Gastric electromyographic activity in the milk‐fed lamb.

Abstract

SUMMARY1. Electromyographic (EMG) activity of the reticulum, reticulo-omasal orifice (ROO) and abomasum was recorded from conscious lambs.2. In fasted lambs diphasic reticular EMG bursts occurred at intervals of 60+13 s. In association with the second phase of the reticular EMG burst there was consistently a period of inactivity of the EMG of the ROO of 2 4-11 0 s (5 5 + 2-0 s, mean + S.D.). This period of quiescence ended with the onset of a burst of EMG activity of the ROO of 4-1 + 0-8 s termed here a long burst of activity. Preceding the following reticular EMG burst there were further long bursts of EMG activity of the ROO at intervals of 11.1 + 1-3 s or intermixing or replacement of long burst activity with short bursts which were of duration 1 I + 0 3 s and which occurred at intervals of 2-4+0 5 s.3. When the lambs were shown milk and at times when they could be expected to anticipate milk being provided, a period of inactivity of the EMG of the ROO developed for up to 60 s. In association with this there was commonly an increase in the frequency of reticular EMG bursts which at times became monophasic.4. With the start of sucking there was quiescence of the EMG of the ROO which persisted throughout periods of sucking for up to 90 s. Simultaneously with the disappearance of activity of the ROO there was a monophasic burst of the reticular EMG, which was followed by either quiescence or disorganized low voltage activity. Inactivity of the EMG of the ROO still developed when lambs sucked milk after administration (i.v.) of atropine, phentolamine or propranolol, but not after hexamethonium.5. In lambs observed over a period 30-60 min after feeding the diphasic reticular bursts occurred every 85+24 s and the duration of the period of inactivity of the EMG of the ROO associated with each reticular burst (3-7 + 1-2 s) was significantly less (P < 0-001) than in fasted lambs. Short bursts of EMG activity of the ROO occurred more frequently than in fasted lambs.6. In fasted lambs bursts of EMG activity of the body of the abomasum occurred at frequencies of 6-12 min-' and those of the antrum and pylorus at ca. 6 min-' but episodes of such activity were intermittent. Within 30 min of lambs first sucking 500 ml of milk the bursts of EMG activity of the body, antrum and pylorus were increased in voltage and duration and the episodes of bursts were more prolonged. When the lambs sucked a further 500 ml milk there was inactivity of the EMG of the A. M. REID AND D. A. TITCHEN body and cessation or diminution of the activity of the antrum and pylorus. Such reductions in activity were also observed when the lambs were shown milk.7. The results suggest that when lambs are anticipating being fed and when they suck milk there is a relaxation of the ROO which is mediated by non-adrenergic, noncholinergic nerve fibres. A concomitant inhibition of activity of the abomasum may lead to relaxation of this structure in reception of milk.

Effect of vasoactive intestinal polypeptide and environmental temperature on forestomach electromyographic activity and gastrointestinal contraction in sheep

“…As well, VIP reduced the frequency of reticular EMG activity of sheep prior to, during and after feeding in a warm, but not in a cold environment . In fasted and milk-fed lambs the inhibition of EMG activity of the ROO was associated with each biphasic reticular EMG activity burst (Reid and Titchen 1988). However, the inactivity of the ROO (relaxation) was not coincidental with the reticular EMG bursts in meal-fed sheep receiving solid diets (Okine and Mathison 1996).…”

“…The increase of duration of ROO opening during VIP infusion suggests that the inhibitory effect of VIP on ROO myoelectric activity might facilitate outflow of digesta from reticulorumen to the omasum because of relative delimitation of its narrowness. Inhibition of contractions of the ROO is believed to occur in the lamb during sucking, permitting passage of milk caudally to the abomasum (Reid and Titchen 1988).…”

Effect of vasoactive intestinal polypeptide infusion on feed intake, digesta flow and nutrient digestion in sheep with access to feed for limited time

“…There is a wide distribution of VIP receptors along the digestive tract, particularly in the inner muscle layer of the reticulo-omasal orifice (ROO) (Wathuta 1986;Zdon et al 1988) and omasal wall (Yamamoto et al 1994) of ruminants. Vasoactive intestinal polypeptide has been shown to relax both circular and longitudinal muscle strips from the omasal canal of the calf (Denac et al 1990) and produce cessation (quiescence) of electromyographic (EMG) activity of the ROO in conscious and anaesthetized lambs (Reid and Titchen 1988;Okine et al 1995 …”