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PLANT GENETIC RESOURCES

Feed-Quality Variation in the Barley Core Collection of the USDA National Small Grains Collection

^a Animal and Range Sciences, Montana State Univ., Bozeman, MT 59717
^b Plant Sciences, Montana State Univ., Bozeman, MT 59717
^c USDA-ARS National Small Grains Germplasm Research Facility, Aberdeen, ID 83210

* Corresponding author (jbowman{at}montana.edu)

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Feed is an important end use of barley (Hordeum vulgare L.). Recent research has identified high starch content, low acid-detergent fiber (ADF), low ruminal dry-matter digestibility (DMD), and large particle size after dry rolling as desirable barley feed-quality characteristics for beef cattle. Knowledge about the variation available may help barley breeders develop strategies for feed-quality improvement. Our objective was to estimate the variation in feed-quality characteristics in barley around the world. The spring barley core subcollection from the USDA-ARS National Small Grains Collection was planted in 1995. Ruminal DMD of 1480 accessions was evaluated. Seventy-three accessions, selected on variation in DMD, were planted in two field replications in 1996 and 1997. These 73 accessions were evaluated for starch, DMD, ADF, and particle size after dry rolling. The range in DMD was 82 to 621 g kg^-1, with a mean of 398 g kg^-1 (SD = 75 g kg^-1). The ranges for other traits of the 73 selected accessions were 387 to 593 g kg^-1 (starch); 15 to 96 g kg^-1 (ADF); 187 to 510 g kg^-1 (DMD); and 1118 to 1572 µm (particle size). Six-row types had greater ADF and particle size (P < 0.001), lower starch, and DMD (P < 0.001), compared with 2-row types. Starch was higher (P < 0.01), and ADF and DMD were lower (P < 0.01), for hulless than for hulled accessions. Substantial variation in the spring barley core collection for feed quality-related characters could be exploited to develop barley cultivars for feed quality.

Abbreviations: ADF, acid-detergent fiber • DM, dry matter • DMD, ruminal dry-matter digestibility in polyester bags

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
FEED IS AN IMPORTANT END USE OF BARLEY. However, barley cultivars are often developed and selected on the basis of only agronomic and malting-quality characteristics. Barley cultivars may differ for chemical composition (Ovenell-Roy et al., 1998), rate of digestion (Boss and Bowman, 1996b; Surber and Bowman, 1998), and animal performance (Boss and Bowman, 1996a; Ovenell-Roy et al., 1998). Currently there is not a widely accepted set of criteria for determining barley feed quality as there is for barley malting quality. Therefore, barley breeders have been limited in their ability to develop cultivars improved for feed-quality characteristics. Most of the effort in feed-quality improvement has focused on poultry and swine and has resulted in the commercialization of hulless barley cultivars (Classen et al., 1988; Beames et al., 1996).

Compared with hulled barley cultivars, hulless cultivars have a reduced fiber content and an increased starch content due to the absence of the hull (Yang et al., 1997). Most of the fiber components in barley are found in the hull, while the starch is located in the endosperm (Hunt, 1996). Hulless barley cultivars have been shown to have higher digestibility and energy value for pigs (Sus scrofa domesticus) than hulled cultivars (Beames et al., 1996). This is primarily due to the reduction in insoluble non-starch polysaccharides and lignin in hulless cultivars. In particular, the cellulose and insoluble arabinoxylan fractions found in the hull were higher in hulled than in hulless cultivars (Beames et al., 1996), and these fractions were resistant to microbial digestion in the large intestine of the pig (Bach Knudsen and Hansen, 1991). Due to the reduced fiber content and increased starch content, it would appear that hulless barley would have better feed quality for beef cattle compared with hulled cultivars.

Very few studies have addressed differences in feed quality for ruminants between hulled and hulless barley cultivars. Zinn et al. (1996) found the net energy value of hulless barley was 5.6% greater than that of hulled barley for feedlot steers (Bos taurus); however, they did not see a corresponding increase in average daily gain. Zinn et al. (1996) did find lower ruminal pH, and increased incidence of liver abscesses in steers fed hulless barley, both indicative of rapid fermentation and excessive accumulation of acid in the rumen. Extremely rapid ruminal fermentation of barley can increase the incidence of metabolic disorders such as acidosis, laminitis, and bloat (Hunt, 1996; Yang et al., 1997).

