G. ORDNER, C. COLARDELLE, C. D. M. d'IETEREN, P. DUMONT, P. ITTY, P. JEANNIN, S.G.A. LEAK, J.H.H. MAEHL, S.M. NAGDA, R. W. PALING, J.M. RARIEYA, W. THORPE, J. C.M. TRAIL and G. YANGARI
The health and performance of two strains of trypanotolerant N'Dama, susceptible Nguni and their crosses, were studied over a three-year period, 1983-1985 at OGAPROV ranch in Gabon where they were exposed to trypanosomiasis. The influences of breed and animal age on the prevalence, species and intensity of trypanosome parasitaemia are presented and the effects of trypanosome infection and breed and cow lactational status on the PCV and reproductive performance are estimated.
In late 1986 an experimental study was implemented to evaluate the effect of a strategic trypanocidal drug regime and its interaction with breed type. Preliminary results on some health and performance characters are presented.
The research protocol applied was that of the ATLN (Murray et al., 1983). The Gabon site has been described by ILCA (1986) and a summary is given in article 3 of these Proceedings.
Mean monthly trypanosome prevalence in Nguni cows averaged 25.9%, this being about three times higher than the prevalences of the two N'Dama strains. The Nguni x N'Dama crosses had an intermediate prevalence, 16.5%. Thus the N'Dama had about one detected trypanosome parasitaemia per cow per year and were either infected less and/or were better able to control parasitaemia than crossbreds or pure Nguni which had 2.1 and 3.2 infections/cow/year, respectively (Table 1). The table shows annual cow mortality in Nguni to be four times that of the other breed groups. Pre-weaner mortality of calves with 75% or more Nguni genes was over two times higher that of pure breed N'Dama calves.
Table 1. Comparison of breeds for mean monthly trypanosome prevalence (%), mean number of trypanosome infections in cows and annual mortality of cows and calves, OGAPROV, 1983-1985.
|
Breed |
No. of cow years |
Preval. in cows (%) |
No. of trypanosome infections/cow/year |
Annual mortality (%) |
|
|
Cows |
Calves |
||||
|
N'Dama Okouma |
119 |
7.5 |
0.97 |
1.8 |
4.9 |
|
N'Dama Senegal |
129 |
10.1 |
1.29 |
2.4 |
|
|
N'Dama x Nguni |
107 |
16.5 |
2.12 |
1.9 |
12.5a |
|
Nguni |
41 |
25.9 |
3.20 |
9.8 |
|
a Pre-weaners with 75% or 100% Nguni genes.
Table 2 shows the relative frequencies of T. congolense and T. vivax infections for the different breeds and animal ages. While the frequencies were very similar in the two N'Dama strains and the crosses, Nguni had a lower frequency of T. congolense and a higher frequency of T. vivax infections. is a result the Nguni vivax: congolense ratio was 0.46 compared to an average of 0.29 for the other breed groups.
The comparison of two animal age groups in Table 2 clearly shows the higher proportion of T. congolense infections in cows compared to calves which were more often infected with T. vivax. This was reflected in a vivax: congolense ratio of below one for cows and greater than one for calves, a result consistent with those from other Network sites (d'Ieteren et al., article 10 of these Proceedings).
These results would therefore suggest that N'Dama and crossbreds compared to Nguni and cows compared to calves have a better acquired immunity to T. vivax infection and that in the study area there are less serodemes of T. vivax than of T. congolense.
A scoring system (1 = low to 6 = high) was used to quantify the intensity of trypanosome parasitaemia in the animal. Table 3 indicates that, in general, 60-80% of all detected parasitaemias were scored 1 or 2, i.e. less than 10,000 trypanosomes/ml blood. An average score of 1.8 for the N'Dama Okouma strain contrasted with an average score of 2.3 for the susceptible Nguni. There was no apparent effect of age on the intensity of trypanosome parasitaemia.
