Evaluation of a mathematical model of rumen digestion and an in vitro simulation of rumen proteolysis to estimate the rumen-undegraded nitrogen content of feedstuffs

Abstract

1. Twelve grain mixtures, one lucerne (Medicago sativa) hay and one maize silage which had been used in mixed diets for which dietary nitrogen undegraded in the rumen (UDN) had been estimated with duodenally-cannulated cows, were studied. Total N in the feeds was fractionated into pool A (N soluble in borate-phosphate buffer), pool B (total N-(pool A+pool C)) and pool C (acid-detergent-insoluble N or residual N after 24 h incubation in protease solution).2. N solubilization in protease solution containing 6.6 units/ml (substrate-saturating enzyme concentration) indicated the presence of subfractions in pool B, with different rates of solubilization. Such subfractions were not detectable from in situ, Dacron bag, estimates of N solubilization.3. UDN was estimated using a dynamic mathematical model and rate-constants obtained from N solubilization in protease solution or in situ. For three grain mixtures tested using the protease technique the model predicted UDN values of 7, 10 and 12% compared with values of 47, 66 and 59% estimated in vivo. The full range of experimental feeds was tested using the in situ technique and UDN values predicted by the model were used to derive UDN values for twelve mixed diets. The latter values were significantly but not closely correlated with those determined in vivo (rz 0.41, P < 0.05).4. An attempt was made to simulate rumen proteolysis in vitro by choosing a protease enzyme concentration (0.066 units/ml) providing a proteolytic activity similar to that of whole rumen fluid. The experimental samples of feed were subjected to simulated rumen proteolysis for 18 or 48 h to resemble the mean retention times in the rumen for grain mixtures and roughages respectively. The residual N at the end of incubation was considered as an estimate of UDN. The UDN values estimated from simulated rumen proteolysis and those determined in vivo for twelve mixed diets were in close agreement (re 0.61, P < 0.01). 5.Simulated rumen proteolysis can serve as a simple, rapid and sensitive method to estimate UDN in a varief y of feedstuffs.

Kinetics of digestion of low-quality forage grazed by beef cattle fed supplements containing increasing levels of rumen undegradable protein

“…In the system proposed by Sniffen et al (1992), iNDIP corresponds to the rumen-and intestine-indigestible and insoluble protein, composed of proteins bound to lignin by proteintannin complexes and Maillard artifacts, which are highly resistant to both microbial and host enzymes. These artifact products, despite some controversy, are considered not degradable in the rumen and do not release absorbable amino acids in the small intestine (Michalet-Doreau and Ould-Bah, 1992;Krishnamoorthy et al, 1983). Therefore, this fraction represents the greatest share of the ingested proteins to be excreted in the feces, and according to Van Soest (1994), 5 to 15% of the total nitrogen from forage plants is bound to lignin, and the values found in the present study lay within this range.…”

Methods to study degradation of ruminant feeds

“…Proteases from different origins have been tested by several researchers to estimate ruminal protein degradation; however, the most commonly used is the one obtained from S. griseus as reported by Chaudhry (14,15) and Krishnamoorthy et al (69) . Table 4 (9,13 -15,69,82 -87) gives the list of enzymes studied in some recent publications on the topic.…”

“…N solubility varies greatly for different feedstuffs. For example, while N of brewer's grains was only 3 % soluble in borate -phosphate buffer, oat N was 55 % soluble (69) . Buffer-soluble N is comprised mostly of NPN, such as ammonia, urea, nitrates, amino acids and small peptides (66 -69) .…”

Effect of Mixed Microbial Culture on Fermentation of Beverage Residues and the Effect of the Fermented Beverage Residues on in Vitro Rumen Fermentation and Methane Production

“…In addition, the maillard reaction and heat damage could occur during beverage production under high heat. Referece [18], and [19] have indicated these reactions and damages that are highly resistant to microbial enzyme to cell wall degradation. Hence, this might be another reason for a lack of an increase in CP in fermented residues.…”