A study of the nutritive value of white clover (Trifolium repens L.) in relation to different stages of phenological maturity in the primary growth phase in spring

A study of the nutritive value of white clover(Trifolium repens L.) in relation to different stagesof phenological maturity in the primarygrowth phase in spring

J. F. Ayres*, K. S. Nandra² and A. D. Turner*

*NSW Agriculture, Agricultural Research and Advisory Station, Glen Innes, New South Wales, Australia, and²NSW Agriculture, NSW Agriculture Beef Centre, University of New England, Armidale, New South Wales2351, Australia

Abstract

This paper reports the effects of onset of phenological

maturity on the nutritive value of white clover

(Trifolium repens L.). The study comprised (i) examina-

tion of an extensive data set on nutritive value and (ii)

investigation of the constituents of nutritive value, in

vivo feeding value, protein degradability and metabo-

lizable protein content of white clover harvested at

three stages of maturity (early-¯owering, full-¯ower-

ing, ripe seed stages) during the primary growth phase

in spring in Australia. The data set on nutritive value

showed a consistent pattern of high nutritive value

during cool season months, progressive decline

through spring and uniformly lower nutritive value

over summer. Results from laboratory determinations,

in sacco degradability studies and a digestibility trial on

white clover harvested at early-¯owering, full-¯ower-

ing and ripe seed stages were consistent with results

from the data set on nutritive value. Onset of maturity

during the primary growth phase in spring was

accompanied by large changes in nutritive value:

neutral-detergent ®bre (NDF) increased from 184 to

301 g kg)1 dry matter (DM), nitrogen (N) declined

from 36 to 20 g kg)1 DM, in vitro digestibility declined

from 0á74 to 0á65 and metabolizable protein content

declined from 144 to 67 g kg)1 DM from early-¯ower-

ing to ripe seed stage. These nutritive value changes

were accompanied by a decline of in vivo digestibility at

the rate of 0á0032 d)1 and an 0á2 reduction in volun-

tary intake.

Introduction

White clover (Trifolium repens L.) is widely acclaimed as

a highly nutritious pasture plant (Thomson, 1977;

Thomson, 1979; Ulyatt, 1980), and there is evidence

for superior feeding value of white clover compared

with companion grasses (Thomson and Raymond,

1969) for beef production (Collins and O'Donovan,

1969), lamb production (Ulyatt et al., 1977) and milk

production (Rogers et al., 1982; Thomson, 1984; Thom-

son et al., 1985). A summary of experiments comparing

animal production from white clover with companion

grasses (usually perennial ryegrass) show a mean

superiority of »0á3 in liveweight gain of beef cattle,

»0á65 in liveweight gain of lambs, and dairy cows

grazing pure white clover swards produce »3 kg d)1

more milk than those grazing monoculture grass (Wil-

kins and Munro, 1988). Lloyd Davies (1989) reported

higher wool production from white clover cv. Haifa

than from perennial ryegrass.

This superiority in feeding value of white clover is

attributed to high protein and low structural ®bre with

positive consequences for intake, digestion and utiliza-

tion (Ulyatt, 1980; Thomson, 1984). White clover has

low retention time in the rumen owing to low struc-

tural ®bre and hence higher voluntary intake at

equivalent digestibility. Utilization of nutrients from

white clover is also high owing to a shift in the site of

Correspondence to: Dr J.F. Ayres, NSW Agriculture, Agricul-

tural Research and Advisory Station, PMB, Glen Innes,

New South Wales 2370, Australia.

Received 22 October 1997; revised 5 February 1998

Ó 1998 Blackwell Science Ltd. Grass and Forage Science, 53, 250±259 250

nitrogen digestion from the reticulo-rumen to the small

intestine (Ulyatt and MacRae, 1971; Thomson, 1984).

However, protein composition of white clover may be a

limiting factor. Signi®cant loss of crude protein (»0á35)

from white clover diets occurs between ingestion and

absorption at the intestines (Cruickshank et al., 1985;

Beever et al., 1986; Ulyatt et al., 1988). Furthermore,

animal production responses have been recorded for

animals feeding on white clover supplemented with

protein at the intestine to replace protein loss in the

rumen (Fraser et al., 1991a; b). Ayres and Poppi (1993)

proposed the need to select for protein degradability,

protein components and protein supply in white clover

breeding to enhance animal performance from new

white clover cultivars.

For forages in general, compositional changes that

accompany advancing maturity include decrease in

plant cell contents and increase in structural ®bre

together with ligni®cation and polymerization of cellu-

lose (Sullivan, 1973; Jones and Wilson, 1987). These

changes with maturity lead to reduced intake and

digestion (Minson et al., 1960; Waite et al., 1964). In

temperate pasture environments the growth cycle of

white clover comprises (i) a cool-season vegetative

growth phase in autumn, (ii) growth quiescence in

conjunction with intensive frosting in winter, (iii) a

primary growth phase in spring and (iv) a regrowth

phase in summer. The nutritive value of cool-season

vegetative growth has been described previously by

Schiller and Ayres (1993), who found that white clover

maintained relatively uniform levels of total nitrogen,

neutral-detergent ®bre, acid-detergent ®bre and in vitro

digestibility during autumn through to mid-winter. The

present study reports on the pattern of change of

nutritive value during the primary growth phase in

spring. Study of the effects of phenological change on

nutritive value will identify whether limitations exist

that may impose nutritional feed-gaps, especially for

intensive grazing enterprises.

