Effect of Supplementary Feeding on Milk Volume, Milk Composition, Blood Biochemical Index, and Fecal Microflora Diversity in Grazing Yili Mares

SIMPLE SUMMARY: Grazing mares were fed concentrate and coated fatty acids via a customized pocket. The milk yield and composition, plasma biochemistry, and fecal flora were compared among Yili mares that either grazed normally or were fed dietary supplements. Milk yield and fat, lactose, and protein levels were significantly higher among the horses fed dietary supplements compared to those that grazed. All the supplementary diets improved the horses’ milk fatty acid profiles, while coated fatty acid supplementation increased plasma glucose levels. Supplementary feeding significantly increased the fecal abundance of Verrucomicrobia, which regulate lipid biosynthesis, metabolism, and energy metabolism. ABSTRACT: Grazing is a common approach to rearing. We investigated the effects of supplementation during grazing on milk yield and composition, blood biochemistry, and fecal microflora in Yili horses. The control mares grazed normally, while those in groups I and II received 1 kg/d of concentrate and 1 kg/d of concentrate + 0.4 kg/d of coated FA, respectively. Milk volumes were significantly higher in groups I and II than in the control group, and among the previous two, milk volumes were significantly higher in group II than in group I. Milk fat, lactose, and protein levels were significantly higher in group II than in the others. BUN was highly significantly lower in group I than in the control group. Specific FAs, total SFA, and total UFA were significantly higher in group II than in the other groups. After feeding, plasma GLU, free FA, TG, LDL, and VLDL were significantly higher in group II than in the other groups. The control group, group I, and group II had 4984, 5487, and 5158 OTUs, respectively, and 3483 OTUs were common to all groups. The abundance of Bacteroidetes and Firmicutes was >75%. The abundance of Verrucomicrobia was significantly higher in groups I and II than in the control group and, among the previous two, significantly higher in group II than in group I. The abundance of Treponema_saccharophilum significantly differed between the control and other groups, and WCHB 1_41, Kiritimatiellae, and Verrucomicrobia abundances significantly differed between groups II and the other groups.