11. Conclusions and recommendations

The trypanosomiasis problem
Unique nature of Mkwaja data
Trypanosomiasis risk at Mkwaja Ranch
Outcome of the Samorin prophylactic strategy
Insecticide application and release of sterile male tsetse flies
Mkwaja and Kenya Boran
Can productivity be increased?
Implications for other tsetse-infested areas

The trypanosomiasis problem

Tsetse-transmitted African trypanosomiasis is the most significant single factor in Africa's deteriorating food production situation. When all the complex factors involved are taken into consideration, it is estimated that livestock and agricultural development of tsetse-infested Africa could generate a further US$ 50 billion annually. The cost of tsetse control, the lack of a field vaccine and the limited prospects of new trypanocidal drugs appearing in the near future make reliance on the trypanocidal drugs currently available an unavoidable necessity.

Unique nature of Mkwaja data

There is a serious lack of fully documented information on livestock productivity levels attainable using trypanocidal drugs in trypanosomiasis-risk situations. The reports published in Africa over the past 25 years on livestock productivity under chemoprophylaxis and chemotherapy are listed in Table 38. A total of 2931 animals are involved, recorded over an average of 1.6 years. The performance traits covered are almost always growth and viability, some 4097 animal-traits being involved (more than one trait can be recorded on an individual animal), this providing a data volume of some 6000 trait-years only.

Thus the availability of 10 years of matching animal productivity and health data at Mkwaja Ranch offered the unique opportunity of evaluating some 134000 trait-years of new data, or more than 20 times as much information on livestock productivity under chemoprophylaxis as had been made available in the whole of Africa over the previous 25 years.

Trypanosomiasis risk at Mkwaja Ranch

At Mkwaja it has been clearly demonstrated in planned experiments that cattle cannot survive without trypanocidal drugs. If left untreated, all die of trypanosomiasis or are killed by predators. Tired anaemic animals suffering from trypanosomiasis must be more liable to attack by predators. Samorin was clearly superior to Berenil in these experiments, including at the pre-weaning stage, where the chemical has not previously been used in large-scale commercial herds.

Outcome of the Samorin prophylactic strategy

a. The Mkwaja cattle maintained under Samorin prophylaxis appear to be highly successful, being 80% as productive as Boran cattle on trypanosomiasis-free ranches in Kenya and 35% more productive than trypanotolerant N'Dama cattle in medium to high trypanosomiasis-risk ranching situations in West and central Africa. In the situation where bush clearance and tsetse control had been carried out, it was possible to achieve the average Kenya ranching productivity level.

b. There were no indications of any resistance to Samorin developing over the 10-year period.

c. The animal health programme employed at Mkwaja and its management appeared excellent; there were very few cases of trypanosomiasis and virtually no tick-borne infections.

d. Samorin appeared to have no deleterious effects on reproductive performance, as gauged by its completely non-significant influence on calving intervals.

e. The multiple inoculation of Samorin did not raise any serious problems for animals in terms of local reactions and did not lead to increased requirements for treatment or to an earlier decline in productivity.

f. The use of Samorin on the basis of treatment when 20% of a 10% herd sample, usually the poorest looking individuals, were slided as positive, gave an average period between treatments of about 80 days. This appeared a very satisfactory regimen. The last 2 years' data suggested that the policy of treatment when the first positive slide was detected, resulting in an average of 70 days between treatments, could well lead to even higher productivity.

Table 38. Published reports on livestock productivity under chemoprophylaxis and chemotherapy, 1960-84.

