle red beef, Brahman beef, Bamei mutton sheep and Juema pork as references, the essential amino acid index (EAAI) was between 0.90～0.94 in ‘Shengsi No.2’ and ‘Youyan 50’, both at FFS. An EAAI value of 0.97 was determined in ‘Shengsi No.2’ at FFS, and values of 0.86 and 0.94 were determined in ‘Shengsi No.2’ at FBS and in ‘Youyan 50’ at FFS. Based on the EAAI values, the protein of ‘Shengsi No.2’ is regarded as excellent or good protein, and that of ‘Youyan 50’ as good protein.