103 Post-ruminally delivered urea improves fiber utilization in ruminants.

Abstract

Ruminants are able to transform non-protein nitrogen (NPN) into animal protein, but efficiency may depend on the site of delivery in the gastrointestinal tract. We hypothesized that post-ruminal NPN supply can be utilized in the rumen, via urea recycling. Four rumen fistulated Holstein heifers (561 ± 42Kg BW) were used in a Latin square design with ruminal and abomasal infusions. Treatments consisted of ammonium hydroxide solution constantly infused into the rumen (AR), or the abomasum (AA), urea solution constantly infused into the abomasum (UA) or urea supplied into the rumen as daily pulse dose (UR). Experimental periods consisted of 12 d for treatment administration and sampling followed by 2 d rest. Treatments were isonitrogenous (59 g N/d) and all heifers were fed hay (6% CP, 70% NDF) ad libitum with 1kg of compound feed (21.7% CP) supplied in the morning through rumen cannula. Indigestible NDF (iNDF) was used as faecal marker. Ruminal pH was analysed to fit a logistic model resulting in two parameters: slope corresponding to the range of cumulative pH and inflection point corresponding to the statistical median. Dry matter intake was highest (P=0.03) for heifers receiving UR or UA while AR led to lowest intake. Higher NDF digestibility was observed with UA compared to UR (P=0.05). The pH inflection point was higher (P=0.05) with AR compared to UR, AA, and UA. The pH range with UR was wider (lower slope; P=0.04), due to the rise in pH following urea infusion, in which ammonia concentration reached 63 mg/dL 3 hours after UR supply, while concentrations for AR, AA and UA were held constant (18.5 ± 3.1, 4.4 ± 0.8, 4.6 ± 1.0 mg/dL, respectively). Our study indicates that urea delivered post-ruminally improves fiber digestibility and rumen stability and offers a unique approach towards improving N utilization and efficiency in ruminant production systems.