Scott Bowdridge

• PhD
• Professor (Full) at West Virginia University

The development of resistance in parasites due to overuse of anthelmintics has resulted in a marked decrease in the efficacy of these drug classes. Recent research efforts have focused on exploring alternatives such as selection for parasite-resistant breeds with the implication that immunocompetence may align with parasite resistance. Two breeds t...

Pathogen recognition is an essential component to achieve the desired outcome of host protection. Nod‐like receptor pyrin containing domain 3 (NLRP3) is a cytoplasmic pattern recognition receptor (PRR) with a wide array of agonists, such as PAMPs, DAMPs, ATP, bacterial product and viral products. Stimulation of the NLRP3 inflammasome results in pro...

The development of resistance in parasites due to overuse of anthelmintics has resulted in a marked decrease in the efficacy of these drug classes. Recent research efforts have focused on exploring alternatives such as selection for parasite-resistant breeds with the implication that immunocompetence may align with parasite resistance. Two breeds t...

Genetic selection focused on feed efficiency may prove to be valuable in reducing feed consumption costs and animal maintenance requirements without compromising growth. The Vytelle Sense system allows measurement of individual lamb DMI and varying feeding behaviors to identify feed efficient lambs. The aim of this study was to evaluate the impact...

Selection for postweaning fecal egg count (PFEC) EBV has revealed that low-PFEC sheep have greater resistance to gastrointestinal nematode infection, greater survivability to weaning, and greater anamnestic response to booster clostridial vaccination. Therefore, it can be hypothesized that selection for PFEC may result in improved generalized immun...

Post weaning fecal egg count (PFEC) estimated breeding value (EBV) has been recently linked with improved immune competence and lamb survival to weaning, thus improving health though selection. Animal movement is also linked to animal health, however little is known about behavior differences in sheep with divergent PFEC EBV. Thirty Katahdin ewes w...

Internal parasites are one of the greatest threats to small ruminant production across the United States and parasitic resistance to anthelmintics continues to increase. Genetic selection and copper oxide wire particles (COWP) are two tools that could help reduce effects of parasites in small ruminants. The objective of this project was to determin...

Parasite-resistant St. Croix sheep (STC) generate a potent neutrophilic response to larval stages of Haemonchus contortus (Hc) as demonstrated by abomasal neutrophil infiltration as early as 3 days after infection. This phenomenon is delayed in parasite-susceptible Suffolk sheep (SUF) potentially contributing to larval establishment. An excretory/s...

Variation in post-weaning fecal egg count (PFEC) estimated breeding values (EBV) has revealed effects beyond the reduction of parasitism. Previous work demonstrated lambs with a PFEC of < -50 (Low-PFEC) have higher survivability to weaning than lambs with a PFEC of > +50 (High-PFEC). In response to clostridial vaccination, Low-PFEC lambs also gener...

The gastrointestinal nematode (GIN) Haemonchus contortus is a major threat to global sheep production, a problem exacerbated by increasing levels of anthelmintic resistance. Genetic selection of sheep for reduced fecal egg count (FEC) is hypothesized to improve parasite resistance. This study measured the biological response and worm burden of Dorp...

Previous work demonstrated that, Katahdin lamb survivability to weaning was affected by post-weaning fecal egg count (PFEC) estimated breeding values (EBV) and favored Low-PFEC lambs. Therefore, selection for PFEC is hypothesized to improve generalized immunity beyond resistance to parasitic infection. This study aimed to compare the effect of PFEC...

The anthelmintic resistance of gastrointestinal nematodes (GINs) poses a significant threat to sheep worldwide, but genomic selection can serve as an alternative to the use of chemical treatment as a solution for parasitic infection. The objective of this study is to conduct genome-wide association studies (GWASs) to identify single nucleotide poly...

Selection for post weaning worm egg count (PWEC) EBV has revealed that lowPWEC sheep have greater resistance to gastrointestinal nematode infection, greater survivability to weaning and generate greater anamnestic response to booster clostridial vaccination. Therefore, it can be hypothesized that selection for PWEC may result in improved generalize...

Nutritional supplementation and genetic selection are potential methods to mitigate the impact of parasitism in sheep. Understanding feeding behavior of growing lambs divergently selected for parasite resistance using the fecal egg count (FEC) estimated breeding value (EBV) may help quantify the impact of supplementation and genetic selection on pa...

