The intake and utilization of urea-treated rice straw by sheep differing in body condition

Abstract

Prior to the experiment two groups of 10 sheep were fed to either gain (group F) or lose (group T) weight. At the beginning of the experiment group F sheep weighed on average 57.7 kg fleece-free liveweight (W) and had a total body fat (TBF) content of 154 kg, while group T sheep weighed 42.6 kg and had a TBF content of 9.7 kg. During the experiment all sheep were given a urea-treated rice straw-based diet ad libitum for 56 days with an intra-ruminal infusion of urea and sodium sulfate. Measurements were made of feed intake and digestibility and of the amounts and composition of digesta in the reticula-rumen (ReRu) and flowing through the abomasum.Group T sheep consumed more feed (dry matter intake 1 170 v. 1040 g day-1, 24.9 v. 19.1 g kg W-1) and spent more time chewing (16.5 v. 14.1 h day-1) than group F sheep. There were no differences in the digestibility of dietary constituents.Associated with the greater feed intakes by group T sheep were increased amounts of total digesta (8.59 v 7.67 kg) and of dry matter (DM) (1040 v. 960 g), organic matter (OM) (820 v. 750 g) and neutral detergent fibre (NDF) (690 v. 620 g) in the ReRu. Flows of total digesta (22.45 v. 18.64 kg day-1), DM (910 v. 800 g day-1), OM (600 v. 510 g day-1) and NDF (330 v. 270 g day-1) through the abomasum were also greater in group T sheep. However, there were no differences between treatments in the proportion of digestion which occurred in the ReRu, in the fractional digestion rate of NDF in the ReRu or in the fractional passage rate of NDF from the ReRu.Group T sheep generally maintained weight (-4 g day-1) throughout the experiment and their TBF only declined from 9.7 to 9.1 kg. In contrast, group F sheep lost weight at 74 g day-1 and TBF declined from 15.8 to 14.1 kg.It is concluded that removal of limitations of essential nutrients enabled sheep in poor condition to consume more of this straw-based diet than those in good condition.