Preference of dhurrin-free sorghum by ewes

Abstract

Sorghum [Sorghum bicolor (L.) Moench] is a resilient forage crop due to its drought tolerance and adaptation to low-N environments. Sorghum produces a cyanogenic glucoside called dhurrin. The breakdown of dhurrin leads to the release of hydrogen cyanide (HCN), which can cause cyanide toxicity in livestock. Dhurrin-free sorghum lines have been developed through chemical mutagenesis by mutagenizing the gene for the first enzyme, CYP79A1, in the biosynthetic pathway. The CYP79A1 mutation was bred into sorghum lines to create a dhurrin-free experimental hybrid. Grazing preference of ewes was assessed when allocated to the dhurrin-free hybrid and three commercial hybrids. Near isogenic lines (NIL), contrasting in dhurrin production, were also compared for grazing preference. Forage mass was measured before and after grazing to determine the amount of forage mass grazed by the ewes. An unmanned aerial vehicle (UAV) was flown to quantify changes in normalized difference vegetation index (NDVI) over time for each hybrid. The nutritive values of the hybrids were also evaluated. The dhurrin-free hybrid was grazed 19% and 13% more (p-value ≤ 0.05) in comparison to the commercial hybrids for the second and third grazing cycles in 2019 and 2020. The NIL Tx623 bmr6 CYP79A1, was grazed 20% more than Tx623 bmr6 in two grazing cycles in 2020. Remote sensing data showed a similar pattern with the dhurrin-free hybrid having the largest decline in NDVI for three grazing cycles in 2019. Nutritive value of the dhurrin-free hybrid was similar to the two hybrids with the brown midrib (bmr) trait.