The suitability of a faecal suspension of sheep as inocula for the estimation of utilizable crude protein of feeds by in vitro incubation

Abstract

The objective of the experiments was to study the suitability of using a faecal suspension of sheep for the estimation of the utilizable crude protein (uCP) of feeds for sheep by an in vitro incubation. Twenty-four single feeds and eight feed mixtures were used as incubation substrates. In Experiment 1, the gas production after the in vitro incubation with rumen fluid or with a faecal suspension of a sheep were compared using the Hohenheim gas test. It was found that there were significant linear regression between the 24, 48 and 72 h gas production with rumen fluid and those with faecal suspensions of 35, 50, 100 and 150 g wet faeces of sheep (which were 18.6, 23.5, 52.0 and 70.5 g faeces DM, respectively) per litre McDougall's buffer (P < 0.0001). The highest regression coefficient (r2) was calculated between the gas production after inoculation with a suspension of 100 g wet faeces per litre McDougall's buffer (x, ml·200 mg − 1 feed DM) for 48 h and the gas production after inoculation with rumen fluid (y, ml·200 mg − 1 feed DM) for 24 h: Based on these results, in Experiment 2 the estimation of utilizable crude protein (uCP) of feeds was compared by using the in vitro incubation technique of Zhao and Lebzien (2000), where feeds were inoculated either with rumen fluid or with a faecal suspension (100 g wet faeces of sheep, i.e. 52 g faeces DM per litre McDougall's buffer). The results indicated that there were no significant differences of the estimated uCP after inoculation with rumen fluid or the faecal suspension (P > 0.05). A significant regression was found between the uCP after incubation for 48 h with 100 g wet faeces (x, g·kg − 1 DM) and the uCP after incubation for 24 h with rumen fluid (y, g·kg − 1 DM): Although this regression was significant, the coefficient r2 was not high. Therefore, further research is needed before sheep faeces could replace rumen fluid as an inocula for the estimation of uCP by the in vitro incubation technique.