Arizona livestock guide

Region: Desert Southwest – Hot and dry; worm transmission is limited to irrigated or monsoon-season pastures.

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Horses in Arizona

Common parasites

• Small strongyles (cyathostomins) – The main worm of adult horses; resistance to common dewormers is widespread. Use fecal egg counts with your vet rather than rotating on a calendar. (source)
• Large roundworms (ascarids) – Mainly foals and weanlings; heavy loads can cause impaction colic. (source)
• Tapeworms – Linked to some colics; usually treated once or twice a year. (source)

Toxic plants & feeds

• Oleander – Landscape shrub; very small amounts are deadly to all livestock. (source)
• Locoweed – Range plant. (source)
• Yew (Taxus) – Ornamental shrub; a few mouthfuls can kill a horse within hours. Never toss hedge clippings into a pasture. (source)
• Ionophore feeds (monensin, lasalocid) – Cattle/poultry feeds and some mineral tubs are deadly to horses and donkeys. (source)
• Blister beetles in alfalfa hay – Crimped alfalfa can trap beetles (cantharidin); buy hay from a known source. (source)
• Lawn clippings – Ferment quickly and can cause colic or laminitis. (source)

Minerals

• Selenium – high in places – Some soils here are seleniferous and accumulator plants (e.g. milkvetch, prince’s plume) can cause selenium poisoning (hoof and mane/tail loss). Check before adding selenium. (source)
• Salt – Free-choice plain or trace-mineral salt for every horse.
• Balance to the forage – Grass hay alone often runs low in some trace minerals; a ration balancer is commonly used. Have hay tested if possible.

Donkeys in Arizona

Common parasites

• Small strongyles and tapeworms – Same worms as horses; donkeys can carry heavy loads while looking fine. Use fecal egg counts. (source)
• Lungworm (Dictyocaulus arnfieldi) – Donkeys often carry it without coughing and can pass it to horses grazing with them. (source)

Toxic plants & feeds

• Oleander – Deadly. (source)
• Yew, ionophore feeds – As deadly to donkeys as to horses. (source, source)
• Rich feeds and lush grass – Not a poison, but a major risk: donkeys easily become obese and develop laminitis or hyperlipemia.

Minerals

• Selenium – high in places – Seleniferous areas exist; do not supplement selenium without testing. (source)
• Salt and a low-calorie balancer – Donkeys usually need straw/low-sugar hay plus a vitamin–mineral balancer, not grain.

Goats in Arizona

Common parasites

• Barber pole worm (Haemonchus contortus) – Blood-sucking stomach worm and a leading cause of goat deaths. Watch eyelid color (FAMACHA) and bottle jaw; resistance to all dewormer classes exists. (source, source)
• Coccidia – Kids 3 weeks to 6 months; diarrhea and poor growth, worse in crowded or wet pens. (source)
• Barber pole worm (irrigated/monsoon) – Watch closely after monsoon rains. (source)

Toxic plants & feeds

• Oleander – Deadly. (source)
• Rhododendron, azalea, mountain laurel – Ornamental and wild shrubs that cause vomiting and collapse in goats. (source)
• Yew and cherry (wilted leaves) – Yew is deadly; wilted wild-cherry leaves release cyanide. (source)
• Avocado leaves – Toxic to goats (heart damage). (source)
• Excess grain – Overeating grain causes rumen acidosis (bloat, collapse).

Minerals

• Selenium – variable – Ranges from deficient to toxic within the region; test hay or blood before supplementing. (source, source)
• Use a GOAT mineral, not a sheep one – Goats need much more copper than sheep; sheep minerals are copper-restricted and can leave goats deficient (rough coat, swayback in kids). Never feed goat mineral to sheep – copper can poison them. (source, source)
• Loose mineral, free choice – Goats generally eat loose minerals better than blocks.

Cattle in Arizona

Common parasites

• Brown stomach worm (Ostertagia ostertagi) – The most damaging cattle roundworm; Cooperia is also common. Young stock suffer most. (source)
• Flies and lice – Horn flies on pasture in summer; lice in winter. (source)

Toxic plants & feeds

• Oleander – Deadly. (source)
• Locoweed, broom snakeweed – Range plants; snakeweed can cause abortion. (source)
• Yew – A leading cause of sudden death in cattle from tossed clippings. (source)
• Nitrate and prussic acid forages – Drought-stressed or frosted sorghum, sudangrass and johnsongrass, and some weeds; test suspect forage. (source)
• Excess grain – Grain overload (acidosis) or sudden diet changes.

Minerals

• Selenium – variable – Seleniferous soils and accumulator plants occur; chronic selenosis (lameness, hoof damage) is possible. Test forage. (source)
• Free-choice trace-mineral salt – Match the mineral to your forage and region; ask your extension agent or vet.
• Magnesium on lush pasture – Grass tetany risk in early spring on lush grass, especially older cows nursing calves; high-magnesium mineral is often used. (source)

Help in Arizona

• Cooperative Extension service
• State Department of Agriculture
• State veterinarian / animal health office

The state veterinarian link goes to the national directory of state animal health officials.

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Last reviewed 2026-10-18. Regional summaries; your county extension office knows your area best.