INTERACTION BETWEEN PHYSIOLOGICAL STATUS IN NDAMA COWS AND TRYPANOSOME INFECTIONS AND ITS EFFECT ON HEALTH AND PRODUCTIVITY OF CATTLE IN GAMBIA

Data collected for three years on incidence of trypanosome infections, degree of anaemia as assessed by packed red cell volume (PCV) and liveweights of four groups of cows of varying physiological status were analysed. The animals were not harbouring trypanosomes during a period of two to three months before exposure to periods of increasing density of tsetse flies (Glossina morsitans submorsitans) while grazing in savannah woodlands. The groups of cows were formed on the following basis: pregnant and lactating (lactating-pregnant) (Group 1, n = 143); pregnant and not lactating (dry-pregnant) (Group 2, n = 69); non-pregnant and lactating (lactating-open) (Group 3, n = 160); non-pregnant and not lactating (dry-open) (Group 4, n = 49). Monthly trypanosome prevalence was highest (17.5 %) in the cows with the highest physiological stress (Group 1), followed by Group 3 (11.1 %) and Group 2 (10.0%) with the lowest prevalence found in the least stressed cows, Group 4 (1.6%). Average PCV values for dry-pregnant cows (Group 2; 27.0%) and dry-open cows (Group 4; 26.2%), whether infected or not, were higher than those lactating (Group 1; 25.3% and Group 3; 23.6%). A body weight gain of 4.3 kg between the month of October and the following June was recorded for dry-pregnant cows (Group 2) whereas a weight loss of 16 kg occurred in the lactating-pregnant and lactating-open cows (Groups 1 and 3), with more severe losses recorded in infected than uninfected cows. Dry-open cows (Group 4) maintained their weight during the observation period. It was concluded that the physiological states of pregnancy and lactation tended to predispose N'Dama cows to trypanosome infections, and that the interaction between physiological status and trypanosome infections appeared to have affected their ability to maintain PCV levels and body weights.