Factors limiting the intake of feed by sheep. 12. Digesta load and chewing activities in relation to lactation and its attendant increase in voluntary roughage consumption

Lactating and non-pregnant, non-lactating ewes were compared with respect to voluntary consumption of a medium quality roughage and various aspects of digestion of the roughage as fed at intakes near ad libitum. The lactating ewes, relative to their control counterparts (i) consumed more roughage, (ii) ate more rapidly, (iii) maintained higher levels of digesta in the rumen, omasum, abomasum, and caecum + proximal colon, (iv) showed no difference in particle size distribution in rumen digesta, (v) exhibited enhanced rumination activities and (vi) on average, cleared a particulate marker more rapidly from the rumen. It was estimated that the lactating ewes had a higher energy deficit than the controls. It was concluded that (i) the greater rate of removal of feed dry matter from the reticula-rumen (mass/time) during lactation was largely attributable to the enhancing effect of the prevailing higher reticulo-rumen digesta load on rumination, digestion and propulsion, (ii) neither capacity to use energy nor physiological capability of the reticula-rumen played a primary limiting role in the regulation of roughage intake, with the control of animals, (iii) the comparative data are consistent with a concept that energy metabolism and digesta load interact in the regulation of roughage intake, and (iv) scope exists for increasing consumption of the roughage by appropriate physiological manipulation of the animal.