Evaluates teh criteria for trypanotolerance including three related characterstics, v.z. the ability to control parasitaemia, the ability to control anaemia, and the ability to develop an effective immune response

Colardelle, C.

D'Ieteren, G.D.M.

Dumont, P.

Itty, P.

Jeannin, P.

Maehl, J.H.H.

Nagda, S.M.

Ordner, G.

Paling, R.W.

Rarieya, J.M.

Thorpe, W.R.

Trail, J.C.M.

Yangari, G.

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  41 - Evaluation of criteria of trypanotoleranceJ.C.M. TRAIL, C. COLARDELLE, G.D.M. d'IETEREN, P. DUMONT, P. ITTY, P.JEANNIN, J.H.H. MAEHL, S.M. NAGDA, G. ORDNER, R. W. PALING, J.M.RARIEYA, W. THORPE and G. YANGARIIntroductionMaterials and methodsResultsDiscussionReferencesIntroductionIt has been established in recent years that the trypanotolerant breeds of cattle, namelyN'Dama and West African Shorthorn, are much more productive than originally believed,despite their small stature. They are therefore increasingly being considered for livestockdevelopment programmes in tsetse-affected areas.Murray (article 15 of these Proceedings) has noted that trypanotolerance appears to beassociated with at least three possibly related but genetically independent characteristics,namely the ability to control parasitaemia, the ability to control anaemia and the ability todevelop an effective immune response. It would appear that under natural tsetse challenge,parasitaemia aspects could in practice be best measured by factors such as number ofinfections per unit time, trypanosome-species effects and parasitaemia-score effects. Anaemiacontrol aspects could be measured by the ability to maintain PCV levels, by the size of dropfrom "normal" PCV levels or by the recovery rates of PCV. Immune response could beevaluated by measuring the effects of varying numbers of previous infections.Materials and methodsAt the Government ranch of the OGAPROV in southeastern Gabon, 179 N'Dama femalecattle, born between June 1985 and January 1986, were exposed to a high naturaltrypanosome challenge from October 1986 to January 1987. Each month, animals wereweighed, the darkground/phase contrast buffy coat technique was used to detect trypanosomepresence and species and quantification of parasitaemia, while anaemia was estimated bymeasuring the PCV. The analysis approach was to estimate the phenotypic relationshipsbetween parasitaemia aspects, anaemia-control aspects and daily liveweight change.All traits were analysed by least-squares fixed- and mixed model procedures (Harvey, 1977),the effects fitted being indicated in each section. Interaction effects fitted were those thatpreliminary analyses had indicated were significant or approached significance for any of thematching traits involved.ResultsThe average monthly trypanosome prevalence (the percentage of animals determined asbeing parasitaemic at a monthly examination) over the four months was 25.5%. Of the 179N'Dama females, 36.6% never had trypanosomes detected, 36.3% had trypanosomesdetected in one month, 18.4% in two months, 9.3% in three months and 1.7% in all fourmonths. Least-squares analyses were carried out, fitting number of months whentrypanosomes were detected, trypanosome species, parasitaemia score, PCV level andpresence of previous trypanosome infection as fixed effects.Parasitaemia aspectThe effect of number of trypanosome infections on daily liveweight gain and average PCV overthe three month period is shown in Table 1.Table 1. Effect of number of trypanosome infections on growth and PCV.Number of months when trypanosomesdetectedNumber ofanimalsDaily liveweight gain(g) PCV (%)Mean s.e. Mean s.e.0 65 381 10.6 34.0 0.411 65 329 9.9 30.7 0.382 33 260 13.8 27.5 0.543 or 4 16 194 20.7 24.0 0.80There was a linear effect of number of months when trypanosomes were detected, on bothtraits, one infection reducing gain and PCV by 52g and 3.3% respectively, two infections by afurther 69g and 3.2% and three or four infections by a further 66g and 3.5%.The effect of trypanosome species on daily liveweight gain and average PCV over the three-month period is indicated in Table 2.The comparison of the effects of the two species, T. congolense and T. vivax, was onlypossible in animals where trypanosomes were detected in one month only. In this case, a T.vivax infection reduced gain and PCV by 32g and 2.7%, respectively compared with 86g and4.4% for a T. congolense infection.Table 2. Effect of trypanosome species on growth and PCV.Number of months whentrypanosomes detectedTrypanosomespeciesNumber ofanimalsDaily liveweightgain (g) PCV (%)mean s.e. mean s.e0 - 65 381 10.5 34.0 0.401 T. vivax 