Factors limiting the intake of feed by sheep. 11. The effect of pregnancy and early lactation on the digestion of a medium-quality roughage

Abstract

Various aspects of digestion were studied at a constant level of roughage feeding in ewes bearing single or twin foetuses during pregnancy, and in ewes suckling a single lamb during early lactation. In pregnancy, ewes with twins responded similarly to those with singles, except that they drank more water. The responses to pregnancy generally increased in magnitude as pregnancy progressed. Late pregnancy was associated with increases in (i) digesta flows through the stomach, (ii) marker clearance rates through the alimentary tract, (iii) absorption rate of volatile fatty acids, (iv) non-ammonia nitrogen flow into the intestines, and (v) faecal water output, and decreases in (i) reticulo-rumen liquor volume, (ii) reticulorumen pools of volatile fatty acids, ammonia, sodium and potassium, and (iii) organic matter digestion. Lactation was associated with increases in (i) digesta flows through the stomach, (ii) marker clearance rate from the reticula-rumen, (iii) non-ammonia nitrogen flow into the intestines, (iv) rumen digesta pH and (v) flow of sodium and potassium from the reticulo-rumen, and decreases in (i) reticula-rumen pools of volatile fatty acids, ammonia, sodium and potassium, (ii) organic matter digestion and (iii) blood urea concentration. It was concluded that (i) the digestion responses were large enough to influence the interpretation of various nutrition studies in pregnancy and lactation, and (ii) the relative contributions of physical and hormonal changes to the altered digestion transactions need elucidation.