Changes in factors affecting the rate of digesta passage during pregnancy and lactation in sheep fed on hay

The objective of this study was to assess feed intake and digesta passage characteristics in five Blackhead ewes fed hay ad libitum during pregnancy [I: d 60-80 post conceptionem (p conc); II: d 105-125 p conc; III: d 128-148 p conc] and lactation [IV: d 10-30 post partum (pp); V: d 35-55 pp]. During pregnancy, feed intake and rumination activity increased. The rumen fluid volume and the daily number of A-cycles did not change significantly. The mean retention time (MRT) of the fluid and particle markers in the reticulorumen (RR) and distal to the RR decreased by 14-32%. During lactation, the rumen fluid volume increased as compared to pregnancy by about 15%. Daily feed intake peaked during period V (83.7 g DM/kg BW0.75). The MRT of particle markers in the RR increased as compared with late pregnancy. Both during pregnancy and lactation, the increased passage rate of digesta was achieved predominantly by an increased amount of digesta passing through the reticulo-omasal orifice during each opening. Sieving of forestomach contents and faeces revealed that the breakdown rate of large feed particles did not limit digesta passage.