Sheep farmers are constantly told to improve their level of flock mortality, but if you can’t measure you don’t know how bad things are. This was one of the opening statements from Seamus Fagan, Athlone regional veterinary laboratory (RVL), speaking at this week’s Teagasc lowland sheep conferences in Leitrim and Carlow.

Seamus said that the level of knowledge on the rate and causes of mortality in Irish sheep flocks has traditionally been quite poor. Against a backdrop of the Food Harvest 2020 report targeting an increase in the value of sheepmeat output by 20% by 2020, it was felt that the level of ewe and lamb mortality could be one constraint in improving the national weaning rate and subsequent output.

To address this, Seamus says an extensive nationwide study was undertaken by the RVLs in conjunction with Teagasc clients, their advisers and veterinary practitioners to explore the rate and causes of mortality in Irish sheep flocks.

The study had a particular focus on identifying causes of mortality, the presence of abortion-causing agents in ewes, rate of abortion incidence and causative agent, while also developing an effective disease surveillance relationship with sheep producers.

The study

In total, 33 flocks with a median size of 195 ewes were included in the study. All aborted foetuses and sheep which died on farms in 2016 were submitted for postmortem to their nearest RVL. Blood samples were also taken from a sample of ewes in January 2016 to investigate abortion agent serology, while tissue mineral analysis was carried out on all animals over two months of age that were submitted.

Results

Seamus said that an average of 7.9 carcases (ewes and lambs combined) were submitted for every 100 adult females while the number of foetuses submitted was 7.6. The abortion serology results are detailed in Table 1.

Toxoplasma antibodies were identified in five flocks, with 18.5% of animals tested exposed to the disease at some stage. Over half the flocks in the study were vaccinating for toxo.

This is in contrast with enzootic abortion, where 17 flocks tested positive with a high seroprevalence of 63%.

This does not mean that all these sheep were infected, rather that the animals were exposed to the disease at some stage in their lifetime. There were five flocks out of the 27 vaccinating for this disease.

Another notable ailment identified is Schmallenberg virus, with five flocks showing exposure.

Seamus says that there has been an increase in the volume of deformed foetuses submitted to the Kilkenny lab, while farmer reports in some areas of the southeast suggest a similar incidence on a wider scale.

Abortion agents

While the above agents were identified in blood tests, the abortion agents identified as being the cause of death in postmortems are listed in Table 2.

Seamus says that internationally, the success of making an accurate diagnosis in an abortion case is about 50%. He urged farmers to submit the placenta/afterbirth along with the foetus as this greatly increases the chance of identifying the cause.

Toxoplasmosis was again the main cause of abortion across all flocks. Seamus explained that toxo is often in flocks at a low level and as such crops up from time to time causing ongoing problems, while, when enzootic abortion hits, it is much more pronounced.

Escherichia coli is listed as the second-most common cause, but Seamus says caution is needed with this result as E coli bacteria are commonly found on a carcase, but may not necessarily be the cause of abortion.

Listeria was highlighted as a risk given the difficulty in making good-quality silage. The advice is, where possible, to avoid feeding sheep silage that has been contaminated with clay or is mouldy.

Perinatal deaths

The cause of 254 perinatal deaths, which are defined as all lambs which were less than two days old when they died, are summarised in Figure 1.

This is the age at which most losses occur and Seamus explains that outside of this study, labs would not normally receive these lambs, especially those that appear as stillbirth.

Dystocia or a difficult lambing were identified as the primary cause followed closely by anoxia/hypoxia, which is essentially death due to a ewe being too long trying to lamb.

Stillbirth is third and this is described as the lamb actually being dead before the lambing process begins. Trauma was a long way back as a cause in fourth. Most traumas were due to factors such as a lamb’s ribs being broken in a hard lambing. Seamus gave a tip to farmers that if a big lamb is coming backwards, do not stay pulling the lamb straight out, instead change the angle a bit (pull towards the ground for example) to take the pressure off the ribs.

Death in young lambs

The main cause of death in lambs aged less than one month was bacteraemia/septicaemia, with the most likely route of infection identified as via the mouth and navel in the first few hours of life.

As mentioned in last week’s management notes, Seamus stressed the importance of ensuring there is good hygiene at lambing and lambs receive sufficient colostrum as soon as possible after birth. Losses at this stage are regularly manifested as navel-ill, joint-ill and liver or kidney abscesses.

Pneumonia was the most common cause of mortality identified in lambs over one month old and adult sheep. Farmers were also made aware that one third of livers examined at postmortem had cobalt levels below the normal range.

Farm health plan

Seamus concluded by urging farmers to be proactive in developing a herd health plan, pointing out that it will ultimately improve animal health and farm profitability. He said that measuring and identifying the incidence of a disease is the starting point in addressing health issues on farms.