External parasites
Ticks and lice are external parasites of cattle. The tick (Haemaphysalis longicornis) can infest cattle, sheep, goats, dogs, horses, deer, and other mammals including humans, and many species of bird. Adult ticks can cause deaths of cattle, sheep and deer from blood loss. They can be controlled using showers, sprays and pour-on treatments.
A big tick
The female cattle tick is a dark-brown, eight-legged insect which inserts her mouthpiece through the skin of an animal or human to drink its blood. The tick will balloon from just 2 millimetres wide and 3 millimetres long to over 10 times that size.
Internal parasites
Gastrointestinal worms are parasites that live in a cow’s abomasum (fourth stomach) and intestines. Large numbers of them can reduce appetite, skeleton growth and the metabolism of protein and minerals – especially in young animals.
Worms lay their eggs inside the cow, and the eggs are passed out in dung onto the pasture. If the pasture is moist, larvae hatch and are eaten by grazing animals. An infected calf may develop diarrhoea and fail to grow and develop. Beef calves can be treated with an anthelmintic drench at weaning. Dairy calves are treated in spring or early summer, including for lungworm, which causes coughing.
Gastrointestinal worms are difficult to control if they become resistant to drenches. Farmers can avoid the problems associated with resistance if they understand how the various drenches work, and use strategies to minimise their animals’ intake of larvae.
Abortions
Several organisms can cause abortions in cattle, the most common being Neosporum caninum, a protozoan parasite. Less frequent causes are bovine viral disease and fungi such as Mortierella wolfii, Aspergillus and bacteria such as Salmonella Brandenburg and Leptospirosis. Eating the leaves of macrocarpa (Cupressus macrocarpa) and radiata pine (Pinus radiata) trees can also cause abortions.
Venereal disease
Campylobacter fetus (subspecies venerealis) causes early foetal loss, but is rare in New Zealand cattle, probably due to the widespread use of artificial insemination. Trichomonasis is also rare, but has been diagnosed more recently in beef cattle.
Mastitis
Mastitis (inflammation of the mammary glands and reduction in milk) is caused by a bacterial infection. The problem is very widespread and costly to the dairy industry. The main strain of infective bacteria has changed with time – in the 1940s it was Streptococcus agalactiae, by the mid-1960s it was Staphylococcus aureus, and since the mid-1990s Streptococcus uberis and coagulase-negative staphylococci have been the most common bacteria. Mastitis is treated with antibiotics, and can be prevented by hygienic milking, dipping or spraying teats with a mild disinfectant, and injecting long-acting antibiotics into the mammary gland at the end of lactation.
Nervous diseases
A number of diseases produce nervousness in cattle: listeriosis, haemophilosis, tetanus, malignant catarrhal fever, polioencephalomalacia, ryegrass staggers, lead poisoning, brain abscess, neoplasia and metabolic diseases.
Facial eczema
In cows, facial eczema appears as sunburn, especially on lightly pigmented areas such as the udder and teats. This is caused by liver damage after eating the toxin sporidesmin, produced by the fungus Pithomyces chartarum, which grows on pasture in late summer and autumn in the North Island and occasionally the top third of the South Island. Spores in pasture and faeces can be counted to assess the risk of disease.
Fungal diseases
Fescue toxicosis, fescue foot, fat necrosis and heat stress have all been associated with cattle grazing tall fescue grass infected by the fungal endophyte Neotyphodium coenophialum.
Other fungus-related diseases are Paspalum staggers and Claviceps (ergot) toxicosis.
Lameness
Lameness in dairy cattle affects milk production, fertility and animal welfare. Lameness, including bruising or abscesses on the sole of the hoof, may be caused by poor-quality raceways, an impatient stockperson bringing in cattle for milking, long walking distances to and from the shed, continuously wet underfoot conditions, and nutritional factors.