A Questionnaire Survey of the Management and Use of Anthelmintics in Cattle and Antelope in Mixed Farming Systems in Zimbabwe

INTRODUCTION Game farming is an important source of revenue for Zimbabwe through trophy hunting and as a tourist attraction. National Parks and other wildlife land cover almost 12 % of the country


INTRODUCTION
Game farming is an important source of revenue for Zimbabwe through trophy hunting and as a tourist attraction.National Parks and other wildlife land cover almost 12 % of the country 26 .
The utilisation of game products in Zimbabwe officially started in 1960, when the government licensed farmers to sell game products 24 .Cattle-and-game rearing in a mixed farming system, however, officially commenced in 1985, when the government permitted farmers to introduce and rear game species on private farms 20 .Farmers on the highveld adapted and fenced parts of their farms not suitable for other forms of agriculture, such as areas with hills, and introduced game species, while on other farms, game species were introduced on cattle ranches.The main sources of the game acquired by the farmers were the lowveld national parks auction sales 20 .
The mixed farming of cattle and antelope has brought about the possibility of cross-infection of helminth parasites.A high stocking density of antelope and domestic ruminants is known to favour such cross-infection 16 .Mixed farming has been associated with a random translocation of game, which may have broadened the endemic 16 and host ranges of internal parasites, a factor that may necessitate the control of helminth infections in antelope species.
As a preliminary investigation to a major study of helminth infections of cattle and antelope species on eleven mixed farming systems, a questionnaire survey was carried out with the objective of gathering information on farm management and use of anthelmintics.Such information is important in assessing the potential for the development of helminth diseases and in evaluating the efficiency of the control measures used on the farms, as well as in preventing the development of anthelmintic resistance.

MATERIALS AND METHODS
Eleven farms where cattle and antelopes are reared together were randomly selected from farming areas around Harare (Fig. 1).The rainfall pattern in the areas of study is seasonal with much of the rain falling from November to April, while the rest of the year is dry.
Between August and September 1999, a questionnaire was delivered to each participating farmer during visits for faecal sample collection.The questionnaire was designed to gather information about the farm and its management, the mixed farming of cattle and antelope, and the control of helminth infections in cattle and antelope, including the anthelmintic dosing programme followed.

RESULTS
All of the farmers responded.Results of the questionnaire survey revealed that antelope are a source of income for the farmers through trophy hunting, live game and venison sales and as a tourist attraction.Crop production was found to be the major activity on most of the farms, in particular tobacco and maize production.
It was established that most farmers started mixed farming of cattle and antelope between 1980 and 1990.National Parks auction sales were the main source of antelopes and a smaller contribution resulted from purchases from established mixed farms.
The areas occupied by the selected farms ranged from 1200 to 3000 ha (Table 1), with a mean size of 1950 ha.An average of 888 beef cattle were kept on the farms.Cattle of all age categories (calves, growing animals and cows) were run together.A total of 17 species of antelope ranging from grey duikers (Sylvicapra grimmia) to eland (Taurotragus oryx) were kept on the farms (Table 2).On any single farm, 5-12 species of antelopes were present (Table 1).Impala (Aepyceros melampus) were the most abundant species of game on the farms, with a mean of 301 animals per farm (Table 2).Although the grey duiker occurred in small numbers, they were present on all the farms.The ratio of cattle to antelope numbers was 1:1 on 63.6 % (n = 7) of the farms (Table 1).Antelopes outnumbered cattle on two farms (Mona and Zindele).The bulk of the antelope species (75.8 %) present on these farms were mixed feeders and grazers (Table 1).Most farmers (n = 8) did not consider the stocking density for cattle and antelope species as an important management factor (Table 1).
Table 3 shows the deworming status for each farm.All the farmers dewormed cattle and 55 % (n = 6) dewormed both cattle and antelope.Antelope were given preventive anthelmintic treatment during the dry season using albendazole-, fenbendazole-, or rafoxanide-medicated supplementary feed blocks.Doramectin injections were given to immobilised roan antelope at Amajuba farm and antelopes at Imire farm.Cattle were dewormed with albendazole, fenbendazole, levamisole or oxyclozanide.Thirty-six per cent of the farmers (n = 4) dewormed cattle at the start and at the end of the wet season.The benzimidazole drugs were the most commonly used class of anthelmintics in both cattle (72.7 %) and antelope (54.5 %).

