RESUMO
1. Ten Friesian male calves of about 100 kg and 3 months old were reared similarly and were worm-free. From 13 weeks of age five calves received a dose of 640 infective larvae (L3) of lungworms (Dictyocaulus viviparus) twice weekly for 8 weeks to simulate continuous infection. Animals not infected were fed to the same level as the infected animals (about 1.2-1.3 kg concentrates and 1.4-1.5 kg good-quality hay/d). 2. Heat production was measured twice weekly during 48 h (days 2 and 3, and days 5 and 6) in each group of experimental animals. 3. Infection caused considerable damage to the lungs, increased respiration frequency and clearly produced antibody titres against D. viviparus. 4. Animals infected with lungworms had on average a lower rate of weight gain, reduced by 70 g/d per animal. Digestibility was not affected. Nitrogen retention was much lower in infected animals (12.0 v. 14.6 g/d per animal in controls). 5. Metabolizability of energy was slightly reduced in infected animals. Heat production as found in infected animals may be associated with an increased maintenance energy requirement of 30 kJ/kg live weight 0.75 per d or reduced partial efficiency of feed conversion above maintenance in animals infected with lungworms (58.5 v. 64.1% in the control animals). 6. It was concluded that the depression in rate of gain was related to reduced intake of feed and to decreased N retention.