Recent research has identified barley-grain characteristics that are important feed-quality traits with respect to beef cattle performance (Surber et al., 2000). These include high starch content, low acid-detergent fiber content (ADF), low ruminal dry-matter digestibility (DMD), and large particle size after dry rolling. Several experiments have demonstrated that significant but limited variation could be found for these traits among barley cultivars commonly grown in the western USA (Bowman et al., 1996; Surber et al., 1999). Most feed-type barley cultivars have been developed from existing cultivars and represent a limited set of germplasm (Martin et al., 1991). If adequate variation in feed-quality characteristics is available, barley cultivars could be selected for improved feed quality.

The USDA-ARS National Small Grains Collection contains 24997 Hordeum vulgare subsp. vulgare accessions. A 2303-entry barley core collection has been developed, of which 1599 have spring growth habit (USDA-ARS, NGRP, 2000). This core collection was selected to represent the genetic diversity found in the germplasm collection. The objective of our study was to determine the maximum range of variation available in feed-quality characteristics in barley germplasm as represented among spring types in the barley core collection of the USDA-ARS National Small Grains Collection.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Fifteen hundred spring barley accessions were selected by Harold Bockleman from the 24997 total Hordeum vulgare subsp. vulgare accessions within the USDA-ARS National Small Grains Collection (USDA-ARS, NGRP, 2000). These accessions represent a spring barley core collection and were selected to reflect broad geographical diversity. This subsample of the spring barley core collection was grown under irrigated conditions at the Arthur Post Research Farm near Bozeman, MT, during 1995. The entries were planted into an Amsterdam silty loam soil, with 60.4 kg N ha^-1, 26.9 kg P ha^-1, and 335.8 kg K ha^-1 fertilizer applied. One field plot per entry was used. Row plots were 2 m in length and spaced 0.33 m apart. Of the 1500 entries seeded, 1480 survived to produce harvestable grain.

Grain samples from the 1480 entries were individually cracked using a Buehler mill (Buehler-Miag, Braunschweig, Germany) to simulate dry rolling processing before feeding barley. To measure ruminal dry-matter digestibility (Vanzant et al., 1998), duplicate 5-g samples of each accession were weighed and placed in 10- by 20-cm, 50-µm pore size polyester bags (Ankom Technology, Fairport, NY). Twenty-nine polyester bags (representing 29 accessions) were placed in the rumen of each of two ruminally cannulated steers at the same time and incubated for 3 h. Two additional empty "blank" bags were included with each incubation to correct for DM content from microbial contamination. A total of 52 sets of 31 polyester bags were placed sequentially in each steer. After removal from the rumen, the bags were rinsed under cold water until the wash water ran clear. The bags were dried at 60°C for 48 h and then weighed. Dry-matter content of the cracked barley samples was estimated by measuring the DM content (AOAC, 1997) of 75 samples and calculating the mean value (948 g kg^-1). Ruminal DMD was calculated according to the following equation:

Seventy-three accessions from the core collection subsample were divergently selected for DMD. The 36 entries with the highest DMD and the 37 entries with the lowest DMD were chosen. Eight contemporary standard spring cultivars (Baronesse, Chinook, Harrington, Lewis, Medallion, Merlin, Morex, and Steptoe) were included. These 81 entries were arranged in a randomized complete block design with two field replications at the Arthur Post Research Farm near Bozeman, MT, in the spring of both 1996 and 1997. Both experiments had two field plots for each entry. Each dryland plot consisted of four rows, 4 m long and 0.33 m apart. Seeding rate was 3 g pure live seed meter^-1 (100 seeds meter^-1). Plots were harvested by a Wintersteiger plot combine when grain moisture was below 120 g kg^-1 as measured by a Motomco automatic moisture meter (Motomco, Inc., Paterson, NJ).

From the selected 73 accessions and eight standard cultivars harvested in both 1996 and 1997, an aliquot of each barley sample was ground through a 0.5-mm screen in a Udy Cyclone Mill (Udy Corp., Fort Collins, CO) and analyzed for ADF content (Van Soest et al., 1991) and starch content (AOAC, 1997). Dry matter (AOAC, 1997) and ruminal DMD (Vanzant et al., 1998) were measured on barley samples that had been cracked through a Buehler mill, using the same method for DMD described above. Residues in the nylon bags were also analyzed for starch content, which allowed the calculation of ruminal starch digestibility. Digestible starch content of the barley was calculated by multiplying starch content by ruminal starch digestibility. Mean particle size was determined on the cracked barley samples by a dry-sieving technique (Fisher et al., 1988).

