Effects of Trypanosoma vivax infection on nitrogen and energy metabolism and serum hormones and metabolites were measured using 24 castrated West African Dwarf bucks. In order to discriminate between the effect of infection and the effect of food intake level on energy and nitrogen balance, food quantity restriction was applied for isonutritional comparison; a number of the animals were not infected and served as controls. Daily dry-matter (DM) intake was measured, and energy and nitrogen balance for a 7-day period in weeks 2, 4 and 6 after infection. Weekly blood sampling for analysis of hormones and metabolites was carried out.
Infected animals had a lower DM intake, compared with control animals, viz. 38·6 (s.e. 3·2) and 16·1 (s.e. 2·0) g/kg M0·75 per day, respectively (P < 0·001). Intake of gross energy and nitrogen followed the same pattern.
Metabolizability was not changed by infection and averaged 0·44. Heat production was increased by infection with an average of 33 kJ/kg M0·75 per day. Energy and nitrogen retention were negative for all groups; infection reduced energy retention and, during week 2 and 4 after infection, also nitrogen retention. The required metabolizable energy (ME) intake for maintenance was increased in infected animals (406 and 335 kJ/kg M0·75 per day for infected and control goats respectively), based on linear regression of energy retention on ME intake. The efficiency with which energy mobilization from body stores was substituted by dietary ME was estimated at 0·809 for both infected and control animals. The relationship between nitrogen retention and energy retention was not changed by infection. Therefore no indications were found for an increased catabolism of protein due to infection. Serum thyroxine and triiodothyronine were reduced by infection; serum metabolites and insulin levels reflected the negative energy balance in infected animals.