Sorghum is the fifth most common cereal crop grown globally, serving as a significant resource for human food, livestock feed, and biofuel production. Its global utility stems from its resilience; most varieties are highly tolerant of drought and heat, thriving in arid and semi-arid regions where other crops fail. This hardiness makes it a reliable source of nutrition, but it also means the plant must contend with a diverse array of animals seeking to consume its energy-rich tissues.
Sorghum as Primary Livestock Feed
Domesticated livestock are the largest consumers of commercially produced sorghum, utilizing the plant in multiple forms. The grain is a common feed ingredient for beef and dairy cattle, swine, and poultry, often serving as a substitute for corn due to its comparable energy content. Sorghum is an effective component in finishing diets for cattle and supports the rapid growth required for broiler chickens and pigs.
Beyond the grain, the entire plant is utilized as forage for ruminants. It is processed into silage, hay, or green chop, providing a nutrient-rich and highly digestible feed option. Modern breeding efforts have largely eliminated naturally occurring tannins in feed-grade sorghum, making it a more palatable and effective feed source for monogastric animals like pigs and poultry.
Mammalian and Avian Crop Predators
While domesticated animals are the intended consumers, wild vertebrate species frequently act as pests, reducing crop yields, particularly near natural habitats. Rodents, such as mice and rats, cause damage early in the season by digging up newly planted seeds or consuming young sprouts. Rabbits and deer are also common mammalian predators that graze on young, tender growth. Deer typically leave a rough, torn edge on stems, while rabbits make a clean, angled cut.
Avian pests pose a significant threat to standing grain crops as the seeds mature. Species like sparrows, blackbirds, doves, and the Red-billed Quelea frequently descend on fields to feed directly on the grain heads. Bird damage can lead to yield losses as high as 52%, as the pests crush kernels during the soft dough stage to extract the juice and starch. Farmers often select sorghum varieties that contain condensed tannins, which impart a bitter taste that repels these granivorous birds.
Insect Pests of the Sorghum Plant
Insects represent a pervasive threat, attacking the sorghum plant at every stage of development, from the root system to the ripening grain. Soil-dwelling pests, such as white grubs and wireworms, feed on the roots of seedlings, leading to stunted growth or the death of young plants. Later in the season, sap-feeding insects like the sugarcane aphid and chinch bug infest the leaves and stems, sucking out plant juices.
Aphids, including the greenbug, remove sap and inject toxins, causing stunted growth and leaf discoloration. Chinch bugs concentrate at the base of the plant, often causing wilting and death, particularly in dry conditions. The Sorghum Midge attacks the developing flower, or spikelet, preventing the formation of a grain kernel and causing direct yield loss. Other insects, such as corn earworms and sorghum webworms, feed on the ripening grain, either consuming the entire kernel or hollowing out the seed, leaving behind only the shell.
Nutritional Profile and Consumption Safety
The widespread consumption of sorghum by animals is due to its favorable nutritional profile, which is high in starch and serves as an excellent energy source. Sorghum grain typically contains 9 to 13% protein, slightly higher than corn, along with beneficial fiber and minerals. The primary safety concern for animals consuming sorghum is the potential for Prussic Acid, or hydrogen cyanide (HCN), poisoning.
Sorghum plants produce a cyanogenic glycoside called dhurrin, which is converted into toxic hydrogen cyanide when the plant’s cell structure is damaged. This risk is highest when the plant is stressed by environmental factors like drought or frost, or when it is young and actively growing. The resulting HCN interferes with cellular respiration, and ingestion of highly toxic concentrations can lead to acute symptoms like labored breathing and convulsions, often causing rapid death in livestock.