Effect of strategic anthelmintic treatment on growth performance and survival rate of native lambs in the subhumid environment in Mali

S. Tembely¹, K. Bengaly² awl W. Berckmoes³

¹Laboratoire central vétérinaire, P. O. Box 2295, Bamako, Mali
²Departement de la recherche sur les systèmes de productions rurales, B. P. 186 Sikasso, Malt
³Koren Bloemstraat 5, 3911 ZG Rhenen, The Netherlands

Abstract
Introduction
Materials and methods
Results and discussion
Conclusion
Acknowledgment
References

Abstract

A study on the effect of strategic anthelmintic treatment on the growth performance and survival rate of native lambs was carried out in a subhumid environment in Mali from May 1989 to April 1990. Daily weight gain was analysed for six observation periods of two months each over the year. The daily weight gain of treated lambs was significantly higher (P<0.05) than that of the control lambs during the rainy season (September to December) with a net return of 206 CFA (1US$=250 cfa) per lamb. However, this weight gain advantage could not be maintained for the rest of the year due to the shortage and poor quality of fodder during the dry season. Overall, there was no significant difference in the daily weight gain of Groups 1 and 2 lambs and anthelmintic treatment did not affect lamb mortality (P>0.10). The average mortality rate in the experimental lambs was 19%.

To maximise lamb productivity fenbendazole alone should be given to lambs twice a year (in the middle and at the end of the rainy season) along with feed supplementation in the following dry season.

The results of this study also suggest that gastrointestinal nematode infection has no cumulative negative effect on lamb growth performance in the Malian subhumid environment with a low plane of nutrition. Primary causes of lamb mortality in this environment should be further investigated as nematode infections do not appear to cause many deaths.

Effet de traitements anthelminthiques stratégiques sur les performances de croissance la viabilité des agneaux indigènes dans la zone subhumide du Mali

Résumé

Une étude de l'effet des traitements anthelminthiques stratégiques sur les performances de croissance et le taux de survie d'agneaux indigènes a été effectuée dans la zone subhumide du Mali de mai 1989 à avril 1990. Les gains moyens quotidiens (GMQ) sur six périodes de deux mois ont été analysés. Le GMQ des agneaux traités était significativement supérieur (P<0,05) à celui des témoins pendant la saison des pluies (de septembre à décembre), ce qui permettait d'obtenir un revenu net de 206 FCFA (I $US = 250 FCFA) par agneau. Cependant, cet avantage pondéral n'a pas été maintenu pendant le reste de l'année en raison du déficit quantitatif et qualitatif des fourrages au cours de la saison sèche. Dans l'ensemble, il n'y avait avait pas de différence significative entre les agneaux des lots 1 et 2 et le traitement anthelminthique n'a pas influé sur le taux de mortalité des agneaux (P>0,10). Ce dernier s'élevait à 19% chez les agneaux de l'expérience.

Pour maximiser la productivité des agneaux, il faut leur administrer du fenbendazole seul deux fois par an (au milieu et à la fin de la saison des pluies) et leur offrir des aliments complémentaires pendant la saison sèche suivante.

Les résultats de cette étude font également apparaître que, dans la zone subhumide du Mali, les nématodoses gastro-intestinales n'ont pas d'effet dépressif sur les performances de croissance des agneaux soumis à un faible niveau d'alimentation. Les principaux facteurs de la mortalité des agneaux élevés dans ce type de milieu devront être recherchés, la mortalité due aux nématodoses se révélant peu importante.

Introduction

In southern Mali, small ruminants (mainly composed of West African Dwarf sheep and goats) are owned by a large proportion of the rural community on account of their ability to tolerate trypanosomiasis which is endemic in that area. Small ruminants serve as the main source of animal protein for the rural community and also provide a valuable income source for smallholder farmers, including women. These small animals are hardy, easy to handle and highly prolific. The main feed supply is the native grassland adjacent to the villages, sometimes supplemented by cereal grain stubble, straw or crop residues.

Because small ruminants are kept by mixed crop-livestock farmers as a sideline to their crop oriented activities, they are very often neglected. They are herded by village children during the cropping season, but during the dry season are allowed to browse and scavenge freely over the compounds and along the roadsides. The animals sometimes stay in the bush for many days without any guard before returning home. Due to poor health management and inadequate nutrition, the productivity of these animals remains low (Wilson, 1982). An important factor responsible for the mediocrity of small ruminant production in tropical Africa is disease, particularly parasitism (Allonby and Urquhart, 1975; Malaki, 1976; Vercruysse, 1985; Shavulimo, 1986; Pandey, 1991; Waller, 1991).

The objective of this study was to evaluate the effect of strategic anthelmintic treatment on growth performance and survival rate of native lambs in a subhumid environment.

Materials and methods

Area of study

The production system is agro-pastoral in which small ruminants are kept indoors at night and herded by village children during the day as described above. The main vegetation is sudanese type with large broad-leaved deciduous trees, tall grasses and shrubs. The climate is subhumid, with rainfall ranging between 900 and 1100 mm per annum. There are two distinct seasons, the rainy season from May to October and the dry season from November to April. Average temperature is around 20°C with a maximum reaching 35°C in March/April and the minimum 10°C in December/January.

Experimental design

Between May 1989 and April 1990, 552 Djallonké lambs were systematically allocated at birth to three treatment groups. Lambs of groups one and two received fenbendazole at 10 mg/kg-1 birth weight at three weeks of age and every month thereafter until October 1989. Lambs of group two received amprolium at the same dose during the same period of treatment. A single treatment was given to lambs born from October onwards. Lambs of group three served as the control group and were left untreated.

