Soluble Non-ammonia Nitrogen in Ruminal and Omasal Digesta of Korean Native Steers Supplemented with Soluble Proteins.

C W Choi,S S Chang,N J Choi,K H Kim

doi:10.5713/ajas.2012.12318

Abstract

An experiment was conducted to study the effect of soluble protein supplements on concentration of soluble non-ammonia nitrogen (SNAN) in the liquid phase of ruminal (RD) and omasal digesta (OD) of Korean native steers, and to investigate diurnal pattern in SNAN concentration in RD and OD. Three ruminally cannulated Korean native steers in a 3×3 Latin square design consumed a basal diet of rice straw and corn-based concentrate (control), and that supplemented (kg/d DM basis) with intact casein (0.24; IC) or acid hydrolyzed casein (0.46; AHC). Ruminal digesta was sampled using a vacuum pump, whereas OD was collected using an omasal sampling system at 2.0 h intervals after a morning feeding. The SNAN fractions (free amino acid (AA), peptide and soluble protein) in RD and OD were assessed using the ninhydrin assay. Concentrations of free AA and total SNAN in RD were significantly (p<0.05) lower than those in OD. Although free AA concentration was relatively high, mean peptide was quantitatively the most important fraction of total SNAN in both RD and OD, indicating that degradation of peptide to AA rather than hydrolysis of soluble protein to peptide or deamination may be the most limiting step in rumen proteolysis of Korean native steers. Diurnal variation in peptide concentration in OD for the soluble protein supplemented diets during the feeding cycle peaked 2 h post-feeding and decreased thereafter whereas that for the control was relatively constant during the entire feeding cycle. Diurnal variation in peptide concentration was rather similar between RD and OD.

Highlights

Studies of feed evaluation using the nylon bag method were performed based on an assumption that the ‘afraction’, which is rapidly degradable nitrogen (N) in the rumen, of feed was infinitely degraded and that only insoluble feed N could escape the rumen (Ø rskov and McDonald, 1979; Madsen et al, 1995; Volden and Harstad, 1995)
Many in vivo studies reported that a substantial soluble non-ammonia N (SNAN) concentration may escape the rumen of dairy cows (Chen et al, 1987a, 1987b; Robinson and McQueen, 1994), which is inconsistent with the assumption of the nylon bag studies
It may be in general accepted that a considerable amount of SNAN from dairy cows fed high crude protein (CP) diets, even soluble protein and non-protein N, can escape ruminal degradation (Choi et al, 2002b)

Summary

Introduction

Studies of feed evaluation using the nylon bag method were performed based on an assumption that the ‘afraction’, which is rapidly degradable nitrogen (N) in the rumen, of feed was infinitely degraded and that only insoluble feed N could escape the rumen (Ø rskov and McDonald, 1979; Madsen et al, 1995; Volden and Harstad, 1995). Data on SNAN fractions of RD and OD determined at each sampling interval were fitted using the MIXED procedure of SAS (2002) for repeated measures according to the following statistical model: Yijkl = +Ai+Pj+Dk+eijk+Tl+(A T)il+(P T)jl+(D T)kl+eijkl where T is a fixed effect of time after feeding, and A T, P T and D T are animal by time, period by time and diet by time interactions, respectively. RD and OD averaging 77.3 and 81.6 mg/L, respectively, intact and acid hydrolyzed casein as protein supplements was quantitatively the most important N in SNAN fractions.

Results

Conclusion