Materials and Methods

ABSTRACT: The purpose of this study was to measure the variation in digestibility characteristics of barley in the rat. Seventy-three barley lines were selected from the USDA Barley World Collection and grown in a field trial in Bozeman during spring 1998. Thirty-two weanling Sprague-Dawley rats were assigned to one of 16 diets based on twelve World Collection genotypes and four control varieties (Morex, Steptoe, Nubet and Shonkin) in a completely randomized design. The twelve World Collection genotypes were selected for feeding to rats on the basis of variation in in situ DMD (ISDMD) in cows. The diet adaptation period consisted of 3 d prior to the 19-d collection period. Rats had ad libitum access to diets consisting of 80% barley, and balanced for 17% CP. The barley used in diets was ground through a 1-mm screen in a Wiley mill. Total fecal collection was from d 8 to d 14. Diet and fecal samples were analyzed for DM, ADF, and starch. The data were analyzed to test the effects of barley genotype. Barley genotype had no effect (P > .10) on ADG (avg 7.73 g/d), starch digestibility (avg 99.96%), or DMI (avg 22.2 g/d) by rats. Rats fed WC115 (CI3709) had the lowest (P < .001) DMD (80.14%), while those fed Shonkin had the highest (91.08%). Genotype WC115 contained the highest level of ADF (9.48%). Percent ADF in the barley lines ranged from 1.91% to 9.48%, with a mean of 4.6% (SD = 1.8) Rats fed WC592 (PI280441) had the lowest (P < .001) ADF digestibility (.79%), and those fed Shonkin had the highest (45.29%). A negative correlation was found between ADF content and DMD (r = -.77, P < .001). Substantial variation existed between barley genotypes for digestibility characteristics in the rat. Available variation in barley genotypes could be exploited for the development of improved feed quality barley.

Key Words: Barley, Feed quality, Digestibility, Rat

Introduction

Research on barley feed quality characteristics in doubled haploid lines (Bowman et al., 1996) and in barley from around the world (Bowman et al., 1997) has established that substantial variation exists in starch, ADF, and in situ DMD. The purpose of this study was to measure the variation in digestibility characteristics of barley genotypes from the World Barley Core Collection in the rat.

Materials and Methods

Twelve genotypes from the USDA Barley World Core Collection (Table 2) and four control varieties (Morex, Steptoe, Nubet and Shonkin) were selected for feeding to rats based on variation in in situ DMD (Bowman et al., 1997). The grains were grown in a field trial in Bozeman during spring 1998. Barley samples for laboratory analysis were ground through a .5-mm screen using a Udy-Cyclone mill (Ft. Collins, CO) and analyzed for DM (AOAC, 1997), ADF (Van Soest et al., 1991), and N (Leco Corporation, St. Joseph, MI). The starch content was determined using an amyloglucosidase/a-amylase method (AOAC, 1997).

Prior to diet mixing, barleys were ground through a 1-mm screen using a Wiley mill (Table 1). Diets were mixed containing 80% barley and balanced for 17% CP, utilizing protein from the grain and purified casein. The percent casein added ranged from 3.0% to 6.47% (Table 1). Lysine and methionine were added to meet nutrient requirements of the rat (NRC, 1995).

Thirty-two male weanling Spague-Dawley rats (2 rats/treatment) were housed in individual metabolic cages with stainless steel mesh bottoms. The cages were kept in a thermoregulated room at 22°C and approximately 18% relative humidity, with a controlled 12-h light/dark period. Rats were assigned test diets in a completely randomized design. Three days were allowed for adaptation to the diets and experimental conditions before the collection period began. The collection period consisted of 19 d, and all animals had ad libitum access to feed and water. The following parameters were measured for each rat: body weight (d 1, d 8, d 14, and d 19), daily feed intake, daily feed refusal, and seven days of total fecal collection (d 8 to d 14).

Lyophilized feces were analyzed for DM (AOAC, 1997), ADF (Van Soest et al., 1991), and starch (AOAC, 1997). The protein efficiency ratio (PER; weight gain/protein intake) and DM, starch, and ADF digestibility of the barley diets were calculated.

