Changes in Forage Yield and Composition of Wheat and Wheat-Ryegrass Mixtures with Maturity1

Changes in Forage Yield and Composition of Wheat and Wheat-Ryegrass Mixtures with Maturity1 D. W. WALKER,2 C. P. WEST,3 R. K. BACON,3 D. E. LONGER,3 and K. E. TURNER3 Altheimer Laboratory 276 Altheimer Dr. University of Arkansas Fayetteville 72703 ABSTRACT

INTRODUCTION

Our objectives were to compare wheat and wheat-ryegrass mixtures for patterns of OM accumulation and forage quality changes with maturity. Two genotypes of soft red winter wheat ('Magnum' and the hybrid 'HW 3015') were grown alone or in mixture with 'Marshall' annual ryegrass. Plots were harvested at six wheat growth stages from beginning of pseudostem elongation to soft dough. Handclipped samples were separated into species and leaf and stem (including inflorescence) components. and the components were analyzed for NDF and in vitro OM disappearance. Annual ryegrass in mixture with wheat did not enhance the forage yield over wheat alone; however, the later maturity of ryegrass in relation to wheat resulted in a slower decline in total mixture leaf proportion with advancing maturity than in wheat alone. Enhanced leafiness did not, however, augment total mixture in vitro DM disappearance over that of wheat alone because of the low in vitro DM disappearance of ryegrass stems. If wheat is to be grown for harvest at the soft dough stage for forage, it should not be grown with annual ryegrass, because the latter dilutes the high quality, wheat grain portion with low quality ryegrass stems. (Key words: stage of maturity, wheat, ryegrass)

Winter wheat (Triticum aestivum L.) grown in the southern United States can provide fall and winter grazing for dairy cattle with an option in the spring fOI hay, silage, or grain production. or continued grazing. Wheat can be utilized as a high quality forage to provide cool season grazing on dormant bermudagrass [eynodon dactylon (L.) Pers.] or to replace endophyte-infected tall fescue (Festuca arundinacea Schreb.) pastures. Owing to its late maturation, annual ryegrass (Lotium multiflorum Lam.) may be grown in mixture with winter wheat to extend the spring grazing season (8). Changes in forage quality with maturity have been well documented for pure stands of wheat (1, 4); however, little is known how the presence of annual ryegrass in mixture with wheat influences quality of the total harvested forage or how leaf and stem fractions of wheat and ryegrass mixtures change with maturity. Most research on wheat forage quality has been done on growth stages from the boot stage through grain filling. Specific information is lacking on quality changes during vegetative stages with wheat in mixture with ryegrass and on the relative contributions of the two species to total forage OM accumulation. As small grain plants develop from vegetative stages through flowering and grain filling in the spring, increases in OM yield are accompanied by decreases in forage quality and leafiness (1). Digestibility and leafiness of whole forages are usually positively correlated (3). Terry and Tilley (11) showed that all parts of cool season, perennial grasses at early stages of growth are highly digestible; however, during stem elongation and flowering, decline in the digestibility of stem than of leaf tissue was more rapid. Hoveland and Monson (5) explained the general decline of forage quality with plant maturity as a combination of struc-

Received June 9, 1989. Accepted December 11,1989. I Published with approval of the Director of the Arkansas Agricultural Experiment Station. 2-rexas A&M University. Dallas 75252. 3Depanment of Agronomy. 1990 J Dairy Sci 73:1296-1303