Previous studies have indicated the importance of Nod-like receptor pyrin containing domain 3 (NLRP3) to early immune response in St. Croix (STC) sheep. NLRP3 is important to Th2 immune response, which is the classical response to Haemonchus contortus larval antigen (HcLA). Th2 response is driven by interleukin (IL) -4 and IL-13 cytokine production...

Parasite-resistant St. Croix sheep generate a potent neutrophilic response to larval stages of Haemonchus contortus. Protective neutrophil responses can be best characterized by increased neutrophil infiltration to the abomasum within the first 3 days of infection. These data indicate breed differences in neutrophil chemotaxis and response to H. co...

Katahdin lambs with decreased post weaning worm egg count estimated breeding values (PWEC EBV) generated greater antibody in response to vaccination and survive better to weaning. Thus, lambs with decreased PWEC values may be more disease resistant and immunocompetent. To test this hypothesis, parasite-resistant St. Croix sheep, (STC, n = 10), and...

Internal parasites, specifically Haemonchus contortus (Hc), are detrimental to flock profitability. Loss of production efficiency and death in severe cases, contribute to the economic burden documented worldwide. Understanding the extensive impact gastrointestinal nematodes (GIN) have on nutritional loss and feeding behavior may prove valuable. The...

Gastrointestinal nematodes (GIN) are detrimental to the health and productivity of sheep across the world, necessitating genetic selection for improved GIN resistance. In this study, we used genomic analyses across- and within- two important breeds in the United States (US), Rambouillet and Dorper, to investigate physiological mechanisms associated...

Terminal sire crossbreeding systems which improve growth performance while maintaining parasite resistance have the potential to enhance the profitability of hair sheep enterprises. Katahdin (KT, n = 5), Suffolk (SU, n = 4), and Texel (TX, n = 5) rams were randomly mated to KT ewes over three years (Y1, Y2, Y3) at the Virginia Tech Southwest Agricu...

Gastrointestinal nematodes (GIN) threaten the productivity and health of sheep worldwide, prompting the need for genetic selection to reduce GIN susceptibility. Fecal egg count (FEC), packed-cell volume (PCV), and various production traits were examined in parasitized Rambouillet sheep and compared to sire FEC estimated breeding value (EBV). Rambou...

We examined the effects of dietary supplementation of a multi-component blend of prebiotics and probiotics on health, immune status, metabolism, and performance of newly weaned beef steers during a 35-d receiving period. Eighty newly weaned crossbred steers (12-hour post-weaning; 206 ± 12 kg of BW) from a single source were stratified by BW into 4...

Improving carcass merit while maintaining parasite resistance in Katahdin crossbred lambs has potential to improve profitability for U.S. sheep producers. To assess crossbred lamb parasite resistance, carcass merit and gain, purebred Katahdin ewes from the Southwest Virginia Agricultural Research and Extension Center (Glade Spring, VA) were mated t...

In a previous study, Katahdin lamb survivability to weaning was affected by sire post-weaning fecal egg count estimated breeding values (PFEC EBV) where lambs sired by low PFEC rams had greater survivability than high-PFEC-sired lambs. Therefore, selection for PFEC may also select for improved generalized immunity. The aim of this study was to comp...

While studying breed differences in immune response of peripheral blood mononuclear cells (PBMC) to Haemonchus contortus (Hc) antigen, RNA sequencing revealed that St. Croix (STC) PBMC upregulated expression of NLRP3 compared to PBMC from Suffolk (SUF) sheep. Nod-like receptor pyrin containing domain 3 (NLRP3) is a cytoplasmic pattern recognition r...

Haemonchus contortous (Hc) infections have decreased profitability of flocks worldwide through loss of production efficiency and in severe cases death. Countless research efforts have been made in order to further understand the extensive impact of this gastrointestinal nematode (GIN). Quantifying the impact feeding behavior after Hc infection may...

Sheep selected for resistance to gastro-intestinal parasites have been shown to have greater survivability to weaning. Data from Katahdin sheep indicates that selection based on post-weaning fecal egg count estimated breeding values (PWFEC EBV) may further improve generalized immunity. However, no data exists to confirm this increased circulating a...

Resistance to anthelmintics, more commonly referred to as “de-wormers,” has been on the rise in parasites that affect cattle. Parasite infection can have severe impacts on calf productivity resulting in reduced profitability. Therefore, we sought to better understand anthelmintic resistance in Appalachia by surveying Angus bulls entering performanc...

