ANIMAL DISEASES AND VETERINARY SERVICES
The clostridial infections are a group of diseases, widespread among sheep and fairly common among cattle, which even today cause heavy losses, although cheap, and efficient vaccines are readily available. Clostridial organisms can form spores and remain dormant in the soil for a long time. Blackleg in cattle or blood poisoning in sheep caused by Clostridium Feseri (chauvoei) often follows docking, shearing, dipping, vaccination, assisted lambing, or any other procedure liable to cause trauma. Enterotoxaemia or pulpy kidney, due to infection with C. perfringens (welchii type D), is an important disease of sheep. It is common in forward single lambs on lush pasture or crops, possible associates with heavy infestations of the tapeworm Moniezia expansa. Wound infection with C. septicum is the common cause of navel ill in lambs; infection can also follow, for example, shear cuts, docking wounds, and dehorning. Black disease in sheep is confined to Hawke's Bay and Gisborne, where it is associated with infestations of the liver fluke Fasciola hepatica. The casual organism C. novyi (oedemations) multiples in areas of liver necrosis caused by the migration of immature flukes. Tetanus (C. tetani) may occur in lambs after docking or castration. Though widespread, it is confined to small areas or to individual farms.
Facial eczema a seasonal disease of sheep and cattle, becomes serious whenever the weather favours the growth of the causal fungas Pithomyces chartarum. Stock eating the dead herbage carrying the spores of this fungus suffer severe liver damage, with consequent photosensitivity and damage to parts of the body not protected by wool or hair. The disease is confined to the North Isoand and small areas of the extreme north of the South Island. It has been described in Victoria, Australia.
Important bacterial diseases of cattle are tuberculosis, Johne's disease, brucellosis, mastitis, and leptospirosis. A national scheme for eradicating bovine tuberculosis has been functioning for some years. It began with cattle used for town milk supply and is being extended to all dairy cattle. The tuberculin test and slaughter method are used in areas where compulsory testing is declared. Before eradication began it was estimated that 10 per cent of dairy cattle in the North Island and 2 per cent in the South Island (though very few beef cattle) were affected. The incidence of the disease has been greatly reduced and within five years will probably be negligible.
Johne's disease is of local importance in, especially, Taranaki and Waikato. In confirmed cases the beasts are slaughtered and compensation paid. Vaccination of calves in the first few days of life has proved an effective control and will probably be used extensively when tuberculosis has been eradicated. Brucellosis is well controlled by vaccinating calves and is part of the routine management of over 80 per cent of dairy farmers and an increasing proportion of beef farmers. When a national vaccinated herd is built up it will be possible to eradicate the disease by testing and subsequent slaughter of the animals which react to the test. Antibiotics have reduced the importance of the various forms of mastitis which for so long severely hindered production in many dairy herds. But the resistant types, particularly those caused by staphylococci, remain and cause serious losses in individual herds. Losses due to leptospirosis are uncommon in adult cattle, but many are carriers; and redwater in calves causes marked seasonal losses on many properties.
The main epidemic viral diseases of cattle do not appear in New Zealand, but malignant catarrhal fever, infectious rhinotracheitis, and cow pox are common. Though the acute form of malignant catarrh (a notifiable disease) is uncommon, a mild infectious nasal catarrh (characterised by marked nasal irritation) is widespread. Its incidence within herds varies from 10 to 100 per cent. This disease can greatly lower milk yield. Cow pox is not caused by the vaccinia virus and is a comparatively mild condition of the udder and teats, with a spontaneous recovery in one to three weeks.