The feed-quality data from 1996 and 1997 were analyzed as a replicated, randomized complete block design, using the GLM procedure of SAS to test the effects of year, genotype, and the year x genotype interaction. A second analysis of variance was conducted, as a replicated 2 x 2 x 2 x 2 factorial, to measure the effects of year, head type (2-row vs. 6-row), hull type (hulled vs. hulless), and aleurone color as determined visually (light vs. dark). All appropriate interactions were tested. When a significant F-value (P < 0.05) was found, the means were separated using Fisher's protected least significant difference values. A Pearson correlation coefficient matrix was calculated. Statistical computations were performed with SAS 7.00 for Windows 98 (SAS Inst., Cary, NC, 1998).

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The frequency distribution for ruminal DMD measured in the USDA spring barley core collection grown in 1995 is presented in Fig. 1. A wide range was found in DMD between the highest (621 g kg^-1) and lowest (82 g kg^-1) plant introductions with a mean of 398 ± 75 g kg^-1.

View larger version (16K): [in this window] [in a new window]   Fig. 1. Frequency distribution for ruminal dry-matter digestibility (DMD) measured in the USDA spring barley core collection (n = 1480) grown in 1995 (black bars), the 73 accessions selected for low (n = 37) and high (n = 36) DMD and grown in 1996 and 1997 (light bars = mean values), and the eight check cultivars grown in 1996 and 1997 (white bars = mean values).

View this table: [in this window] [in a new window]   Table 4. Population means and ranges for feed-quality characteristics of 73 barley accessions from the USDA spring barley core collection, selected for low (n = 37) and high (n = 36) ruminal dry-matter digestibility (DMD), and eight check cultivars grown in 1996 and 1997.

In the 73 selected accessions grown in 1996 and 1997, 6-row types had greater (P < 0.001) dry matter, ADF content, and particle size, and lower (P < 0.001) starch content, DMD, ruminal starch digestibility, and digestible starch content, compared with 2-row head types (Table 5). Six-row check cultivars had greater (P = 0.03) ADF content (42 vs. 34 g kg^-1) and lower (P = 0.01) starch content (526 vs. 553 g kg^-1) than 2-row check cultivars. All of the other feed-quality characteristics were similar (P > 0.10) between 6-row and 2-row checks. Lehman et al. (1995) evaluated 12 2-row cultivars and 10 6-row cultivars that had been grown at three locations in Alberta, Canada, and reported 6-row types to have lower DMD than 2-row types. Grain of 2-row head types have been shown in other studies to elicit higher animal performance compared with grain of 6-row types, when fed in high-concentrate diets (Boss and Bowman, 1996a; Ovenell-Roy et al., 1998). The higher animal performance shown with 2-row barley cultivars may be due to the higher starch content and lower ADF content found in 2-row types compared with 6-row types.

Aleurone color did not affect (P > 0.10) DM, starch content, ADF content, or particle size of the 73 selected core collection accessions. However, DMD, ruminal starch digestibility, and digestible starch content were greater (P < 0.05) for accessions with light-colored aleurone than for those with dark aleurone. None of the check cultivars had dark aleurone, so no comparison of the effect of aleurone color could be made among the checks. Dark aleurone color in barley is due to anthocyanin and proanthocyanidin pigments. These flavonoids have been shown to inhibit growth of certain microorganisms, bind to proteins and polysaccharides, and interfere with enzyme activity (Shirley, 1998). Yu et al. (1995) reported proanthocyanidins in cottonseed hulls reduced the ability of rumen microorganisms to degrade cottonseed proteins. Interference with enzyme activity or growth of rumen microbes by flavonoids could result in the observed reduced DMD for dark pigmented aleurone accessions.