Interleukin 13 (IL-13) is a critical cytokine involved in development of Type 2 (Th2) immunity, necessary for generating full host protective response against Haemonchus contortus (Hc). St. Croix (STC) sheep have well-documented resistance, generating a robust immune response to larval stages of infection, thus preventing establishment of adults du...

Gastrointestinal nematodes (GIN) pose a significant risk to the health and productivity of Rambouillet sheep, a noted wool and meat producing breed, in the United States. Capturing phenotypic measurements of Rambouillet while infected with GIN is essential for the calculation of estimated breeding values (EBV) as a selection tool to improve host re...

Experimental Haemonchus contortus (Hc) infections revealed that Texel sheep have fecal egg counts (FEC) comparable to parasite-resistant St. Croix but adult worm burden comparable to parasite-susceptible Suffolk sheep. The aim of these studies was to further investigate the mechanism causing this disparity. Cellular and humoral immune responses to...

Residual feed intake (RFI) is quickly becoming the preferred measurement of efficiency in many species due to its inherent independence of most other important production traits. Making meaningful improvement in feed efficiency of sheep will require a consistent methodology to accurately identify efficient individuals. Due to difficulty in measurin...

Over the past two years of mating high (Hi) or low (Lo) fecal egg count (FEC) EBV Katahdin rams randomly mated to Katahdin ewes, reduced FEC in lambs has been the hallmark trait observable at weaning. Upon additional analysis, death loss in lambs also segregated with sire FEC EBV; whereas, HiFEC-sired lambs had a death loss of 29.9% in 2018 and 14....

Parasitism in weaned calves and anthelmintic resistance can negatively impact performance and reduce profitability. To better understand anthelmintic resistance, bulls were evaluated for fecal egg count (FEC) at performance test facilities in Virginia and West Virginia. Over a two-year period, 532 Angus bull calves were tested at bull development f...

Selection for reduced fecal egg count (FEC) is an important management tool to combat anthelmintic resistance in worm populations. To understand consequences of selection for parasite resistance, a divergent mating scheme was established whereby Katahdin rams with high (HiFEC; n = 4) or low fecal egg count (LoFEC; n = 4) estimated breeding values (...

Improvements in growth and carcass conformation through terminal sire crossbreeding systems may improve lamb value in a pasture-based system. Therefore, the aim of this study was to replicate the previous model of this experiment and compare the effects of different terminal sires on parasitism, growth, composition and marketability of grazing lamb...

Mixed‐species grazing offers a means to diversify livestock production systems for cool‐temperate regions typified by the Appalachian plateau of the USA. Our objective was to determine how mixed grazing influenced herbage and animal production, and sward botanical composition of three grazing systems including cattle and sheep. Three replicated sys...

Parasitic gastro-intestinal nematodes (GIN) are a serious challenge to sustainable small ruminant health and performance on pasture. Management practices including protein supplementation can help mitigate the deleterious effects of GIN and sustain livestock performance. We postulated that a combination of protein supplementation and grazing manage...

Aims The objective of this study was to identify and characterize cell populations within ovine peripheral blood mononuclear cells (PBMC) associated with Haemonchus contortus ( Hc) larval morbidity and impairment in vitro. Methods & Results Monocytes and lymphocytes were separated from PBMC from parasite‐resistant St. Croix (STC) sheep and parasit...

Aims Interleukin‐13 (IL‐13) is a Th2‐associated cytokine that typically induces gut contractility and mucus secretion to eliminate helminth parasites from the digestive tract. Little evidence exists of IL‐13’s direct effect on Haemonchus contortus larvae (L3), and thus were the objective of this study. Methods To test effects of IL‐13 on H. contor...

Mechanisms of immune activation in effector cells during Haemonchus contortus infection in sheep are currently unknown. Microarray experiments have been performed on tissues of H. contortus infected sheep of varying parasite resistance during early and late points of infection, but not in immune effector cells. The purpose of this study was to comp...

Host protective immunity to Haemonchus contortus (Hc) infection in parasite‐resistant St. Croix (STC) sheep is initiated early and characterized by an influx of innate cells and robust interleukin‐4 (IL‐4) production, resulting in T helper type 2 immune (Th2) responses. The purpose of these studies was to elucidate the source of early IL‐4 producti...

Genetic selection for internal parasite resistance in sheep is a valuable tool to mitigate effects of parasitism especially when significant within breed variability exists. To better understand the mechanism underpinning this variability, a divergent mating scheme was established. Katahdin rams (n = 4) were selected based on their estimated breedi...

