Effects of a commercial buckwheat rhizome flavonoid extract on milk production, plasma pro-oxidant and antioxidant, and the ruminal metagenome and metabolites in lactating dairy goats

Buckwheat is a common straw crop that contains an abundance of flavonoids and could be used as an antioxidant additive in animal diets. In this study, the effects of a commercial buckwheat rhizome flavonoid extract (BRFE) on milk production, plasma pro-oxidant and antioxidant, the ruminal metagenome, and ruminal metabolites in dairy goats were evaluated. Forty healthy, multiparous, nonpregnant Guanzhong dairy goats were blocked by DIM (122 ± 5.1 d), milk yield (1,461 ± 91 g/d), parity (3.80 ± 0.76 lactations), and BW (44.18 ± 2.47 kg), and were assigned to 1 of 4 diets. The control (CON) goats were fed the basal total mixed ratio, whereas the goats in treatment groups 1, 2, and 3 were fed the CON diet supplemented with 70, 140 (MB), and 210 mg/kg of a commercial BRFE (Shaanxi Haiyisi Biotechnology Co. Ltd., Xian, China) on a DM basis of the diet, respectively. The goats were fed these diets for a total of 63 d, with a 21-d adaptation period and a 42-d experimental period. Individual DMI and milk yield were recorded daily. Milk component samples were collected on d 6, 7, 13, 14, 20, 21, 27, 28, 34, 35, 41, and 42 of the experimental period; blood and ruminal fluid samples were collected on d 1, 21, and 42 of the experimental period. The results indicated that all milk production variables (milk yield, 3.5% FCM, fat, protein, lactose, and SNF yields) linearly and quadratically increased with increasing BRFE supplementation, and these variables were the highest in the MB group. The plasma total antioxidant capacity and superoxide dismutase increased linearly and quadratically with increasing BRFE supplementation. The plasma malondialdehyde and superoxide anion contents linearly and quadratically decreased with increasing dietary BRFE content. The ruminal fluid propionate content linearly and quadratically increased with BRFE supplementation. The ruminal acetate:propionate ratio linearly and quadratically decreased with increasing BRFE content. Compared with CON, feeding 140 mg/kg BRFE reduced the ruminal fluid abundances of Synergistetes at the phylum level and Quinella at the genus level. Dietary supplementation with BRFE increased the abundance of carbohydrate-digesting enzymes in ruminal fluid, among which glycoside hydrolase family 2 was the most dominant. Metabolomic analysis indicated that supplementation with BRFE enriched tryptophan metabolism in the rumen. Overall, this study revealed that dietary supplementation with BRFE increased plasma antioxidant capabilities and milk production and improved ruminal fermentation, the ruminal metagenome, and ruminal tryptophan metabolism in lactating dairy goats.