1. The relations between food intake, reticulo-ruminal motility and abomasal digesta outflow were investigated in ewes receiving lucerne (Medicago sativa) v. orchard grass (Dactylis glomerata) hay. Abomasal digesta outflow was recorded continuously by means of an electromagnetic flowmeter probe inserted into a duodenal T-shape cannula and the motility using strain-gauge force transducers. Volumes and turnover rates of both rumen and abomasal liquid phases were measured by CrEDTA dilution.
2. The voluntary intake of lucerne was higher (60%) than that of orchard grass hay, and paralleled by an increased abomasal outflow (65%) corresponding to an increased number of gushes of digesta through the flowmeter probe: 129/h instead of 78/h on orchard grass hay. Abomasal motor activity was enhanced (35%), and periods of regular spiking activity were seen passing along the duodenum at a higher velocity for the lucerne diet than for the orchard grass diet. The increased abomasal outflow with lucerne hay was associated with a higher reticulo-ruminal turnover rate, but not abomasal turnover rate. Abomasal, but not reticulo-ruminal volume, was increased (30%) when lucerne hay was fed ad lib.
3. The total number of reticulo-ruminal contractions was increased by 6.6% when the dry matter entering the duodenum was increased by 70.6%, suggesting the level of voluntary intake, rather than reticulo-ruminal motility, as a major factor governing abomasal outflow in sheep.
4. More frequent passages of digesta, unrelated to duodenal contractions, were recorded in ewes receiving lucerne compared with orchard grass. Both a higher viscosity of the contents due to the addition of guar gum and the impairment of antroduodenal motility by 5-hydroxytryptophan were able to reduce the flow rate of orchard grass digesta, but did not affect the higher flow rate of lucerne digesta. The findings suggest that the high abomasal outflow in sheep fed on lucerne ad lib. is related to a low viscosity of the contents that are propelled, even in the case of antral contractions of low magnitude.