Straw degradability as a predictor of intake and growth rate in sheep

Abstract

AbstractThe dry-matter (DM) intake and growth rate in male lambs were predicted from rumen degradability characteristics, rumen DM losses at different times, neutral- or acid-detergent fibre (NDF or ADF) contents and DM apparent digestibility of roughages. Four different straws consisting of wheat, barley, oat and rice were each offered ad libitum to 24 Merino male lambs with 200 glday concentrate for 4 weeks to determine DM intake and growth rate. Apparent digestibilities of the straws were measured with three Merino male sheep. Measurements were made during the last 10 days of each 20-day period. The degradation characteristics of the straws were measured by incubating samples in nylon bags for 8, 16, 24, 48, 72 and 96 h in the rumens of three Merino male sheep fitted with rumen cannulae. The exponential model p = a + b(l - er^) was fitted to the data. Potential degradabilities of DM (defined as a + b) and apparent digestibilities of DM ranged from 530 to 679 and 440 to 560 g/kg, respectively. The mean DM intake of the straws varied from 543 to 745 glday, the digestible DM intake from 236 to 417 glday and growth rate from 17 to 95 glday. Using the degradation characteristics A, B and c in a multiple regression analysis, the correlation coefficients with DM intake and growth rate were 0·79 and 0·70, respectively. NDF and ADF were related to DM intake (i = 0·65; r = 0·64) and growth rate (r = 0·55; r = 0·56). The correlation coefficient between DM apparent digestibility and DM intake was 0·76. It is concluded that the rumen degradation characteristics have potential for predicting intake of straws and growth rate in sheep.