Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 19 EFFECT OF RUMINAL NaCl LOADING ON WATER INTAKE, URINE OUTPUT AND RETICULAR MOTILITY IN SHEEP R. R. CARTERA and W. L. GROVUM B *Bayer Australia Ltd., P.O. Box 903, Pymble, N.S.W. 2073. BUniversity of Guelph, Dept of Biomedical Sci., Guelph, Ontario, Canada NlG2Wl. SUMMARY Water intake, urine output and reticular motility were monitored after injecting 50 g NaCl into the rumen of sheep. Water consumption and urine output were restored to pre-injection levels after 11.5-15 h. Reticular motility was unaffected by ruminal NaCl injection or by NaCl infusions into the reticulum. These results are discussed in relation to food intake and the tonicity of rumen fluid and plasma. Keywords: osmolality, salt, food intake, urine output, motility. INTRODUCTION Carter and Grovum (1990a) reported the results from experiments designed to ascertain whether the intake depressing effect of NaCl loading the rumen of sheep was mediated via the reticula-rumen, abomasum or the circulation. They concluded that the inhibition in food intake resulted from increased osmolality of fluid in the reticula-rumen which was sensed by the wall of the reticula-rumen. The intake inhibition was not mediated by hypertonicity of abomasal contents or blood. In these studies, rumen NaCl loading was imposed on successive days because preliminary experiments had shown that this allowed sufficient time for the salt to be cleared from the sheep. The authors also stated that preliminary experiments showed that NaCl loading did not affect the frequency or amplitude of reticular contractions. This paper describes those preliminary experiments. They were designed to determine the time required for water consumption and urine output to return to pre-ruminal NaCl loading levels. Reticular motility was recorded after ruminal NaCl loading or NaCl infusions into the reticulum as a depression in reticular-ruminal motility per se may have contributed to an inhibition in food intake. MATERIALS AND METHODS Sheep, housing and feed Cannulae were inserted in the rumen of 5 crossbred Suffolk wethers weighing 46.2 k 2.5 kg (mean + s-e.) 2 weeks prior to commencement of experiments. All sheep were treated for internal parasites with ivermectin before the start of the experiments (` Ivomec' MSDAGVET, Div. Merck , Frosst Canada Inc.). The sheep were held in metabolism crates in a temperature controlled room with 24 h lighting for the duration of the experiments. Fresh water was available at all times except for a period described in experiment 2. Ground and pelleted luceme (Medicago sativa) hay was available ad Zibitum except for short periods of deprivation described in experiments 1 and 2. The feed contained ww 908 dry matter, 165 crude protein, 44 fat, 79 ash, 323 acid detergent fiber, 14 calcium and 3 phosphorus. Experimental procedure Experiment 1. The effect on water consumption, urine output and reticular motility was studied in sheep after injecting 500 mL of a solution containing 0.1 g NaCVmL (i.e. 50 g NaCl) into the rumen compared with the same volume of normal saline (control). Five sheep were used in a cross-over type design such that on 1 day 3 sheep received the high salt load while the other 2 received normal saline. After a 1 day rest, the treatments were reversed. Motility measurements were made in 4 of the 5 sheep. Water consumption was measured by recording the decrease in volume of water contained in the drinkers attached to each metabolism crate. Urine output was measured by recording the volume of urine which drained into a bucket located under each metabolism crate. Reticular motility was recorded manometrically (Grovum 1981) using an air filled balloon tied to the end of a stiff polyethylene tube. The probe was held in the reticulum by securing it in a double holed stopper in the rumen cannula stem. The other hole held a tube directed into the ventral sac for injecting the warm NaCl solution (50 g made up to 500 mL with distilled water) or an equal volume of normal saline (control). Water consumption and urine output were recorded for 90 or 120 min prior to the injection of solutions. Reticular motility was recorded for 30 min prior to the injection of the solutions. The solutions were injected into the rumen between 0847 and 0930 hours. Food trays were removed from 406 Proc. Aust. Sot. Anim. Prod. Vol. 19 the sheep immediately prior to injecting solutions but were returned 45-58 min later after reticular motility had been recorded. Water consumption and urine output were recorded after the injection of solutions, initially at 30 min and later at 60 min intervals until pre-injection levels were restored. Food intake was similarly recorded during this period. Digesta was obtained from the rumen using a sampling probe positioned in the ventral sac and blood was obtained by jugular venipuncture. Rumen fluid and jugular blood samples were taken from the sheep just prior to and after the injection of the solutions and again 4 hours after feeding. Student' paired t-tests were used to analyse the difference in water s consumption and urine volumes between the pre-injection period (90 or 120 min) and the period when pre-injection values appeared to be restored (90 or 120 min also used). Reticular motility measurements for 30 min before and 30 min after solution injection were compared using Student' paired t-tests. s Experiment 2. The effect of infusing NaCl into the reticulum on reticular motility was investigated. Two vinyl