SHEEP LOSSES

Timaru Herald, Volume CXLI, Issue 20312, 10 January 1936, Page 4

SHEEP LOSSES

RAVAGES OF PARASITIC GASTRITIS PREVENTIVE MEASURES There have been considerable losses among sheep from internal parasites in some parts of the foothills of South Canterbury, where there have been frequent showers, and the feed is rank and moist. Up to and more than 10 per cent, of the lambs on some properties have died. Advice to farmers as to the best method of dealing with the trouble is given by members of the local Stock Department. It is advisable to liberally dose the lambs with a solution of bluestone, and to move them on to fresh pastures. Young sheep are more subject to attack, and the source of infection is by picking up the larvae from the grass. These larvae develop in the course of a few weeks into adult worms, and after the pairing of the sexes, the female lays eggs which are shed on the grass, and became a source of infection for other sheep.

The matter is most thoroughly and fully dealt with in an article by Mr E. L. Taylor, M.V.Sc., M.R.O.V.S. The writer states that parasitic gastritis is generally recognised as the most important disease of sheep throughout the world, and exercises a controlling influence over all sheep fanning practices. Its development in a mild form is so frequent an occurrence as to call for little or no comment by the sheep farmer, and the losses resulting from an unthrifty condition of the lambs, accompanied by occasional deaths in the less severe outbreaks, appear to be regarded rather as one of the several unfortunate circumstances incidental to sheep-farming than as the result of a specific disease which calls for special preventive measures. Great Care Necessary Unlike the microscopic parasites that cause many of the less prevalent diseases of sheep, the worms responsible for parasitic gastritis are present wherever sheep are kept, and the possibility of their developing to diseaseproducing members is a constant menace to all who farm on good land. This circumstance necessitates the greatest care in the management of sheep, and restricts the size of the flock to numbers greatly below what the land would otherwise carry. The most important step that has yet been taken towards the satisfactory control of this disease has been the discovery of the parasiticidal effect of copper sulphate or “bluestone” upon the “twisted wireworm.” Treatment with this drug is a most effective measure where infestation with the twisted wireworm is concerned, but it is still not so widely known as it ought to be that several different species of parasitic worms are responsible for this disease, and that copper sulphate only serves for the removal of the twisted wire worm, and the prevention or cure of parasitic gastritis caused by that species of worm, the several other species being untouched by the treatment.

Research workers at two or three different centres have recently observed, however, that a mixture of copper sulphate and nicotine sulphate has a certain action in expelling the minute stomach worms known as trichostrongylus, but none of the many drugs that have been tried appear

to have any effect upon the several other species, some of which are a frequent cause of severe disease.

Disease Studied Pending such time as a cheap, safe and efficient drug treatment is found, it is therefore, important to ensure that everything possible is done to prevent the occurrence of parasitic gastritis. In order to probe more deeply into the question of prevention, a study of the disease has been made from a new angle, and efforts have been made to discover the causes underlying the multiplication of the parasitic worms and the reasons (apart from mere presence of parasites) that lead to the development of outbreaks of the disease.

In explanation of this new line of work, a significant point, not generally recognised by farmers, should first be mentioned, namely, that the parasitic worms responsible for this disease occur wherever sheep are kept, but do not cause any apparent harm unless they are present in very large numbers. Further, they are incapable of any increase in numbers within the sheep, and every individual of the tens of thousands that may be present in a diseased sheep requires to be picked up from the pasture along with the herbage.

Margin of Safety It is clear, therefore, that disease is not merely a matter of the infection of susceptible sheep by the parasitic worms, but that it results from the operation of all those factors that lead to the ultimate collection of sufficient worms to cause disease. Inquiries on the site of actual outbreaks in the field, and controlled observations in the laboratory, suggest that the margin of saftey between a harmless infestation, and a disease-producing infestation is a wide one. Whereas the average number of parasites in healthy lambs is only a matter of hundreds, some 15,000 or 30,000 are necessary to induce disease. Any hindrance that can be put in the way of accumulation of excessive numbers of parasites in the stomachs of lambs, will, therefore, help to keep the infestation within the limits of safety.

Since overcrowding is so obviously of importance, it might be thought that parasitic gastritis is merely the outcome of a sufficient number of sheep per acre grazing the herbage for a sufficient length of time. Field observations show, however, that this is not so and that other factors also have a powerful influence, and there is reason to believe that slight alterations in management may make all the difference between the continuation of health, on the one hand, and a condition of unthriftiness, or even a disastrous outbreak of disease on the other. A thorough understanding of the several less obvious factors that contribute to the increase of parasitic worm will be of great value in directing intelligent management along the most advantageous lines. Results of Value The beginning that has recently been made in this line of investigation has already produced results of practical value for the prevention of the disease, and has provided satisfactory explanations for some of the perplexing questions concerning its development. The factors that operate for the increase of parasitic worms in sheep may conveniently be considered under three headings: (1) The productivity of the eggs of the parasite (i.e. the proportion of the parasitic eggs that reach the infective stage on the ground). (2) The transmissibility of the infective larvae (i.e. the proportion of

the infective larvae picked up by the sheep). (3) The susceptibility of the sheep (i.e. the proportion of infectious larvae reaching the sheep’s stomach that ultimately develop to maturity.) (To Be Continued.)