• Species Susceptibility to HCN (Cyanide) Poisoning: Cattle are the most susceptible domestic livestock species to hydrocyanic acid (HCN) toxicity from cyanogenic plants (e.g., young sorghum/chari, white clover).
• Physiological Basis:
• The bovine rumen maintains a neutral to slightly acidic pH ($6.0\text{--}6.8$), abundant moisture, and dense microflora that rapidly hydrolyze cyanogenic glycosides via microbial $\beta$-glucosidases into lethal free $HCN$.
• In contrast, monogastric animals (horses, pigs) have gastric hydrochloric acid ($pH \lt 2$) that rapidly destroys plant $\beta$-glucosidase enzymes, minimizing cyanide release. Sheep are less susceptible than cattle due to lower intake rate and higher hepatic rhodanese efficiency.

Correct option: (2) Cattle