Quantification of the relative importance of trypanotolerance measurements on productivity of N'Dama cattle (Addendum)

Matching information on animal health and performance aspects was collected from 255 N'dama post-weaners from September 1986 to December 1991. Records covered for each animal a two years period from weaning at 10 months of age until 34 months of age. Curative trypanocidal drug treatment was given when an animal appeared by a clinical examination to be badly affected by trypanosomiasis. Trypanosoma vivax and T. congolense infections had equal effects on number of trypanocidal drug treatments required, an average of 0.61 treatments being administered to each infected post-weaner. A reduction of one standard deviation in length of time infected reduced the number of treatments required by 0.23 or 36 percent and an increase of one standard deviation in PCV reduced the number required by 0.27 or 43 percent. Changes in parasitaemia score were not important. In the case of growth, a T. congolense infection reduced growth by 12.4 g per day or 8 percent more than a T. vivax infection. A reduction of one standard deviation in length of time infected increased growth by 9.8 per day or 6.5 percent. a reduction of one standard deviation in parasitaemia score increased growth by 9.0 g per day or 6.0 percent, and an increase of one standard deviation in average PCV increased growth by 8.4 g per day or 5.6 percent. The necessity for simultaneously considering the infection aspects of trypanosome species, length of time parasitaemic and intensity of parasitaemia, and the anaemia measure of average PCV, is illustrated by their approximately equal effects on the final performance trait of daily liveweight gain. Absence of information on any of these criteria would significantly reduce the accuracy of the estimate of an animal's overall trypanotolerance phenotype in this Central African situation and reduce the progress possible by selection in these N'Dama cattle.