Data were analyzed using the GLM procedure of SAS (1996) to test for diet effects. When a significant F value was detected (P < .10) means were separated using Duncan’s New Multiple Range Test. Correlations were made using PROC CORR, and regression analysis with PROC STEPWISE (SAS, 1996).

Results and Discussion

Protein efficiency ratio is the simplest method for evaluating protein quality in non-ruminants, and was used as early as 1917 (Osborne et al., 1919). Diet had no effect (P = .18) on ADG, but did affect (P = .02) PER, even though diets were isonitrogenous (Table 3). There was no relationship (P > .10) between PER and percentage casein added to the diet. Rats fed the WC1256 diet had a 24% higher (P < .01) PER than those fed the WC88 diet (2.37 vs 1.91, respectively). Rats fed Shonkin had the highest (P = .01) PER and those fed Morex had the lowest (2.40 vs 1.88, respectively). Average daily gain was positively correlated with DMI (r = .66; P = .0001), N intake (r = .48; P = .006), and starch intake (r = .37; P = .04). Stepwise regression analysis indicated the following equations represented the relationships between ADG and PER, and digestible DMI (DDMI), starch digestibility (SDIG), ADF digestibility (ADFDIG), barley starch content (BSTAR), and DMD:

ADG = -173 + .41(DDMI) + 1.72(SDIG) - .01(ADFDIG)

- .05(BSTAR) + .07(DMD)

(R² = .71; P = .0001)

PER = -47 + .04(DMD) + .49(SDIG) - .004(ADFDIG)

(R² = .61; P = .01)

Diet had no effect on DM intake (P = .74), starch digestibility (P = .22), or DDMI (P = .63; Table 4). The range in starch digestibility (99.41 to 99.83%) demonstrated normal values in the rat. Previous studies have shown that the digestibility of starch in non-ruminants approaches 100% (Haung et al., 1998). Diet affected (P = .0005) digestible starch intake (DSI). Rats fed a diet based on Nubet had 50% greater (P = .0005) digestible starch intake than rats fed the WC1506 diet (15.52 vs 10.34 g/d, respectively).

The range in DMD was from 79.9 to 91.6%, with a mean value of 85.5% (Table 4). Rats fed diets based on Shonkin had 13.65% higher (P = .0002) DMD than rats fed WC115 (91.08 vs 80.14%, respectively). We found DMD to be negatively correlated with diet ADF content (r = -.70; P = .0001). The diet based on WC115 had the highest ADF content (8.0%), and ranked eighth of 16 diets in ADF digestibility. This may be partially explained by differences in kernal morphology. Shonkin is a hulless 2-row variety, and WC115 is a covered 6-row genotype.

Diet affected ADF digestibility (P = .0001; Table 4). Rats fed WC592 had the lowest (P = .0001) ADF digestibility, while those fed Shonkin had the highest (.79 vs 45.29%, respectively). Barley ADF content ranged from 1.99 to 9.48%, with a mean of 4.6%. Examination of the ADF content of diets based on World Collection barley genotypes shows that the WC115 diet contained the highest level of ADF (8.0%) and the WC1064 diet the lowest 2.24% (Table 2). However, the ADF digestibility was very similar for these two diets (13.0 and 13.79%; Table 4). In addition, the WC1506 diet had 47% higher (P = .0001) ADF digestibility than the WC592 diet (34.94 vs .79%, respectively). The ADF contents of these diets were 5.0% and 4.0%, respectively. It appears the most influential factor affecting variation in barley DM digestibility in the rat was ADF content and digestibility.

Cellulose, hemicellulose, pectin, lignin, and digestion resistant starch have modifying effects on energy metabolism and digestibility of starch and fats in the non-ruminant intestinal track (Craig et al., 1998). Inclusive of these fiber fractions are the soluble and insoluble b-glucans. Studies have has shown that the ileal digestibility of starch and N were decreased when broiler chicks were fed barley diets (Hesselman and Aman, 1986). It is suggested that the increased viscosity of intestinal contents, due to b-glucans may play an important role in depressing the digestion and absorption of nutrients (Almirall et al., 1995).

