عنوان مقاله [English]
Introduction Barley is a major cereal grain in Iran. It is the primary constituent of concentrate rations for dairy and beef cattle as sources of energy and protein. The cultivation areas of barley is about 1.68 million ha which normally produce 3.4 million tones of grains. Depending upon local climate condition in Iran, plant breeding experts developed different types of barley (moderate, cold, and dry). Differences in the nutritional characteristics among barley varieties have been reported. Barley cultivars differ in chemical composition and ruminal digestion characteristics. In-vitro gas production results also show there are significant differences in ruminal dry matter disappearance among Iranian barley cultivars. These differences may be attributed to carbohydrate and protein fractions such as rapidly degradable protein and carbohydrate (PA and CA). Little research has been conducted to determine the differences between and within varieties of barley in terms of carbohydrate and protein fractions. This study was carried out to determine protein and carbohydrate fractions of barley cultivars.
Materials and Methods Barley cultivars including: 1- cv. Yousef, 2- cv. Nosrat, 3- cv. CB.79.10, 4- cv. Makooei, 5- cv. Abidar, and 6- cv. Sararood were obtained from Karaj Research Station which is located in central Tehran. Samples were ground using a Retsch ZM200, Rose, Scientific Ltd., Canada through a 0.5 mm screen for starch analysis and through a 1 mm screen for other chemical analyses. Dry matter (DM), ash, crude fat, and crude protein (CP) contents were analyzed according to the procedure of the AOAC. The acid detergent fiber (ADF), neutral detergent fiber (NDF), and acid detergent lignin (ADL) values were analyzed. The starch was analyzed using the Megazyme Total Starch Assay Kit (Megazyme International Ltd., Wicklow, Ireland). The non protein nitrogen content was obtained by precipitation of true protein in the filtrate with trichloroacetic acid and determined as the difference between total N and the N content of the residue after filtration. The amount of CP associated with NDF was determined by analyzing the NDF residues for CP. Soluble crude protein was determined by incubating the sample with bicarbonate-phosphate buffer and filtering through Whatman filter paper. The carbohydrate (CHO) was calculated according to formulas of the NRC dairy. Crude protein and carbohydrate fractions were partitioned according to the Cornell Net Carbohydrate Protein System. The CP fractions are: (1) non protein nitrogen (PA), (2) true protein, and (3) unavailable protein (PC). The true protein fraction is divided into three fractions: (1) rapidly degradable (PB1), (2) intermediately degradable (PB2), and (3) slowly degradable (PB3). The rapidly degradable fraction was determined as the trichloroacetic acid-precipitable fraction. The intermediately degradable fraction of true protein is insoluble in buffer, but soluble in neutral detergent. The slowly degradable fraction is believed to be more slowly degraded in the rumen than fractions rapidly and intermediately degradable because of its association with the plant cell wall; thus, a large proportion of this fraction is believed to escape the rumen. The unavailable protein fraction is the acid detergent insoluble N. Carbohydrate was fractionated into (1) soluble fraction (CA), which is composed of fermentable soluble sugars, (2) intermediately degradable fraction (CB1), which is starch and pectin, (3) slowly degradable fraction (CB2), which is the available cell wall with a slow degradation rate of 0.02-0.10 h-1, and an unfermentable fraction, which is the unavailable cell wall (CC).
Results and Discussion Barley cultivars had 49-55 % of DM starch and 9-14 % of DM crude protein. They differed in crude protein, soluble protein, neutral detergent fiber, non-protein nitrogen, and neutral detergent insoluble protein. Makooei had the greatest amount of crude protein and non-protein nitrogen, and the lowest amount of neutral detergent insoluble protein. Barley cultivars differed in protein and carbohydrate fractions. Makooei had the greatest amount of PA and the lowest amount of PB1and PB3. Abidar had the greatest amount of PB1, NSC and the lowest amount of CB2.
Conclusion Type of cultivar had significant effect on the protein and carbohydrate fractions of barley. Difference in protein and carbohydrate fractions can be influenced the protein and carbohydrate availability in ruminants. Results of the current study can be used to select and improve barley cultivars and accurate ration formulation in ruminants.