The effect of barley cultivar on in vitro digestibility and rumen degradability of NDF *

The objective of this study was to determine the effect of winter, spring, and naked barley cultivars on in vitro true digestibility (IVTD) and NDF degradability in the rumen determined by the in situ method. Differences in IVTD and effective rumen degradability (ERD) of NDF between barley cultivars were revealed. The highest IVTD and ERDNDF values were found for naked-, and the lowest, for winter cultivars. It is recommended to use the different nutritive values of each barley type (winter, spring, naked) in feeding tables instead of one common value.


INTRODUCTION
The chemical composition and rumen degradability parameters of individual barley cultivars are variable.In general, winter cultivars have a higher content of structural carbohydrates, which is responsible for the lower availability of nutrients in the rumen (Micek et al., 2005).The rate and extent of their fermentation in the rumen are, therefore, strongly correlated with some fibre components (Firkins et al., 2001) that are needed for proper nutritive evaluation of barley.The well-known variability in the nutritive value of barley is still not being taken into consideration in feeding tables for ruminants.The objective of this study, therefore, was to determine the effect of winter, spring, and naked barley cultivars on in vitro dry matter digestibility and NDF degradability in the rumen, and to find the most effective parameters affecting dry matter digestibility and rumen NDF degradability.

MATERIAL AND METHODS
The chemical composition of five winter cultivars (Gregor, Gil and Sigra -multiline; Bombay and Tiffany -two-line), four spring cultivars (Stratus and Rudzik -brewery; Rodos and Rodion -fodder), and one naked spring cultivar (Rastik) was determined using standard methods (AOAC, 1995).Barley samples were also analysed for starch content by the method of Faisant et al. (1995) and NDF, ADF and ADL according to Goering and Van Soest (1970).Prior to the in situ and in vitro experiments, the barley samples were ground to pass through a 1.5 mm screen.In situ ruminal degradability was determined by the method of Michalet-Doreau et al. (1987), using 3 rumen fistulated heifers fed standard diets.The effective rumen digestibility (ERD) and the digestibility rate constants (A, B, C) were calculated according to Ørskov and McDonald (1979) at a ruminal outflow (k) of 0.06 h -1 .In vitro true digestibility (IVTD) was estimated in a Daisy II Incubator (Ankom Co, Fairport, NY) based on the Van Soest et al. (1966) tube procedure (incubation in buffering ruminal fluid for 48 h).The data were subjected to one-way analysis of variance using the GLM procedure of SAS (SAS, 1995).

RESULTS
Barley cultivars differed in chemical composition (Table 1) and rumen DM degradability (Table 2), with the spring cultivars having generally higher susceptibility to DM degradation in the rumen.There were also significant differences between cultivars in rumen NDF degradability parameters (Table 2 and Figure 1).The average ERD NDF of spring cultivars (53.4%) was significantly higher than that of winter ones (39.9%;P<0.01).Similarly, IVTD for spring (89.4%) was higher than for winter ones (86.6%;P<0.05).The highest ERD NDF and IVTD were found for naked barley (80.6 and 95.8%, respectively).IVTD was strongly correlated with ERD NDF (r 2 =0.88,P<0.01).A significant correlation between ERD NDF and fraction A of NDF degradability

DISCUSSION
The results of this study confirm the variation in DM digestibility and rumen NDF degradability among barley cultivars.This variability can strongly affect the precision of diet formulation (Firkins et al., 2001).The most important factor responsible for both NDF degradability and IVTD was the easily degradable fraction of NDF (A).On the other hand, ADF was the most significant chemical variable influencing the nutritive value of barley.The other chemical variables seem to be less important for its nutritive evaluation.

CONCLUSIONS
The use of three different nutritive value parameters for each of type of barley (winter, spring and naked) instead of one common value in feeding tables should be recommended.

Figure 1 .
Figure 1.Effect of barley cultivar on ruminal NDF degradability

Table 1 .
Chemical composition of barley cultivars, g kg -1 DM

Table 2 .
In vitro true digestibility (IVTD) and in situ DM and NDF degradability parameters