Causes of Lamb Mortality in Bighorn Sheep in British Columbia
Poor lamb survival in bighorn sheep herds has been a long‐standing problem in many areas throughout the western United States and Canada. Reported causes of lamb mortality vary depending on the location and year, and include predation, inclement weather and disease. However, pneumonia appears to be the most significant cause of mortality in lambs. The causes of pneumonia are complex and include lungworm (Protostrongylus sp.), several species of bacteria, viruses and stress. Pneumonia die‐offs in bighorn sheep are frequently associated with contact with domestic sheep, which carry many of this disease‐causing agents. The variable causes of pneumonia and the involvement of multiple host species has made the management of bighorn sheep pneumonia difficult.
In 2011, the Canadian Cooperative Wildlife Health Centre, in collaboration with the British Columbia Ministry of the Environment, began a research program to study the causes of persistently poor lamb survival in herds of bighorn sheep in the East Fraser Valley northwest of Kamloops, BC. Herds in this area have seen a steady decline in numbers and sick lambs have been observed in early to mid‐July. Autopsies of a limited number of dead lambs and ewes have revealed pneumonia as the cause of death.
To better understand factors causing lamb mortality, lambs and ewes were monitored daily for approximately 4 weeks from late June to mid‐July. Coughing lambs were observed throughout the study period and, by the middle of July, approximately a third of the lambs were sick. In addition to coughing, lambs often had diarrhea and were thin. Two sick lambs were euthanized and a third died; autopsies revealed the presence of Mycoplasma bacteria, including Mycoplasma ovipneumoniae. Lungworm was not involved in the pneumonia.
M. ovipneumoniae appears to be the initiator of pneumonia in these lambs. It is likely that secondary infection with opportunistic bacteria, predation of sick lambs, and other factors subsequently increase mortality. Research in the Fraser Valley will continue in 2012 to determine if M. ovipneumoniiae this is a consistent finding among herds and years, to identify sources of this bacterium, and to begin to identify the relative importance of other factors in lamb mortality. The identification of a single pathogen, which is potentially responsible for initiating many, if not most, of the bighorn sheep pneumonia outbreaks, is an important first step in developing techniques to control this devastating disease.
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