Natural infection with Dictyocaulus arnfieldi in pony and donkey foals

From June to October 1978 four pony mares and foals and two donkey mares and foals grazed a paddock contaminated with Dictyocaulus arnfieldi larvae. No signs of respiratory disease were seen in the foals but within 11 weeks of exposure to the paddock all six developed patent lungworm infections. In October 1978 one donkey and two pony foals were killed. At post mortem examination parasites in various stages of development and measuring up to 8 cm in length were found in the lungs. At this time the three surviving foals were stabled for the remainder of the experiment. Two of these ceased passing D arnfieldi larvae during the winter months but in one pony foal patency persisted until the study ended in August 1979. Patent lungworm infections were not seen in the pony mares, although two started to cough four to six weeks after starting to graze the infected paddock. One of the affected mares was killed in October 1978 when seven small (less than 7 mm) D arnfieldi were recovered. The other continued to cough until the end of the study over a year later.