Widespread anthelmintic resistance in trichostrongyle nematodes of ruminants has created an urgent need for alternatives to commercial anthelmintics. The bacterium Bacillus thuringiensis (Bt) can produce crystal proteins during sporulation, which can be lethal to insects in multiple orders when ingested. One protein, Cry5B, has demonstrated effectiveness against multiple parasitic nematodes. We hypothesized that Cry5B would be effective against Haemonchus contortus, a highly pathogenic parasite, in sheep. Two experiments tested efficacy of Cry5B in sheep experimentally infected with H. contortus. In the first, a live genetically modified, asporogenous strain of B. thuringiensis expressing cytosolic Cry5B protein (BaCC) was administered orally daily for four days (~40mg/kg Cry5B/day). The mean fecal egg count (FEC) of treated animals was reduced by 94% three days after treatment, and at necropsy the female worm burden was significantly reduced by 98%. In the second experiment inactivated, asporogenous Bt expressing cytosolic Cry5B (IBaCC) was used. Treated animals received 60mg/kg Cry5B, administered daily for three days. By 72 hours after the first treatment FEC was reduced by 91%. Mean total worm burden of treated sheep at necropsy was significantly reduced, with female worms reduced by 95%. A third study tested the effect of BaCC and IBaCC on development of eggs to infective larvae in feces under laboratory and outdoor environmental conditions. Cry5B (15mg) added to feces (10g) reduced numbers of infective larvae by 99% in both environments within 12 days. Cry5B appears to have potential for controlling H. contortus in sheep. All protocols approved by VT IACUC and IBC. / Master of Science / Many animals and humans can be infected with roundworm, also called nematode, parasites. Infection of animals and humans by parasitic nematodes can result in disease. Some animals like ruminants (cows, sheep, and goats) can be infected with multiple species at once with few effects on the host. However, certain species can cause major disease, and even kill their ruminant host. Younger animals like lambs can easily become overwhelmed by these parasites. Anthelmintics are the type of drug used to treat those infected with these parasitic worms. However, just like bacteria are becoming resistant to antibiotics, these worms are also becoming resistant to anthelmintics. Because of this, researchers are looking for new compounds and materials that are lethal to the parasite and can be used to treat infected animals. One species of bacterium, Bacillus thuringiensis, is usually found in the soil. This bacterium can produce a large crystal structure that is made up of proteins. These crystal (Cry) proteins can be lethal to pest insects like beetles, caterpillars, and mosquitos. When the insect eats the protein, it binds to cells in the insect intestine, creating holes in the insect gut. These proteins can be lethal to nematodes as well when they are eaten by the worms. Because of this, these proteins are being investigated as potential alternative treatments for parasitic nematodes. One type of protein, Cry5B, has been tested in hamsters, mice, and pigs. We hypothesized that Cry5B would also be effective against a sheep stomach worm called Haemonchus contortus. We tested the Cry5B in two different formulations and found that the protein was effective against both the adult worm in the stomach, and the young worms in the feces of the host. This protein could potentially be used to treat parasitic nematodes that have become resistant to anthelmintics.

Diet selection and self-medication are fundamental to the survival of all species. The abilities to choose healthy foods in response to past consequences are basic elements of evolution. This study explores self-medication regarding tannins both as a medication and as a dietary challenge. In the first study, sheep with natural parasite infections were offered a low quality supplement containing a dose of tannins considered to be therapeutic (medicine), while the control infected lambs received the same supplement without tannins (placebo). This study included a group of parasite-free lambs. The parasitized lambs ate more of the tannin containing supplement than non-parasitized lambs for the first 12 d of the study, when parasite burdens were high, but differences became smaller and disappeared towards the end of the study when parasite burdens decreased. This result indicated lambs ability to detect the presence of internal parasites and to learn to ingest tannin when followed by relief from parasite burdens.In the second study, lambs grazed on pastures with forages containing saponins (alfalfa),iiialkaloids (endophyte-infected tall fescue) and tannins (birdsfoot trefoil). I observed the foraging behavior of groups of lambs after intra-ruminal infusions of tannins (treatment). Lambs that first received intraruminal infusions of tannins and then were offered 2-way choices between varieties of forages with high and low concentrations of either saponins, alkaloids, or tannins increased their preference for the high-saponin variety of alfalfa and the high-alkaloid variety of tall fescue relative to lambs not infused with tannins (controls). Lambs infused with tannins and offered choices among the 3 forages with high concentrations of secondary compounds also manifested higher preference for the high-alkaloid variety of tall fescue than control lambs. In contrast, lambs infused with tannin reduced their preference for the high-tannin variety of birdsfoot trefoil.This research has implications for many situations where forages with secondary compounds are available but underutilized. Landscapes where such forages are available could be used effectively with little or no harm to livestock if medicinal forages or supplements are made available and offered as alternatives so animals can learn about their benefits of chemical complementarities among different plant species.

Les infestations par les strongles gastro-intestinaux (SGI) constituent une cause majeure de morbidité et de mortalité chez les petits ruminants élevés au pâturage et entraînent donc des pertes de production. En raison de l'émergence de la résistance aux anthelminthiques et des préoccupations des consommateurs concernant les résidus chimiques dans les produits animaux, des stratégies alternatives de contrôle sont nécessaires. L'objectif n'est plus l'éradication totale de la population parasitaire, mais plutôt un meilleur contrôle de ces populations pour atteindre un équilibre favorable à la production animale entre l'hôte et les parasites. Une stratégie prometteuse pour le contrôle des SGI est l'amélioration de la réponse de l'hôte par le statut nutritionnel des animaux. Bien que les chèvres soient plus sensibles que les moutons aux infestations par les NGI, la plupart des programmes de recherche visant à caractériser les interactions hôtes-NGI est menée chez les ovins. Contrairement à l’idée que les résultats acquis chez le mouton seraient applicables aux chèvres du fait de leur proximité, de nombreuses études soulignent des différences significatives entre ces modèles. L’objectif de ce travail de thèse était d’étudier l’impact du statut nutritionnel en termes de quantité de protéines et d’énergie et de la qualité des protéines apportée par la ration sur les réponses (production vs réponse contre le parasitisme) de caprins Créole infestés expérimentalement par Haemonchus contortus. Nous avons montré que le statut nutritionnel permettait de réduire la sévérité et la durée de l’anémie régénérative et de la thrombopénie induite par H. contortus chez le caprin Créole. La ration enrichie en protéines était associée à de la résilience vis-à-vis de l’infestation plutôt que de la résistance. / Gastrointestinal nematode (GIN) infections are a major cause of morbidity and mortality in small ruminants at pasture and therefore lead to production losses. Due to the emergence of anthelmintic resistance and consumer concerns about chemical residues in animal products, alternative control strategies are needed. The objective is no longer the total eradication of the parasite population, but rather a better control of these populations to achieve a favorable balance between the host and the parasites to improve animal production. A promising strategy for NGI control is to improve the host response through the nutritional status of the animals. Although goats are more susceptible than sheep to NGI infestations, most research programs to characterize host-NGI interactions are conducted in sheep. In contrast with the idea that the results obtained in sheep will be applicable to goats because of their proximity, many studies highlight significant differences between these models. The objective of this research project was to study the impact of nutritional status in terms of protein and energy quantity and protein quality provided by the diet on the responses (production vs response against parasitism) of Creole goats experimentally infested by Haemonchus contortus. We have shown that nutritional status reduces the severity and duration of regenerative anemia and H. contortus-induced thrombocytopenia in Creole goats. The protein-enriched diet was associated with resilience to infection rather than resistance