Prevention and control of parasitism in livestock
Contd from previous issue
A variety of birds rely heavily on coprophagous invertebrates as a food source and in seeking these, they tear bovine dung pats apart thus destroying the environmental buffering capacity of these large faecal masses. It is their invertebrate prey, notably dung beetles, scarabs and to lesser extent earthworms, however, that is capable of rapid and often complete dung removal and thus is indirectly responsible for significant reductions in the number of free-living stages of parasites (Waller and Faedo, 1996).
The supplement is also a major strategy to control parasites. The plane of nutrition is an important determinant of the response by animals to parasitism by affecting the development and establishment of parasites and also influencing the magnitude of their pathogenic effects. Many reports in the literature attest to the synergistic relationship between helminth infection and malnutrition. Well-nourished animals are generally more resistant to the effects of parasite infection. Therefore, nutritional supplementation may reduce the requirement for chemotherapeutic control. Feed supplementation, particularly with high quality protein, is often necessary to maintain a better immune response to internal parasites than animals whose nutritional status is compromised low protein diets are responsible for causing infection because they produce less IgA (immunoglobulin). High protein diets have been shown to improve the pregnant ewe’s immune response to parasites after lambing. Lambs receiving protein supplementation have reduced faecal egg counts. Additional dietary protein, selenium, as well as minerals may each play a role in countering infections presumably through mechanisms such as enhancing host immunity or maintaining digestive tract integrity. Parasite-inhibiting plants have also been tested for their ability to reduce egg shedding and pasture seeding density. Copper wire particle (COWP) capsules were developed to overcome the copper deficiency in ruminants grazing on mineral deficient and marginal grazing lands. The copper particles pass to the abomasum where they lodge in the mucosal folds and release ionic copper over an extended period. An additional important benefit of ultra-low-dose copper therapy is on reducing certain parasite infections in grazing livestock. Research has shown that 2-5 g COWP capsules administered orally to sheep resulted in a high-level anthelmintic effect against H. contortus, as well as extended protection (approximately 3 months) against incoming infection of this parasite.
Genetics of host resistance
One alternative approach to controlling parasitic nematode infections is to use the natural diversity of the host genome to reduce parasite transmission. In cows, studies have shown that the number of nematode eggs/gram (EPG) in faeces was influenced by host genetics with an estimated heritability of 0.30. A small percentage of the herd was responsible for the majority of parasite transmission, a distribution strongly suggesting that genetic management could reduce overall parasite transmission. Breeding to obtain livestock that is genetically resistant to nematode infection is the ultimate in sustainable parasite control. Good examples of genetic resistance can be found across the wide spectrum of animal parasitic disease entities of the tropics; such as the resistance of Bos indicus cattle to the cattle tick, Boophilusmicroplus, trypanotolerance of the N’dama and West African shorthorn cattle, nematode (specifically H. contortus) resistance in the East African Maasai, Florida ad Louisiana Native, Barbados Blackbelly and the St. Croix breeds of sheep, and trematode resistance in Javanese thin-tailed sheep. Cattle breeds of Ongole/Nellore, Sahiwal, Ponwar hill cattle and buffaloes and resistance to tick infestation.
The use of anthelmintic is still the mainstay for nematode control. The successes have been cyclical and directly related to the timely introduction of new drugs as resistance to older drugs has surfaced. Effective drug utilization dates back to the 1960s with the development of benzimidazoles (BZ), followed by the imidothiazoles-tetrahydropyrimidines in the 1970s, and the production of macrocyclic lactones (avermectins and milbemycin) in the 1980s. Avermectins and milbemycin emerged as compounds having a high efficacy against ectoparasites and effective in simultaneously killing nematode worms in the host. As result invermectin, doramectin and milbemycin became well accepted for the treatment of parasitic invasions in livestock. During the last 35 years, the pharmaceutical industry has produced a succession of highly effective, broad-spectrum anthelmintic and veterinarians and livestock producers have come to expect that worm control is easy, either by drenching or injecting cattle, sheep and goats with these products. This has made helminth control easy but has not fostered conservative use of the products. Control of ectoparasites with acaricides may be directed against the free-living stages in the environment or the parasitic stages on the host. Acaricides can be used by dipping, washes, spraying, pour-on, spot-on or by injections. Insecticide ear tags are commercially available in some countries for the control of ear ticks. The following are the strategies for the use of chemical anthelmintic.
1. Regular treatments at intervals at or near the length of the pre-patent period of the parasite.
2. Animals are treated therapeutically, whenever production losses and /or uncontrolled disease is considered to be significant
3. Treat all animals in the herd or flock. To be contd