Beiträge zur Quantifizierung der N-Umsetzungen in den Vormägen von Milchkühen

Protein and fiber digestion, passage, and utilization in lactating cows. Microbial growth and flow as influenced by dietary manipulations

The accuracy of prediction of microbial growth in the rumen and flow of microbial protein to the small intestine is important in predicting protein and carbohydrate utilization in dairy cattle as well as the development of a protein and carbohydrate feeding system that will be an improvement over present systems. Empirical multiple and simple regression equations are presented that demonstrate the impact of body size, proportion of forage in the diet, and dry matter intake on flow of microbial protein into the small intestine from the rumen. Concepts are developed and validated for a mechanistic, dynamic approach for prediction of microbial growth and flow of microbial protein based on Michaelis-Menton equations, microbial substance affinities, and rumen liquid flow kinetics. Emphasis is placed on the importance of quantifying dynamics of rumen function, the need for experimentation to develop a carbohydrate system that will include methods for analysis, and a factorial approach to digestion and utilization.

[Nutrient digestibility and nitrogen utilization in lactating cows under restricted protein supply and subsequent refeeding]

The effects of a 17% deficiency of crude protein for four weeks on nutrient digestibility and parameters of N metabolism were investigated using four pairs of monozygotic twin cows. During a period of realimentation of three weeks with slight nutrient oversupply and a further period of three weeks with nutrient supply adjusted to the lactation trend it was examined if residual effects remain. Protein restriction enhanced the excretion of fecal dry matter by 7.7%. Total fecal nitrogen was a high in the restricted group as in the control group. Apparent digestion coefficients for dry matter, organic matter and N-free extracts were lowered by 2 to 3 percent points with deficient protein nutrition. Crude fiber and nitrogen digestibilities declined by 4.5 and 9.8 percent points, respectively. The reduction of urine nitrogen excretion amounted to 47% as consequence of a drastically diminished nitrogen content of urine. Total nitrogen retention (milk-N and body-N) was lowered by 14%. The sum of the relative nitrogen losses via faeces and urine was not different between the protein-deficient and the normal diet. The utilization of feed nitrogen for milk nitrogen excretion was 28.2% in protein deficiency and 25.9% in control feeding. After realimentation no relevant residual effects of the previous protein deficiency were found neither with respect to nutrient digestibility nor to parameters of the nitrogen balance. So far the observed permanent effect in reduced milk yield by 6% of the expected performance can not be explained with changes in digestibility or nitrogen balance.

Rumen protein degradation and biosynthesis. I. A new method for determination of protein degradation in rumen fluid in vitro

A method is described for the determination of protein degradation based on measurements of ammonia concentration and gas production (Menke et al. 1979) when a feedingstuff was incubated with rumen fluid in vitro. NH3 liberated during incubation is in part used for microbial protein synthesis. Production of carbon dioxide and methane can be regarded as a measure of energy available for protein synthesis. The ratio, gas production: incorporation of NH3-nitrogen was estimated by addition of starch to the substrate. The response in gas production was linear in the range 0-200 mg starch, when starch was added to 0-200 mg feedingstuff dry matter and 30 ml rumen fluid-medium mixture. Linear regression between NH3-N concentration (y, mg) and gas production (x, ml) yielded an intercept (bo) representing that amount of NH3-N which would be released when no fermentable carbohydrates were available and consequently no bacterial protein synthesis took place. The difference between this intercept bo and NH3-N content in the blank (rumen fluid without substrate added) indicated the amount of NH3 liberated from protein and other N-containing compounds of the feeding-stuff incubated. In vitro-degradable N (IVDN) was calculated as a proportion of total N by the equation: (formula; see text).

[Effect of the content of plant crude protein in the ration on the utilization of urea by the milk cow. 1. Nitrogen digestibility and utilization of urea for bacterial protein synthesis in the rumen]

