Effects of urea infusion and ruminal degradable protein concentration on microbial growth, digestibility, and fermentation in continuous culture1

Abstract

The effects of urea and rumen-degradable protein (RDP) on microbial growth, digestibility, and fermentation were examined using dual-flow continuous culture. The experimental design was a 4 x 4 Latin square with a 2 x 2 factorial arrangement of treatments. Factors were urea infusion (0.4 g/L of artificial saliva) and RDP concentration, and the treatments were as follows: 1) low RDP (8% of dietary dry matter) without urea (LDNU), 2) high RDP (11% of dietary dry matter) without urea (HDNU), 3) low RDP (8% of dietary dry matter) with urea (LDU), and 4) high RDP (11% of dietary dry matter) with urea (HDU). The LDNU (i.e., negative control) and HDNU treatments were formulated to be nitrogen limiting. Results indicated that infusion of urea increased all digestibility measurements (P < 0.05), which in turn increased (P < 0.05) volatile fatty acid, NH3 nitrogen, trichloroacetic acid-soluble nitrogen, and soluble protein concentrations. Increasing dietary RDP improved dry matter and organic matter digestibility (P < 0.05) but did not alter acid detergent fiber or nonfiber carbohydrate digestibilities (P > 0.05). Isobutyrate concentration decreased (P = 0.05) with increased RDP. Increased dietary RDP increased crude protein degradation and soluble protein concentration (P < 0.05), but NH3 nitrogen, trichloroacetic acid-soluble nitrogen, and peptide nitrogen were unaffected by changing RDP levels. Microbial growth efficiency was 19.9, 24.9, 28.0, and 32.2 g N/g organic matter truly digested for LDNU, HDNU, LDU, and HDU, respectively, and was significantly improved both by urea infusion (P = 0.002) and increased RDP concentration (P = 0.021). The interactions of urea and RDP (P < 0.05) were explained by the high digestibility of neutral detergent fiber, nonstructural carbohydrate, and especially hemicellulose, with the HDNU treatment. The results of this study indicated that hemicellulose-degrading bacteria were able to effectively compete with nonstructural carbohydrate-degrading bacteria for available peptide and amino acid nitrogen. Further, the extent of protein degradation was dependent on the availability of NH3 nitrogen in the system.

Effects of Degradable Protein and Non-Fibre Carbohydrates on Microbial Growth and Fermentation in the Rumen Simulating Fermenter (Rusitec)

“…However, Ariza et al (2001) reported that EMS was greater for citrus pulp treatment than for hominy feed treatment. Supplementation of RDP tended to increase EMS in the present study, which is in agreement with results obtained by Griswold et al (2003).…”

“…Supplementation of RDP significantly increased microbial N flow including LAM and SAM in the present study, which is in agreement with the continuous culture results obtained by Griswold et al (2003). Compared with starch, pectin produced similar microbial N to several previous studies (Strobel and Russell, 1986;Chester-Jones et al, 1991).…”

Effect of maize silage to grass silage ratio and feed particle size on ruminal fermentation in vitro

“…However, the degradability of CP was not affected by diet, probably because the solubility of CP in grass silage and maize silage is similar (Givens and Rulquin, 2004). In addition, differences in the availability of N sources between diets were indicated by changes in iso-acid production (Griswold et al, 2003).…”

Evaluation of protein supplementation for growing cattle fed grass silage-based diets: a meta-analysis

“…A shortage of rumendegradable feed protein (RDP) has been shown to reduce microbial digestion of carbohydrates (Griswold et al, 2003;Klevesahl et al, 2003), reduce synthesis of microbial protein (Martín-Orue et al, 2000;Griswold et al, 2003), decrease feed intake (Wheeler et al, 2002) and decrease weight gain of growing cattle (Zinn et al, 1994 and. A shortage of absorbed AA by cattle, either because of decreased synthesis of microbial protein or less than required intakes of rumen-undegraded protein (RUP), decreases weight gain of growing cattle (Lammers and Heinrichs, 2000).…”