Effect of fibrolytic enzyme supplementation of urea-treated wheat straw on nutrient intake, digestion, growth performance, and blood parameters of growing lambs

This research aimed to evaluate the effects of the supplementation of an exogenous fibrolytic enzyme (EFE; 1:1 v/v mixture of cellulase PLUS and xylanase PLUS, Dyadic International Inc, USA) to untreated (Control(WS)) and urea pretreated wheat straw (UWS) on feed intake, digestibility, nitrogen balance, ruminal fermentation, growth performance and blood metabolites of meat lambs. The diet contained 50 % wheat straw and 50 % concentrate (DM basis), and the EFE was applied at 1 mL/ kg DM to the straw. Lambs were arranged in a completely randomized design with four treatments (n = 5 lambs per treatment): Control(WS), WS+EFE, UWS, UWS+EFE. The lambs were housed individually in metabolic crates for 56 d divided into three experimental periods: d0-21 adaptation period, d21-28 digestibility trial and average daily gain (ADG) measurements and d28-56 for only ADG measurements. All studied treatments have no effect on nutrients intake. As compared to the control WS, only the EFE supplementation affected the nutrients digestibility. The EFE addition improved the digestibility of dry matter by 9 % and 14 %, organic matter by 8 % and 13 %, crude protein by 7 % and 6 %, neutral detergent fiber by 24 % and 47 %, and acid detergent fiber by 30 % and 48 % for WS+EFE and UWS+EFE as compared to Control(WS) and UWS, respectively. The ruminal NH3-N concentrations measured during d21, d24 and d28 were lower for animals fed WS+EFE and UWS+EFE than those fed on Control(WS) and UWS. The nitrogen retention improved only for UWS+EFE. The EFE supplementation to straw had no effect on ruminal pH and blood metabolites. For the ADG, the highest total ADG improvement (22 %) was recorded for UWS+EFE. These results indicate that urea treatment alone was inefficient in improving straw digestibility and lamb growth performance. However, the EFE supplementation was efficient on lamb growth, especially when combined with urea treatment due to increased ruminal digestibility and nitrogen retention.