The utilisation of feed urea in the rumen was tested in 2 experiments with a total of 4 newly lactating dairy cows (13 . . . 15 and 17 . . . 19 kg resp. milk/animal and day) with rumen and duodenal re-entrant cannulae. With the energy supply remaining constant in each case, the rations in experiment A contained 8.7, 12.4 and 14.6 and those of experiment B 10.7, 13,7 and 17.1% crude plant protein in the dry matter. After the supplementation with 120 and 150 g resp. urea/animal and day there were 11.9, 15.7 and 17.8 (A) and 13.8, 16.7 and 20.2 (B) % resp. crude protein in the dry matter. The rations consisted of maize silage and a pelleted mixture of straw and concentrated feed (A) resp. maize silage, alfalfa hay and concentrated feed (B). They contained 10.3 . . . 10.6 (A) and 13.6 (B) kg dry matter with 5.6 . . . 6.0 (A) and 8.2 (B). With the increase of the crude protein level of the ration to 16.7 . . . 17.8, the absolute amount of non-NH3-N (NAN) in the duodenum increased as well. Between N-intake (g/d, x) and NAN-passage corrected by the amount of the endogenous quota (g/d, y) the relation y = 87.3 + 0.55 x (r = 0.80) could be established. NAN-passage (y) as related to N-intake decreased with the N-concentration in the dry matter of the ration (x) according to the equation y = 0.35 + 1.22x-1 (r = 0.57). 70, 62 and 61% (experiment A) and 55, 61 and 51% (experiment B) of the consumed amount of N were apparently absorbed in the intestines as NAN (without endogenous quota). The bacterial N-yield of the rumen (g, y), determined with diamino pimelic acid as microbe marker, was dependent on the consumed digestible organic matter (g, x) as follows: y = 67.3 + 0.021x (r = 0.69). There was no connection with the level of N-supply. The measuring results of the bacterial N-yield show that the utilisation rate of the urea-N decreased rapidly when there was more than 11 . . . 12% crude plant protein in the dry matter of the ration. For the tested ration type (570 . . . 600 EFUcattle/kg dry matter) the urea utilisation potential in the rumen for crude plant protein concentrations of 8.7, 10.7, 12.4, 13.4, 13.7, 14.6 and 17.1% in the dry matter was 13.0, 6.9, 4.1, 2.6, 1.3 and -9.6 g urea/kg dry matter.

Nitrogen metabolism in the forestomachs of cows fed ammonia treated barley straw supplemented with increasing amounts of urea or soya bean meal

Der N‐Stoffwechsel in den Vormägen der Kuh nach Fütterung mit Ammoniak behandeltem Stroh

Untersuchungen über die mikrobielle Proteinsynthese und den Proteinabbau in den Vormägen nach Verabreichung von Ammoniakbehandeltem Gerstenstroh wurden an zwei Kühen mit Pansenfistel und Umleitungskanüle (Re‐Entrant Cannulae) am Duodenum durchgeführt. Das NH3‐behandelte Stroh wurde mit 4% Ammoniak‐Gas behandelt und mit 5% Melasse vermischt und jeweils mit zwei unterschiedlichen Mengen Harnstoff und Sojaschrot verfüttert. Der Stickstoffgehalt der Grundration betrug 1.53% der TM und stieg auf 2.87 beziehungsweise 2.60% N in den Harnstoff‐ und Sojarationen an. Es wurden im Durchschnitt 7.0 kg Trockenmasse pro Kuh und Tag verabreicht. Die scheinbare Verdaulichkeit der organischen Substanz in den Vormägen wurde nicht durch Harnstoff‐ oder Sojazulage beeinflußt und schwankte von 53.3–54.5%.

Die mikrobielle Proteinsynthese sowie die Proteinabbaurate in den Vormägen wurde mit Hilfe der Regressionsmethode bestimmt, wobei der im Duodenum enthaltene Nicht‐Ammoniak Stickstoff (NAN) dem im Futter zugelegten Stickstoff gegenübergestellt wird (Abb. 1). Der berechnete Abbau des Harnstoffs betrug 102% welches eine völlige Spaltung des Hamstoffs im Pansen andeutet. Der Abbau von Sojaschroteiweiß in den Vormägen betrug 75%. Die mikrobielle Eiweißsynthese der Harnstoff‐ bzw. Sojarationen betrug im Durchschnitt 29.5 und 29.4 g N pro kg in den Vormägen verdaute org. Substanz. Die Zulage von Harnstoff erhöhte die durchschnittliche NH3‐Konzentration im Pansensaft von 12.5 mg NH3‐N pro 100 ml der mit NH3‐behandelten Grundration auf 36.3 mg NH3‐N durch Harnstoffzulage, ohne die mikrobielle Proteinsynthese zu beeinflussen.

Die auf Grundlage der DAPA Konzentration bestimmte mikrobielle Proteinsynthese war nicht mit der der Regressionsmethode bestimmten Proteinsynthese in Übereinstimmung (Tabelle 7).

Vom Nicht‐Ammoniak Stickstoff am Duodenum betrug der Aminosäurenanteil durch‐schnittlich 58%.