HERD HEALTH
PIH-44
pork
industry
handbook
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • WEST LAFAYETTE, INDIANA
Internal Parasites
Authors
LeRoy G. Biehl, University of Illinois
R.F. Behlow, North Carolina State University
E. Batte, North Carolina State University
Reviewers
Ralph F. Hall, University of Tennessee
Gerald M. Sandidge, Marshall, Missouri
Even though excellent deworming programs are available, it is estimated that internal parasites cost the pork industry an astonishing 250 million dollars or $3.00 per pig produced annually. Forty-three million pounds of liver were condemned by USDA inspections from 90 million hogs slaughtered in 1980. Nearly all of these livers were condemned because of “white spots” which are tissue wound scars left from the migration of immature worms (larvae).

Worm infections reduce growth rate and feed efficiency directly by competition for food and damage from larval migration through various organs. In addition, the tissue injury enhances the deleterious effects of other disease-producing microorganisms such as Mycoplasma hyopneumoniae or Treponema hyodysen-teriae.

Some degree of worm infection occurs on most swine farms. Studies indicate that 80-90% of U.S. swine herds are infected with one or more species of worms. Efficacious swine dewormers are available and a magazine survey indicated that 74% of the producers deworm their hogs an average of 1.8 times during a production cycle. If such deworming practices really exist, it is difficult to ascertain why worm prevalence is so high in U.S. swine. To effectively lower the worm population in a swine herd, several management practices must be used. Proper selection of dewormers and proper timing of the deworming are important. Additional management tools include manure removal and good sanitation practices during the production cycle. A
knowledge of the life cycle and the tremendous reproductive capabilities of the various swine worms will aid one in understanding how best to break the life cycles of different parasites.

Characteristics of the Common Worms
Roundworms
The large roundworm (Ascaris suum) is the most common and largest worm that infects young swine. The roundworm (Fig. 1) may be 10-15 in. long and is often observed in feces or hanging from the rectum of a pig. The large roundworm normally lies in the anterior small intestine, but will occasionally migrate into the stomach. When this happens, the pig may vomit material containing the worms. The female adult roundworm can produce up to 1,000,000 eggs per day. Roundworm eggs are remarkably resistant to adverse climate conditions and disinfectants.

Worm eggs must embryonate before they become infective. Under optimal conditions of high humidity and warm temperature, eggs embryonate and become infective about 10-14 days after they are passed. Therefore, fresh manure is not infective and, if ingested by pigs, the eggs will pass on through undigested and unhatched. Cold exposure delays or completely halts embryonation.

Once the embryonated infective eggs are swallowed, they hatch and the larvae penetrate through the intes-
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U.S. Department of Agriculture cooperating. H. A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the Acts of May 8 and June 30, 1914. It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have equal opportunity and access to its programs and facilities without regard to race, color, sex, religion, national origin, age or handicap.