PSV-1 - A comparison of Dhurrin-free and conventional varieties of sorghum sudangrass baleage

Abstract: Dhurrin is a cyanogenic glycoside present in sorghum cultivars. Dhurrin is converted to prussic acid after a catalytic event, such as frost, wilting, or trampling. Prussic acid is toxic to grazing cattle, and death occurs within minutes after consumption. The objectives of this study were to compare a naturally selected, dhurrin-free (DF) sorghum sudangrass with a conventional brown midrib sorghum sudangrass (CON) to assess the nutritional composition and in-vitro ruminal disappearance. Plots were cut twice (CUT; Aug 21, 2023 and Oct 23, 2023), baled, and in-line wrapped. Bales were cored following a 28d fermentation and duplicate samples by variety (TYPE) and CUT were analyzed for dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and organic matter (OM). Sub-samples were sent for commercial analysis via near infrared spectroscopy (NIR). Samples were composited by TYPE and CUT for analysis of in-vitro ruminal disappearance. Ruminal fluid was collected and used as inoculum for incubation in an automated incubator (Daisy II, ANKOM Technology, Macedon, NY) lasting for 4, 12, 48, and 72 hours (HOUR). Samples were subsequently analyzed for DM and NDF to calculate dry matter disappearance (DMD) and neutral detergent fiber disappearance (NDFD). There was a TYPE × CUT interaction (P < 0.01) for DM where no differences were observed between CON and DF at 2^nd cut, however, DF was 33.34% DM compared to CON which was 26.37% at 1^st cut. The CP concentration was greater (P < 0.01) at 2^nd cut, while NDF, ADF, and OM were all reduced, when compared to1^st cut, regardless of TYPE. There was an impact of TYPE on ADF concentration (P < 0.01); where DF had 3.56% more ADF than CON, regardless of CUT. Regression models adequately related lab analysis and NIR for all variables (P < 0.01), validating the use of NIR to analyze dhurrin free sorghum sudangrass. There were no interactions between TYPE, CUT, and HOUR (P > 0.05) for DMD. However, 2^nd cut had 4.86% greater (P < 0.01) DMD than 1^st cut, regardless of variety; and, DMD increased (P < 0.01) over time. A TYPE x HOUR interaction (P = 0.02) occurred for NDFD at hour 48 where NDFD was 3.98% greater for CON than DF; however, NDFD was not different by variety at other time points. There was also a CUT x HOUR interaction (P = 0.03) for NDFD, where the 1st cut had a slower rate of disappearance at all time points. Final NDFD at hour 72 was 69.9% and 75.1% for the 1^st and 2^nd cut, respectively. Little difference existed between the nutritional composition and in-vitro ruminal disappearance of conventional and dhurrin free sorghum sudangrass when harvested at two different cuts for baleage.