Abstract
ABSTRACTIn the absence of livestock contact, recurring lamb mortality in bighorn sheep (Ovis canadensis) populations previously exposed to pneumonia indicates the likely presence of carriers of pneumonia-causing pathogens, and possibly inadequate maternally derived immunity. To investigate this problem we commingled naïve, pregnant ewes (n=3) with previously exposed rams (n=2). Post-commingling, all ewes and lambs born to them acquired pneumonia-causing pathogens (leukotoxin-producing Pasteurellaceae and Mycoplasma ovipneumoniae), with subsequent lamb mortality between 4-9 weeks of age. Infected ewes became carriers for two subsequent years and lambs born to them succumbed to pneumonia. In another experiment, we attempted to suppress the carriage of leukotoxin-producing Pasteurellaceae by administering an antibiotic to carrier ewes, and evaluated lamb survival. Lambs born to both treatment and control ewes (n=4 each) acquired pneumonia and died. Antibody titers against leukotoxin-producing Pasteurellaceae in all eight ewes were ‘protective’ (>1:800 and no apparent respiratory disease); however their lambs were either born with comparatively low titers, or with high (but non-protective) titers that declined rapidly within 2-8 weeks of age, rendering them susceptible to fatal disease. Thus, exposure to pneumonia-causing pathogens from carrier ewes, and inadequate titers of maternally derived protective antibodies, are likely to render bighorn lambs susceptible to fatal pneumonia.
Highlights
Over the last several decades, pneumonia of bighorn sheep (BHS) has resulted in up to 75-90% mortality in herds across North America (Rush, 1927; Buechner, 1960; Schwantje, 1986; FestaBianchet, 1988; Valdez and Krausman, 1999; Miller, 2001)
Ram T113 tested polymerase chain reaction (PCR)-negative for M. ovipneumoniae pre-commingling but was positive postcommingling (Table 1)
They can act as sources of infection to other herds, especially through dispersing males (Cassirer and Sinclair, 2007); it is not clear whether they become carriers, and/or develop high antibody titers, with respect to either one or both pathogens
Summary
Over the last several decades, pneumonia of bighorn sheep (BHS) has resulted in up to 75-90% mortality in herds across North America (Rush, 1927; Buechner, 1960; Schwantje, 1986; FestaBianchet, 1988; Valdez and Krausman, 1999; Miller, 2001). The main pathogens involved are Mycoplasma ovipneumoniae (Besser et al, 2008, 2012, 2013; Dassanayake et al, 2010) and leukotoxinproducing members of Pasteurellaceae (lkt+ Pasteurellaceae), especially Mannheimia haemolytica and Bibersteinia trehalosi. BHS populations that are afflicted with pneumonia may have originally acquired lkt+ Pasteurellaceae as well as M. ovipneumoniae from livestock, domestic sheep (Schillenger, 1937; Buechner, 1960; Coggins, 1988; Miller, 2001; George et al, 2008; Wolfe et al, 2010)
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