Studies on the Control and Pathophysiology of Bovine Nematodiases

Presented in this thesis are data from two parasitological studies on bovine parasitic gastroenteric and respiratory tract infections. In the first of these the control and epidemiology of naturally acquired infections of Ostertagia ostertagi, Cooperia oncophora, Nematodirus battus and Dictyocaulus viviparus in treated and untreated calves were studied. Treatment was by an experimental pour-on formulation of the relatively new anthelmintic Ivermectin. In the second the pathophysiological effects of an experimental daily trickle infection of O. ostertagi given to calves treated with a morantel tartrate sustained release device (MSRB) were compared with those of infected and clean control animals. In Chapter 1 the General Introduction deals with the epidemiology, treatment and control of bovine helminthiasis in the United Kingdom and this is followed by the general Materials and Methods in Chapter 2. Chapter 3, which begins with a revue of the recently developed anthelmintic Ivermectin, deals with the treatment and control of naturally acquired infections with gastrointestinal and respiratory tract nematode parasites. It is clear from the data presented that topically applied ivermectin can be successfully used to control bovine gastrointestinal parasites and that it is also extremely effective against the lungworm Dictyocaulus viviparus. Increasingly, it would appear that Nematodirus battus, or at least the strain of this species on pasture at the Glasgow University Veterinary Hospital, is adapting to cattle and can now cause clinical disease in this host. Radioisotopic methodology was a main feature of the second study, described in Chapter 4, which also highlights some of the problems associated with experimental infections designed to simulate a natural uptake of infective larvae under field conditions. While the daily infection dose level of 2,000 O. ostertagi L3/calf/day was insufficient to cause clinical disease it was nevertheless enough to alter the physiological parameters under study which revealed some of the adverse effects of a subclinical infection of Ostertagia species. Although it was shown that the activity of the MSRB was probably greatest against the adult rather than the larval stages of the parasite, it remains to be determined at which parasitic stage the anthelmintic action of this device primarily occurs. Finally the data obtained from both experiments is discussed in Chapter 5