PS1-26. Optimizing Corn-sorghum Blends: Impact on Rumen Fermentation, Volatile Fatty Acid Profiles, and Digestibility.

Abstract Sorghum is a water-efficient, regionally available crop suitable for areas from South Dakota to southern Texas. Its use in finishing cattle diets has been limited due to lower rapidly fermentable carbohydrate content, which can reduce performance. Inclusion of sorghum alongside corn in feedlot diets represents an untested strategy to leverage the water-efficient stability of sorghum while maintaining the performance outcomes associated with traditional corn-based feeding systems. However, few studies have evaluated how partial replacement affects rumen fermentation, a key driver of nutrient utilization and animal performance. The objective of this study was to assess the impact of varying corn-to-sorghum ratios on in vitro dry matter digestibility (IVDMD), volatile fatty acids (VFAs), ammonia, and pH. Rumen contents from two rumen-cannulated Holstein steers consuming a high-energy diet were used in an in vitro fermentation study. Diets included 0, 25, 50, 75, or 100% dry-rolled sorghum replacing corn, with five replicates per treatment (n = 5). Fermentations ran for 48 hours, after which pH was measured, and samples were collected for VFA and ammonia analysis. In vitro dry matter digestibility was calculated by measuring residual diet after incubation. Data were analyzed using the MIXED procedure in SAS 9.4 with diet as a fixed effect and replicate as a random effect; orthogonal contrasts evaluated dose-dependent responses. Diet affected IVDMD (P = 0.022), with a significant linear decline as sorghum inclusion increased (P = 0.007). Digestibility was highest for the 0% sorghum diet (0.908) and lowest for the 100% sorghum diet (0.753), with intermediate values for the blends (25% = 0.792, 50% = 0.765, 75% = 0.794), indicating that including corn in sorghum-based diets helps maintain digestibility relative to feeding sorghum alone. Ammonia concentrations were not affected by diet (P ≥ 0.22), indicating stable nitrogen availability across treatments. Acetate and valerate were also unaffected (P ≥ 0.24), while propionate decreased linearly with increasing sorghum (P = 0.011). The acetate-to-propionate ratio (A:P) increased with sorghum inclusion (diet P = 0.04; linear P = 0.007), with higher A:P in the 75% and 100% sorghum diets compared to 0%. Butyrate, isobutyrate, and isovalerate showed quadratic responses (P = 0.036, 0.043, 0.007, respectively), increasing from 0% inclusion at moderate sorghum inclusion and decreasing at 100% sorghum inclusion. Collectively, these fermentation results demonstrate that integration of sorghum into corn-based diets maintains a rumen environment favorable for VFA production. These results indicate that partial sorghum inclusion in corn-based diets supports propionate production while maintaining digestibility and nitrogen stability. Overall, sorghum can be incorporated without major disruptions to fermentation, offering flexibility for feed formulation and resource-efficient production. Future research should evaluate how blended corn–sorghum diets influence growth and feed efficiency in finishing steers.