Partition of organic matter, fibre and protein digestion in ewes fed at a constant rate throughout gestation

Abstract

The digestion of dietary organic matter, fibre constituents and protein in the stomach and intestines of multiparous Corriedale ewes was studied at different stages of gestation. As gestation progressed, the digestion of organic matter and cell wall organic matter in the rumen decreased. Digestibility in the whole tract declined to a small extent. The degradation of dietary protein was reduced from 72% In non-pregnant ewes to 37% at day 139 of gestation. Protein digestion distal to the stomach increased by 20%. Microbial protein synthesis in the rumen decreased, and it is suggested that the unexpected decrease in the efficiency of microbial synthesis may have been due to reduced rumen osmolalities as a result of the polydipsia exhibited in this experiment in late gestation. Rumen ammonia levels were related to the degradation of dietary N compounds, and caecal ammonia levels increased as protein digestion in the intestines increased. Plasma glucose levels remained normal, and D-3-OH-butyric acid levels remained low until the gravid uterus reached about 4.5 kg (equivalent to about day 120 in single- and day 90 in twin-bearing ewes). Thereafter glucose levels fell and D-3-OH-butyrate levels rose. The latter rise was associated with an increase in the urinary excretion of ammonia N. Plasma urea levels declined to day 90, then rose to day 139, and plasma amino acid N levels rose in late gestation; these increases may reflect tissue mobilization and increased fetal use of amino acids as an energy source.