Untersuchungen über die Regulierung des Wasserhaushaltes im Ziegenpansen

The fate of water in the rumen

1. The 51Cr complex of ethylenediamine tetra-acetic acid was used as a soluble marker substance in sheep fed restricted amounts (700 g daily) of roughage diets. It was injected into the rumen at various stages of the feeding cycle and rumen volumes and flow rates were calculated.

2. The average resting rumen volume for sixteen sheep (average body-weight 39 kg) was 3.9 l.; the average resting dilution rate was 0.077 h-1 so that the net inflow rate averaged 0.29 l./h; the average rate of absorption of water from the resting rumen into the blood was 0.05 l./h.

3. There were marked differences in all these values, both within sheep on different days (coefficient of variation nearly 20%) and between sheep (coefficient of variation more than 25%). The resting salivary inflow rate was also found to fluctuate considerably.

4. During feeding, the salivary inflow rate increased; there was usually both an expansion of rumen volume and an increased rate of outflow. There was no evidence of diffusion of water from the blood into the rumen.

5. Following eating, return to resting conditions was slow.

6. When the sheep drank, there was an expansion of the rumen volume and usually an increased outflow rate. The rate of absorption of water from the rumen increased slightly, but only for a short time. Occasionally after drinking it was found that rumen marker concentrations were slightly higher than expected probably because a small part of the imbibed water bypassed the rumen down the reticular groove into the omasum.

7. Most of the water drunk in a day was consumed in a few minutes. Compared with this rapid rate of drinking, the rate of absorption of water from the rumen was always a very slow process; this finding is in disagreement with recent views expressed in the literature. However, when considered over the whole day, the amount of water absorbed from the rumen may have been approximately equal to the amount of water drunk.

8. During periods of both feeding and drinking, the mean outflow rate was about 0.7 l./h in several series of experiments.

9. When sheep were held without food or water past their normal time for eating and drinking, the net inflow rate into the rumen soon started to decrease, but there was no immediate effect on rumen volume.

10. The present work reveals the potential usefulness of the soluble marker technique in defining the changing patterns of fluid movement in the rumen throughout the day.

Adrenoceptor heterogeneity in the ruminal epithelium of sheep

The pre-gastric rumen of sheep plays a crucial role in the fermentation of nutrients and in the absorption of nutrients and minerals. Adrenaline has been shown previously to increase ruminal absorption of glucose and water. The present study was intended to elucidate whether ruminal ion transport is also altered by adrenaline. In Ussing chambers, changes of I(sc) were recorded in isolated ovine ruminal epithelia after the serosal additions of adrenoceptor agonists or antagonists. I(sc) increased after the addition of adrenaline (10(-4) M) or clonidine (alpha2-agonist, 10(-4) M), but decreased after the addition of isoproterenol (beta-agonist, 10(-4) M) or terbutaline (beta2-agonist, 10(-5) M). The effect of adrenaline on I(sc) was augmented by the adrenoceptor antagonists prazosin (alpha(1), 10(-4) M) and bupranolol (beta, 10(-6) M), but inversed by yohimbine (alpha(2), 10(-5) M). Adrenaline induced an increase in Na+ net flux across the epithelium that was larger than the increase in equivalent current flow. It is concluded that adrenaline differentially regulates ion transport across the ruminal epithelium via alpha1-, alpha2-, and beta2-receptors. The main effect is a stimulation of electroneutral and electrogenic Na+ absorption. This stimulated Na+ absorption might be causative of increased water absorption from the rumen as described previously.

Changes in intraruminal function of sheep when drinking saline water

1. A study was made of the changes in electrolyte concentrations and ruminal function which resulted from the provision of 1.3% sodium chloride solutions instead of fresh water to sheep consuming roughage rations in chaffed and in ground pelleted forms.

2. Significantly higher osmotic pressures were observed in the rumen fluid of the sheep drinking saline water, the change being especially marked when the ration was ground and pelleted.

3. Of the individual electrolytes measured, chloride showed a larger rise in concentration than did sodium plus potassium and it appeared that the sodium and chloride ions in the ingested saline water were differentially removed from the rumen.

4. Provision of 1.3% NaCl solution in place of fresh water resulted in greater voluntary intakes of fluid and consequently in greater flows of fluid through the rumen.

5. Based upon measurements of deoxyribonucleic acid and polysaccharide, there appeared to be a tendency for the total microbial populations in the rumens of sheep drinking 1.3% NaCl solution to be smaller than for the sheep drinking fresh water.

6. The total metabolic activity of the rumen flora, measured calorimetrically, was not appreciably changed when saline water was drunk and the chaffed ration eaten, but was significantly reduced when the ration was ground and pelleted.

7. Adaptation of the rumen microflora to high concentrations of NaCl was demonstrated in animals accustomed to drinking 1.3% NaCl solution.