Age affected: Gilts, sows.
Causes: Teat injuries from floors or piglets; bacterial infection; poor hygiene.
Effects: Hot hard swollen udder, or chronic lumps, may be sow illness, piglet mortality.
Mastitis in sows is caused by ascending infection of the teats by bacteria. The organism most commonly involved is Escherichia coli or related organisms (coliforms). Bacteria such as Arcanobacterium pyogenes, streptococci and staphylococci may cause infections of single glands. Acute and severe mastitis caused by Klebsiella spp. may occur in outbreaks of fatal disease following trauma to the teats caused by rough sawdust bedding. A wide variety of E. coli serotypes may be isolated from mastitis, often differing from gland to gland. The E. coli types concerned all possess fimbriae (adhesive fibres), can adhere to epithelial surfaces and 95% are serum resistant (not easily destroyed by the body). Traumatic injury resulting from unclipped piglet teeth, sawdust bedding, or poor quality flooring predisposes to infection. One or both glands supplying a single teat may be infected. Infection enters via the teat canal following teat contamination and bacteria multiply in the gland. Infection may be transient, or colonisation, multiplication and acute mastitis with systemic signs and agalactia may result from the effect of E. coli endotoxin on prolactin production. Introduction of endotoxin into the mammary gland will cause mastitis and agalactia and endotoxin can be detected in the blood in mastitis.
Mode of transmission
As infection results from exposure to bacteria present in the sow’s environment, in faeces or on pig skins and affects individual glands, direct transmission between sows is unlikely. Outbreaks may occur when particular organisms are introduced to farrowing accommodation, but the predisposing factors such as teat damage are usually required. Mastitis will recur in successive batches of animals after farrowing if the environmental factors are not addressed.
Acutely affected sows are usually depressed, inappetent and fevered (temperatures of 40.5-42°C, 105-107°F are not uncommon). The udder is usually swollen and oedematous, often with massive congestion. Any secretion that may be obtained after oxytocin injection contains pus. Pain in the udder may lead to restlessness in the sow when piglets attempt to suck. The litter rapidly loses condition. Acute mastitis usually occurs within 1-3 days of parturition. The body temperature falls below normal, the animal can no longer rise and respiratory distress develops frequently leading to death. Coliform mastitis appears to regress within 3-4 days although in severe cases lactation may cease entirely. Sub-acute infection or infection in one or more glands occurs much more commonly and may be recognised by the increased hardness of the gland and, in its early stages, by a square area of reddening or the skin over the affected gland. The litter loses condition. Secretion may appear grossly normal in sub-acute or sub-clinical infection but cytology demonstrates raised cell counts (>106/ml). Mastitis in a single gland is often noted only when an affected gland fails to return to normal after weaning. There is often teat injury, especially in the thoracic and anterior abdominal pairs of teats.
Acute mastitis is easily recognisable as affected sows are off their feed and have obvious swelling of the udder, sometimes with reddening and oedema. The litter is usually in poor condition. Animals are often recumbent, but must be made to rise in order to confirm that mastitis is present. The udder should be palpated (felt) on both sides by running the hand under both lines of glands. Individual affected glands feel firm and hot. Laboratory examination of expressed secretion confirms that presence of mastitis by means of cell counts and the organism(s) responsible can be identified. Collection requires oxytocin injection as milk let down is under voluntary control. Sub-clinical mastitis may only be detected after cell counts on expressed milk which may reach 2.0 x 108/ml with 75% white blood cells. Normal milk contains 1 x 106 cells/ml. Chronic mastitis is easily palpable upon inspection during lactation and easily seen in dry sows. Physical damage to the teat or its end may be found.
At post-mortem examination in acute cases, the skin over the udder may be discoloured red or even purple, the carcase muscle and the liver may be pale and the subcutaneous tissue over the affected mammae is oedematous. The cut surface of affected glands is diffusely or focally reddened and pus can be expressed from the cut mammary tissue. Subacute or chronic mastitis is rarely fatal and is seen incidentally or at slaughter when residual lesions are very prominent.
Treatment and prevention
Acutely ill sows may be saved by injection with neomycin, tetracyclines, ampicillin, amoxicillin, streptomycin, fluoroquinolone, ceftiofur or trimethoprim: sulphonamide for 2-4 days. Oxytocin should also be given. The litter should be fostered or reared artificially. After recovery it may be necessary to cull the sow. Severely affected cases have a poor prognosis but rehydration with hypertonic saline given intravenously by flutter valve may cause a dramatic improvement in moribund animals. Other supportive treatment may include anti-inflammatory drugs such as flunixin meglumine where registered. In sub-acute cases, rehydration is not necessary. Antimicrobial injection may improve the condition where single glands are affected, but results are poor where abscessation has occurred or teat ends are damaged. Control depends upon hygiene, use of soft bedding other than sawdust, clipping piglets' teeth, early treatment and, possibly, the use of commercial E. coli vaccine if the condition is due to E. coli. Where the condition is recurring and pre-farrowing infection is suspected, treatment with trimethoprim:sulphonamide at 15 mg/kg given in the feed from day 112 of gestation to day 1 post-partum may eliminate early lesions and prevent the development of clinical disease, as may feed medication with other agents. Animals which have had severe or repeated bouts of mastitis should be culled. Affected sows should only be retained if they have sufficient functioning teats.