Parasite risks this spring
The weather conditions this spring could increase the risk of coccidiosis with some very high oocyst counts already recorded in earlier born lambs and suckled calves. The persistent cold, wet weather has created muddy conditions and will have encouraged both lambs and calves to congregate in sheltered areas potentially increasing coccidial challenge.
In beef herds the incidence of coccidiosis peaks in calves between one and two months of age. Disease risk, particularly in the youngest calves, can be increased due to factors such as poor cow condition and colostrum quality, delayed turn out and grass shortages in long, cold springs. Similar conditions could influence disease risk in lambs with four- to eight-week-old animals most likely to be clinically affected.
If suitable sites are available, then regularly changing the position of shelters or troughs in fields can be helpful, as can keeping stocking density as low as possible. Fields where coccidiosis was diagnosed in 2023 will be a risk again this year and should be avoided for the highest risk age groups. Also consider the risks to later born lambs and calves. They could experience significant coccidial challenge if they are being turned into fields that have already been grazed by older lambs/calves this spring.
Coccidial oocyst counts can be difficult to interpret as the patent period can be very short and diarrhoea can be present both pre and post patency. In addition, large numbers of oocysts can have originated from the less pathogenic species. If coccidiosis is suspected, then it is useful to submit three or more samples for individual oocyst counts. It is not uncommon for there to be a wide variation in oocyst counts with at least one high count detected. The presence of typical clinical signs and response to treatment can assist in confirming the diagnosis. If oocyst speciation is required, this can be done fairly rapidly on bovine samples as the different coccidial species produce distinctive oocysts that vary in size and shape. This is not the case in sheep and speciation requires the oocysts to be incubated and sporulated before they can be identified. It therefore takes three or more days before a result is available. Only a limited number of chemicals are available for the treatment and prevention of coccidiosis and assessing treatment efficacy is not straightforward. If you would like to investigate suspected treatment failure please get in touch.
Long cold springs tend to increase the nematodirus risk in six to twelve week old lambs. The hatch of overwintered eggs occurs later by which time the main crop of lambs are eating enough grass to ingest significant numbers of infectious larvae. As a rule, cases are seen in May but usually peak in June. We recommend keeping an eye on the SCOPS nematodirus forecast.
Fields where there was an issue in 2023 will be high risk this year and should not grazed by the most susceptible lambs. Remember that diarrhoea and death can occur before infection is patent therefore postmortem examination can be required to confirm the diagnosis. Concurrent infection with coccidiosis can increase the severity of outbreaks.
Posted by SRUC Veterinary Services on 19/04/2024
