Effects of weaning pigs to different diets have been investigated in terms of the changes in the small intestinal morphology, and in the absorption of short-chain fatty acids (SCFA) and sodium from the large intestine. One piglet from each of six litters containing nine pigs was sampled on the day of weaning; the other eight piglets were divided into four equal groups and fed different diets as follows: unweaned, weanling diet, or sow's milk at high or low level. Four and seven days after weaning, measurements of the intestinal tissue and contents were made; the plasma concentrations of SCFA, aldosterone and sodium were also measured. The villous height in the small intestine was highest in the unweaned group and greater in the high milk group than in either the weanling diet or low milk group (P < 0.001). Apparently, villous atrophy was due more to the level of feed intake than to the composition of the diet. The concentrations of SCFA in the large intestine and portal blood were highest in the weanling diet group and lowest in the low milk group. The low milk group tended to have higher blood concentrations of aldosterone (P = 0.15), which may have compensated for the low concentrations of SCFA in maintaining a higher percentage of dry matter in the intestine. Pigs fed weanling diet may use the energy from the SCFA to maintain a body weight comparable to that of pigs fed milk at a low level.

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The pharmacokinetics of oxytetracycline (OTC) in three weaned piglets was studied following three routes of administration: intravenously, orally as drench, both at a dose of 20 mg/kg, and orally as medicated (400 ppm OTC) pelleted feed administered during 3 consecutive days. Analysis of the intravenous data according to the three compartment pharmacokinetic model revealed that OTC was well distributed in the body (Vf: 1.62 l/kg), had an overall body clearance of 0.25 litre/kg/h, and the elimination half-lives were in the range between 11.6 and 17.2 hrs. The mean OTC binding to plasma proteins was 75.5 +/- 4%. Following the drench route of administration the maximum plasma OTC concentration was achieved between 1 and 5 h post application and ranged between 1.18 and 1.41 micrograms/ml. The mean maximum plasma OTC concentration during medicated feed administration was 0.20 +/- 0.06 microgram/ml, which was achieved approximately 30 hours after the onset of the administration. A steady state OTC plasma level (approximately 0.2 microgram/ml) was maintained till the end of the trial. Within 48 hours after cessation of medicated feed administration the plasma OTC levels were beneath 0.06 microgram/ml. The mean OTC bioavailabilities of the oral routes were low: after the drench route of administration 9.0 +/- 0.67%, and after medicated pelleted feed administration 3.69 +/- 0.8%. The mean OTC renal clearances of each piglet ranged between 10.1 and 13.9 ml/min/kg (based on free OTC plasma fractions). The renal OTC clearance values were urine flow dependent in all piglets and significantly correlated with the renal creatinine clearance (P less than 0.005), being 3-5 times higher than the latter. It is concluded that in piglets OTC is excreted mainly by glomerular filtration and partly by tubular secretion. The potential clinical efficacy of 400 ppm OTC as medicated feed with respect to treatment, e.g. atrophic rhinitis, is discussed.

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Pharmacokinetics and tissue distribution experiments were conducted in pigs to which sulphadimidine (SDM) was administered intravenously, orally, and intramuscularly at a dosage of 20 mg SDM/kg. SDM was acetylated extensively, but neither hydroxy metabolites nor their derivatives could be detected in plasma, edible tissues or urine. Following i.v. and two oral routes of administration, the N4-acetylsulphadimidine (N4-SDM) concentration-time curve runs parallel to that of SDM. The percentage of N4-SDM in plasma was in the range between 7 and 13.5% of the total sulphonamide concentration. The bioavailability of SDM administered in a drench was 88.9 +/- 5.4% and administered mixed with pelleted feed for 3 consecutive days it was 48.0 +/- 11.5%. The renal clearance of unbound SDM, which was urine flow related, was 1/7 of that of creatinine, indicating reabsorption of the parent drug. The unbound N4-SDM was eliminated three times faster than creatinine, indicating that tubular secretion was the predominant mechanism of excretion. After i.v. administration, 51.9% of the administered dose was recovered in urine within 72 h p.i., one quarter of which as SDM and three quarters as N4-SDM. Tissue distribution data obtained at 26, 74, 168, and 218 h after i.m. injection revealed that the highest SDM concentration was found in plasma. The SDM concentration in muscle, liver, and kidney ranged from one third to one fifth of that in plasma. The N4-SDM formed a minor part of the sulphonamide content in edible tissues, in which the SDM as well as the N4-SDM concentration parallelled the plasma concentrations. Negative results obtained with a semi-quantitative bioassay method, based on monitoring of urine or plasma, revealed that the SDM concentration levels in edible tissues were in that case below 0.1 mu/g tissue.