Date of Award
1-1-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Biological and Environmental Sciences
Department
Fisheries, Animal and Veterinary Science
First Advisor
Katherine Petersson
Abstract
Alternative control methods are necessary for both conventional andorganic producers as anthelmintic resistance leave producers without efficacious treatment options. In this dissertation we assess two alternative strategies for gastrointestinal nematode (GIN) parasite control: 1) Bacillus thuringiensis crystal (Cry) proteins as an Inactivated Bacteria with Cytosolic Crystals (IBaCC) against Haemonchus contortus in lambs and 2) dietary β-glucan supplementation in periparturient ewes naturally infected with GIN from the previous grazing season.
In vivo anti-parasitic efficacy was evaluated in several Cry proteins against H. contortus in experimentally infected lambs: Cry5Ba in Trial One, Cry14Ab in Trial Two, a combination of CryH18 and Cry14Ab in Trial Three. All three studies were conducted in a similar manner with Cry proteins administered to experimentally infected lambs once the infections were mature. Fecal egg counts (FEC) were monitored daily until end of trial when lambs were euthanized and abomasal contents were quantified for worm burden and identified by sex. In Trial One lambs, were orally administered one of three treatments (n=5): 1) Cry5Ba IBaCC (40 mg/kg BW), 2) Cry5Ba IBaCC (10 mg/kg BW), or 3) untreated control. In Trial Two, lambs were orally administered one of three treatments (n=5): 1) Cry14Ab IBaCC (30 mg/kg BW), 2) Cry14Ab IBaCC (15 mg/kg BW), or 3) untreated control. In Trial Three, lambs were administered one of five treatments (n = 6 per treatment): Group 1 (G1) CryH18 (6 mg/kg BW), G2) CryH18 (12 mg/kg BW), G3) Cry14Ab (10 mg/kg BW), G4) a combination of Cry14Ab (10 mg/kg BW) and CryH18 (6 mg/kg BW), or G5) untreated control. In Trial One, in lambs administered Cry5Ba 10 mg/kg BW and 40 mg/kg BW there was an 67% and 92% reduction in FEC and 40% (976 ± 249 worms, mean ± SEM, p = 0.04 versus control 1636 ± 161) and 82% (296 ± 115 worms, p = 0.0002 versus control) reduction in abomasal worm burdens, respectively. In Trial Two, in lambs administered Cry14Ab 15 mg/kg BW and 30 mg/kg BW there was an 85% and 97% reduction in FEC and 69% (632 ± 143.89 worms, p < 0.0001 versus control 2046 ± 173.4) and 93% (142 ± 59.61 worms, p < 0.0001 versus control) reduction in abomasal worm burdens, respectively. In the third trial there was a reduction in FEC by 57%, 44%, 63%, and 69% in FEC for lambs in G1 through G4 versus the control (G5) lambs, respectively. Abomasal worm burdens were reduced by 21% (1505 ± 217.21 worms), 28% (1378 ± 620 worms), 27% (1392 ± 389.91 worms), and 44% (1062 ± 199 worms) in lambs G1 through G4 versus the control (1910 ± 639 worms). These studies have demonstrated the anti-parasitic activity of Bt Cry proteins. With further research and development Bt Cry proteins could be an effective alternative control method to manage GIN in small ruminants.
Dietary supplementation of β-glucan was assessed on the immunomodulatory, anti-parasitic, and overall production parameters of the periparturient ewe and her offspring. Periparturient Dorset (University of Rhode Island) and Katahdin (US Meat Animal Research Center) ewes, naturally infected with gastrointestinal nematodes (GIN) from the previous grazing season, were utilized in Trial One and Two respectively. In Trial One, Dorset ewes were supplemented with 0.25g/day of β-glucan incorporated into a commercially pelleted 16% protein pellet (BG; n=10) or control pelleted (CON; n=9) grain 8 weeks prior to parturition through 8 weeks of lactation. In Trial Two, Katahdin ewes were supplemented with the same quantity of BG per day contained within the commercially available 16% pelleted grain (n=8), CON pelleted grain (n=8), or not supplemented (Unsupplemented) with grain (n=8) 6 weeks prior to parturition through 1 week of lactation. FEC, hematological parameters (Trial One: packed cell volume, IgG; Trail Two: complete blood count, IgG) and colostrum parameters (Trial One only) and milk parameters (protein, fat, total solids, milk urea nitrogen, and somatic cell count), ewe and lamb body weights were measured. Overall, there was modest effect of β-glucan supplementation in periparturient Dorset ewes. Findings from Trial One demonstrated a treatment*week effect for both FEC and PCV in BG supplemented Dorset sheep. FEC in BG supplemented ewes increased after parturition but at a slower rate with a mean FEC at 8 weeks of lactation 30% lower than the control supplemented ewes. The PCV of ewes supplemented with BG supplemented was maintained through 3 weeks of lactation prior to declining versus the steady decline in PCV from birth in control supplemented ewes. The consistency in hematocrit from the beginning of the trial through week one of lactation were similar to that observed in Trial One. IgG values in both Trials demonstrated an expected decrease prior to partition. The reported hematological values in Trial Two demonstrated expected changes an increase in white blood cells one week prior to parturition driven by the physiological changes and stress associated with parturition. Notably an increase in milk fat and total solids was reported in β-glucan supplemented ewes in Trial One, although no effect on offspring growth was reported in either trial, this is an area that warrants further exploration. Additional research is needed to determine the potential efficacy of β-glucan on beneficial changes in the ewe’s immune system, associated anti-parasitic properties, and production parameters.
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Recommended Citation
Kass, Elizabeth, "ALTERNATIVE METHODS TO CONTROL AND MANAGE GASTROINTESTINAL NEMATODES IN SMALL RUMINANTS" (2025). Open Access Dissertations. Paper 4456.
https://digitalcommons.uri.edu/oa_diss/4456