Pigs in Nurseries - The Merck Veterinary Manual

Pigs in Nurseries

By the time pigs are weaned, diseases that affected the locomotor system during the nursing phase most likely will have resolved spontaneously, responded to aggressive therapy, or resulted in death, or the pig may have been culled. Because pigs that survive episodes of polyarthritis generally remain lame, have ≥1 swollen “knotty” joints, and are in poor condition, they should be culled.

Infectious Arthritis or Polyarthritis:

Causes include Mycoplasma hyorhinis , Haemophilus parasuis , Streptococcus suis , or Erysipelothrix rhusiopathiae , which are found sporadically among groups of pigs or herds. As with many infectious diseases, management or environmental factors that stress the pig or depress the immune response can precipitate infectious arthritis. Moving and mixing pigs; overcrowding; cold, damp, or drafty environments; or changing rations are major stresses and can lead to the development of infectious arthritides. In addition, active infection due to porcine reproductive and respiratory syndrome virus ( Porcine Reproductive and Respiratory Syndrome: Introduction) often predisposes groups of nursery pigs to these infectious causes of polyarthritis.

The clinical signs seen in infections caused by M hyorhinis , S suis ( Streptococcus suis Infection), and H parasuis , (Glässer’s disease, Glässer’s Disease: Introduction) are similar, because these organisms cause polyarthritis and polyserositis. The upper respiratory tract of the sow is the source of the organism for the baby pig and, presumably, some older pigs are also carriers. Infection with M hyorhinis usually results in moderate morbidity and low mortality, but H parasuis and S suis can cause infection in 50-75% of pigs and mortality of up to 10%. Outbreaks of Glässer’s disease have been particularly severe in SPF herds. Fever is associated with both conditions but can be highest in Glässer’s disease (>107°F). A shifting-leg lameness occurs, and joints are warm and swollen. Pneumonia develops with all 3 conditions, and sometimes H parasuis and S suis cause neurologic signs. Susceptible, stressed, adult pigs can succumb to M hyorhinis with a higher fever and a more severe lameness than is seen in nursery pigs. Boars may develop scrotal edema and discomfort.

At necropsy, polyarthritis and polyserositis are seen with both mycoplasmal arthritis and Glässer’s disease, and pneumonia may have developed. In Glässer’s disease and S suis , there may also be a meningitis. However, whereas the exudative response is usually serous or serofibrinous with a mycoplasmal infection, typically it is fibrinous or fibrinopurulent with Glässer’s disease and S suis . Hence, M hyorhinis causes a mild synovitis with villous hypertrophy and hyperplasia; an excess of clear, yellow, or brown synovia; and a serofibrinous pericarditis, pleuritis, and peritonitis. H parasuis initiates a fibrinopurulent synovitis with periarticular edema and a fibrinopurulent meningitis and polyserositis with pseudomembranes. The articular surface is usually unaffected in either condition. Stunted pigs in the grower/finisher group that have chronic, severe, fibrinous, fibrinopurulent, or fibrous pleuritis, peritonitis, and arthritis could have been affected by either condition earlier in their lives and are best culled rather than kept as a source of infection for other pigs. They are unlikely to reach market weight.

Diagnosis is based on clinical signs, necropsy findings, and the isolation of the organism; however, if any treatment has been instituted, the chances of finding the organisms are reduced. Treatment for either disease must be aggressive and start soon after the onset of clinical signs. The effectiveness of treating M hyorhinis infections with tylosin (not labeled for this use), tetracycline, or lincomycin has been variable. Provided that the organism is susceptible to an antimicrobial compound, treatment of S suis and Glässer’s disease with penicillin, ampicillin, streptomycin, tetracyclines, ceftiofur, or sulfa drugs has been more successful. Penicillin is the only drug labeled for use against arthritis caused by S suis or Glässer’s disease. Appropriate changes in management to reduce stress, strict “all-in/all-out” housing, and control of porcine reproductive and respiratory syndrome help to minimize the impact of these diseases. Herds that maintain an SPF status may be free of both M hyorhinis and H parasuis , but if outbreaks of Glässer’s disease occur in these herds, morbidity and mortality are high and production is decreased. Vaccination with Haemophilus bacterin may alleviate the problem in SPF herds, and it is important to vaccinate SPF pigs that are to be shipped to conventional herds. Vaccination of sows against H parasuis reduces the prevalence of the problem in nursery pigs through passive immunity.

Erysipelas:

Although acute erysipelas can be seen in nursery pigs, it may be more typical of growing/finishing pigs (see below). If the acute form of the disease affects nursery pigs and is not treated appropriately, the subsequent progression of the disease to the chronic form is seen in the grower/finisher pigs anyway. (See also Swine Erysipelas.)

Vertebral Deformities:

Kyphosis or lordosis and cuneiform deformities of vertebrae have been seen in weaned pigs, but a cause has not been identified. “Humpy back” pigs are seen sporadically in some herds; the spine is curved in the vertical plane such that the lumbar vertebrae are higher than the thoracic vertebrae, and there is a “kink” between the 2 segments. However, grossly, there is not always evidence of incomplete or deformed vertebrae. The condition may have a genetic predisposition, but multiple fractured ribs found in the same pig increase suspicion of an underlying or aggravating, perhaps intermittent, nutritional deficiency, such as that which can cause rickets. Rickets is usually not seen clinically until the grower phase, but lesions must have begun to develop earlier.