Description

Climate change has made resilient crops more valuable in many agricultural production systems. Sorghum is an important resilient grain and forage crop due to its high drought tolerance and ability to thrive in low-N environments. All current commercial sorghum varieties produce the cyanogenic glucoside dhurrin. Cell maceration causes the conversion of dhurrin to hydrogen cyanide (HCN), which is toxic to animals. Toxicity symptoms range from labored breathing and convulsions to death within minutes. The dhurrin biosynthesis pathway was altered to inhibit dhurrin production by a mutation that inactivated CYP79A1, the first enzyme in the pathway. The dhurrin-free phenotype eliminates the risk of hydrogen cyanide (HCN) poisoning in animals; however, agronomic performance and livestock responses when the dhurrin-free is grazed has not been studied. This study focused on the impacts of the cyp79a1 mutation on sorghum forage production and utilization. Over two months, weight gains were compared for stocker calves grazing either a dhurrin-free hybrid and a conventional hybrid (S&W SP4105). Presence or absence of HCN, nutritional quality, and yields were also determined before and throughout the grazing trial. The dhurrin-free hybrid and SP4105 had equivalent biomass yields (kg ha-1) throughout the trial. The dhurrin-free hybrid’s neutral detergent fiber and acid detergent fiber were 35 and 20 mg g-1 lower, respectively, when compared to SP4105 on the first sampling date (P-value < 0.1). Rumen degradable protein and total digestible nutrients were higher as well for the dhurrin-free, but the two hybrids were similar by the second sampling date for nutritional quality. Average daily gain was similar between the dhurrin-free hybrid and the conventional sorghum hybrid. Taken together, dhurrin-free sorghum has many beneficial aspects as a forage; no fear of HCN toxicity and competitive weight gains of stocker calves, with excellent biomass yields and forage quality.

DOI

https://doi.org/10.13023/xd9z-cc37

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Inhibiting Dhurrin Biosynthesis Effects on Stocker Cattle Daily Gains

Climate change has made resilient crops more valuable in many agricultural production systems. Sorghum is an important resilient grain and forage crop due to its high drought tolerance and ability to thrive in low-N environments. All current commercial sorghum varieties produce the cyanogenic glucoside dhurrin. Cell maceration causes the conversion of dhurrin to hydrogen cyanide (HCN), which is toxic to animals. Toxicity symptoms range from labored breathing and convulsions to death within minutes. The dhurrin biosynthesis pathway was altered to inhibit dhurrin production by a mutation that inactivated CYP79A1, the first enzyme in the pathway. The dhurrin-free phenotype eliminates the risk of hydrogen cyanide (HCN) poisoning in animals; however, agronomic performance and livestock responses when the dhurrin-free is grazed has not been studied. This study focused on the impacts of the cyp79a1 mutation on sorghum forage production and utilization. Over two months, weight gains were compared for stocker calves grazing either a dhurrin-free hybrid and a conventional hybrid (S&W SP4105). Presence or absence of HCN, nutritional quality, and yields were also determined before and throughout the grazing trial. The dhurrin-free hybrid and SP4105 had equivalent biomass yields (kg ha-1) throughout the trial. The dhurrin-free hybrid’s neutral detergent fiber and acid detergent fiber were 35 and 20 mg g-1 lower, respectively, when compared to SP4105 on the first sampling date (P-value < 0.1). Rumen degradable protein and total digestible nutrients were higher as well for the dhurrin-free, but the two hybrids were similar by the second sampling date for nutritional quality. Average daily gain was similar between the dhurrin-free hybrid and the conventional sorghum hybrid. Taken together, dhurrin-free sorghum has many beneficial aspects as a forage; no fear of HCN toxicity and competitive weight gains of stocker calves, with excellent biomass yields and forage quality.