Rumen liquor

Menke KH, Raab L, Salewski A, Steingass H, Fritz D, Schneider W. The estimation of the digestibility and metabolizable energy content of ruminant feeding stuffs from the gas production when they are incubated with rumen liquor. Journal of Agricultural Science. 1979 93 217-222. 

Khan, S.U. and M.H. Akhtar. 1983. In vitro release of bound (nonextractable) atrazine residues from com plants by chicken liver homogenate and bovine rumen liquor. Jour. Agric. Food Chem. 31 641-644. 

To obtain the in vitro true digestibility, the residue from the first buffered rumen liquor stage of the Tilley and Terry (1963) procedure is digested with neutral detergent solution. The ordinary true digestibility is found by... 

This eponymous method is widely used and as originally proposed or in modified form has served as a benchmark for other methods. In fact, it is often referred to simply as the in vitro digestibility. The first stage involves anaerobic incubation at 38°C in the dark with partially filtered rumen liquor which has been buffered with McDougall s artificial saliva solution, previously saturated with CO. ... 

There are several ways of expressing the in vitro rumen liquor digestibility of a sample the DOMD or D-value, the DMD value and the OMD value. These are defined below ... 

We are interested in the first component, so need to subtract the other components. The residue from the rumen liquor blank contains both blank organic matter and blank ash. When this value is subtracted from the above we get the sum of sample organic matter plus sample ash. 

When planning for Tilley and Terry digestibilities, it is common practice to ensure that the sheep or cattle have been fed for a couple of weeks on a basal diet similar to the test samples to be analysed. This is to ensure a buildup of the appropriate rumen flora resulting in a corresponding optimal activity. Whether or not this is necessary is open to question, and this and other sources of error have been discussed by Ayres (1991). It is also customary not to feed the animal on the morning planned for extracting the rumen liquor. 

The % indigestible cell wall in DM is the residual DM after digestion in rumen liquor (48 h) followed by the neutral detergent procedure and expressed as % sample DM. 

Fig. 9.1. The NIR spectra from strained and freeze-dried whole rumen liquor from sheep fed on ryegrass (solid line), and the bacterial (dotted line) and protozoal (dashed line) fractions. The standard normal variate and detrended data (SNV-DT) Is plotted vs. wavelength. Log 1/R = - log (Reflectance) and Is equivalent to absorbance.

Protozoa none in Trichomonas vaginalis,78 and in oligotrich and holotrich ciliates from sheep-rumen liquor.89... 

The dry matter and cellulose digestibilities of all the samples were determined using a modification of the in vitro procedure of Tilley et al. (57). Rumen liquor collected from a rumen fistulated steer fed alfalfa... 

The simple sugars produced in the first stage of carbohydrate digestion in the rumen are rarely detectable in the rumen liquor because they are immediately taken up and metabolised intracellularly by the microorganisms. For this second stage, the pathways involved are in many respects similar to those involved in the metabolism of carbohydrates by the animal itself, and are thus discussed in Chapter 10. However, the main pathways are outlined in Fig. 8.7. The key intermediate (i.e. linking the pathways of Fig. 8.6 with those of Fig. 8.7) is pyruvate, and Fig. 8.7 shows the... 

Table 8.4 Volatile fatty acids (VFAs) in the rumen liquor of cattle or sheep fed on...

The production rate of VFAs in the rumen can be measured by infusion of isotopically labelled forms of the acids into the rumen via a cannula and by recording their dilution by newly formed VFA. If only one VFA is infused, production of the others can be estimated from their relative proportions in rumen liquor. However, infusion of all three major acids provides more reliable estimates because it allows for differences between them in rates of production and/or absorption. 

The ammonia in rumen liquor is the key intermediate in microbial degradation and synthesis of protein. If the diet is deficient in protein, or if the protein resists degradation, then the concentration of rumen ammonia will be low (about 50 mg/1) and the growth of rumen organisms will be slow in consequence, the breakdown of carbohydrates will be retarded. On the other hand, if protein degradation proceeds more rapidly than synthesis, then ammonia will accumulate in rumen liquor and the optimum concentration will be exceeded. When this happens, ammonia is absorbed into the blood, carried to the liver and converted to urea (see Fig. 8.8). Some of this urea may be returned to the rumen via the saliva and also directly through the rumen wall, but the greater part is excreted in the urine and thus wasted. 

Estimates of the optimum concentration of ammonia in rumen liquor vary widely, from 85 mg/1 to over 300 mg/1. Rather than expressing the optimum as the concentration in rumen liquor, it would probably be more realistic to relate ammonia to fermentable organic matter, since it is known that for each kilogram of organic matter... 

If the food is poorly supplied with protein and the concentration of ammonia in rumen liquor is low, the quantity of nitrogen returned to the rumen as urea from the blood (see Rg. 8.8) may exceed that absorbed from the rumen as ammonia. This net gain in recycled nitrogen is converted to microbial protein, which means that the quantity of protein reaching the intestine may be greater than that in the food. In this way the ruminant is able to conserve nitrogen by returning to the rumen urea that would otherwise be excreted in urine. 

Collection of rumen liquor used in the first stage of this laboratory procedure presents a number of difficulties. Rumen liquor is collected from animals that have been fitted with a rumen fistula that allows direct access into the rumen. Alternatively, it can be obtained by stomach tube. However, there are animal welfare implications associated with both of these techniques. In addition, rumen liquor may vary in its fermentative characteristics and solids content depending on the diet of the animal from which it is collected. In an attempt to obtain more repeatable estimates of... 

Fig. 10.1 Laboratory methods for estimating the dry matter digestibility of forages, (a) Incubation in rumen liquor followed by digestion with pepsin, (b) Digestion with pepsin followed by digestion with cellulase.

The digestibility of foods may be estimated in the laboratory (in vitro) by incubating them in rumen liquor or various chemical and enzymatic techniques. Near-infrared reflectance spectroscopy (NIRS) is now used routinely to estimate the digestibility of foods for farm advisory work. 

Molar proportion of acetic acid in the volatile fatty acids of rumen liquor... 

It contains 408 g N/kg, equivalent to 2550 g CP/kg. Biuret is utilised by ruminants, but a considerable period of adaptation is required. Adaptation is speeded by inoculation with rumen liquor from an adapted rumen. The nitrogen of biuret is not utilised as efficiently as that of urea, and it is very much more expensive. It has the considerable advantage that it is non-toxic even at levels very much higher than those likely to be found in foods. 

The fatty acids originate from the decomposition of both carbohydrate and protein. McDonald found that ammonia is normally present in small concentrations in the rumen liquor and the introduction of protein causes an increase. This increase is associated with the production of fatty acids, which El Shazly has shown includes isomers of butyric and valeric acids and carbon dioxide. 

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