1296

WHEA T-RYEGRASS MIXTURES FOR FORAGE

1297

tural cell wall accumulation, increased leaf loss, and decrease in leaf proportion. Cherney and Marten (1) studied morphological and anatomical changes with maturity in small grain forages to explain better the changes in quality. Results indicated that lignin concentrations increased with maturity in the leaf blade, leaf sheath, and stem. Increased lignin concentration corresponded to decreased in vitro DM digestibility of each plant component. These authors further reported a progressive increase in inflorescence digestibility and an increase in its proportion of the total shoot dry weight during grain filling. Accumulation of highly digestible, low fiber grain in the inflorescence partly offset the declining digestibility of the stem, leaf blade, and leaf sheath. Lignin accumulation in the stem was the major factor associated with reduced whole plant digestibility with increased maturity. An analysis of forage quality changes of a mixture over stages of maturity necessitates that such changes be determined for the individual components of the mixture in relation to their respective DM contributions. Roberts et al. (9) evaluated the effect of vetch (Vida villosa Roth) seeding rates on total forage mixture and individual species quality parameters at three growth stages. Inclusion of vetch improved CP and NDF concentrations and in vitro DM disappearance (lVDMD) of the mixture. The objectives of this research were to compare wheat and wheat plus ryegrass for patterns of DM accumulation and forage quality compositional changes from early vegetative to soft dough stage and to determine the effect of annual ryegrass presence on forage DM accumulation and composition.

respectively, on September 25, 1984 and September 17, 1985. Plots were 1.5 m x 6.1 m and were planted with a seven-row cone seeder. The experimental design was a split-plot, randomized complete block in four replications per year with harvest at six stages of wheat maturity in the whole plots. Stage of maturity of the plot was defined as that attained by 50% of the wheat tillers. Stages were as follows with the Zadoks et al. (13) growth stage number in parentheses: beginning of pseudostem elongation (stage 30), second node detectable (stage 32), flag leaf collar just visible (stage 39), boot swollen (stage 45), inflorescence completely emerged (stage 59), and soft dough (stage 85). Subplots consisted of a 2 x 2 factorial of two wheat genotypes, the cultivar 'Magnum' and the hybrid 'HW 3015', each grown alone or in mixture with 'Marshall' annual ryegrass. Magnum attained the soft dough stage 4 d earlier than 'HW 3015'; thus, 'Magnum' was harvested 4 d earlier at the last growth stage. During that 4-d period, annual ryegrass was at late anthesis to early milk stage (mean stage 70). Harvest treatments were imposed during the spring of 1985 and 1986. Four interior rows were cut with a sickle-bar mower at a 7.5-cm stubble height and weighed. A subsampIe was dried at 65"C for calculating DM yield. Hand-clipped plant samples were taken from the plots at 7.5-cm height before harvesting the plots. Samples collected from mixtures were separated into species. Within each species, leaf blades (henceforth referred to as leaf) were separated from the remainder of the plant (referred to as stem). All samples were dried to constant weight at 65"C in a forced-air oven, ground to pass a 2-mm screen in a Wiley mill (Arthur A. Thomas Co., Philadelphia, PA) and then ground to pass a I-mm screen in a Tecator MATERIALS AND METHODS cyclone mill (Tecator Inc., Herndon, VA). Plant This trial was conducted at the Main Experi- parts from three replications were assayed. ment Station of the University of Arkansas, Neutral detergent fiber (2) and IVDMD (7) Fayetteville, for 2 yr on a Captina silt loam soil were determined. The IVDMD procedure in(fine, silty, mixed, mesic Typic Fragiudult). volved direct acidification at the end of a Fertilization consisted of 67-30-56 kg·ha- I of 48-h stage 1 followed by a 24-h stage 2. Stem N-P-K incorporated before planting and 90 kg samples at the soft dough stage were subjected N·ha- I as ammonium nitrate top-dressed in the to a diastase enzyme pretreatment to remove spring at the early jointing stage each year. Soft starch before NDF analysis. Staining NDF resired winter wheat seed was drilled into a pre- due of samples from the other growth stages pared seedbed at 134 kg·ha- I for the pure wheat revealed no significant amounts of starch. Leaf treatments. For the mixtures, wheat and annual proportion was calculated from the leaf-stem ryegrass were seeded at 134 and 22 kg'ha- I , separations as leaf dry weight/(leaf plus stem) Journal of Dairy Science Vol. 73.

