Sheep and lambs: update on the key disease and health concerns

One major concern around lambing time is reducing neonatal lamb disease.

With increasing pressure to reduce unnecessary use of antibiotics in sheep, neonatal lamb use must be reduced when possible. To achieve high levels of lamb survivability, colostrum quality and quantity must be maximised, and high levels of hygiene maintained. Lambs should receive 50ml/kg of colostrum as soon as possible after birth and within four to six hours.

In the 24 hours following birth, a lamb should receive 200ml/kg bodyweight in colostrum. This timing is particularly important, as after the first six hours of life, the lamb’s ability to absorb immunoglobulins into the bloodstream from the intestines has reduced significantly.

Also, it should be noted that IgG concentration in milk decreases rapidly after birth at approximately 3.3mg/ml per hour, dropping to practically zero by 23 hours post-lambing (Agriculture and Horticulture Development Board; AHDB).

The quality of colostrum is just as important as the volume used. Colostrum quality can be assessed via a refractometer. Previously, a level of more than 22 per cent was considered an indicator of adequate quality, but this level is currently thought to need to be higher. Any colostrum that measures above this point can be kept and frozen for any lambs from ewes that have not produced enough quality colostrum.

Note that the disease status of flocks – especially iceberg diseases such as Johne’s disease – must be known before sharing colostrum to prevent disease spread.

Artificial colostrum can be used to supplement lambs, but the quality of products must be ascertained if they are to be relied upon. Cow colostrum can be used, but pooling of cows should be used to minimise the risk of fatal anaemia in the lambs, and again, the disease status of the cows should be known to minimise disease spread.

Lambs can also be blood sampled within seven days of life to assess failure of passive transfer. This can be done effectively in practice by measuring total protein with a refractometer.

Cryptosporidium

After Escherichia coli causing scour and watery mouth in neonatal lambs, one of the next most important causes of neonatal lamb disease is Cryptosporidium.

This waterborne parasite can build up in the environment and transmit from calves to lambs. This disease is often overlooked, but can have devastating effects on the flock.

Monitoring ewe health to minimise lamb loss

To maintain maximum quality of colostrum from the ewes, the ewe’s nutrition should be carefully monitored, and metabolic profiling can be used to help assess this and plan for any concerns moving forward.

Trace element monitoring is also essential, as deficiencies and excesses of trace elements can affect both colostrum quality and the absorption/utilisation by the lambs. Cobalt-deficient lambs may be slower to stand and suckle, therefore, decreasing the chances of good-quality colostrum feeding and potentially leaving lambs susceptible to diseases. Selenium deficiency has been linked not only to infertility, but also to reduced immune ability in lambs and poor lamb survivability.

Iodine is important both in terms of deficiency and excess. If in excess, it has been linked to decreased IgG concentrations in lambs and, therefore, reduced immune capability (McGovern et al, 2017).

Presence of parasites or concurrent diseases, such as the iceberg diseases, will affect ewe colostrum quality and production, and hence, neonatal survivability.

Iceberg diseases

The iceberg diseases are becoming of increasing prominence, mainly due to increased farmer interest and testing.

An accreditation scheme now exists through Scotland’s Rural College for Johne’s, as well as the existing maedi visna testing scheme. At present, commercial tests exist for maedi visna, Johne’s, caseous lymphadenitis and border disease virus, but no economically viable commercial blood test exists for ovine pulmonary adenocarcinoma – although, a blood test is available that can detect advanced cases of the disease. This has led to the prevalence of ultrasound scanning of lungs to detect ovine pulmonary adenocarcinoma, both in individual animals and flocks.

Some discussion exists around the success of this technique, but if performed by an experienced practitioner, and with good communication with the farmer regarding the limitations of testing, then this technique can be beneficial – especially to flocks with a high prevalence of disease.

Macrocyclic lactone-resistant scab

More and more cases of macrocyclic lactone (ML) resistant sheep scab are being reported, leaving the only treatment option as full plunge dipping in organophosphate.

Any cases of suspicion should be investigated, both through skin scrapes and antibody testing. Antibody testing is particularly useful with quarantined sheep after purchase or returning to farm after overwintering.

Parasite resistance testing

Research at the University of Glasgow’s veterinary school has demonstrated that antibody responses against the larval stages of Teladorsagia circumcincta can be used as a biological marker for host response to infection.

This phenotype potentially provides new ways to identify genetic differences between sheep and their ability to be resistant to high worm burdens.

High levels of IgA have been shown to regulate both worm growth and fecundity, leading to decreased worm output and, therefore, reduced environmental contamination. Funding is available for IgA testing within English flocks.