40 349 12.4 31.3 0.481 T. congolense 25 295 16.7 29.6 0.642 T.c. or T.c. + T.v. ormixed33 260 13.7 27.5 0.533 or 4 T.c. or T.c. + T.v.and/or mixed16 195 20.4 24.0 0.79The effect of parasitaemia score on daily liveweight gain and PCV over the three-month periodis shown in Table 3.Table 3. Effect of parasitaemia score on growth and PCV.Number of months when Trypanosome Average Number ofDaily live PCV (%)trypanosomes detected species score animalsweight gain (g)mean s.e. mean s.e.0 - - - 382 10.3 34.0 0.401 T. vivax 1 9 340 27.5 30.8 1.071 T. vivax 2 22 344 16.2 31.4 .631 T. vivax 3.4 9 369 25.1 31.7 .901 T. congolense 1 6 316 34.8 30.4 1.361 T. congolense 2 13 296 21.8 29.5 .851 T. congolense 3.4 6 278 31.4 29.0 1.232 T. congolense+1.7 15 302 19.3 28.6 .762 T. vivax ormixed2.9 18 221 18.3 26.4 .723 or 4 T. congolense+2.2 9 192 27.3 24.2 1.073 or 4 T. vivax and/ormixed3.4 7 200 28.5 23.8 1.11Each monthly trypanosome grouping was divided into those above and those below averagefor parasitaemia score. Only in the group where trypanosomes were detected in two months,was there a significant effect of score on both gain and PCV, the above-average score grouphaving significantly lower growth and PCV than the below-average.Anaemia control aspectEach monthly trypanosome grouping was divided into those maintaining their PCV levelsabove the average for the group and those whose PCV level fell below the average. Theaverage PCV levels in each of these categories and their growth over the three month period,are shown in Table 4.Table 4. Effect of ability to maintain PCV level on growth.Number of months whentrypanosomes detectedTrypanosomespeciesNumber ofanimalsMean PCV(%)Daily live weightgain (g)mean s.e.0 - 30 31.8 390 14.30 - 35 36.1 373 13.71 T. vivax 19 28.9 336 17.41 T. vivax 21 33.6 360 16.51 T. congolense 12 26.8 285 24.11 T. congolense 13 31.8 303 21.72 T. congolense + 16 25.1 225 18.82 T. vivax or mixed 17 29.8 294 18.83 or 4 T. congolense + 9 22.4 179 24.93 or 4 T. vivax and/ormixed7 26.9 223 33.5The mean difference in PCV levels in each of the five groups was 4.6 percentage units. Whenno trypanosomes were detected, there was no indication of any linkage between a higher PCVlevel and growth. In all other cases, animals maintaining their PCV levels above the averageof their parasitaemia group had superior growth.Immune response aspectThe very limited data on previous trypanosome infection, as an indication of the ability tomount an immune response, are shown in Table 5. There was no indication of a previousinfection having an effect on growth or PCV.Table 5. Effect of previous trypanosome infection on growth and PCV.Previous trypanosome infection Number of animalsDaily liveweight gain (g) PCV (%)Mean s.e. Mean s.e.No 148 296 7.7 29.6 .29Yes 31 297 16.3 28.6 .61DiscussionKey points from the study designed to indicate phenotypic relationships between aspects ofparasitaemia, anaemia control and immune response with animal performance are indicatedin Table 6.Table 6. Indications of comparative sizes of influences on daily liveweight gain (g), overthree months of exposure to trypanosomiasis risk at OGAPROV Ranch.1. Average daily liveweight gain of non-infected cattle 381gParasitaemia aspect2. Each monthly T. congolense of mixed infection detected -60g3. Each monthly T. vivax infection detected -22g4. Above-average parasitaemia score recorded within a monthly infection relative to a below-average score-26gAnaemia control aspect5. Below-average PCV level reached within each monthly infection relative to an above-averagelevel-23gImmune response aspect6. A trypanosome infection detected in the eight months prior to study, relative to no infectiondetected0gThe results in Table 6 indicate that phenotypic variance in growth associated withparasitaemia aspects can be at least as large as that associated with anaemia-controlaspects. One important implication relates to the use of artificial challenge in research onmanagement and breeding methods for the exploitation and improvement of trypanotolerantcattle. As in artificial challenge, either by syringe or by infection with captured flies, virtually allanimals become parasitized; in research using artificial challenge a significant proportion of thevariance in animal growth is being ignored.ReferencesHarvey, W.R. 1977. User's Guide for Least-Squares and Maximum Likelihood ComputerProgram. Columbus: Ohio State University.  

Evaluation of criteria of trypanotolerance

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Evaluation of criteria of trypanotolerance

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