No.5, 1990

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WALKER ET AL.

dry weight. Concentrations of NDF and IVDMD in the whole-shoot were calculated as a weighted average of the leaf and stem values according to the proportional dry weight yields of the leaf and stem fractions. Likewise, forage quality estimates of the whole harvested forage either as pure wheat or as wheat-ryegrass mixtures were calculated as a weighted average of the species components. Data were analyzed by analysis of variance (Table 1) with SAS (10) with the year effect tested on replications nested within years. Growth stage and year x stage interactions were tested on replication (year) x stage. All other effects were tested on the residual mean square (Table 1). RESULTS AND DISCUSSION

Dry Matter Yield

There was a significant difference between years for whole forage yield (Table 1), and this difference was due to variation in the wheat stem yield; stem yield was higher in 1985 than in 1986 (Table 2). Mean daily temperature during March through May was similar between the two years. Precipitation in 1985 was above normal during January through March, whereas 1986 was characterized by substantially lower than normal precipitation, which may have inhibited tillering and stem elongation. Leaf proportion of the total forage was higher in 1986 than in 1985 as a result of higher leaf proportions of both wheat and ryegrass portions at stages 39 and 45 (year x stage interaction means not shown). The main effect of growth stage was highly significant for all variables and usually interacted with year and ryegrass treatment. The main effect of wheat genotype had no influence on yield of whole forage or on any of the species or plant-part components of yield, except that ryegrass leaf yield was slightly higher when grown with 'HW 3015' than with 'Magnum' (Table 2). Wheat genotype did influence proportional yields in that ryegrass proportion was greater when growing with 'HW 3015' than with 'Magnum'. The 'HW 3015' was apparently less competitive with ryegrass than was 'Magnum' in that the elevated ryegrass content for 'HW 3015' occurred at essentially all growth stages (stage x wheat genotype interaction was not significant, P>.OS). Leaf JoW11al of Dairy Science Vol. 73, No.5, \990

proportion of whole forage was higher in the hybrid, 'HW 3015', than in 'Magnum' when grown alone (Table 2); however, there was no difference between the wheat genotypes when in mixture with ryegrass. Greater competitiveness of ryegrass toward 'HW 3015' than toward 'Magnum' may have suppressed the expression of greater leafiness. Presence of ryegrass in the mixtures reduced forage yields of wheat, wheat leaf, and wheat stem portions for both genotypes (Table 2). There was an interaction (P<.OI) between wheat genotype and ryegrass presence for DM yield of whole forage. Ryegrass yield more than compensated for depressed 'Magnum' yield by raising mixture yield over that of .Magnum' alone. In contrast, ryegrass yield simply compensated for depressed yield of 'HW 3015' in that mixture yield was unchanged from 'HW 3015' alone. Ryegrass had a higher leaf proportion than that of the companion wheat when averaged over growth stages, which is explained at least partially by the fact that the phenological development of ryegrass lagged behind that of both wheat genotypes. This phenomenon resulted in the total wheat-ryegrao;s mixture being more leafy and containing, on average, tissue of lesser maturity than that of the wheat forage alone. Greater leaf proportion of the whole forage mixture over that of the pure wheat was first detected at early internode elongation of wheat (stage 32) (Figure 1). At this point, internodes in ryegrass had not yet begun to elongate. Interactions between wheat genotype and ryegrass presence were detected for yields of wheat, wheat leaf, and wheat stem components; and for whole forage leaf proportion (Table 2). The 'HW 3015' produced more leaf, stem, and total mass than did 'Magnum' when grown alone, but forage yield of the hybrid was suppressed by the presence of eyegrass. This same trend was evident in the growth stage x wheat x ryegrass interaction (Figure 2) for whole forage only at the final growth stage (soft dough). Dry matter accumulation patterns of the four forage treatments were similar up to stage 59 (inflorescences emerged). The 'HW 3015' is generally considered a high grainyielding hybrid when grown for grain in pure stands (12), and it was during grain filling (stages 59 to 85) that 'HW 301S' attained a greater whole plant yield than did 'Magnum'

TABLE I. Analysis of variane.' for OM yield. ryegrass pmportion. leaf pmportion. and in vitro DM digeslibilily (lVOMD) of wmponellt, of wheal and wheal·ryegrass forage as innueneed hy year. wheal genOlypc. and maturity stage.

