The effect of animal physiological state on site and extent of digestion in sheep.

Abstract

THE EFFECT OF ANIMAL PHYSIOLOGICAL STATE ON SITE AND EXTENT OF DIGESTION IN SHEEP C. LEMERLE,* A.R. EGAN** Digestibility depression at AND T.E. TRIGG* and Moe 1972) is the result of an increased digesta rate of passage (Grovum and Williams 1977) which reduces the time With increased intake the available for digestion in the rumen. increased feed intake (Tyrrell changing relationship between digestion rate and passage rate can also cause shifts in site as well as extent of digestion,thus affecting nutrient supply to the animal. An experiment was carried out to investigate the changes in digesta pool size, flow rates and rate and site of digestion which accompany the differences in forage intake due to different physiological demands. six ewes were offered either chaffed ryegrass (3 sheep) or chaffed paspalum (3 sheep) -----w-D- in ad-libitum Each ewe was two physiological states (lactating, then dry). fistulated at the rumen and the duodenum. Mean values for voluntary feed intake (VFI), dry matter digestibility (DMD), proportion digestion occuring in the rumen (DMDR), rumen liquor mean retention time (MRT), and rumen liquid volume (V) are presented in the table. The effect of physiological status on intake and digestion in ewes The results demonstrate a shift in digestion towards the hindgut when roughage fed sheep are lactating, the effect being more pronounced on the lower quality paspalum diet. Although liquid MRT only decreased in the lactating sheep fed ryegrass, there was an increase in rumen volume in all lactating ewes regardless of diet. There are implications in this .for both patterns of nutrient yield (eg. protein : energy ratio) and interactions between fibre components and energy concentrates (eg. microbial population changes) in the rumen. The influence of this on intake and substitution rates in sheep receiving supplements requires further attention. GROVUM, W.L. and WILLIAMS, V.J. (1977). Br. J. Nutr. 38 : 425 TYRRELL, H.F. and MOE, P.W. (1972). J. DairySci. 1106 * Kyabram Research Institute, Kyabram, Victoria, 3620 WE School Agriculture & Forestry, University of Melbourne, Parkville, Victoria, 3052