Performance of pigs with mixed nematode infections before and after ivermectin treatment.

Ninety crossbred parasitized pigs were used in two controlled experiments to compare performance before and after ivermectin treatment. Four groups of 15 pigs were sequentially infected with 2000 Ascaris suum, 10,000 Oesophagostomum spp. and 10,000 Strongyloides ransomi beginning at average pig weights of either 38 kg (Experiment I) or 14 kg (Experiment II). Two infected groups of pigs were treated with ivermectin on Day 34 (Experiment I) or 37 (Experiment II) of the experiments and all pigs were fed to slaughter weights of approximately 100 kg. Average daily gain (ADG) of heavier ivermectin-treated pigs was greater than that of infected non-treated pigs (P less than 0.03) and feed conversion was numerically greater by 5% (P greater than 0.10). ADG was not different between lighter treated or non-treated pigs, but feed conversion was numerically 4% greater in ivermectin-treated compared to non-treated pigs (P greater than 0.10). No differences existed in carcass dressing percentage among the three groups of heavier pigs, but among the lighter groups ivermectin-treated pigs had a higher dressing percentage (P less than 0.03) than infected non-treated or control pigs. Results of the calculation of production costs based on combined data from the two experiments for the post-treatment period, including feed, drug and maintenance costs, indicate that the production cost for ivermectin-treated pigs was $1.53 per pig less than that for infected non-treated pigs when the cost for each group to attain control pig weights is compared with the actual cost for control pigs.

Effect of fenbendazole and pyrantel tartrate on the induction of protective immunity in pigs naturally or experimentally infected with Ascaris suum.

An experiment was conducted with 96 weanling pigs (avg initial wt 18.5 kg) divided into six treatment with two replicates of eight pigs each. Pigs in Treatments 1, 2 and 3 were penned in outside pens with dirt lots that previously were contaminated with A. suum ova to induce a natural ascaris infection. Pigs in Treatments 4, 5 and 6 were penned in an open-front building with solid concrete floors and were experimentally infected with 2,000 embryonated A. suum. ova on d 1, 15 and 29 of the experiment. Pigs in Treatments 1 and 4 were medicated with fenbendazole (FBZ, 3 mg/[kg BW.d]) for three consecutive days during three consecutive time periods. Pigs in Treatments 2 and 5 were medicated with pyrantel tartrate (PT, 106 mg/kg feed) for 28 d. Pigs in Treatments 3 and 6 served as infected, unmedicated controls. All pigs were challenged with 100 A. suum eggs 7 d after termination of the final FBZ treatment. All pigs were killed 66 d after challenge and worms were recovered. Fenbendazole treatment resulted in greater (P less than .07) average daily gain than PT treatment in pigs penned outside. Among inside pigs, FBZ treatment resulted in better (P less than .02) feed utilization than in controls. The FBZ and PT treatments reduced (P less than .03) the total number of A. suum, the length and weight of female ascarids and the length of male ascarids compared with controls. A natural continual infection with A. suum was less effective than experimental infection in inducing protective immunity in pigs.