The Effect of Energy Supplementation on Intake and Utilisation Efficiency of Urea-treated Low-quality Roughage in Sheep I. Rumen Digestion and Feed Intake

Inefficient rumen microbial fermentation is a major factor limiting intake of low quality roughage in ruminants. In this study, the effect of energy supplementation on rumen microbial fermentation, absorption of balanced digestion products and voluntary feed intake in sheep was investigated. A basal diet of a urea-treated mixture of wheaten chaff and barley straw (3:1 DM) containing 22.2 g N/kg DM was used. Four Merino-cross wethers weighing $45{\pm}4.38\;kg$ and fitted with permanent rumen and abomasal cannulae were allocated to four treatments in a $4{\times}4$ Latin square design. The dietary treatments were basal diet ($E_0$), or basal diet supplemented with sucrose (112.5 g/d) administered to the animals intra-ruminally ($E_R$), abomasally ($E_A$), or through both routes (50:50) ($E_{RA}$). Feed intake (basal and dietary) was increased (p<0.05) by sucrose supplementation through the rumen ($E_R$) or abomasum ($E_A$). However, there was no difference (p>0.05) in intake between animals on the control diet and those supplemented with sucrose through both intraruminal and abomasal routes ($E_{RA}$). The digestibility of DM and OM was highest in $E_R$ and $E_A$ supplemented animals. Although the rumen pH was reduced (p<0.001) in animals supplemented with sucrose entirely intra-ruminally ($E_R$), the in sacco degradation of barley straw in the rumen was not adversely affected (p>0.05). Intra-ruminal sucrose supplementation resulted in a higher concentration of total VFA, acetate and butyrate, while the pattern of fermentation showed a higher propionate: acetate ratio. Intra-ruminal supplementation also increased (p<0.05) the glucogenic potential (G/E) of the absorbed VFA. However, there was no difference (p>0.05) in microbial protein production between the four dietary treatments. Protozoa numbers were increased (p<0.05) by intra-ruminal supplementation of sucrose.