Correlation analysis was conducted between rat digestibility data and laboratory measures collected by Bowman et al. (1997) for the World Collection genotypes grown during 1995 and 1996. Barley ADF was correlated with rat DMI (r = .59; P = .03) and rat DMD (r = -.67; P = .01). Additionally, rat DMD was correlated with cow in situ DMD (r = .67; P = .01) and barley particle size after dry rolling (r = -.83; P = .0003).

Implications

Substantial variation in digestibility characteristics in the rat existed in the World Collection barley genotypes tested. Research to determine the effects of the various fiber components on digestibility may be warranted and aid in developing barley feed quality criteria.

Literature Cited

Almirall, M., M. Francesch, A. M. Perez-Vendrell, J. Brufau, and E. Esteve-Barcia. 1995. The differences in intestinal viscosity produced by barley and b-glucanase alter digesta enzyme activities and ileal nutrient digestibilities more in broiler chicks than in cocks. J. Nutr. 125:947-955.

AOAC. 1997. Official Methods of Analysis (15th Ed.). Association of Official Analytical Chemists, Arlington, VA

Bowman, J.G.P., T. K. Blake, L.M.M. Surber, D. K. Habernicht, T. K. Daniels, and J. T. Daniels. 1996. Genetic factors controlling digestibility of barley for ruminants. Proc. West. Sect. Am. Soc. Anim. Sci. 47:257-260.

Bowman, J.G.P., L.M.M. Surber, T. K. Daniels, D. P. Kirschten, N. T. Cote, and T. K. Blake. 1997. Variation in feed quality characteristics in the world barley collection. Proc. West. Sect. Am. Soc. Anim. Sci. 48:161-163.

Craig, S.A.S., J. F. Holden, J. P. Troup, M. H. Auerbach, and H. I. Frier. 1998. Polydextrose as soluble fiber: physiological and analytical aspects. Cereal Foods World. 43 (5):370-376.

Huang, S. X., W. C. Sauer, M. Pickard, S. Li, and R. T. Hardin. 1998. Effect of micronization on energy, starch and amino acid digestibility in hulless barley for young pigs. Can. J. Anim. Sci. 78:81-87.

Hesselman, K., and P. Aman. 1986. The effect of b-glucanase on the utilization of starch and nitrogen by broiler chickens fed on barley of low and high viscosity. Amin. Feed Sci. Technol. 15:83-93.

NRC. 1995. Nutrient Requirements of Laboratory Animals (4th Revised Ed.). National Academy Press, Washington, DC.

Osborne, T. B., L. B. Mendel, and E. L. Ferry. 1919. A method of expressing numerically the growth-promoting value of proteins. J. Bio. Chem. 37:223-229.

SAS. 1996. Release 6.12. SAS Inst. Inc., Cary, NC.

Van Soest, P. J., J. B. Robertson, and B. A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74:3583-3597.

Table 1. Composition of barley diets fed to rats.
	Barley	80.0%
	Casein	3.0-6.47%
	Soybean Oil	3.86%
	Corn starch	4.46-7.55%
	Vitamin mix (AIN 76A, ICN Pharmaceuticals)	1.0%
	Mineral mix (AIN 93G, ICN Pharmaceuticals)	3.5%
	L-Lysine	to equal .92%
	Methionine	to equal .98%

Table 2. Chemical composition of barley diets fed to rats (DM basis).

Barley Genotype diet	Plant/crop introduction number	Hull type*	Head Type	CP, %	Starch, %	ADF,%
WC1064	PI370970	N	6-row	17.75	54.41	2.24
WC115	CI3709	H	6-row	16.65	50.05	8.00
WC1256	PI420463	H	6-row	17.12	56.18	4.09
WC1271	PI428499	H	2-row	17.32	53.68	3.79
WC1299	PI436140	H	2-row	17.33	55.67	3.56
WC1304	PI436149	H	2-row	17.48	52.45	4.51
WC1506	PI564478	H	2-row	18.49	49.18	5.00
WC179	CI5003	H	6-row	17.13	51.02	5.01
WC297	PI539120	H	6-row	16.69	52.37	5.80
WC387	PI188831	H	2-row	17.27	51.55	5.01
WC592	PI280441	H	2-row	16.72	52.28	4.00
WC88	CI2631	H	2-row	17.04	61.00	5.78
Steptoe		H	6-row	15.74	53.76	4.74
Morex		H	6-row	18.82	59.47	4.62
Nubet		N	2-row	17.05	65.57	1.77
Shonkin		N	2-row	16.17	60.00	2.32

*N = hulless, H = covered.

