Effect of a source of sustained-release non-protein nitrogen on beef cattle

Improving the efficiency of N use in beef cattle diets can contribute to cost-effective production. This study investigated the effects of including a sustained-release ruminal NPN source in the diet of young bulls as a partial replacement of true protein (with a ~1% reduction in crude protein, CP) on beef production parameters. Charolais bulls (n=56) were allocated to one of two dietary treatments: control (n=28; basal diets of corn silage, corn meal, concentrate, brewer’s grains, straw and SBP) and treated (n=28; basal diets reformulated to partially replace true protein with sustained-release NPN (Optigen®, Alltech Inc.) decreasing CP from 147 to 135, 152 to 136 and 153 to 137g/kg DM for adaptation, fattening and finishing, respectively). Animals were on treatment for 140d (40d adaption, 30d fattening, 70d finishing). Dry matter intake (DMI), feed conversion rate (FCR) and average daily gain (ADG) were measured at 0, 40 and 100d. Chemical and visual evaluation of faeces and analysis of bload urea were carried out. Data were evaluated by ANOVA using the GLM procedure (SAS 8.02). The treated group had significantly (p<0.05) higher ADG from 40 to 100d compared with control (1.63 vs. 1.46kg/d, respectively). Additionally, feed intake was lower (p<0.05) in treated animals indicating that increasing ruminal N availability resulted in positive effects (p=0.023) on FCR (7.40 vs. 6.85 for control and treated, respectively). No differences were observed in rumen N concentration or faecal chemical analysis. Visual fecal evaluation of residue showed greater presence of mucin and undigested portions in the control group. Blood urea levels were similar between groups indicating that, despite more soluble protein in the treated group, its sustained release allowed for complete utilization for microbial synthesis. These data support the optimisation of soluble protein in beef cattle diets using sustained-release NPN to improve ruminal synthesis whilst also reducing dietary CP.