Evaluation of available energy value and digestive metabolism in dairy goats: A comparative study of grain types and processing methods

Background The diverse types and processing methods of grains intricately influence the sites and digestibility of starch digestion, thereby impacting energy utilization. This study aimed to explore the impact of grain variety and processing methods on the net energy (NE) in dairy goats, analyzing these effects at the level of nutrient digestion and metabolism. Methods Eighteen castrated Guanzhong dairy goats (44.25 ± 3.59 kg BW) were randomly divided into three groups, each consisting of six replicates. The substitution method was employed to determine the net energy (NE) values of the dry-rolled corn (DRC), dry-rolled wheat (DRW) or steam-flaked corn (SFC, 360 g/L). Briefly, two phases were performed. Throughout the basal phase, all goats were fed the same basal diet. In the substitution phase, 30% of the basal diet was replaced with DRC, DRW and SFC, respectively. Results The NE values of the DRC, DRW and SFC were 7.65, 7.54 and 7.44 MJ/kg DM, respectively. Compared to the DRC group, the DRW group showed increased digestibility of starch and crude protein (CP). Similarly, the SFC group exhibited increased organic matter (OM) and starch digestibility and a trend towards higher dry matter (DM) digestibility, reduced fecal OM and starch content. Additionally, fecal volatile fatty acid (VFA) concentrations decreased in goats fed SFC. Correspondingly, digestible energy (DE) in the DRW and SFC groups tended to be higher than in the DRC group. DRW increased total VFA concentration compared to DRC, while SFC increased the proportion of propionate and decreased the acetate-to-propionate ratio in the rumen. Both the DRW and SFC diets elevated serum glucose levels. Furthermore, heat increment (HI) and GasE (gas energy) related to fermentation were significantly higher in the DRW and SFC groups compared to the DRC group. Conclusion Our findings indicated that DRW and SFC increased rumen starch fermentation in goats, thereby improving total tract starch digestion and DE. However, DRW and SFC failed to improve NE value due to increased heat and gas energy production from fermentation. Therefore, for dairy goats, excessively refined processing of grains in the diet does not effectively improve energy efficiency.