Haematological changes in N'Dama and Gobra Zebu bulls during Trypanosoma congolense infection maintained under a controlled feeding regimen.

Haematological changes were monitored in Gobra-Zebu and N'Dama bulls following infection with Trypanosoma congolense. The cattle were offered a diet which provided levels of protein and energy above maintenance requirement and a pair feeding regimen was used in order to eliminate the confounding anorexic effects of trypanosomosis on the traits studied. Packed red cell volume (PCV), red blood cells (RBC) and haemoglobin (Hb) were monitored weekly. Mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), and mean corpuscular volume (MCV) were derived by computation. Significant breed differences (P < 0.001) were observed in the baseline data collected with N'Dama bulls having higher (P < 0.001) values for RBC and Hb. PCV levels were similar in both breeds pre-infection. Post-infection, there was a significant (P < 0.001) infection effect on the RBC, Hb and PCV in both breeds. The pathogenic effects were more severe in the Gobra-Zebu bulls where three out of ten bulls compared with only one out of eight infected N'Dama bulls attained the low PCV threshold, treated and withdrawn from the study along with their pair mates. Throughout the infection in N'Dama cattle and during the first 6 weeks of infection in the Gobra-Zebu bulls, the infection presented a normochromic normocytic anaemia. However, in the chronic phase, the Gobra-Zebu bulls became macrocytic. The infection reduced total dry matter intake in both breeds although this persisted longer in the Gobra-Zebus. However, their pair-fed controls showed no haematological changes indicating that the anorexia was not compounding the effects of the infection. The severity and type anaemia in N'Dama correlates with their innate ability to resist the effects of trypanosome infection compared to the Gobra-Zebu bulls.