The Influence of Feeding and Oral Rehydration on the Bioavailability of Oxytetracycline in Calves

Abstract

The influence of feeding on the bioavailability of oxytetracycline was studied in preruminant calves. Oxytetracycline was given in water as a drench to fasting calves or was mixed in the milk replacer. Compared to water the bioavailability was significantly reduced (53.5%) when oxytetracycline was mixed in the milk re-placer. A further reduction, 83.3 %, occurred when the calves were treated one hour post milk feeding. Also concentrate was found to reduce the bioavailability. Very high serum levels were recorded when the drug was given in an oral rehydration solution, pH 4.9, containing glycine. The values obtained when an alkaline (pH 8.3) solution without glycine was used did not differ from the levels recorded when oxytetracycline was given in water. It was suggested that the use of oxytetra-cyclines in feeds may be questioned because of their well-known complex forming ability.

Sammanfattning

Effekten av utfodring på tillgängligheten av oxitetracyklin studerades hos kalv. Oxitetracyklin gavs i vatten eller blandades i mjölknäringen till fastade kalvar. Jämfört med vatten reducerades tillgängligheten signifikant (53,5 %) när oxitetracyklin blandades i mjölknäringen. Tillgängligheten reducerades ytterligare, 83,3 %, när kalvarna behandlades en timme efter utfodring. Kraftfoder visades också reducera tillgängligheten påtagligt. Mycket höga serumkoncentrationer uppnåddes när oxitetracyklin gavs i en oral rehydreringslösning, pH 4,9, innehållande glycin. De värden som uppnåddes med en alkalisk rehydreringslösning utan glycin, pH 8,3, var inte signifikant skilda från de värden som erhölls med oxitetracyklin i vatten. På grund av tetracyklinernas komplexbildande förmåga kan inblandning i foder under vissa förhållanden ifrågasättas.