Digestion and utilization of 35S-labelled bacteria placed in the caecum of the sheep

Abstract

Suspensions of ruminal bacteria made radioactive by growth in the presence of 3% were injected into the caecum of sheep. The sheep were each given a daily ration of 540 g roughage and 235 g concentrates in 12 equal portions at 2-hourly intervals. Faeces and urine were collected, and peripheral blood was sampled at frequent intervals for up to 14 days after the caecal injection of radioactive bacteria. More than 99% of the 35S in the bacterial suspensions was in the organic sulphur fraction. The percentages of administered 35S appearing in faeces and in urine (mean ? SEM) were respectively 69 ? 1 .8 and 21 ? 1.1; the corresponding percentages of this excreted 35S as inorganic sulphur were 16 ? 0.7 and 91 ? 2.3. The apparent digestibility of the 35S -labelled bacteria was 31%, and the adjusted digestibility was about 42%. The appearance of organic 35S in plasma immediately after the caecal injection of radioactive bacteria indicates that some organic 35S was absorbed from the hindgut. Of the 10 ? 2.3% of the injected 35S dose retained by sheep at the end of the sampling period, about 3% was present in the fleece.