Genotype effect was significant (P < 0.005) for all feed-quality traits measured in the 73 selected accessions. Among the check cultivars, only ADF content differed among genotypes (P = 0.0001). Merlin had the lowest (P = 0.0001) ADF content (22 g kg^-1) and Steptoe had the highest (P = 0.0001) ADF content (65 g kg^-1), followed by Medallion (58 g kg^-1), Baronesse (50 g kg^-1), Harrington (46 g kg^-1), Lewis (44 g kg^-1), Chinook (43 g kg^-1), and Morex (40 g kg^-1). Molina-Cano et al. (1997) reported genotype effects for nutritional characteristics measured in five barley cultivars in Spain. No year x genotype interactions (P > 0.10) were detected.

Significant correlations (P < 0.01) were found among all of the feed-quality characteristics (Table 6). Digestibility traits were positively correlated (P = 0.0001) with starch content and negatively correlated (P < 0.01) with ADF content and particle size. Starch content was negatively correlated (P = 0.0001) with ADF content and particle size, while ADF content and particle size were positively correlated (P < 0.01). Surber et al. (1999) reported correlations between laboratory feed-quality characteristics and animal performance by steers fed barley high-concentrate diets, and found ADF content was negatively correlated with DMD (r = -0.81; P = 0.01), and DMD was negatively correlated with steer average daily gain (r = -0.63; P = 0.01). Fairbairn et al. (1999) found ADF content of five barley cultivars to be negatively correlated and starch content to be positively correlated with digestible energy content for pigs. In addition, of the barley physical, chemical, and digestibility characteristics they measured, ADF content was determined to be the most significant variable influencing energy value. Negative correlations were found between fiber content and apparent digestible energy of barley for swine (Beames et al., 1996) and poultry (Molina-Cano et al., 1997). Engstrom et al. (1992) reported that feed efficiency in beef cattle fed barley-based diets declined as the ADF content of barley increased, and improved as starch content increased. In addition, they concluded that measuring ADF content could be used to predict barley feed quality.

Barley net energy content, feed efficiency, and average daily gain are all economically important performance parameters in feeding beef cattle and appear to be successfully predicted from starch content, ADF content, particle size, and DMD (Surber et al., 2000). High starch content would provide more available energy to the animal, while low ADF content would reduce the amount of less digestible cellulose and lignin (Hunt, 1996). Lower DMD of barley would shift more of the starch digestion from the rumen to the small intestine, in effect making barley more like corn in site of digestion. Starch digestion in the small intestine has been estimated to provide 42% more energy than starch digestion in the rumen (Owens et al., 1986) due to reductions in energy loss via methane production and more efficient use of glucose as an energy source compared with volatile fatty acids. In addition, lower DMD would reduce excessive fermentation acid production and reduce the incidence of bloat, acidosis, and laminitis (Hunt, 1996). Larger particle size has been shown to provide a relatively smaller available surface area for microbial colonization and subsequently a slower rate of digestion, compared with smaller particle size (Ewing et al., 1986). Therefore, larger particle size will reduce DMD and have the same effect on animal performance as lower DMD. In addition, larger particle size in grain has been linked to improvements in palatability and intake by cattle (Hunt, 1996). Selection of barley grain for low DMD, low ADF content, high starch content, and large particle size should allow progress in breeding for improved feed quality.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Substantial variation exists among accessions selected from the barley core collection grown in Montana for starch content, ADF content, particle size, DMD, ruminal starch digestibility, and digestible starch content. The barley core collection appears to contain a wider range in variation for these traits than is present in a sample of western North American contemporary cultivars in production. The recently released cultivar ‘Valier’ (PI 610264) was developed as an improved feed-quality barley using the narrow genetic base of European 2-row germplasm in production in western North America. With the availability of greater variation in feed-quality traits from the accessions in the barley core collection, it seems probable that greater improvement could be made in feed-barley quality. The potential exists to exploit this variation in starch content, ADF content, particle size, and DMD for the development of improved barley germplasm specifically designed for feed quality.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Contribution of the Montana Agric. Exp. Stn.

Received for publication August 10, 1999.

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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (12) Citing Articles via Google Scholar Google Scholar Articles by Bowman, J.G.P. Articles by Bockelman, H. Search for Related Content PubMed Articles by Bowman, J.G.P. Articles by Bockelman, H. Agricola Articles by Bowman, J.G.P. Articles by Bockelman, H. Related Collections Other Grain Crops Plant Genetic Resources