tubes were taped to the probe used for measuring motility, 1 for infusing NaCl solutions, the other for sampling reticular digesta. The tip of the sampling tube was positioned about 4 cm beyond the tip of the infusion tube and on the opposite side of the probe. The tip of the infusion tube was covered with nylon and that of the sampling tube with mesh (Proxplast, 8 holes per cm, Goshen Labs., Goshen, N.Y., U.S.A.) forming a small bulb preventing particulate matter from occluding the tube. A second stiff polyethylene tube directed into the ventral sac was used for sampling rumen fluid. Fresh food and water were provided from 0800 to 0900 hours each day and then food was withheld for 5.5 h. Water was withdrawn at 1400 hours and returned at the end of the feeding period. At 0900 hours probes were inserted into the reticulum and rumen and motility recording begun. Solutions containing 8,50, 100 or 200 g NaCl/L were prepared and 10 rnL/min of each solution was infused into the reticulum (Gilson Minipuls II, infusion pump). The control infusion was calculated to maintain an osmolality of 270 mOsmol/kg which was identical to that of rumen fluid in the sheep after a 5 h fast. The infusions commenced 4 min before offering food at 1430 hours and continued for the first 10 min of a 60 min feeding period. Treatments were imposed according to a 4 x 4 Latin square design. Reticular and ruminal digesta were sampled 30 min before feeding and after 10, 20, 30 and 60 min of feeding. Reticular motility was recorded throughout the meal. RESULTS Experiment I Water consumption and urine volume returned to pre-injection levels after 11.5-13.5 h in 3 sheep and after 13.5-15.0 h in the other 2 sheep (P > 0.05). Rumen fluid samples taken 16 min after injecting 50 g NaCl into the ventral sac had an osmolality of 435 (s-e. 27.8) mOsmol/kg. Neither frequency nor amplitude of reticular contractions were affected significantly in the 10, 20 or 30 min periods after injection (P > 0.05) compared with pre-injection values. The mean frequencies were 1.2, 1.16 and 1,22/min for -10, -20 and -30 min and 1.2, 1.25 and 1.28/n-k for +lO, +20 and +30 min respectively. The mean amplitudes per contraction were 23.5, 23.3 and 23.3 mm Hg for -10, -20 and -30 min and 15.8, 16.5 and 16.8 mm Hg for +lO, +20 and +30 min respectively. The amplitude reduction was not significant as the s.e. associated with the 10, 20 and 30 min comparisons were 3.26, 3.19 and 3.13 respectively. Four hours after rumen injections, there was no difference in cumulative food intake between the normal saline control (219 g) and the 50 g NaCl injected sheep (274 g; P > 0.05). At this time the rumen fluid tonicity for the NaCl injected sheep was 278 (s-e. 7.9) mOsmol/kg compared with 281 (s-e. 16.6) mOsmol/kg before NaCl injection. Hence digesta tonicities had returned to pre-injection levels (P > 0.05; n = 4). There was, however, a significantly higher plasma tonicity at this time (300 mOsmol/kg; s-e. 1.86) compared with pre-injection (291 mOsmolkg; s-e. 1.41; P < 0.001). By contrast, there was no change in plasma tonicity over this time period for the control sheep. Experiment 2 NaCl infusions into the reticulum had no significant effect on either the frequency or amplitude of biphasic reticular contractions (P > 0.05) in spite of the tonicity of reticular digesta reaching 774 (s.e. 287) mOsmol/kg after 10 min and that of the ventral sac being 445 (s-e. 34) mOsmol/kg after 20 min. However, in 1 of the 4 sheep, biphasic reticular contractions could not be recognized with infusions of 1.0 g and 2.0 g NaCl/min, when tonicities in the reticulum were 767 and 1632 mOsmol/kg respectively. DISCUSSION Water consumption and urine output in sheep remained elevated for 11.5-15 h after ruminal salt loading. Hence NaCl loading treatments were imposed on successive days in the experiments of Carter and Grovum (1990a). Four hours after the injection of 50 g NaCl there was no difference in cumulative 407 Proc. Aust. Sot. Anim. Prod. Vol. 19 food intakes between the normal saline control and NaCl injected sheep. At this time there was no difference in the tonicity of rumen fluid between the 2 groups, but the salt-injected sheep had higher plasma tonicities than the control sheep. Thus, cumulative food intake was not affected at 4 hours post salt injection despite a significant increase in plasma tonicity. Carter and Grovum (1990a) found no consistent relationship between food intake and changes in plasma tonicity following solute loading and drinking. However, they did find a consistent inverse relationship between the tonicity of rumen fluid and food intake. Frequency and amplitude of reticular contractions were not significantly affected after the injection of NaCl into the rumen or when the NaCl was directed into the reticulum. Hence, reductions in reticuloruminal motility would not have contributed to the inhibitory effects of salt loading on food intake observed by Carter and Grovum (1990a). This confirms the observations of Phillip et al. (1981). The results reported here were used by the authors to further study the mechanism whereby hypertonic@ inhibits food intake and this subject has been recently reviewed by Carter and Grovum (1990b). CARTER, R. R. and GROVUM, W .L. (1990a). Br. J. Nuts: 64: 285-99. CARTER, R. R. and GROVUM, W. L. (1990b). J. Anim. Sci. 68: 2811-32. GROVUM, W. L. (198 1). BE J. Nutr. 45: 183-201. PHILLIP, L. E., BUCHANAN-SMITH, J. C and GROVUM, W. L. (1981). J. Agric. Sci. 96: 439-45. REFERENCES