Improvements in growth and carcass conformation through terminal sire crossbreeding systems may improve lamb value in a pasture-based system. Therefore, the aim of this study was to compare the effects of different terminal sires on parasitism, growth, composition, and marketability of grazing lambs. Suffolk (SU; n = 2) and Texel (TX; n = 2) sires...

The objective of this experiment was to determine how grazing a parasite-free, established stand of a high-tannin cultivar of birdsfoot trefoil influenced the prevention or treatment of Haemonchus contortus (Hc) infection in lambs. To determine preventative (PREV) effects of trefoil on Hc infection, parasite-naïve lambs were transitioned onto pastu...

High-tannin forages can be used to help mitigate the serious limitations associated with gastro-intestinal nematode (GIN) infections on efficient small ruminant production. The objective of this experiment was to determine how grazing a GIN-free, established stand of a high-tannin cultivar of birdsfoot trefoil (Lotus corniculatus L.) influenced the...

This study aimed to characterize neutrophil response to Haemonchus contortus (Hc) in vitro using cells from parasite‐resistant St. Croix (STC), and parasite‐susceptible Suffolk (SUF) sheep. Neutrophils from Hc‐primed and naive STC and SUF sheep were incubated with Hc larval antigen (HcLA), Hc worm antigen (HcWA) or complete media (CM). After HcLA e...

Growth performance and carcass merit of Katahdin sheep may be improved through utilization of terminal sires. However, forage-based production settings necessitate maintenance of parasite resistance. Katahdin (KT), Suffolk (SU), and Texel (TX; n=2/breed) sires were mated to KT ewes (n = 52) at the Southwest Virginia Agriculture Research and Extensi...

In year 3 of this study two different Katahdin (KT), Suffolk (SU) and Texel (TX) sires were mated with Katahdin ewes to examine sire breed difference. The objective of the study was to show differences in FEC, PCV, growth and carcass measures between offspring. Lambs raised in confinement at the Virginia Tech Southwest Agricultural Research and Ext...

The objectives of this study were to measure Haemonchus contortus larval aggregation by complement/antibody complexes, determine effect of breed resistance and infection status, and determine the effect of larval maturation on larval aggregation in vitro. Larval binding assays were performed on H. contortus L3, exsheathed L3 and L4 incubated with s...

The objective of this study was to determine the effects of peripheral blood mononuclear cells (PBMC), derived from parasite-resistant St. Croix (STC) hair sheep and parasite-susceptible Suffolk (SUF) sheep, on Haemonchus contortus L3 stage larval death in vitro, with or without autologous serum. Larval morbidity was quantified by measuring larval...

Improvement of carcass merit while maintaining parasite resistance is critical to retain profitability in Katahdin sheep. In year 2 of this study different Katahdin (KT), Suffolk and Texel (TX) sires were used to mate Katahdin ewes. Lambs were born and raised in confinement until weaning, then shipped to the West Virginia University Animal Science...

Early immune events associated with reduced larval burden remain unclear in parasite-resistant breeds of sheep. Therefore, our objective was to determine breed differences in immune-related gene expression following infection with H. contortus. Gene expression in abomasal tissue and mucosa, and in abomasal lymph nodes (ALN) was measured in 24 St. C...

Previous studies indicated that lambs supplemented with fishmeal when rotationally grazed (using 3-d rotation) had less gastrointestinal nematode (GIN) fecal egg counts (FEC) but failed to gain at an acceptable rate. Thus, the objective of thisstudy was to determine effect of increasing grazing time (GR)and supplementation rate (SR) on parasitism a...

The objective of this experiment was to determine effects of peripheral blood mononuclear cells (PBMC), derived from parasite-resistant St. Croix (STC) and parasite-susceptible Suffolk (SF) sheep, on motility of Haemonchus contortus L3 stage larvae in vitro. Peripheral blood mononuclear cells were collected from 10 lambs of each breed, 5 naïve and...

St. Croix sheep generate a classic T-Helper cell type-2 (Th2) immune response during Haemonchus contortus infection whereby interleukin-4 (IL-4) is the hallmark cytokine. Previous data have indicated that increased IL-4 gene expression occurs early during H. contortus infection in St. Croix sheep. Therefore, the objective of this experiment was to...

Management of gastrointestinal parasites is a critical issue for sheep producers worldwide. Increases in the prevalence of drug-resistant worms have complicated parasite control and increased economic losses. Therefore, other methods of parasite control need to be assessed, including the use of genetically resistant animals in breeding programs. Ha...

