Globally, livestock production accounts for 40 per cent of the gross value of agricultural production. In Pakistan about 30 to 35 million people are engaged in livestock raising with a holding of two to three cattle/buffalo and five to six sheep/goat per family which helps them derive 30 to 40 per cent of their income.

Sheep and goats are raised for mutton, wool and dairy. Any reduction in the produce is a loss to livestock economy. Most parasitic diseases are sub-clinical among which helminths are the major types which infect domestic animals and man, equally. Of various species of helminths, the prevalence of nematodes in animals has been reported at 25.1 to 92 per cent. The nematodes residing in gastrointestinal tract (GIT) are of particular concern.

Haemonchus contortus, Ostertagia ostertagi and Trichostrongylus colubriformis are notorious owing to impaired productivity of small ruminants. The parasites negatively affect the livestock industry. Each worm of H. contortus removes about 0.05ml blood/day by ingestion and by the seepage of blood. A sheep with 5000 H. contortus may loose about 250ml blood/day. Loss of up to Rs19.68 million in sheep and Rs11.74 million in goats due to H. contortus alone is estimated in Faisalabad.

The gastrointestinal parasitism with nematodes is a major impediment in the production of small ruminants. These cause retarded growth, low productivity, haematological and biochemical alterations, loss of appetite, loss of body weight, decrease in protein, impaired digestive efficiency and poor reproductive performance.

The control of these diseases is based on the repeated use of anthelmintcs. Various problems are evolved with the chemotherapeutic control practices as parasites are developing resistance to several families of drenches with the presence of chemical residues in milk and meat, toxicity, non-adaptability and unavailability of it in remote areas, in addition to side effects.

It adversely affects milk and meat production in treated animals, while some are contra-indicated in the pregnancy. The gastrointestinal nematode populations are a serious threat to livestock. The treatment failure is also an impediment.

According to a WHO census, an estimated 80 per cent of the population of developing countries depend on traditional medicines for primary healthcare. The same figure seems to hold for livestock and ethnoveterinary care. The plant kingdom is known to provide a rich source of botanical anthelmintics, antibacterial and insecticide.

Medicinal plants are a vulnerable natural resource and safe drugs. Herbal medicines are primary healthcare systems of rural and remote areas. The reason for their popularity is due to high cost of allopathic medicines and their side effects. Pakistan has lush and diverse flora.

The public demand to reduce the use of chemicals in farm products has generated interest in alternative, sustainable methods to control the gastrointestinal nematodes in ruminants. The positive effects of tannins in parasitized hosts are becoming well documented in sheep.

The tannins are polyphenolic compounds present in root, stem, trunk, bark, leaves, fruit and even in the hair of a plant. It can occur either as isolated individual cells, in groups or chain of the cells, or in special cavities or sacs. The tannins are usually concentrated in the inner bark (cambium layer). An old tree has more tannins than a young one, and the lower parts of a tree have higher concentration. 

These are classified either hydrolysable tannins (HT) or condensed tannins (CT) based on their molecular structure. The molecules of former contain a carbohydrate (generally D-glucose) as a central core. The hydroxyl groups of these carbohydrates are esterified with phenolic groups, such as ellagic acid or gallic acid. The CTs are the most common type found in forage legumes, trees, and shrubs. Structurally, the CTs are complexes of oligomers and polymers of flavanoid units linked by carbon-carbon bonds without a monosaccharide nucleus.

The tannins can be beneficial or detrimental to a ruminant, depending on concentration. These compounds are widespread in woody plants, but are also found in certain forages. Different combinations of monomeric units and the C-C bonds can lead to thousands of possible CT structures, many of which may potentially effect livestock digestion.

The condensed tannins are a part of the polyphenols present in plants and are found at the greatest concentration in dicotyledons such as leguminous plants. It seems plausible that consumption of plants containing the CT may affect the GI nematode numbers and the animal’s performance. This is due to indirect effect of the CT. These condensed tannins have other functions, also. It has been reported that the CT containing plants like Lotus corniculatus can maximize the reproductive efficiency in animals under commercial dryland farming conditions.

Milk is a major source of income for poor farmers. Plants containing tannins are reported to increase production, protein and lactose contents of milk. It is observed that the wool production in sheep can be increased by feeding them L. corniculatus due to the absorption of sulphur-containing amino acids (SAA) from small intestines as the CT in L. corniculatus reduces degradation of the SAA in rumen, increases irreversible loss rate (IRL) of cysteine – a SAA, from blood plasma increases the flux of cysteine to body synthetic reactions.

Bloat is a condition in which there is an accumulation of foamy material in stomach due to feeding of ruminants on fresh forage of high protein solubility, such as spring primary growth of the legumes white clover, red clover and lucerne. Bloat affects large numbers of animals whose annual cost is estimated in the US at $310 million, in Australia at AU$ 180 million, and in New Zealand at NZ$ 25 million to the dairy industry.

The forages containing substantial concentrations of the CT are non-bloating. The CT destabilizes plant protein foams in a dose-dependant manner with no difference between the CT extracted from different forage legume species, despite wide differences in their chemical structure. Therefore, the introduction of moderate concentrations of the CT into forage legumes may render them bloat-safe.

There are reports that an increase in the supply of digestible protein will improve the resilience and resistance in sheep to the GI nematodes. The CT in feeds/forages improves utilization of some nutrients like the proteins by its binding capacity.

Laboratory studies have revealed variable anthelmintic activity of studied plants and Dhak (Butea monosperma) was found to have maximum activity followed by Jamen (Syzgium cuminii), Aak (Calotropis procera), Toot (Morus alba), Supari (Areca catechu), Neem (Azadirecta indica), Afsanteen (Artemisia brevifolia) and Eucalyptus (Eucalyptus camaldulensis). Field experiments on sheep having natural infection of mixed population of nematodes exhibited that plants reduced eggs per gram of faeces of different parasites. However, the efficacy of these plants varied with plant species and tannins content. Maximum effect was observed in Amaltas (Cassia fistula) 93.3 per cent reduction in parasite eggs per gram of feces followed by Dhak (Butea monosperma) 91.4 per cent, Jamen (Wthania somnifera) 88.4 per cent, Jangli beri (Zizyphus nummularia) 88.2 per cent, and Argen (Terminalia arjuna) 87.3 per cent.

Based on the results of a study, it is inferred that: i) The tannin content in plants and trees collected in and around Faisalabad are good enough for its beneficial activity; ii) The plants used in study for tannins analysis should be subjected to digestibility studies, growth performance and other biological effects for improving animal production; iii) Condensed tannins cover all stages of parasites; iv) The CT can also decrease larval pasture contamination because the CT excreted in faeces also stopped egg hatching and larval development.

Hence taniferous plants should be preferred for controlling the gastrointestinal nematodes. Butea monosperma remains best anthelmintic plant in the study. The findings suggest that it may be possible to design appropriate feeding strategies to utilize taniferous materials in the tropics to alleviate helminthiasis and in reducing the inputs of synthetic chemicals. Thus, the CT offers a natural and ecologically-sound means of solving problems in animal husbandry.