DISORDERS OF THE HEART AND CIRCULATION

As with respiratory diseases, many conditions of the heart and general circulation have been discussed already, for example:

• degeneration of the heart muscle in white muscle disease (Chapter 3)

• pericarditis, an infection of the heart sac caused by a wire (page 400)

• pulmonary haemorrhage, redwater and tick fever, described in the previous section.

This section describes two other conditions.

Endocarditis

The word endocarditis means inflammation of the inside of the heart and is normally used to describe infection of the heart valves. Plate 13.21 shows a typical example. The infection could have originated from any site in the body, for example a foot infection, mastitis or liver abscess, and travelling through the bloodstream it is by chance that it localises on the heart valve. If small abscesses have also developed in the liver, lungs and kidneys, the animal is said to have pyaemia. Pyaemia can only be diagnosed at post-mortem and may be a cause of carcase rejection at the abattoir. It could also be that the heart valve infection (i.e. endocarditis) was primary and pyaemia spread from there.

Plate 13.21 Endocarditis: large lumps of pus on the valves cause the heart to ‘leak', producing an animal with poor circulation.

Streptococcus uberis is becoming an increas­ingly common cause of endocarditis. Infection is seen particularly in first lactation heifers in high stress housing situations.

In the early stages of endocarditis the animal will be a bit lethargic, with a drop in milk yield and a mild temperature. High level antibiotic for seven to ten days at this stage can sometimes produce a cure. However, when the general circulation starts to fail (see next section) casualty slaughter is usually the best option.

Congestive Heart Failure

This occurs as a result of endocarditis, but can also be due to pericarditis (caused by a wire) or any other condition interfering with heart function. With endocarditis the valve fails to close properly and when the heart contracts to pump blood into the lungs, some of the blood is pushed back into the circulation again. This results in a swelling of blood vessels, particularly seen in the jugular vein in the neck (Plate 13.22) and an accumulation of fluid (dropsy) under the jaw (bottle jaw) and ster­num. The Limousin steer in Plate 13.23 was so badly affected that the whole of his lower body, from brisket to belly, and all four legs were swollen. At post-mortem he was found to have pericarditis.