Table 2. Relative frequencies (%) of T. congolense and T. brucei infections in cattle of different breeds and age, OGAPROV, 1983-1985.
|
Source of variation |
No. of infections |
T. congolense (%) |
T. vivax (%) |
Vivax: cong ratio | |
|
Breed | |||||
|
|
N'Dama Okouma |
120 |
78 |
22 |
0.28 |
|
|
N'Dama Senegal |
187 |
75 |
23 |
0.31 |
|
|
N'Dama x Nguni |
243 |
78 |
22 |
0.28 |
|
|
Nguni |
169 |
68 |
31 |
0.46 |
|
Agea | |||||
|
|
Cows |
307 |
76 |
23 |
0.30 |
|
|
Calves |
182 |
46 |
53 |
1.20 |
a N'Dama.
Table 3. Relative frequencies (%) of parasitaemia scores of T. congolense infections in cows of different breeds, OGAPROV, 1983-1985.
|
Breed |
Number of infections |
Parasitaemia score classes |
|
|
1-2 |
3-6 |
||
|
N'Dama Okouma |
93 |
80 |
20 |
|
N'Dama Senegal |
140 |
71 |
28 |
|
N'Dama x Nguni |
189 |
75 |
25 |
|
Nguni |
114 |
64 |
36 |
Table 4. Effect of trypanosome infection in the cow during the breeding year on average PCV (%) in the breeding year, OGAPROV, 1983-1985.
|
Trypanosome infection |
No. of cow-years |
Least-squares mean |
|
No infection |
123 |
35.0 |
|
1 or more infections |
273 |
31.0 |
|
Diff. |
|
4.0 |
|
s.e. |
|
0.60 |
|
Prob. |
|
P<0.001 |
As shown in Table 4 one or more trypanosome parasitaemic months detected in the cow during the breeding year (Dec-Nov) depressed the average PCV in the same period by 4.0 percentage units (P<0.001). More data will be required to allow the effect of trypanosome species to be estimated independently from the number of infections.
In Table 5 breeds are compared for the average PCV of cows during the breeding year. The results suggest a superior level of trypanotolerance in N'Dama Okouma, which maintained the highest PCV of 33.3 as compared to the apparently less adapted N'Dama from Senegal (31.3%) and the susceptible Nguni which had the lowest PCV, 30.5. Crosses had a similar mean PCV to the N'Dama Senegal strain.
Table 5. Effect of cow breed on average PCV (%) in the breeding year, OGAPROV, 1983-1985.
|
Breed |
No. of cow-years |
Least-squares mean |
s.e. |
|
N'Dama Okouma |
119 |
33.3a |
0.29 |
|
N'Dama Senegal |
129 |
31.3bc |
0.27 |
|
N'Dama x Nguni |
107 |
31.6ab |
0.29 |
|
Nguni |
41 |
30.5c |
0.46 |
Means with a common superscript do not differ significantly (P<0.05).
Lactational status of the cow significantly affected average PCV level during the breeding year (Table 6). PCV was 1.4 percentage units lower in lactating as compared to dry cows (P<0.001).
Table 6. Effect of lactational status on average PCV (%) in the breeding year, OGAPROV, 1983-1985.
|
Lactational status |
No. of cow-years |
Least-squares mean |
|
Dry |
264 |
32.4 |
|
Lactating |
132 |
31.0 |
|
Diff. |
|
1.4 |
|
s.e. |
|
0.36 |
|
Prob. |
|
P<0.001 |
Calving percentage was depressed by one third when cows were infected with trypanosomes for two or more months during the year preceding the calving season (Table 7).
Table 7. Effect of trypanosome infection during the breeding year on calving percentage of N'Dama cows, OGAPROV, 19831985.
|
No. of trypanosome infections |
Number of cow-years |
Calving percentage |
|
|
L.S. Mean |
s.e. |
||
|
0 |
106 |
55.7a |
5.18 |
|
1 |
67 |
55.3a |
6.99 |
|
2 or more |
75 |
38.3a |
8.56 |
Means with common superscript do not differ significantly (P<0.05).
L.S. = least squares.