Measurements

Faecal samples were taken directly from the rectum of each animal every month from May to November 1989, then every two months from December 1989 to April 90. They were examined by the modified McMaster technique for faecal egg counts (FEC). Liveweight change as a measurement of growth performance was monitored by lift-weighing individual animals every 45 days. Mortality was recorded as it occurred. Temperature and rainfall data were obtained from the local climatology station.

Statistics

Average daily gain (ADO) analysis was performed only on animals which had been weighed at least twice. Each age group was analysed by one-way analysis of variance (ANOVA) using the SPSS package. Animals over 365 days old were not included in the analysis.

Results and discussion

Faecal egg counts

No strongyle eggs were found in the faecal samples of the treated lambs three days after drenching, indicating a good treatment response to fenbendazole. However, three weeks later massive re-infestation was observed in treated animals resulting in higher egg counts in some cases than in the control animals. This is indicative of loss of host resistance following the total absence of worms within the host as described by Georgi (1974). Faecal egg count of the control lambs and the rainfall pattern are shown in Figure 1. Lambs started excreting eggs in July with a peak in September (mean of 1700 eggs per gram of faeces). Few eggs could be detected from November to April, which corresponded to the dry season.

Figure 1. Faecal egg counts for the control lambs and mean monthly rainfall.

Growth performance

The average daily gain was significantly (P<0.05) affected by period of year in all groups combined (Tables 1). Differences of 7 to 15 g/day between the treated lambs (Group 1) and the untreated lambs (Group 3) were observed in October/November but could not be maintained for the rest of the year. Shortage of forage and its poor quality may account for this. A study of the availability and quality of forage in the region indicated that quality was low between November and the onset of the rainy season, i.e. May-June (Berkmoes and Diabate, 1988).

Table 1. Average daily gain of experimental lambs for different age groups.

Treatment group	Period of the year
	1	2	3	4	5	6
	May-June	July-Aug	Sept-Oct	Nov-Dec	Jan-Feb	Mar-Apr	Mean
				0-183 days
All groups combined	94.1	66.5	22.4	49	52.7	60	57.45
Group 1	88.6	71.5	33.3	52.1	54.9	64.0	59.8
Group 2	97.0	66.3	29.0	48.1	52.4	54.7	54.0
Group 3	96.3	64.8	13.3	48.1	50.1	64.0	54.5
				184-385 days
All groups combined	42	24.1	-10.0	18.3	22.8	40.5	20.18
Group 1	50.9	22.4	-7.5	25.8	18.1	30.3	20.6
Group 2	39.8	22.1	0.08	20.9	32.9	44.6	24.2
Group 3 (control)	39.4	25.7	-16.8	4.8	18.7	51.6	17.3
				0-365 days
All groups combined	71.9	43.6	5.2	31.3	34.8	35.9	37.17
Group 1	75.4	41.1	9.2b	37.4a	35.8	29.8	36.2
Group 2	68.4	46.1	15a	35a	41.7	39.4	38.2
Group 3 (control)	71.5	43.3	-2.6c	22.1b	27.4	40.1	32.2

abc =Means within a column that have different superscripts are significantly different (P<0.05)

Rate of mortalities

Table 2 shows that mortality rates varied according to the period of the year. Mortality rates were similar for all groups during the pre-weaning period at four to five months of age. Peaks were observed in June/July and October/November, corresponding to the beginning and the end of the rainy season respectively.

These observations agree with reports by Traore and Wilson (1988), Bourzat (1984) and Wilson (1982) in the agro-pastoral system in West Africa. Causes of mortality were not fully investigated, but apparently were not associated with parasite burdens. Earlier studies in the zone by Berkmoes et al (1988) indicated that deaths of lambs were more likely to be due to malnutrition, disease and management (losses, predators).

Table 2. Rate of mortality (0-12 month old lambs).

Date of birth	Number of births	Mortalities	Rate of mortality %
May/June	45	11	24.0
June/July	24	8	33.3
July/August	16	2	12.5
August/September	12	1	8.3
September/October	38	9	23.7
Nov 89-May 90	50	5	10.0
Total	185	36	19.0

Cost-benefit analysis

In an attempt to estimate the influence of anthelmintic treatment on liveweight change under field conditions, a cost-benefit analysis was performed. Labour costs were omitted from the analysis because the opportunity costs were negligible. Variations in growth rates (Table 1) had a negative impact on returns. Table 3 shows the net profit for lambs of Group 1 at the end of the rainy season, but this advantage could not be maintained for the rest of the year.

Table 3. Cost-benefit analysis of anthelmintic treatment at the end of the rainy season (Oct. 89) for lambs of Group 1.

ADG (gm)	Period (day)	Gain (kg)	Gross return (CFA)	Anthelmintic cost(CFA)	Net benefit of treatment (CFA)
13.5	120	1.62	406	200	206

1 US$ = 250 CFA

Conclusion

Although fenbendazole at the dose of 10 mg/kg^-1 body weight was found to be highly effective against gastro-intestinal nematodes, the strategy adopted in the experiment could not maintain a low level of eggs. It eliminated the existing worm population but the animals were quickly reinfested. Unless treatment is continued it is unlikely to reduce the worm burden. However, continuing treatment also precipitates drug resistance, as pointed out by Nansen (1991) and Waller (1991). The most effective approach is a combination of good management, veterinary care and an improved plane of nutrition. However, anthelmintic and other drugs must be available to the farmers at an acceptable price.

Acknowledgment

The authors gratefully acknowledge the contribution made to this report by R H Bosman and extend appreciation to Y Waigalo, P A Diarra, Z M Yattara and D Diabate for their valuable technical assistance.

References

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