Short-term effects of in-feed supplementation of tetracyclines for disease control on feed intake pattern and growth in weaned pigs

Abstract

Chlortetracycline (CTC) and oxytetracycline (OTC) are often administered in feed to pigs at extra-label doses to increase the efficacy of disease control strategies, but the bitterness of these antibiotics may significantly depress the voluntary feed intake of pigs at risk, compromising growth and the efficacy of the therapeutic regimen. We examined individual feed intake patterns and growth of 5-week-old pigs that received either drug-free feed ( n=36 pigs) or feed medicated with CTC or OTC at 12-h intervals for a period of 5 days. Each tested drug was mixed in feed at concentrations of 550, 1100, 1650 and 2200 mg/kg ( n≥8 pigs/dose/drug). Neither drug nor dose significantly affected the rate of feed intake (excluding interruptions), duration of meal, and the likelihood of leaving feed uneaten at the end of at least one meal. Average daily gain and feed conversion ratio (FCR) showed similar mean values across treatment groups, but variance of FCR varied significantly: CTC<OTC<drug free. Meal duration and feeding rate, and the likelihood of leaving feed uneaten were significantly influenced by the size of pigs, the occurrence of infection or spontaneous feeding interruptions during the meal. Feeding rate increased with experimental days. Results show that CTC and OTC are not feed deterrents in weaned pigs in the range of therapeutic doses currently used, but other sources of variation in feed intake indicate that drug input could vary among pigs.