Calving percentage appeared to be related to average PCV level in the breeding season. PCVs below 30 were associated with relatively lower calving rates and PCVs above 34 with higher calving rates (Table 8). This indication was confirmed by similar results from other Network sites where the relationship between average PCV during the lactation and subsequent calving interval could be analysed (Thorpe et al., article 21 of these Proceedings).
Table 8. Effect of average PCV in the breeding season on the subsequent calving percentage of N'Dama cows, OGAPROV, 1983-1985.
|
PCV class |
Number of cow-years |
Calving percentage |
|
|
L.S. Mean |
s.e. |
||
|
<30 |
65 |
37.6a |
6.35 |
|
30 - 32 |
59 |
45.6a |
6.45 |
|
33 - 34 |
32 |
55.9a |
8.64 |
|
>34 |
91 |
56.7a |
5.42 |
Means with common superscript do not differ significantly (P<0.05).
Strategic chemoprophylaxis
With the reorganisation of herds at OGAPROV in 1986 it is possible to experimentally evaluate the effect of strategic trypanocidal drug use and its interaction with breed type on animal health and performance. The chemoprophylactic regime aims at protecting breeding cows against trypanosome infections during a three month breeding season (December to February) in order to increase reproductive performance. Cows are treated with isometamidium chloride (Samorin) in November, preceded by a sanative Berenil treatment.
Figure 1. Mean monthly trypanosome prevalence (%) and PCV (%) of non-prophylactic N'Dama cows.
Figure 2. Mean monthly PCV (%) in cows of different breeds following chemoprophylactic treatment, OGAPROV.
Figure 3. Effect of chemoprophylaxis on trypanosome prevalence
(%) in cows of different breed type, OGAPROV.
Figure 1 shows the monthly variation in trypanosome prevalence and PCV of the untreated N'Dama control group. Trypanosomiasis risk reached a peak at the beginning of the breeding season in December with a mean trypanosome prevalence of nearly 20% therefore justifying the chemoprophylactic treatment in November. Figure 1 also shows a close relationship between the monthly means of trypanosome prevalence and PCV level, confirming the depressive effect of trypanosome infection on blood packed cell volume percent.
Following Samorin treatment in November PCV was higher in all three breed groups and higher than that of the N'Dama control population. The superiority was maintained over at least a five month period to April 1987 as shown in Figure 2.
The duration of the protective effect of Samorin is presented in Figure 3. Trypanosome infections were first detected 4 months after treatment in the N'Dama and 6 months after treatment in the small group of F1 and purebred cows. This result suggests that there may not be any differential breed effect on the period of protection for this particular trypanocidal drug regime.
Did the strategic use of Samorin also affect reproductive performance? Table 9 gives the preliminary results for the conception rate of N'Dama cows. Treatment shortly before the breeding season gave only a small increase in conception rate. With more data available it will be possible to evaluate accurately the effect of the trypanocidal drug regime on all health and performance parameters under study.
Table 9. Effect of strategic chemoprophylaxis on the fertility of N'Dama cows, OGAPROV, 1987.
|
Prophylactic regime |
No. of palpations |
Cows pregnant |
|
|
N |
% |
||
|
No prophylaxis |
231 |
169 |
73 |
|
Partial prophylaxisa |
230 |
177 |
77 |
a Berenil/Samorin treatment in November before breeding season.
When exposed to a medium tsetse challenge at the management level and conditions of OGAPROV, N'Dama performed well, but Nguni could not survive without chemotherapy and have average performance without chemoprophylaxis. The Nguni x N'Dama crosses were intermediate between the two parent breeds for the indications of trypanotolerance. Response to prophylaxis may be better in the crosses than in the N'Dama and Nguni.
ILCA. 1986. The ILCA/ILRAD Trypanotolerance Network: Situation Report. Proceedings of a Network meeting held at ILCA Nairobi, December 1985. ILCA, Addis Ababa.
Murray, M., J.C.M. Trail, D.A. Turner and Y. Wissocq. 1983. Livestock Productivity and Trypanotolerance. Network Training Manual. Addis Ababa: ILCA.
