Effect of Dietary Vitamin a on the Innate Resistance of Cattle to Infestation by Larvae of Hypoderma Lineatum (Diptera: Oestridae)

The mean levels of vitamin A in the serum of 6-month-old Hereford calves fed complete or vitamin A-deficient diets for 85 days were 51.6 and 14.0 μ/100 ml, respectively. The animals deficient in vitamin A were more susceptible than normal animals to infestation by larvae of Hypoderma lineatum that hatched from eggs laid on the hair (39.7 vs 21.2% recovery of larvae) but not to infestation by similar numbers of newly hatched larvae injected subcutaneously (57.9 vs 52.7% recovery of larvae). Avitaminosis A apparently reduced the resistance of calves to percutaneous invasions by the parasites.