Principal cause of mastitis in ewes identified

Two bacterial pathogens have been identified as the principal causes of mastitis in commercial sheep flocks involved in a Farming Connect-funded Welsh study.

Fourteen different strains of bacteria were found in milk samples from the 12 flocks during the 2023-24 lambing season.

Staphylococcus aureus (in 43% of samples) and Mannheimia haemolytica (in 17% of samples) were the most common.

See also: Tips for managing ewe mastitis during lambing

Farmers in the Farming Connect study were mostly members of its sheep discussion group in Montgomeryshire, led by independent sheep consultant Kate Phillips.

Flocks averaged 563 ewes, but ranged in size from 100 to 1,415, and scanned at an average of 155%. The mastitis incidence averaged 3.8%.

The study was to understand the factors influencing mastitis incidence, to enable farmers to develop strategies to improve ewe health and reduce culling for this disease.

Of the ewes in the study with mastitis, 10% died – the 90% that survived were all culled.

Antibiotics resistance 

During a recent webinar, Kate said the study had looked at which pathogen strains on individual farms were resistant to antibiotics.

Only 7% of samples with Staph aureus were resistant to the first-line antibiotics tetracycline and tylosin, while 25% of those with M haemolytica were resistant to tetracycline only.

However, tetracycline was not effective at treating Streptococcus dysgalactiae, the third most common pathogen found in milk samples from the 12 flocks – and the main cause of joint-ill in lambs.

As many as 25% of ewes in a flock can be affected with mastitis.

Some studies have shown much higher rates, but when one ewe has it, the flock is at increased risk because of its contagious and transmissible nature, Kate said.

“Underfeeding protein and energy in pregnancy and lactation increases the risk of mastitis, so make sure appropriate levels are fed,’’ she advised.

Poor condition score

Low body condition score at lambing has also been linked to subclinical and clinical mastitis, she added, while poor hygiene at lambing time allows environmental bacteria to multiply, increasing the chance of infection.

Good udder conformation is associated with decreased risk of mastitis, according to AHDB, although 81% of the ewes in the Farming Connect study had normal udders and 71% of teats were undamaged.

The chance of developing acute mastitis increases when ewes rear two or more lambs, regardless of ewe age, and the mastitis risk increases the longer ewes and lambs stay indoors.

This study found that most of the ewes with mastitis were rearing twins.

Some 86% of the recorded ewes lambed inside, and were housed for an average 6.6 weeks, with all flocks bedded on straw.

Silage and concentrates were fed pre-lambing to 80% of ewes; 20% had hay and concentrates, though some ewes were grazing.

While creep feeding is thought to have a role in reducing the demand for milk, thereby avoiding aggressive suckling, half of the flocks that had cases of mastitis fed lamb concentrates.

The study also looked at orf levels and found it present on only 3% of udders.

Of the ewes in the study with mastitis, farmers reported that 83% were given some form of pain relief, which vet Dr Fiona Lovatt, of Flock Health, said was “really good news it because it is an incredibly painful disease”.

She added that while a vaccine is available for Staph aureus (given five weeks and two weeks pre-lambing), a farmer needs to be confident it was the mastitis pathogen in their flock before deciding whether to vaccinate ewes just before lambing in the following year.