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Browsing by Author "Bowdridge, Scott A."

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    Effect of sire fecal egg count estimated breeding value on Katahdin lamb parasite resistance in pasture-based system
    Weaver, Andrew R.; Wright, Donald L.; Greiner, Scott P.; Bowdridge, Scott A. (Elsevier, 2023-07)
    Significant genetic variability exits within sheep breeds for gastrointestinal nematode (GIN) resistance. There-fore, selection may be an important tool to combat anthelmintic resistance in GIN populations. To better un-derstand the effect of selection based on the fecal egg count (FEC) estimated breeding value (EBV) on lamb GIN resistance in a pasture-based system, a divergent mating scheme was established. Over two years, Katahdin rams with exceptionally high (High FEC; n = 5) or low (Low FEC, n = 5) FEC EBV were mated to random groups of Katahdin ewes at the Southwest Virginia Agricultural Research and Extension Center (Glade Spring, VA). Lambs were born mid-March and managed as one contemporary group (Weaning: June 4). In Year 1 (YR1), FEC was collected on all lambs June 26 with no prior anthelmintic treatment. In Year 2 (YR2), beginning at 60 days of age, body weights and FAMACHA scores were collected weekly and FEC biweekly. Anthelmintic administration occurred based on FAMACHA >= 3 in YR2. Lamb survival determination excluded first 7 days of age. Statistical analysis was performed using SAS (SAS Institute, Cary, NC) with fixed effects of sire type. Lamb FEC EBV cor-responded to sire type validating the mating scheme. Lamb FEC was similar and variable prior to and shortly after weaning. After this point, High FEC-sired lambs had greater FEC compared to Low FEC-sired lambs (P < 0.05) and anthelmintic treatment corresponded to FEC EBV type (P < 0.05). In YR1, death losses were greater for High FEC-sired lambs (P < 0.05) and those lambs that died had greater FEC EBV than those that survived (P < 0.05). In YR2, post-weaning FEC EBV difference between High FEC-sired lambs that survived to 120 days of age and those that died was significant (73% vs. 138%, P < 0.01). Therefore, selection for improved GIN resistance using FEC EBV is effective and the FEC EBV is also associated with lamb survival in a pasture-based system.
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    Effect of sire fecal egg count estimated breeding value on parasite resistance traits in Haemonchus contortus infected Katahdin lambs
    Wright, Donald L.; Greiner, Scott P.; Bowdridge, Scott A. (Elsevier, 2023-06)
    In the midst of anthelmintic resistance, genetic resistance to gastrointestinal nematodes (GIN) in lambs could reduce anthelmintic requirements; therefore, the fecal egg count (FEC) estimated breeding value (EBV) was developed as a measure of genetic merit for parasite burden. One of the first breeds to effectively implement the FEC EBV was Katahdin. To better understand the relationship between the FEC EBV and Haemonchus contortus (Hc) challenge infection, a divergent mating scheme was established with extremely high (High FEC, n = 5) or extremely low (Low FEC, n = 5) FEC EBV Katahdin rams over 2 years. Purebred lambs sired by these rams were born beginning in mid-March and managed on pasture until approximately 120 days of age. A primary infection was established based on FEC during this period. At this point, lambs (n = 109 in Year 1, n = 114 in Year 2) were removed from pasture, treated with an anthelmintic to reduce FEC and transported to the Animal Sciences Farm at West Virginia University. After a rest period, lambs were given 10,000 (Year 1) or 5000 (Year 2) Hc L3. Body weights, FEC, and packed cell volume were collected weekly. Lambs were harvested (n = 60/year) at 5 weeks post-infection. Abomasum worm counts were determined, and worm length was measured using Image J. Sta-tistical analysis was performed by year using the Mixed Model procedure of SAS (SAS Institute, Cary, NC) with fixed effects of sire EBV type. Change in FEC after the prepatent period was greater in Year 1 High FEC-sired lambs compared to Low FEC-sired lambs (210 vs. 34 eggs/g, respectively; P < 0.05). At harvest in Year 2, a greater proportion of Low FEC-than High FEC-sired lambs had worm counts of zero (P < 0.05). Worm fecundity was lower in lambs sired by Low FEC rams (P < 0.05). Taken together, sire selection for low FEC EBV will lower FEC and worm count and improve GIN resistance in progeny.