Effects of rumen degradable starch on growth performance, carcass, rumen fermentation, and ruminal VFA absorption in growing goats

The objective of the present study was to investigate the effects of dietary rumen degradable starch level (RDS) on growth and carcass performance, rumen fermentation, and rumen papillae development in growing goats. Forty healthy, weaned, 3-month-old male goats (BW=13.6 +/- 0.23 kg) were randomly enrolled to receive either a low rumen degradable starch diet (LRDS, diet based on whole corn, RDS = 13.85 %, n = 20) or high rumen degradable starch diet (HRDS, diet based on crashed corn, RDS = 20.74 %, n = 20). After 90 d of feeding, 8 goats of each group were randomly selected and humanely slaughtered at 3 h after morning feeding. HRDS diet decreased the average daily weight gain, lean meat percentage of carcass, and the ratio of meat to bone (P < 0.05), whereas HRDS diet increased the feed conversion ratio (P < 0.05). HRDS diet decreased the plasma glucose level before morning feeding and 6 h postprandial (P < 0.05), and increasing the plasma glucose level at 2 h postprandial (P < 0.05). HRDS diet up-regulated rumen acetate proportion before morning feeding to 8 h postprandial (P < 0.05) and down-regulated the butyrate proportion before morning feeding to 4 h postprandial (P < 0.05). HRDS diet also increased the ratio of acetate to propionate during 6 h (P < 0.05) to 8 h postprandial (0.05 < P < 0.10). HRDS diet decreased the length and the surface area of rumen papilla (P < 0.05). Further, HRDS diet decreased the mRNA expression of HCO3- /volatile fatty acid (VFA) cotransporter SLC4A2 and SLC26A3, and Na+/HCO3- cotransporter SLC4A4 (P < 0.05). In summary, feeding HRDS diet to growing goats changed rumen fermentation, reduced rumen papilla development, rumen epithelial VFA absorption, and the capacity to maintain the rumen epithelial homeostasis, thereby decreasing the supply of precursors for hepatic gluconeogenesis and repressing the goats' performance. These findings provided further insights for improving growth performance by reducing dietary RDS in goats' diets.