Estimation of the degradability of dietary protein in the sheep rumen by in vivo and in vitro procedures

Abstract

1. Estimates of degradability of nitrogen in the sheep rumen for a basal hay diet and for soya-bean meal (SBM), groundnut meal (GNM) and fish meal (FM), when given together with the hay, were determined from measurements of (1) duodenal N flow, (2) ammonia kinetics and (3) rumen N disappearance from polyester bags and rumen outflow rate. The ability of various in vitro procedures to predict in vivo N degradability was also examined.2. Four sheep were given a basal hay diet (800 g dry matter (DM) and 19 g N/d) either alone or supplemented with isonitrogenous amounts (15 g N/d) of SBM, GNM or FM. Duodenal non-ammonia-N flow (g/d) was increased more by FM (8.0) than by GNM (5.9) and SBM (5.8), whilst microbial N flow (g/d) was increased more by SBM (3.9) than by GNM (2.3) and FM (1.6). N degradability values calculated from these results were 0.88, 0.76 and 0.57 for the SBM, GNM and FM respectively. The corresponding value for hay was calculated to be 0.76.3. The irreversible loss of ammonia in the forestomachs (g N/d) was increased more by SBM (1 1.9) than by GNM (7.2) and FM (5.Q whilst ammonia outflow from the rumen (g N/d) was increased to a similar extent by all supplements ( I 'I, 0.9 and 0.8 respectively), as was the amount of microbial N (g/d) synthesized from sources other than rumen ammonia (1.8, 2.0 and 1.9 respectively). N degradability values calculated from these results were 0.84, 0.54 and 0.45 for the SBM, GNM and FM respectively.4. The fractional rate of N disappearance (/h) when the feedstuffs were incubated in polyester bags in the rumen of sheep receiving the basal hay diet (800 g DM/d) was the highest for SBM (0,145) and lowest for FM (0.037), with the hay (0.082) and GNM (0.071) intermediate, whilst the fractional outflow rates from the rumen (/h) of the three supplements were similar (0.034, 0.038 and 0,030 for SBM, GNM and FM respectively). N degradability values calculated from these results were 0.82, 0.67 and 0.60 for the SBM, GNM and FM respectively; the value for the hay was 0.73.5. Of a number of in vitro procedures tested, only N solubility in sodium hydroxide and ammonia or total non-protein-N (NPN) production during incubation with rumen fluid in the absence of hydrazine sulphate ranked the supplements, although not the hay, in the same order as the in vivo degradability procedures. In terms of absolute values, N solubility in NaOH, at room temperature, gave estimates similar to those derived from the duodenal flow measurements; estimates derived from ammonia and total NPN production were lower.

Contribution of dietary nitrogen and purine bases to the duodenal digesta: comparison of duodenal and polyester-bag measurements

“…Comparing both methods, Mathers and Miller (1981) and Siddons et al (1985b) found a close agreement and protein degradability ranked in the same order but other reports in the literature have not found such an agreement (Kennedy et ah, 1984). Comparing both methods, Mathers and Miller (1981) and Siddons et al (1985b) found a close agreement and protein degradability ranked in the same order but other reports in the literature have not found such an agreement (Kennedy et ah, 1984).…”

The effects of increasing the level of dietary wormwood (Artemisia montana Pampan) on intake, digestibility, N balance and ruminal fermentation characteristics in sheep

“…Ruminal NH 3 -N concentrations were consistently higher ( P b 0.05) in sheep fed diets containing wormwood within 2 h after feeding, reflecting higher CP digestibility in sheep fed wormwood diets (Chamberlain and Thomas, 1979;Siddons et al, 1985;Kim et al, 2002a). Ruminal total VFA concentrations were generally higher in sheep fed MW and LW than those fed the other diets between 1 and 2 h after feeding.…”

Nutrient availability during the early stages of colonization of fresh forage by rumen micro‐organisms

“…It is crucial for the efficient use of ingested forage by ruminants that release of energy derived from plant carbohydrates is matched with the liberation of protein degradation products. Often, however, nitrogen availability in the rumen exceeds energy supply leading to reduced microbial production efficiencies, increased deamination of plant proteins and excessive production of rumen ammonia and loss of nitrogen in urine (McRae et al ., 1985; Dewhurst et al ., 1995; Siddons et al ., 1995; Dewhurst et al ., 2000). Determining the underlying causes of poor nitrogen use efficiency in the rumen would help remedy these problems and would contribute to improve the efficiency of livestock production and reduce excessive nitrogen excretion to the environment.…”