DISCUSSION
Crop production is known to be the major activity in the wet highveld areas in the northern parts of Zimbabwe where the study was conducted, while animal production activities dominate in the drier southern areas of the country.
Grazers and mixed feeders compete for grazing with the cattle, especially for the early flush of nutritious grass before the first rains 5 .There is, therefore, potential for close interaction between antelope and cattle at this time, which would facilitate the cross-infection of helminth parasites.
The impala (Aepyceros melampus) was the most abundant antelope species on all the farms perhaps because of its high adaptability to new environments 20 and its relatively high breeding capacity.
Other studies in Zimbabwe have also indicated that the impala is the most abundant antelope species and that this species occupies diverse habitats 18,26 .Being mixed feeders that share grazing pastures with cattle, this species of antelope is expected to play an important role in the cross-infection of helminth parasites.
Although 72.7 % (n = 8) of the farmers in the survey did not determine the stocking density for cattle and antelope, the general observation from this study was that the stocking density was fairly low and, therefore, worm burden and the crossinfection of parasites are expected to be low.The few areas of good grazing such as around waterholes during the dry season as observed on most of the farms may, however, periodically result in temporary over-population due to a concentration of animals.This may lead to an acceleration in the transmission and cross-infection of helminths 21 .Studies in Zambia have shown that a stocking density of one large antelope per 4.7 ha is high enough to facilitate cross-infection 27 .On the basis of this criterion, the cross-infection of helminth parasites and helminth disease may be important on two farms (Imire and Matepatepa) in the survey.
Results from the survey show that helminth parasite control using anthelmintic treatment was the only method practised and that the benzimidazoles were the most frequently used anthelmintics in both cattle and antelope.The findings are in agreement with the results of similar studies in sheep in Zimbabwe 2,23 .The intensive and haphazard use of these drugs in low doses available in medicated supplement blocks during the dry season may speed up the develop-  ment of anthelmintic resistance 25 .This is because anthelmintic treatments during the dry season result in selection for resistant nematode parasites at a time when the proportion of the nematode population in refugia is too low to have a significant diluting effect on the resistant population 1 .Benzimidazole-resistant Haemonchus contortus and Cooperia species have been reported in sheep in Zimbabwe 2,23 .Reports of anthelmintic resistance in cattle parasites in Zimbabwe are limited.Fasciola gigantica has been incriminated in mortalities of sable antelope 18 and impala 20 in Zimbabwe and hence the justification for the use of rafoxanidemedicated blocks by some farmers.Doramectin was used on two farms only (Table 3), despite being effective against endoparasites and ectoparasites.The periodic alternating of anthelmintics with different modes of action to prevent the development of anthelmintic resistance and enhance efficacy was not practised on most farms.The farmers were not aware of management techniques such as the separation of age groups and the determination of the stocking density as methods for the control of helminth parasites.
Based on epidemiological studies in Zimbabwe, strategic deworming at the beginning and/or the end of the rains coupled with tactical treatments during the rainy season are recommended for the control of helminth infections 22 .Thirty-six per cent (n = 4) of the farmers in the survey dewormed their cattle according to the recommended strategic programme, but did not give tactical treatments during the rainy season.Failure by these farmers to implement tactical treatments during the rainy season as suggested by epidemiological studies places cattle at risk of heavy infections because the level of infective larvae on pasture is high during this period.However, the contrary can also be argued that the absence of tactical treatments reduces the frequency of anthelmintic treatments that may result in the emergence of anthelmintic resistant parasites.The rest of the farmers (n = 7) dewormed their cattle when general body condition was poor and were therefore at risk of production losses due to subclinical infections.It is important to note that all age categories of cattle (calves, growing and adult cattle) were run together and dewormed.This increases the cost of the control programme, as it may not be necessary to deworm cows as frequently as the calves, because the former may have acquired immunity to helminth parasites.In addition, the separation of age groups would prevent continued transmission of helminth parasites from resistant older animals to susceptible calves.
Fenbendazole and albendazole have a broad spectrum of activity against nematodes and cestodes 12 , which justifies their incorporation into feed blocks.The advantages of using anthelmintic medicated feed blocks in antelope during the dry season are that much of the worm population is in the host and little infection is on pasture and antelope are more inclined to take feed blocks because of the seasonal shortage of grazing at this time 15 .The anthelmintics supplied in medicated feed blocks are in low concentrations and therefore animals need to consume the blocks over several weeks for optimal effect.Consumption by different species is unpredictable, especially with the shy 0038-2809 Tydskr.S.Afr.vet.Ver.( 2002) 73(2): 70-73  feeders such as duiker species as they need to be accustomed to supplementary feeding before the introduction of medicated blocks 15 .There was, however, no anthelmintic treatment of game during the rainy season because of difficulties in keeping the medicated feed blocks dry.This survey showed that the farmers perceived helminth infections to be important on mixed cattle and game farming systems and that all eleven farmers interviewed were aware of the potential detrimental effects of helminths infection and disease on animal production in both cattle and antelopes.The farmers were not aware of the need to integrate the control of helminth parasites in domestic and antelope hosts.Any helminth control programme implemented in cattle must take into account the potential role of antelope as reservoir hosts.There is the likelihood of development of anthelminticresistant helminth parasites as a result of low doses of anthelmintics supplied to antelope through medicated feed blocks during the dry season.
It is difficult to recommend control programmes that are applicable to all farms owing to varied management systems practised on different farms.The effective separation of different age groups of cattle, erection of game fences, determination of stocking densities for both cattle and antelope species and breeding of resilient cattle may be a good starting point.It is recommended that preventive treatments be given to growing animals and that adult animals are dewormed if symptoms that suggest helminth infection are observed 9 .However, studies are necessary to determine the spectra of helminth species common to cattle and antelope in order to design and recommend appropriate control practices.

Fig. 1 :
Fig. 1: Map of Zimbabwe showing the location of the study farms.

Table 1 :
Characteristics of the farms.