Abstract:
Background: Animal trypanosomosis in sub-Saharan Africa is a major obstacle to livestock based agriculture.
Control relies on drugs with increasing incidence of multiple-drug resistance. A previous mapping experiment in
an F2 population derived from the indigenous trypanotolerant N’Dama cattle crossed to susceptible (Kenya)-Boran
cattle under controlled challenge, uncovered a number of trypanotolerance QTL (T-QTL). The present study was to
determine expression of N’Dama trypanotolerance in a backcross to the Boran under conditions of field challenge,
and whether chromosomal regions associated with trypanotolerance in the F2 experiment showed similar effects
in the BC population.
Methods: 192 backcross animals to the Boran were produced in six batches from June 2001 to December 2006. At
one year of age animals were moved to the field and exposed to natural challenge over about one year in
Southwest Kenya (Narok). The animals were individually recorded weekly for body weight, packed cell volume,
parasitaemia score, and drug treatments, and were genotyped using 35 microsatellite markers spanning 5
chromosomes found in the F2 study to harbour T-QTL.
Results: The F1 were most trypanotolerant, Boran least, and BC intermediate. Females showed distinctly higher
trypanotolerance than males. There was a positive correlation in the BC population between trypanotolerance and
number of N’Dama origin marker alleles. QTL mapping revealed T-QTL distributed among all five targeted
chromosomes, corresponding in part to the results obtained in the F2 experiment.
Conclusions: N’Dama origin trypanotolerance is expressed in a BC population under field conditions in proportion
to N’Dama origin marker alleles. Consequently, marker assisted selection in such populations may be a means of
increasing trypanotolerance, while retaining the desirable productive qualities of the recurrent parent.