Management of gastrointestinal parasites is a critical issue for sheep producers worldwide. Increases in the prevalence of drug-resistant worms have complicated parasite control and increased economic losses. Therefore, other methods of parasite control need to be assessed, including the use of genetically resistant animals in breeding programs. Ha...

The objective of this study was to determine breed differences in immune response shortly following Haemonchus contortus infection. Peripheral and local cellular and humoral immune responses were evaluated in 24 St. Croix hair lambs and 24 Dorset×(Finn-Rambouillet) wool lambs at 0, 3, 5 and 7 days after infection with 10,000 L3 H. contortus larvae....

The objective of this study was to investigate the effect of vitamin E supplementation on an experimental Haemonchus contortus infection in lambs. Twenty lambs were stratified into two treatment groups based on fecal egg count. Worm-free lambs, 28–32 weeks of age, were supplemented with vitamin E (d-α-tocopherol) for 12 weeks following the recommen...

Previous data have indicated that interleukin-4 (IL-4) expression increases from day 3 to 7 and is associated with local lymph node hypertrophy in challenged St. Croix lambs whereas no IL-4 expression or lymph node hypertrophy was observed in parasite-susceptible lambs during this time. Immune responses occurring from day 7 to 14 during a Haemonchu...

A two-year study was conducted to determine peripheral cellular responses to Haemonchus contortus in parasite resistant St. Croix and parasite susceptible Suffolk crossbred sheep. In year one, transient increases of immune cells in blood were observed on specific days and were associated with a decrease of FEC in challenged St. Croix sheep. Therefo...

Antibody levels produced in response to gastro-intestinal nematode (GIN) parasite infection are typically higher in GIN-resistant breeds than susceptible breeds. Consequently, GIN-resistant ewes should generate greater parasite-specific antibody in colostrum and milk, potentially providing greater passive immunity to young lambs. To test this hypot...

Parasite resistant St. Croix sheep and susceptible Suffolk crossbred sheep were randomly assigned to three infection groups (n=5/breed/trmt): naive, primary and challenge, and given 10,000 L3 Haemonchus contortus larvae. Blood and fecal samples were collected daily for 14 days then weekly for 5 weeks. During primary infection St. Croix lambs reduce...

Introduction Spring-born lambs are exposed to gastrointestinal parasite infection following contamination of grassland by the ewes. Thirty ewes were introduced to the transitioning WVU Organic Crop Livestock Research Farm in 2001. These animals formed the nucleus for the organic sheep flock. This flock is grazed all year, primarily on permanent gra...

Helminths induce potent T helper 2 (TH2)-type immune responses that can mediate worm expulsion, but the role of this response in controlling the acute tissue damage caused by migrating multicellular parasites through vital tissues remains uncertain. We used a helminth infection model in which parasitic nematode larvae migrate transiently through th...

The regulation of gene expression through changes in chromatin structure is increasingly recognized as a chief component of activation of cells of the immune response. It now seems that histone demethylation of the promoter of the gene encoding the transcription factor IRF4 contributes to alternative macrophage activation.

B cells may be critical in mediating protective immunity by aiding Th2 cell development and/or antibody production. To examine the role of B cells during helminth infection B cell-deficient mice were inoculated with one of two intestinal nematode parasites: Nippostrongylus brasiliensis (Nb) and Heligmosomoides polygyrus (Hp). A similar pattern in e...

The parasitic nematode Nippostrongylus brasiliensis (Nb) third-stage larvae (L3) migrate to the host lung at about 24 to 48 hrs after infection, causing lung damage, inflammation and a potent Th2-type response. Yet, little is known about the mechanism causing lung damage and whether components of the Th2-type immune response contribute to acute lun...

B cells can mediate protective responses against nematode parasites by supporting Th2 cell development and/or by producing Abs. To examine this, B cell-deficient mice were inoculated with Nippostrongylus brasiliensis or Heligmosomoides polygyrus. B cell-deficient and wild type mice showed similar elevations in Th2 cytokines and worm expulsion after...

In moth pheromone communication signals, both quantitative and qualitative intraspecific differences have been found across geographic regions. Such variation has generally been hypothesized to be due to selection, but evidence of genetic control of these differences is largely lacking. To explore the patterns of variation in pheromone signals, we...

Gastrointestinal nematode infection in sheep is currently considered to be a problem of great magnitude in sheep production worldwide. This problem has been compounded by the overuse of anthelmintics used to treat parasite infection. In efforts to reduce chemical dependant production, research has focused on selection for parasite resistance based...