Water movements after an intraruminal water load in pregnant and lactating Sardi sheep

The effects of an intraruminal load of 3 litres of water on body water movements was compared in Sardi sheep during the last month of pregnancy, lactation and a non-pregnant, non-lactating control period. Before the water load, rumen fluid volume, estimated by polyethylene glycol was similar in pregnant, compared to control, animals and 27% higher in lactating sheep. After the water load, rumen volume returned to pre-hydration level in 1 h during pregnancy, after 3 h during lactation and in the control period. Rumen osmolality decreased by 40% and remained at this low level for 3 h after the water load in all physiological periods. When the water load was tritiated water (TOH), the rate of TOH transfer into plasma was faster during the last month of pregnancy than during the control period. Plasma osmolality and proteins decreased in response to the water load. No differences in these responses were observed between pregnancy, lactation and the control period. Water diuresis began in the first 30 min following the water load in pregnant ewes and in the second 30 min in lactating and control ewes. The diuresis was also more pronounced in pregnant, than in non-pregnant, states. These results indicate that water is more rapidly absorbed from the gastrointestinal tract in pregnant, rather than in non-pregnant, sheep. This may partly explain the increased water turnover seen during pregnancy.