In dairy cattle, it’s all about the udder. In meat sheep, which form the majority of sheep in the UK, we tend to overlook this part of the sheep’s anatomy. Without an udder there is no milk and without milk there is no lamb growth.
Inflammation of the udder (mastitis) reduces milk production and threatens lamb survival. Mastitis also threatens the health and survival of ewes. Unlike cattle, where mastitis is almost invariably caused by bacteria, sheep may get mastitis through infection with bacteria or with viruses.
This distinction is important, because prevention and treatment strategies differ between the two. There is no point in treating viral infections with antimicrobials as they don’t work. Testing, culling and certification programmes are the best way to deal with viral mastitis, which is mostly caused by the Maedi-Visna virus.
In the case of bacterial mastitis, the worst offender is Mannheimia haemolytica (formally Pasteurella haemolytic). Mannheimia generally causes acute mastitis, resulting in blue and cold udders, often leading to the immediate death of the animal or to sloughing off of the udder, with secondary infection and delayed death as a consequence. For those animals, treatment usually comes too late and euthanasia may be the most humane way to deal with cases. However Mannheimia is quite common for healthy animals to carry although usually it is the lambs carrying it in their mouths.
In rare cases Staphylococcus aureus can cause a blue udder and also chronic mastitis, leading to localised abscesses in the udder, or shrinkage and hardening of an udder half. Like Mannheimia, Staphylococcus aureus can be carried by healthy animals.
Damage can be the result of severe weather conditions or lack of milk production, resulting in excessive sucking by hungry lambs. Thus, the prevention of mastitis may need to happen not via the animals’ udder, but via their stomachs. Adequate nutrition, particularly adequate protein supply in the last 10 weeks before lambing, helps to ensure adequate milk production, providing protection for lambs and ewes alike.
Some of the tools available for mastitis control in dairy cattle cannot be recommended for use in sheep. Therefore, culture of bacteria from aseptically collected milk samples is still the preferred way to identify mastitis causing organisms in sheep. There hasn’t yet been a vaccine developed either for sheep for mastitis. The best tools for mastitis control continue to be prevention through good nutrition and hygiene; checking udders at lambing, weaning and before mating; and treatment of cases with your vet.