Blood screening service strives to improve lambing percentage

Data collected nationally shows that the most commonly diagnosed causes of abortion in all sheep are enzootic abortion (EAE) and toxoplasmosis, accounting for 50% and 23% of cases respectively.   The data puts campylobacteriosis next at 16%, followed by abortion caused by salmonella at 8%.   Listeria has the lowest levels at 2.6% (national laboratory survey).

“These figures show little change over the past few years,” states IanAnderson, vet at Intervet.   “And what is potentially even more worrying is that despitethe availability of effective vaccines to protect flocks against EAE and toxoplasmosis, in unvaccinated flocks cases are still running at high levels across the country.   The 2005 season showed record high levels of EAE exposure in Intervet-tested flocks.”

Intervethas been running its subsidised FlockCheck service for the last 10 lambing seasons.   It aims to assist farmers to diagnose abortion problems, or lower than average lambing percentages, by showing whether a flock has been exposed to either EAE or toxoplasmosis.

In 2005 a staggering 81% of unvaccinated flocks tested through the scheme were positive for exposure to either enzootic abortion (EAE) or toxoplasmosis, showing no signs that either disease is on the decline.   The percentage of flocks testing positive for EAE alone was 61%, the highest it has ever been since FlockCheck started.

The 2005 survey examined blood samples taken from over 270 flocks in England, Scotlandand Wales, where the average flock size was 535 and the lambing percentage averaged 151%.

“Unfortunately, calculating the true cost of lamb losses due to infectious abortion has always been difficult.   Data on the direct and indirect costs associated with keeping an empty ewe for an unproductive season has been largely unavailable meaning that, at best, most advice has been based on lambing percentage or live lambs per 100 ewes tupped,” adds IanAnderson.

Independent sheep consultant, Lesley Stubbingshas taken a new approach to understanding the extent of lamb losses and what improvements producers could expect to see if they are prepared to invest in preventative vaccination.

“The cost to the business is not only the direct cost of running an unproductive ewe for a year, but you have to add that ewe’s share of overheads such as labour in order to understand the true scale of the loss,” Ms Stubbings explains. 

“Surveys show that many producers do not consider they have an abortion problem in the flock until in excess of 5% of ewes have aborted,” she remarks.   “However, detailed analysis shows that the extent of the impact lambing percentage has on profit margin is very substantial.”

Using national statistics, the unit costs of production and associated profit margins for an average flock have been calculated. The chart below shows figures for a 

lowland flock, based on an average lambing percentage of 156% (which equates to 87 ewes/100 rearing 1.8 lambs each).  

Diagram to show the effect of abortion and vaccination on profit per ewe

The cost of vaccinating against enzootic abortion (with Enzovax) and toxoplasmosis (with Toxovax) is easily justified using Ms Stubbings’ data.   “Assuming a ewe is vaccinated with both vaccines at the start of her productive life in the flock (which is normally five years), the group of 100 ewes only needs to deliver an additional 3.5 lambs or an increase of two productive ewes across the group to pay for the investment.   This is something that should be readily achieved and exceeded in most flocks.”

Intervet’s IanAnderson adds that: “As is clear, many sheep will have been exposed to both causes of abortion and while there are alternative vaccines available, only Enzovax and Toxovax are licensed to be used at the same time.   This means having to gather the sheep in only once, therefore saving time, money and effort.”

Key signs that infection may be present:

Summary

·     Typical flock of 87 ewes/100 rearing 1.8 lambs each = lambing percentage of 156% 

·     Average profit/ewe for this flock is £4.64

·     Abortion storm occurs and productive ewes falls to 70 ewes/100 results in loss of £6.22 per ewe

·     Raising number of productive ewes from 87 to 90 = a profit increase of 70% per ewe

·     Vaccinating all ewes with both Toxovax and Enzovax (the only two abortion vaccines licensed to be used at the same time) at the beginning of their productive lives needs to deliver only an extra 3.5 lambs per 100 ewes to pay for itself

·     By vaccinating with both Enzovax and Toxovax, most farmers see a much great increase than 3.5 lambs born/100 ewes making vaccination clearly cost-effective

The 2006 FlockCheck service is currently underway and will run until the end of July.   The scheme, which is run via vets, analyses blood samples taken from ewes which have had still born or aborted foetuses with a view to determining the cause.   Once the diagnosis is complete, appropriate action can be taken to prevent the diseases causing losses in next year’s lamb crop.   Where enzootic abortion, toxoplasmosis, or both diseases, are found to be present, farmers are recommended to discuss vaccination strategies with their veterinary surgeon.

The estimated cost of one abortion as a result of either disease is in excess of £100.   Where losses exceed 2% of the lamb crop, Intervet suggests that a diagnosis is made and if the results show that it is enzootic abortion or toxoplasmosis exposure, then vaccination against both diseases will more than pay for the cost of the two vaccines.   Further information about FlockCheck 2006 can be obtained from your vet, or by calling Intervet on 01908 685685.

Article first published 13/04/06