Table 3. Protein intake and weight change in rats fed diets containing different barley genotypes.

Barley	Protein intake, g/d	ADG, g/d	Protein efficiency ratio*
WC1064	3.70	7.45	2.02^def
WC115	3.92	8.53	2.18^abcdef
WC1256	3.86	9.13	2.37^ab
WC1271	4.02	8.58	2.13^abcdef
WC1299	3.67	7.87	2.15^abcdef
WC1304	3.60	7.42	2.07^bcdef
WC1506	3.81	7.53	1.98^def
WC179	4.03	8.27	2.05^cdef
WC297	3.70	8.21	2.22^abcd
WC387	3.70	8.32	2.25^abcd
WC592	3.76	8.77	2.33^abc
WC88	3.75	7.21	1.91^ef
Steptoe	3.57	7.74	2.17^abcdef
Morex	4.27	8.00	1.88^f
Nubet	3.85	8.48	2.20^abcde
Shonkin	3.63	8.69	2.40^a
P	.59	.18	.02
SEM	.20	.44	.09

*[none1] Weight gained (g/d)/protein intake (g/d).

^abcdef Within a column, means without a superscript letter in common differ (P < .05).

Table 4. Digestibility of diets based on different barley genotypes in the rat.

Barley	DMI, g/d	Starch intake, g/d	ADF intake, g/d	DMD, %	Starch digestibility, %	ADF digestibility, %	Digestible DMI, g/d	Digestible starch intake, g/d	Digestible ADF intake, g/d
WC1064	20.84	11.68^def	.48ⁱ	85.34^cd	99.47	13.00^cde	17.76	11.62^def	.06^d
WC115	23.57	12.13^cdef	1.89^a	80.14^e	99.52	13.79^cde	18.89	12.07^cdef	.26^bc
WC1256	22.56	13.03^bcd	.94^efg	86.53^bc	99.67	9.46^de	19.53	12.98^bcd	.09^d
WC1271	23.21	12.91^bcde	.86^fg	86.17^bc	99.60	1.29^e	19.99	12.86^bcde	.01^d
WC1299	21.18	12.25^cdef	.74^gh	86.38^bc	99.61	5.22^e	18.28	12.20^cdef	.04^d
WC1304	20.58	11.06^ef	.97^ef	86.22^bc	99.66	26.42^bc	17.73	11.02^ef	.25^bc
WC1506	20.63	10.37^f	1.09^cde	86.04^bcd	99.76	34.94^ab	17.75	10.34^f	.38^ab
WC179	23.52	12.27^cdef	1.20^bcd	83.04^d	99.64	8.36^de	19.52	12.23^cdef	.10^d
WC297	22.16	11.67^def	1.40^b	84.71^cd	99.81	32.81^ab	18.77	11.64^def	.46^a
WC387	21.45	11.70^def	1.04^def	84.71^cd	99.75	8.64^de	18.16	11.67^def	.09^d
WC592	22.50	12.17^cdef	.88^efg	85.88^bcd	99.61	0.79^e	19.32	12.12^cdef	.01^d
WC88	22.01	14.34^ab	1.31^bc	82.94^d	99.53	26.76^bc	18.27	14.27^ab	.35^ab
Steptoe	22.67	12.32^cde	1.10^cde	84.69^cd	99.61	1.21^e	19.19	12.27^cde	.01^d
Morex	22.67	14.25^ab	1.09^cde	85.54^cd	99.66	23.88^bcd	19.39	14.20^ab	.26^bc
Nubet	22.59	15.57^a	.43ⁱ	88.74^ab	99.69	30.65^ab	20.03	15.52^a	.13^cd
Shonkin	22.45	13.85^abc	.59^hi	91.08^a	99.80	45.29^a	20.44	13.82^abc	.27^bc
P	.74	.0006	.0001	.0002	.22	.0001	.63	.0005	.0001
SEM	1.15	.56	.07	.92	.08	4.96	.95	.55	.04

^abcdefghi Within a column, means without a superscript letter in common differ (P < .05).

COLLECTION IN RATS