Twenty-five species of Nematode have been found to be present in sheep in Manawatu district. The species of greatest economic importance were found to be in most cases of importance in other temperate climates.

In the cases of certain species, saturation of Manawatu district has not yet occurred, e.g., in the cases of Cooperia oncophora, C. punctata and Ostertagia ostertagi.

The countries of origin of the foundation stock have limited the number of species. Most of the importations have been made from Britain and Australia.

As few nematodes of the sheep require intermediate hosts, their entrance to a new country, New Zealand, has not been prevented to any extent on this ground. Muellerius capillaris has been able to survive on account of the abundance of its normal host, which has been introduced also.

The climate of Manawatu is such that the extremes of summer and winter are not severe enough to exert complete control on the various species. Infective stages are well able to survive these less favourable periods. The climate is sufficiently equable to enable out of door pasturing throughout the year, so that in the cases of most species of nematoda infection it is possible also throughout the year.

The farming systems in vogue involve almost solely the use of permanent pasture which is mostly of high carrying capacity. This enables concentration of stock and in conjunction with continuous grazing throughout the year, enables the excessive multiplication of the various species of nematodes.

The prominence placed on the fat lamb industry means that much attention is devoted to the raising of a population susceptible to worm infection.

A prevailing practice is to introduce culls from the surrounding hill districts for purposes of fattening, and sheep from the Hawke's Bay district in time of drought. There is consequently a continual introduction of parasites in these animals.

Cattle are the chief reservoir hosts of nematodes of sheep in Manawatu district. These occur in large numbers in the district and frequently dairying is combined with sheep farming, so that they become important sources of infection to sheep in respect to some species of worm, e.g., Cooperia oncophora, C. punctata and Ostertagia ostertagi.

It would seem that the tendency in the district is towards the increasing of the carrying capacity of pasture. This should result in the multiplication of parasites, particularly Nematodes, to a greater extent than has been the case.