Yield

Source

'-

o

3e. o....,

o e.

~

Whole forage

df

Year (Y)

I

Error a.

6

SLage (S) 5 Y x S 5 Error h 30 Wheal (W) I Ryegr.» (R) I W x R I YxW I Y x R I Y x W x R I S x W 5 S x R 5 SxW.xR 5 Y x S x W 5 Y x S x R 5 YXS(WxR 5 Error e lOS

•

.

Whole

Leaf NS

Ryegra
.

Stt:.m

Whole

Lear

Slem

Ryegrass prupor- Whole tion forage

NS

NS

NS

NS

.. ..•• .. .... .... ....

....

....

NS

•

NS NS NS NS NS

NS

....

NS NS

..

NS NS NS

....

NS

NS

NS

.

NS

NS NS

....

..

NS NS

..

NS

...

NS

NS NS NS NS

NS

NS NS NS NS

....

..

NS

IVOMO

Leaf proportion

Wheal

. .

NS

.. NS

NS

en

IError e for ryegrass variables was Replicalion (Y) x S x W with df

~f

·P<.05.

....

NS

NS

NS

NS

••

.... ....

..

NS

NS

NS

....

Wheal

.. ....

NS NS

· .. NS

NS NS

..

NS

Ryegr.»

Wholr forage

Whole

Leaf

••

NS

NS

NS

· · · .. · · ·..

••

....

NS

NS NS

NS

NS

NS

·· . .. ... NS

~

Wheal

....

NS

NS

..

..

NS NS

NS

NS

NS NS NS NS

NS NS NS

NS NS NS

NS NS NS

NS

..

.. NS

NS NS NS NS NS

•

NS NS NS NS

~

Ryegrass

Slem

.. .... NS NS

·· ..

Whole

Leaf

Slem

NS

NS

NS

.... .. .... NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

·.. ....

NS

:Xl

trl

Cl

'"

> en en

:::

X

NS

NS

> -I

-I

c::

rn 'Tl

0

::10

NS

NS

NS

a '"

>

Cl tTl

= 36.

Mixlure and wkat IVOMO df

= 72

and ryegrass IVDMl> df

= 24.

(')

(')

"<

··P<.OI.

~

--.l

;-'

z

"

~

~

N

~

...

0'

I,,;J

3

8

Eo....,

o e.

.:=!

(I)

"( i' ~ n

';i

=:w

TABLE 2. Dry mailer yield and ryegrass proponion in \he mixlure and leaf proponion of species eomponenlS as affccled by year and forage type, means of four replications, and six growth stages. DM Yield

Z 9

~

~

Parameter

Whole forage

Leaf proportion

Wheat Whole

Leaf

Ryegrass Stem

Whole

Leaf

Stem

Ryegrass proportion

Whole forage

.445

Wheat

Ryegrass

.572

.483 .016

.420 .451 .012

42.5 45.0

42.5 45.0

...

(kg.ha- I ) - - - - - - - - - - - - Year 1985 1986 LSD.05! Forage type2 'Magnum' 'HW 3015' 'Magnum' plus ryegrass 'HW 3015' plus ryegrass LSD05

4227

35119 530

3606

3413 2714 697

749

2665

722

1991

NS

492

1122

1627 1627

577 576

1051 1174

.311 .367

NS

NS

NS

NS

.636 .018

4060

3606 4060

9511

2785 3102

4042

2395

603

1792

1647

543

1104

31.3

48.9

43.7

(,0.4

3923 254

2192 25M

588 68

1634 223

1731

610 55

1121

36.6

60.4

NS

49.2 1.2

43.1

NS

2.9

1.3

!Lcasl significant difference (P<.05). 2Wheat genolype x ryegrass presence interaclion means for wheal measurements and wheal genotype means for ryegrass measuremenls: means of 2 yr.