Trypanocide(s)a	Number of records for				Duration of trial (months)	Source
	Growth	Viability	Reproduction	Untreated controls
P, A	-	210	-	75	12	Lyttle (1960)
M, MS, P, A	120	120	-	8	6	Smith and Brown (1960)
M, MS	10	10	-	2	-	Stephen (1960)
M, A	-	38	-	5	6	Kirkby (1961)
M, E, A	28	28	-	4	6	Kirkby (1961a)
A, P, M	21	21	-	2	9	Kirkby (1961b)
A, M, ME, MS	20	20	-	5	8	Gray and Stephen (1962)
A, M, S	-	76	-	26	13	Robson (1962)
M, B	-	60	-	-	17	Fairclough (1963)
E, S, B	-	69	-	-	13	Fairclough (1963)
S, N, A	-	12	-	4	3	Kirkby (1963)
S, P, A, B, N	-	60	-	5	6	Kirkby (1964)
S	15	15	-	5	3	Jones-Davis (1967a)
A, P, S	-	400	-	10	9	Wiesenhutter et al (1968)
S	-	60	-	20	1	Na'Isa (1969)
B	25	39	45	-	45	Wilson et al (1975)
S, B	40	40	-	15	29	Wilson et al (1975a)
B, S	-	450	-	-	60	Bourn and Scott (1978)
S, B	80	80	-	20	21	Blaser et al (1979)
S, B	60	60	-	20	24	Blaser et al (1979)
S	15	15	-	2	15	Omwero-Wafula and Mayende (1979)
A, S, B	51	51	-	73	8	Griffin and Allonby (1979)
SD	20	20	-	3	4	Aliu and Sannusi (1979)
S, B	10	10	-	5	11	Specht (1982)
S	89	89	-	146	6	Kanyari et al (1983)
S, B, P	280	280	-	30	9	Wilson et al (1983)
S, B	59	66	18	-	21	Logan et al (1984)

^a Key for trypanocides:

A = Antrycide (quinapyramine)
B = Berenil (diminazene aceturate)
E = Ethidium (homidium bromide)
M = Metamidium
ME = Metamidium embonate
MS = Metamidium suramin salt
N = Novidium (homidium chloride)
P = Prothidium (pyrithidium chloride)
S = Samorin/Trypamidium (isometamidium chloride)
SD = Isometamidium-dextran complex

Insecticide application and release of sterile male tsetse flies

The reduction of the G. m. morsitans populations following insecticide application in the northern area of the ranch appeared to have little effect on positive blood smear results or trypanocidal treatments required. Livestock productivity did appear to increase relative to the control area, but as bush clearance work was taking place only in the northern area, this must be interpreted with caution.

Mkwaja and Kenya Boran

As far as pre-weaning growth traits were concerned, the higher grade Kenya Boran progeny were shown to be superior, but their superiority could not be expressed in the harsher location of the uncleared southern block.

Can productivity be increased?

a. The animal health programme at Mkwaja and its management would appear to be working well. Based on post-mortem examinations, there are few cases of trypanosomiasis under Samorin prophylaxis, despite the fact that in experimental studies at Mkwaja all cattle left untreated became infected with trypanosomes. In the same way, the acaricide control programme is highly effective with no cases of theileriosis or babesiosis being reported in the 10-year study period. Based on these good results, one must be hesitant in making any recommendations for improvement. Nevertheless, one consideration might be to change the method used for detecting trypanosomes from the thick blood smear to the buffy coat phase-contrast technique, a method which is significantly more sensitive (Paris et al, 1982). This would help improve decision-making with regard to the timing and dosage of trypanocidal drug administration. In addition, the measurement of packed red cell volume (PCV) as an estimation of anaemia would help to give a better overall picture of the health status of the herd.

b. The clinical and post-mortem findings indicated that the major problems on the ranch that were not always effectively controlled were anaplasmosis, presumably transmitted by biting flies, salmonellosis in calves, plant poisoning and predators. Better control of any one of these should be given consideration as it is likely that this would make a significant contribution to improved production.

c. Because of the high persistent tsetse challenge at Mkwaja and the lack of evidence of drug resistance to Samorin, no obvious advantages in the use of Berenil emerged in the overall drug regime. However, its continued use instead of Samorin in individual adult animals which become infected in the interval between Samorin treatments of the herd, as well as in pre-weaners, is recommended in order to reduce the risk of development of drug resistance to Samorin.

d. The pasture improvement that has taken place in one major location in the northern block has had a very significant effect on livestock productivity. The attachment of economic parameters to the biological increase in productivity demonstrated, will allow decisions on further pasture improvement at other locations to be made.

e. Breeding season has been shown to have a major effect on productivity, and the fact that two thirds of cows are already bred in the optimal periods shows this to have been well recognised.

Implications for other tsetse-infested areas

The results of this study have shown that cattle production under Samorin prophylaxis is possible in areas heavily infested with tsetse. The fact that this result is based on one of the largest data sets ever analysed offers immediate hope for increased exploitation of tsetse-infested areas by encouraging the more widespread rational use of chemoprophylaxis as an integral part of management. These findings should also provide encouragement to pharmaceutical companies and international agencies to develop new and improved trypanocidal drugs.