To utilize the larval development assay (DrenchRite® Assay) to characterize the levels of gastrointestinal nematode resistance on small ruminant farms in Delaware.
The in vitro larval development assay method will be used to determine levels of anthelmintic resistance in small ruminant GIN populations in Delaware. This is an alternative to the laborious task of performing fecal egg count reduction tests (FECRT) in order to determine GIN resistance in small ruminants. The results from this objective will be used to educate producers of the resistance levels in Delaware and to identify the most effective drug that can be used to treat small ruminant parasites in Delaware.
The control of parasites in the U.S. rely on the use of broad-spectrum anthelmintics which is administered in some cases every 2-3 weeks (Miller, 1996) without regards to the specific diagnosis or symptoms of parasites. Due to this indiscriminate use of the available dewormers, there have been reports of increased resistance selection for internal parasites of sheep and goats throughout the world (Jackson, 1993; Zajac and Gipson, 2000; Mortensen et al., 2003; Kaplan et al., 2007;Howell et al., 2008; Crook et al., 2016). Research conducted in the southern (Mortensen et al., 2003) and Mid-Atlantic (Crook et al., 2016) United States (U.S.) confirmed that there is a high prevalence of anthelmintic resistance on sheep and goat farms. Five years after the research conducted in southern U.S., another research using the Drenchrite® Larval Development Assay (LDA) to detect resistance in southern states, Puerto Rico, St. Croix, and the U.S. Virgin Islands found that forty-eight percent of the farms tested (11 sheep, 11 goat) had resistance to all three classes of anthelmintics (Howell et al., 2008). Additionally, an even more recently (2016) research conducted on sheep farms in Maryland, Virginia, and Georgia, has indicated a higher prevalence of anthelmintic resistance (S. Schoenian, personal communication). This indicate that the prevalence of anthelmintic resistance is increasing across the U.S. Therefore, it is dire that more information on this topic is researched and producers educated on how to deal with this issue.
The proposed project is geared towards identifying the current status of GIN anthelmintic resistance in Delaware with overall aim of informing producers of the parasites in their herd/flock and telling them the most effective drug that they should be using on their farm. This will lead to producers deworming their herd/flock less times in the year and allowing them to only deworm the animals that actually need drug. This will preserve the population of worms that are not exposed to the drugs, hence, reducing anthelmintic resistance. Due to the implications that increased parasite resistance has on small ruminant production in the Delaware and worldwide, this research could potentially impact not only local (state), regional, national, but also the international sheep and goat industry. Understanding the level of the problem in our area could thus greatly impact profitability and sustainability of small ruminant industries in similar areas nationally and internationally. This project is very similar to several projects that have been conducted in the U.S. However, if the data on anthelmintic resistance is updated every three to four years it allows producers to understand how their current dewormers are controlling the parasite load and give them an insight into the idea of changing the dewormers earlier or using more than one dewormer to the kill the parasites that may be resistant to one specific dewormer.
To fulfill the objectives of this study, five farms were visited over the summer and fall of 2018. The farms were visited on July 26, 2018 (Wayside Farm), August 07, 2018 (Union Ridge Farm), September 27, 2018 (Cornerstone Acres), October 2, 2018 (Delaware Nature Society: Coverdale Farm Preserve), and October 15, 2018 (Sandyland Boer Goat Farm). Fecal samples were collected rectally from individual animals with a FAMACHA© score of 3, 4 or 5 on each participating farm (Wayside Farm = 19 goats; Union Ridge Farm = 12 goats; Cornerstone Acres = 20 goats; Coverdale Farm Preserve = 9 sheep; Sandyland Boer Goat Farm = 15 goats) and placed in labeled plastic zippered bags in a cooler on the opposite side of the ice to prevent direct contact. Once the samples were back at Delaware State University, a pooled sample was created by adding fecal from individual animals into one bag to weigh at least 20 grams (This was done for each farm on day samples were collected). The remaining fecal material in the individual bags were then refrigerated for individual fecal egg count (FEC) analysis and the composite samples were vacuum sealed and shipped off to the University of Georgia Infectious Disease laboratory for analysis. Individual fecal samples were analyzed for FEC using the modified McMaster technique (Henricksen and Aagard, 1986) and reported as eggs per gram (epg). Pooled samples made up of fecal from individual animals from each farm with greater than 500 epg were used for DrenchRite ® Larval Development Assay (LDA) analysis of anthelmintic resistance. The LDAs were conducted in the parasitology laboratory of Dr. Ray Kaplan at UGA.
Of the five farms tested, one farm (sheep farm) did not have enough parasites to be able to conduct the DrenchRite ® Larval Development Assay while the other farms (goat farms) had adequate parasite loads to conduct the LDA. The LDA results indicated that all the farms tested had resistance to the Benzimidazole (Panacur, Safeguard, Valbazen) class of dewormer with one having about 50% efficacy. Additionally, Ivermectin had no effect on the parasites from all the farms tested (IVM), indicating high IVM resistance (0% efficacy) on these farms. Two of the four farms tested had parasites with resistance to Levamisole while the other two farms had a suspected resistance that indicated the drug being about 65-85% effective again both Trichostrongylus and Haemonchus contorts. Haemonchus contorts was found to be the most predominant parasite on 3 of the 4 farms tested, with Trichostrogylus being the most predominant on one farm.
As a project out come, one of the producers on this study purchased a livestock scale to weigh his animals in order to give the correct dose of the dewormer (anthelmintic) that is adequate to kill these parasites.