...

NS

:.E ~

?:j

"~ ~

1301

WHEAT-RYEGRASS MIXTURES FOR FORAGE

TABLE 3. In vitro DM disappearance of whole forage, species components, and plant parts of four wheat and ryegrass Uearment combinations; means of 2 yr, four replications. and six growth stages. Wheat

Whole forage

Forage type

Whole

Leaf

718

725 718

729 727

710

711

725 12

716 9

Ryegrass stem

Whole

Leaf

Stem

708 703

... ...

... ...

... ...

715

695

749

775

614

719 11

704 10

149 NS

778

665

NS

NS

(gkg-l) ‘Magnum’ ’HW 3015’ ‘Magnum’ plus

725

ryegrass

‘HW 3015’ plus ryegray uD.05

’Least significant difference (P<.05).

(Figure 2). Although the grain portion was not teau at the emerged inflorescence stage with measured at the soft dough stage, the higher ‘Magnum’ attaining a lower yield than ‘HW forage yield of pure-stand ‘HW 3015’ over 3015’ (Figure 2). Dry matter accumulation pat‘Magnum’ could have resulted from the greater terns of ‘Magnum’ and ‘HW 3015’ during regrain-yielding ability of ‘HW 3015’. Another productive development were accounted for alconmbuting factor may have been that ‘Magnum’ attained the soft dough stage an average of 4 d earlier than ‘HW 3015’ and had a shorter loo00 grain accumulation period than did ‘HW 3015’. Patterns of DM accumulation for the wheat and ryegrass portions were analyzed to under- :8000 B stand further the trends in DM accumulation in 0 whole forage. When grown with ryegrass, both - 6000 t wheat genotypes had yields that reached a pla_I

E

4000

c

I > 2000

n 2 ‘5

35

45

55

65

75

85

GROWTH STAGE

25

35

45

55 65 GROWTH STAGE

75

85

Figure 1. Leaf proponion of whole harvested forage for pure wheat and wheat-ryegrass mixtures in relation to wheat growth stage (Zadoks scale); means of 2 yr, four replications, and two wheat genotypes: Without (-) or with (---) ryegrass. Least significant difference (P<.05) within growth stages = .02 and across growth stages but within ryegrass treatment = .02.

Figure 2. Forage DM yield of wheat growing alone and in mixture with annual ryegrass, and wheat and ryegrass components of the mixtures for ‘Magnum’ and ‘HW 3015’ in relation io wheat growth stage (Zadoks scale); means of 2 yr and four replications: ‘Magnum’ alone (TFJ).‘ HW 3015’ alone (M). ’Magnum’-ryegrass mixture (%-!7), and ‘HW 3015’-ryegrass mixture (0-0).Least significant difference (Pc.05) for comparing whole forage treatments within growth stages = 628 and across growth stages but within wheat-ryegrass mixtures = 535. ‘Magnum’ portion ‘HW 3015’ ponion of mixture (0-0). of mixture (c-l) ryegrass portion of ‘Magnum’ mixture ( m - 4 ) . and ryeLeast signifigrass portion of ‘HW 3015’ mixture (-.). cant difference (P<.05) for comparing wheat-portion yields of mixtures within growth stages = 216; for comparing wheat-ponion yields of mixtures across growth stages but within wheat genotype = 189; for comparing ryegrass yields within gowth stage = 340; and for comparing ryegrass yields across growth stages = 326.

