Flow of Soluble Non-ammonia Nitrogen in the Liquid Phase of Digesta Entering the Omasum of Dairy Cows Given Grass Silage Based Diets

C W Choi,C B Choi

doi:10.5713/ajas.2003.1460

Abstract

An experiment was conducted to quantify the flow of soluble non-ammonia nitrogen (SNAN) in the liquid phase of ruminal (RD) and omasal digesta (OD), and to investigate diurnal pattern in SNAN flow in OD. Five ruminally cannulated Finnish- Ayrshire dairy cows in a 5×5 Latin square design consumed a basal diet of grass silage and barley grain, and that supplemented with four protein feeds (kg/d DM basis) as follows: skimmed milk powder (2.1), wet distiller's solubles (3.0), untreated rapeseed meal (2.1) and treated rapeseed meal (2.1). Ruminal digesta was sampled using a vacuum pump, whereas OD was collected using an omasal sampling system at 1.0 h interval during a 12 h feeding cycle. Both RD and OD were acidified, centrifuged to remove microbes and precipitated with trichloroacetic acid followed by centrifugation. The SNAN fractions (free amino acid (AA), peptide and soluble protein) in RD and OD were assessed using ninhydrin assay. Free AA, peptide and soluble protein averaged 60.0, 89.4 and 2.1 g/d, respectively, for RD, and 81.8, 121.5 and 2.5 g/d, respectively, for OD. Although free AA flow was relatively high, mean peptide flow was quantitatively the most important fraction of SNAN, 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. Diurnal pattern in flow of peptide including free AA in OD during a 12 h feeding cycle peaked 1 h post-feeding, decreased by 3 h post-feeding and was relatively constant thereafter. Protein supplementation showed higher flow of peptide including free AA immediately after feeding compared with no supplemented diet. There were no differences among protein supplements in diurnal pattern in flow of peptide including free AA in OD. (Asian-Aust. J. Anim. Sci. 2003. Vol 16, No. 10 : 1460-1468)

Highlights

Due to low concentration of free amino acid (AA) in ruminal digesta (RD), it was suggested an observation that hydrolysis of protein to peptide or deamination is the ratelimiting step in proteolysis in the rumen (Wright and Hungate, 1967; Tamminga, 1979; Van Straalen and Tamminga, 1990)
The cows were offered grass silage and rolled barley grain ad libitum during an adaptation period, and the DMI was restricted to 90% of the ad libitum intake
Data on rumen pH, ammonia N, flow measurement and soluble nonammonia nitrogen (SNAN) fractions determined at each sampling interval were fitted using the MIXED procedure of SAS (Littell et al, 1998) for repeated measures according to the following statistical model: Yijkl=μ+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

Summary

INTRODUCTION

Due to low concentration of free amino acid (AA) in ruminal digesta (RD), it was suggested an observation that hydrolysis of protein to peptide or deamination is the ratelimiting step in proteolysis in the rumen (Wright and Hungate, 1967; Tamminga, 1979; Van Straalen and Tamminga, 1990). Studies on responses of the flow of soluble nonammonia nitrogen (SNAN) in the liquid phase of omasal digesta (OD) to various protein feeds are limited. Most of previous SNAN data (Chen et al, 1987c; Broderick and Wallace, 1988; Robinson and McQueen, 1994) were obtained from RD, the extent of SNAN flow escaping the rumen was still unclear. The present study using omasal sampling technique aimed to assess the flow of SNAN fractions and to investigate diurnal pattern in the flow of SNAN fractions escaping the rumen of cows fed grass silage based diets with various protein supplements containing different soluble N content

MATERIALS AND METHODS

Sampling procedures and chemical analysis

AND DISCUSSION