Internal parasites of cattle normally affect animals under two years and usually less than one year old. Important nematodes are Osteryagia and Trichostrongylus axei; Haemonchus contortus, Cooperia spp., and Bosicola radiatum are also found, but are seldom significant. Pulmonary helminthiasis in young stock is commonly caused by Dictyocaulus viviparus; infestation with the liver fluke, Fasciola hepatica, is found in Hawke's Bay, Gisborne, Central Otago, and other smaller areas, the intermediate hosts being the freshwater snails, Simlimnea tomentosa and Limnea alfredi. Infestation with the cattle tick, Haemaphysalis bispinosa, is sometimes heavy in scrub and rough grazing in the north of the North Island, but there are no tick-borne diseases. Coccidiosis in calves and trichomoniasis in adult cattle are the only protozoal diseases worth mentioning. Infection with coccidia of the Eimeria species causes many losses in dairy calves between three weeks and six months; Trichomonas foetus, although probably widespread, rarely causes abortion and infertility.

Bacterial diseases of sheep (other than clostridial) are widespread. Foot rot, caused by Fusiformis nodosus in association with Spirochaeta penortha, is a main cause of loss, especially in high-rainfall country in the west and north. Outbreaks are common in wet weather and up to a third of all sheep in a flock may be affected. Less common in distribution and sporadic in its occurrence, foot abscess, due to infection with Spherophorus necrophorus, also causes much severe lameness, though it is less widespread, and occurs only spasmodically. Infection with Brucella ovis associated with epididymitis in rams and abortions late in pregnancy in ewes was formerly common. Preventive vaccination has reduced the importance and incidence of this disease. Caseous lymphadenitis is common in the South Island; less common in the North Island. Although the causal organism, Corynebacterium pseudotuberculosis, seldom affects the general health of the animal, the typical lesions in the lymph nodes prevent the export of diseased carcasses. When hygiene at shearing is neglected as many as 30 per cent of the older sheep in a flock may catch the disease. Contagious ophthalmia (pinkeye), common in flocks in late summer, is due to the organisms Colesiota conjunctivae. Recovery is normally spontaneous after a few weeks, but the complaint may affect half of the animals on a property and interfere with normal husbandry. When flocks are held in close confinement for a day or more there may be outbreaks of salmonellosis. The disease is uncommon, but is found throughout New Zealand. Up to 25 per cent of a flock may be affected, usually fatally. Most cases are associated with Salmonella typhi-murium, but occasionally other types of salmonella are involved. Abortion in ewes caused by infection with Vibrio foetus is common all over the country and may reach a very high incidence within flocks infected for the first time. It shows itself typically as an abortion storm early in the lambing season, which grows less as the main lambing commences. Recovery is normal and a solid immunity results. On some farms in South Canterbury Johne's disease is regularly diagnosed in older sheep and up to 5 per cent a year became clinical cases. Experimental vaccination has given promising results. The disease has not been reported elsewhere. Fleece abnormalities associated with bacterial invasion are widespread, particularly in prolonged wet or humid seasons. Discolouration of wool fleece rot and mycotic dermatitis are regularly diagnosed and lead to the rejection or downgrading of fleece wools.

The virus disease contagious ecthyma or scabby mouth is common in summer and may spread to every animal in a flock. Sheep rapidly lose condition because of difficulty in feeding; thus the disease is especially serious in fattening lambs. Vaccination is widely used on those infected farms which are known.

Internal and external parasites still cause large losses by death and emaciation and entail immense expenditure in prophylaxis and treatment. The primary parasite, Haemonchus contortus, is ubiquitous and causes severe outbreaks of disease in warm wet weather. Common nematodes secondary to poor nutrition are Ostertagia circumcincta, Trichostrongylus axei in the abomasum, and other Trichostrongylus species in the small intestine. Of less general importance, but capable of causing severe losses within flocks, are parasites of the Cooperia, Namatodirus, Strongyoides, Bunnostomum, Trichuris, Chabertia, and Oesophagostomum species. Heavy infestations of tapeworms of the Monezia species are found in lambs and may predispose to enterotoxaemia. Lungworm, Dictyocaulus filaria, is occasionally responsible for severe losses, but is not common.

External parasites are widespread. Annual dipping is required by law. It is an offence to drive lousy sheep or to offer them for sale. Parasites include the body louse, Damalinia ovis, the lice, Linognathus pedalis and L. ovillus, the ked, Melophagus ovinus, and (in the North Island) the tick, Haemophysalis bispinosa. Fly strike is common in summer, the primary blowflies being Lucilia sericata and Calliphora stygia. Scrotal and leg mange from Chorioptes ovis is widespread and the itch mite Psorogates ovis has been confirmed in a few fine-wool flocks in the South Island. The only important protozoal disease of sheep is toxoplasmosis, due to Toxoplasma gondii. This is common in pregnant ewes and is responsible for perinatal deaths of the lambs of up to a third of the ewes in a flock.