Journal of Dairy Science Vol. 73, No. 5, 1990

1302

WALKER ET AL.

most entirely by growth in the stem fraction in that leaf yield peaked at stage 45 and declined thereafter (data not shown). The ryegrass yieldaccumulation patterns indicated no difference between that grown with 'HW 3015' or with 'Magnum' (Figure 2). Ryegrass exhibited an essentially linear growth pattern in relation to wheat growth stage, which led to a rise in ryegrass proportion in mixtures as the wheat matured. In Vitro Disappearance Trends in NDF were the inverse of those of IVDMD; therefore, only IVDMD data will be presented. The interaction of wheat genotype and ryegrass presence (P<.05) for whole forage IVDMD indicated that ryegrass depressed IVDMD of the 'Magnum' mixture compared with 'Magnum' alone, whereas ryegrass had no influence on IVDMD of the 'HW 3015' mixture relative to that of 'HW 3015' alone (Table 3). The negative effect of ryegrass presence on 'Magnum' mixture IVDMD was caused by depressions of both wheat leaf and wheat stem IVDMD. Ryegrass leaf was the plant fraction having the highest IVDMD and ryegrass stems had the lowest IVDMD. The IVDMD of ryegrass was not high enough to raise IVDMD of whole forage significantly above that of wheat

alone. Low stem IVDMD limited ryegrass digestibility. Wheat genotype had no influence on any variable. Whole forage IVDMD declined with advancing growth stage similarly for both the pure wheat and the wheat-ryegrass mixtures to stage 59, after which IVDMD of the mixture was lower than that of pure wheat (Figure 3). Enhanced leafiness from including ryegrass in mixture with wheat compared with pure wheat (Figure 1) would potentially result in higher whole forage digestibility (4, 6); however, calculated values for whole forage IVDMD were not higher for the mixture in this trial. The reason can be seen by comparing the changes in IVDMD of the individual plant parts in relation to wheat phenology (Figure 4). All plant parts declined in IVDMD from early developmental stages to stage 59, after which ryegrass leaf and stem and wheat leaf continued to decline while wheat stern increased to the soft dough stage. The latter increase in IVDMD of wheat stem was attributed to increasing relative DM contribution of highly digestible grain in the inflorescence (l). Ryegrass stem had the lowest IVDMD of all the plant parts at the final growth stage despite the fact that ryegrass,

9OOr------------------, <>'<>-"'\

900r-------------------, 800

't::::-<>-

800

'''.

_ --A..

~ 2700 o ::!' o > 600

600 ',~------o

--------0

500 L - _ - ' -_ 25 ~

____'_ _- ' -_ ~ ~

____'-:--_-=:-_---::':---' ~

~

~

GROWTH STAGE 500'------'------'---'------'~----'------'~

25

35

45

55

65

75

85

GROWTH STAGE

Figure 3. In vitro DM disappearance of the whole harvested forage for pure wheal and wheat-ryegrass mi,,tures in relation to wheat growth stage (Zadoks scale); means of 2 yr. three replications. and two wheat genexypes: Without ryegrass (-) and with ryegrass (---). Least significant difference (P<.05) within growth stages = 20 and 17. across growth stages but within ryegrass treatment

=

Journal of Dairy Science Vol. 73.

No.5, 1990

Figure 4. In vitro DM disappearance of wheat leaf and stem and annual ryegrass leaf and stem in relation to wheat growth stage (Zadoks scale); means of 2 yr, three replications, and two wheat genotypes. Wheat leaf (t.-t.), wheat stem (A-A). ryegra~s leaf (t.--~) and ryegrass stem (A---A). Least significant difference (P<.05) across growth stages but within plant pans 17. 20, 25. and 25 for wheal leaf. wheat stem, ryegrass leaf. and ryegrass Stem. respectively.

=

WHEAT-RYEGRASS MIXTURES FOR FORAGE

which was postanthesis to early milk stage (approximately stage 70), was less mature than wheat. Visual inspection indicated that ryegrass stems were longer and had longer internodes than those of wheat at the final growth stage. The NDF of ryegrass stem at this point averaged 666 g·kg- 1 compared with 532 for the wheat stem. Because ryegrass does not produce a large seed, kernel development would not be expected to contribute to enhanced forage digestibility as observed in wheat. Therefore, the rapid decline of ryegrass stem IVDMD contributed to reduced digestibility of whole forage of a wheat-ryegrass mixture when wheat was at the soft dough stage. CONCLUSIONS

