VET’S DIARY: Spring brings it problems

WHILE most of us have been enjoying the unusually good weather, some of us have had other things to consider, writes Dominic Plumley.

The growing grass and consequently growing lambs in the pastures encapsulate what is good about this time of year, though as you might imagine, all may not be quite so simple.

Coccidia and nematodirus are both gut parasites that affect young lambs.

The clinical signs are similar. Affected lambs have poor weight gain, scour and can die. However, the life cycles, treatment and prevention advice differs for the two parasites.

Nematodirus is a worm, typically transmitted from the lamb crop of one year to the lamb crop of the next.

Lambs are susceptible from one to three months of age, and will develop immunity at around three months which is strong by six months.

Nematodirus eggs on the pasture deposited by lambs the previous year will all hatch into larvae at a similar time when weather conditions allow. Eggs are resilient and persist on pasture for two years.

For nematodirus, egg-hatching occurs after a chill followed by warmer weather, creating a flush of larvae on the pasture.

In the UK, such conditions are seen in April to June. If this larval flush coincides with susceptible lambs (four to 12 weeks of age) then nematodirus will cause problems.

Coccidia are protozoa (single celled organisms). Ewes will shed some coccidia around lambing, but are unaffected themselves. Housed lambs meet the biggest risk.

Most outbreaks are seen in lambs three to eight weeks old.

Oocysts in the ewes’ faeces will develop into infective stages quickly in the warm moist lambing shed.

Increased contact with dung in the shed means that lambs are much more likely to ingest more coccidia.

Inside the lambs’ gut, the coccidia life cycle takes place, causing multiplication of the coccidia and increasing contamination of the housed environment further. Oocysts (coccidia eggs) are also resilient on the pasture so coccidiosis can also be seen in lambs at pasture.

Dung samples need to be collected from scouring lambs and given to your veterinary practice, in order to make a diagnosis of coccidiosis or nematodirus, or both.

Both parasites are capable of causing gut damage, and with a high challenge, lamb deaths can occur before oocysts or nematodirus eggs are seen in dung. In this case, a postmortem of a dead lamb will yield a diagnosis.

Sometimes, it is necessary to diagnose the species of coccidia in the lambs, not all coccidia species will cause disease.

Lambs can suffer with concurrent nematodirus and coccidiosis, and require dual treatment.

Coccidiosis is best treated with an anti-coccidial drench.

It is important to identify the risk factors for your lambs with your vet, whether it be hygiene in the sheds, colostrum intakes, an extended housing period, grazing mixed ages of lambs or using contaminated pastures in subsequent years.

Coccidiosis will be a sub-clinical disease in some lambs, they may not scour, but will suffer a depressed growth rate.

In some flocks, anti-coccidials can be added to feed buckets or creep feed under veterinary prescription as a method of control.

Timely use of the anti-coccidial drenches is a further management tool to be discussed with your vet.

Nematodirus needs to be treated with an oral wormer. We recommend using white (Group One – benzimidazole) or yellow (Group Two – Levamisole) drenches providing there is not a mixed worm infection. Clear (Group Three – ivermectins) tend not to be so effective for nematodirus.

To date, there has been no resistance reported for Group One and nematodirus, but this situation may change, so continue to seek advice from your vet.

The best way to prevent nematodirus infection is to avoid grazing lambs of one-three months of age on pasture which carried lambs of a similar age in the previous two years.

On many farms, this is not possible, and lambs need a prophylactic drench or two during the risk period.

Disease can be seen in lambs before eggs are seen in faeces, so monitoring worm egg counts is not a reliable way to time drenching lambs for this particular worm.

Instead, you need to use the nematodirus forecast The forecast will predict egg hatching depending on the weather conditions and advise on prophylactic drenching of age susceptible lambs accordingly.