19 March 2025
Two bacterial pathogens have been identified as the principal causes of mastitis in commercial sheep flocks involved in a Farming Connect-funded Welsh study.
Although 14 different strains of bacteria were found in milk samples from the 12 flocks during the 2023-24 lambing season, it was Staphylococcus aureus and Mannheimia haemolytica that were most common. Staphylococcus aureus was found in 43% of samples and Mannheimia haemolytica in 17%.
A similar pattern was confirmed in a separate project run by the Animal and Plant Health Agency (APHA) Small Ruminant Expert Group project over the same period, and is also in line with previous studies.
The participating farmers in the Farming Connect study were mostly members of the Farming Connect sheep discussion group in Montgomeryshire, which is led by independent sheep consultant Kate Phillips, but also included seven other discussion group farmers from across Wales.
During a recent Farming Connect webinar, she said the study had also looked at which pathogen strains on individual farms were resistant to antibiotics.
Only 7% of samples with Staphylococcus aureus were resistant to the first line antibiotics tetracycline and tylosin while 25% of those with Mannheimia 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, which is also the main cause of joint-ill in lambs.
The study was undertaken to gain a better understanding of the factors that influence the incidence of mastitis, to enable farmers to develop strategies to improve ewe health and management and to reduce culling for this disease.
Mastitis is one of the most important diseases affecting ewes, costing the UK sheep industry more than £120 million a year in direct and indirect costs - 10% of the ewes in the Farming Connect study with mastitis died and the 90% that survived were all culled.
As many as 25% of ewes in a flock can be affected, but some studies have shown much higher rates.
When one ewe has mastitis, the flock is at increased risk because of its contagious and transmissible nature, Mrs Phillips told the webinar.
“Underfeeding protein and energy in pregnancy and lactation increases the risk of mastitis, so make sure appropriate levels are fed,’’ she advised.
Low body condition score (BCS) at lambing has been linked to subclinical and clinical mastitis, Mrs Phillips added, while poor hygiene at lambing time allows environmental bacteria to multiply, increasing the chance of infection.
According to evidence gathered by AHDB as part of its Better Returns Programme, good udder conformation is associated with decreased risk of mastitis – although 81% of the ewes in the Farming Connect study had normal udders and 71% of teats were undamaged.
The AHDB Understanding mastitis in sheep resource also advises that the chance of developing acute mastitis increases when ewes rear two or more lambs, regardless of ewe age, and the risk of developing mastitis increases the longer ewes and lambs stay indoors. This study found that most of the ewes with mastitis were rearing twins.
The flocks in the Farming Connect study averaged 563 ewes but ranged in size from 100 to 1,415.
They scanned at an average of 155% and had a mastitis incidence averaging 3.8%.
Eighty-six per cent of the ewes recorded lambed inside, with the housing period averaging 6.6 weeks and all of those flocks bedded on straw, and the majority of the farms are in upland locations.
Eighty per cent of ewes recorded were fed silage and concentrates pre-lambing and 20% hay and concentrates, but some ewes were grazing.
While creep feeding is thought to have a role in reducing the demand for milk, and helping to avoid aggressive suckling, half of the flocks in the study which had cases of mastitis did feed lamb concentrates.
The study also looked at orf levels and found it present on only three per cent of udders.
Of the ewes in the study with mastitis, farmers reported that 83% were given pain relief or an anti-inflammatory, which Dr Fiona Lovatt, of Flock Health Ltd, said was “really good news’’.
“We know that a lot of farmers don’t necessarily give a pain killer to sheep with mastitis but we would always recommend it because it is an incredibly painful disease,’’ she said.
A vaccine is available for Staphylococcus aureus, which is given at five weeks and two weeks pre-lambing, but to be cost-effective, Dr Lovatt said a farmer needed to be confident that this was the pathogen causing mastitis in the flock.
Sampling ewes with mastitis, such as demonstrated in this project, is a great way to determine the bacterial cause and it is an important way for vets and farmers to take appropriate decisions as to whether to vaccinate the ewes just before lambing in the following year, she said.