Including annual ryegrass in mixture with wheat did not enhance the DM yield over wheat alone; instead, ryegrass yield substituted for wheat yield. The forage yield advantage of 'HW 3015' over 'Magnum' in pure stands was due to superior stem DM accumulation from anthesis to soft dough. This advantage disappeared when in competition with ryegrass. Ryegrass proportion increased as wheat developed and ryegmss was leafier and less mature than wheat at a given wheat growth stage. This resulted in a slower rate of decline in leaf proportion of the whole forage mixtures in relation to the pure wheat genotypes. The enhanced leafiness and delayed maturity of ryegrass compared with the companion wheat did not improve the whole forage digestibility. mainly because of the rapid decline of ryegrass stem IVDMD from inflorescence emergence onward. If wheat is to be harvested at the soft dough stage for forage. it should not be grown with annual ryegrass because the latter dilutes the high quality, wheat grain portion with low quality, ryegrass stem, unless a ryegrass culti-

1303

var with higher stem digestibility or later maturity than 'Marshall' is used. REFERENCES 1 Cherney. J. H.• and G. C. Marten. 1982. Small grain crop forage potential: II. Interrelationships among biological. chemical, morphological, and anatomical determinants of quality. Crop Sci. 22:240. 2 Goering. H. K.• and P. J. Van Soest. 1970. Forage fiber analyses. Agric. Handbook No. 379. Agric. Res. Serv., US Dep. Agric.. Washington, DC. 3 Hacker. F. B., and D. J. Minson. 1981. The digestibility of plant parts. Herbage Abstr. 51:459. 4 Helsel. Z. R.. and J. W. Thomas. 1987. Small grains for forage. J. Dairy Sci. 70:2330. 5 Hoveland. C. S.. and W. G. Monson. 1980. Genetic and environmental effects on forage quality. Page 139 in Crop quality, storage. and utilization. C. S. Hoveland, cd. Am. Soc. Agron. and Crop Sci. Soc. Am.. Madison, WI. 6 Marten. G. C. 1985. Factors influencing feeding value and effective utilization of forages for animal production. Page 89 in Proc. XV Int. Grassl. Congr., Aug. 24-31, 1985. Kyoto. Jpn. Sci. Counc. Jpn and Jpn Soc. Grassl. Sci.. Nishi-nasuno, Jpn. 7 Manen. G. C.• and R. F. Barnes. 1980. Prediction of energy digestibility of forages with in vitro rumen fermentation and fungal enzyme systems. Page 61 in Proc. In!. Workshop Standardization Anal. Methodol. Feeds. IORC-134c. W. J. Pigden. C. C. Balch. and M. Graham. ed. Ottawa, ON, Can. 8 Riewe. M. E.• and C. L. Mondart. Jr. 1985. The ryegrasses. Page 241 in Forages. the science of grassland agriculture. 4th ed. M. E. Heath, R. F. Barnes, and D. S. Metcalfe. ed. Iowa State Univ. Press. Ames. 9 Roberts. C. A.• K. J. Moore, and K. D. Johnson. 1989. Forage quality and yield of wheat-vetch at different stages of maturity and vetch seeding rates. Agron. J. 81: 57. 10 SAS® User's Guide: Statistics. Version 5 ed. SAS Inst.. Inc .• Cary. NC. II Terry.R. A.. and J.M.A. Tilley. 1964. The digestibility of the leaves and stems of perennial ryegrass. cocksfoot. timothy. tall fescue. lucerne, and sainfoin as measured by an in vitro procedure. 1. Br. Grassl. Soc. 19:363. 12 Walker. T. K.. and S. H. Moore. 1986. Small-grain performance tests. Ark. Agric. Exp. Stn. Res. Ser. 349. 13 Zadoks. J. D.• T. T. Chang. and C. F. Kinzak. 1974. A decimal code for the growth stages of cereals. Weed Res. 14:415.

Journal of Dairy Science Vol. 73.

No.5. 1990