Carbadox and Lincomycin in the Treatment and Carrier State Control of Swine Dysentery
Authors: Rainier R. H. , Harris D. L. , Glock R. D. , Kinyon Joann Μ. , Brauer Μ. A. 
Published: February 2025

SUMMARY
In 2 experiments, using conventionally raised pigs, clinical and microbiologic effects of carbadox and lincomycin against Treponema hyodysenteriae and swine dysentery (sd) were comparatively evaluated.
The 1st experiment lasted 125 days and involved 4 separately isolated groups of 12 pigs each, of which 3 groups were infected with T hyodysenteriae inoculum by gavage. Treatments included: (T-1) noninfected, nonmedicated; (T-2) infected, nonmedicated; (T-3) infected, carbadox [55 mg/kg of feed (50 g of carbadox/US ton) for 29 days]; and (T-4) infected, lincomycin [110 mg/kg of feed (100 g of lincomycin/US ton) for 21 days followed by 44 mg/kg of feed (40 g of lincomycip/US ton) for 8 days]. Medication was administered in the feed beginning at disease onset; after drug withdrawal, pigs were fed nonmedicated feed. The T-1 pigs remained free of sd and were negative for T hyodysenteriae. Swine dysentery first occurred among infected pigs on day 3. During the initial 32 days, clinical signs of sd, shedding of T hyodysenteriae, and growth suppression persisted in the T-2 group and 5 pigs died; in T-3 and T-4 groups during the same period, clinical signs of sd and T hyodysenteriae shedding were negative by 7 days, initially asymptomatic pigs remained normal and 1 T-3 pig and 2 T-4 pigs died. After drug withdrawal, clinical sd and T hyodysenteriae shedding did not occur in the T-3 group, but did occur among 5 of 10 pigs in T-4, 2 of which died. Body weight gains of only T-1 and T-3 pigs were significantly (P < 0.01) increased over weight gains of T-2 controls.
In the 2nd experiment, the sd carrier-state status was evaluated after withdrawal of previously administered treatments. Four groups of 6 principal pigs each, 3 groups of which were infected with T hyodysenteriae inoculum by gavage, were previously administered the following treatments beginning at disease onset: T-5 (noninfected, nonmedicated), T-6 (infected, nonmedicated), T-7 (infected, carbadox [55 mg/kg of feed for 29 days]), and T-8 (infected, lincomycin [110 mg/kg of feed for 21 days, 44 mg/kg of feed for 8 days]).
After the 29-day treatments, all pigs were cleaned and disinfected externally and were transferred to 4 separated aseptic isolation rooms. Twenty-four T hyodysenteriae-negative and similarly cleaned sentinel pigs were equally placed in each of the 4 rooms of principal pigs and were co-mingled for 93 days. At the beginning of co-mingling, rectal cultures of all pigs, except 2 T-6 principals, were negative for T hyodysenteriae. Swine dysentery was not observed among T-5 principals and their sentinels or among T-7 principals and their sentinels and all rectal cultures remained negative for T hyodysenteriae. Clinical signs of sd appeared in 1 T-6 principal pig after 14 days and in 1 sentinel after 6 days of co-mingling, but each recovered. Beginning 12 days after the 1st co-mingling, sd was observed in 5 of 6 T-8 principals, of which 2 died, and in 5 of 6 sentinels, of which 4 died; T hyodysenteriae was recovered from pigs clinically affected, but not from the 2 pigs that remained asymptomatic.