Step 1: Understanding the Concept:
Nutritional piglet anemia (piglet thumps): lack of placental and milk iron reserves in rapidly growing neonatal pigs causes severe microcytic hypochromic anemia and spasmodic dyspnea.
Step 2: Detailed Explanation:
Pathophysiology of Piglet Anemia ('Thumps'):
- Newborn piglets are born with minimal iron reserves ($pprox 50 ext{ mg Fe}$), while sow milk provides only $1 ext{ mg Fe/day}$ (against a daily requirement of $7 - 10 ext{ mg}$).
- In intensive confinement rearing on concrete floors without access to soil, rapid growth causes acute Iron Deficiency Anemia within 2 to 3 weeks of age.
- Severe anoxia causes compensatory tachycardia, cardiomegaly, and spasmodic diaphragmatic jerking/jerky laboured respiration, clinically termed 'Thumps'.
- Prevented by administering $150 - 200 ext{ mg}$ iron dextran intramuscularly on the 3rd day of life.
Step 3: Final Answer:
Therefore, 'Thumps' is caused by deficiency of Iron, matching option (A).