Materials and methods

Location

The white clover forage that is the subject of this

study was grown at Glen Innes Agricultural Research

and Advisory Station (29°42¢S, 151°42¢E) located on

the northern tablelands of New South Wales, Austra-

lia. The climate is characterized by average annual

rainfall of 853 mm with a summer incidence of

drought, a wide temperature range and precipitation

exceeding evaporation only in the winter months

when pasture growth is relatively inactive because of

cold conditions (Table 1). The environment is suited

to introduced temperate perennial pasture species and

white clover is the most suitably adapted pasture

legume.

Preparation of the diets

White clover (cv. Haifa) was established in monocul-

ture on a 0á4-ha block by planting with a combine disc

seeder in May 1989. The seeding rate was 10 kg seed

per hectare, tri¯uralin pre-emergent herbicide was

applied to the soil and incorporated with harrows to

prevent grass contamination, and superphosphate was

applied at planting at the rate of 250 kg of molybdena-

ted superphosphate per hectare. The white clover was

grazed during the establishment year and until July

1990. Forage was harvested in 1990 from separate

0á1 ha sub-blocks on three successive occasions; 18

October (early-¯owering stage), 8 November (full-

¯owering stage) and 12 December (ripe seed stage).

The harvested forage was cumulative growth to each

harvest date, so that forage samples represented

discrete phenology stages, not regrowth between har-

vest dates. A ¯ail-type forage harvester mowed each

sward to »1 cm above ground level, and the forage was

transported directly to a forced-draught batch drier for

dehydrating under ambient temperature conditions to

150 g kg)1 moisture content. A representative subsam-

ple of each white clover batch was obtained before

drying, sorted into leaf (including petiole) and in¯or-

escence (including pod) components, dried at 80°C,

and data were expressed as a proportion of the aerial

shoot system on a DM basis (Table 3). The dried forage

was subsequently chopped to »2á5 cm length and

stored in synthetic packs. This provided three batches

of white clover for subsequent studies: (a) chemical

analysis, (b) in vivo digestibility study and (c) in sacco

degradability assay. This study was supported by (d)

examination of an extensive data set of nutritive value

records of white clover held in the Glen Innes feeds

laboratory database.

Chemical analysis

Nitrogen (N) content was determined using the

Kjeldahl procedure (Association of Of®cial Agricultural

Chemists, 1980) using a Kjeltec Auto 1030 (Tecator AB,

Sweden). Organic matter (OM) was determined by

ashing at 600°C for 16 h in a muf¯e furnace. The cell

wall organic matter (CWOM) and acid-detergent ®bre

(ADF) contents were estimated by re¯ux (Faichney and

White, 1983). Neutral-detergent ®bre (NDF) was mea-

sured by the procedure of Van Soest and Wine, 1967).

Hemicellulose was estimated as the difference between

CWOM and ADF, and cellulose was estimated as the

difference in mass between ADF and residues after

digestion in 0á72 sulphuric acid. Lignin was measured as

Effect of maturity on white clover nutritive value 251

Ó 1998 Blackwell Science Ltd, Grass and Forage Science, 53, 250±259

the dry-matter (DM) loss from the latter after ashing at

600°C for 3 h. Acid-detergent insoluble nitrogen was

measured by performing N analysis on the ADF residue.

The fat content was determined by Soxhlet extraction

in chloroform for 16 h (Association of Of®cial Agricul-

tural Chemists, 1980). In vitro OM digestibility was

determined by a two-step procedure comprising 48-h

incubation in rumen ¯uid/arti®cial saliva followed by

48-h incubation in pepsin solution as described by

Ayres (1991).

In vivo digestibility and voluntary intake

The three batches of white clover were fed to sheep for

a 10-day introductory period and a 10-day collection

period. Fifteen crossbred wether sheep (progeny of

Border Leicester ´ Merino ewes mated to Dorset Horn

rams) with a mean liveweight of 38á6 kg were allocated

randomly to three groups with ®ve sheep per group.

The three batches of white clover were fed daily ad

libitum (feed offered each day was adjusted to 1á2 times

the voluntary intake of the previous day) to each of the

®ve sheep in their corresponding groups; sheep were

housed individually in metabolism crates. During the

collection period, feed refusals were collected at 08.00 h

each day and retained for subsequent weight determi-

nation. Solid excreta was collected three times daily

(08.00 h, 12.00 h and 17.00 h) using faecal collection

harnesses and stored at 4°C for subsequent weight

determination, subsampling and OM determination.

Voluntary intake was estimated as the difference

between feed on offer and feed refusals and was

expressed on a dry-matter basis. In vivo digestibility

was determined as voluntary intake less faecal output as

a quotient of voluntary intake.

In sacco degradability studies

The degradability of protein of the three batches of

white clover was measured using six Merino wether

sheep (3±4 years old) ®tted with rumen cannulae. Two

sheep were randomly allocated to each white clover

batch and fed ad libitum morning and evening for a 12-

day period comprising 10 days of preliminary feeding

and 2 days of in sacco measurements. The sheep were

then reallocated into different pairs for different

batches of white clover and subjected to a second

period. This design provided data from four replica-

tions (two sheep ´ two periods per batch of white

clover). Subsamples of chopped feeds were ground

through a Christie and Norris mill to pass through

a 2á25 mm screen for degradability studies. Samples

(2 g) were placed in polyester bags (80 mm ´ 120 mm

size, 36- to 38-lm pores) manufactured from Nittral

single thread woven fabric with welded cross-threadsTab

le1

Clim

ate

sum

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(29

°42

¢S,151

°42¢E

),N

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Wal

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ralia

±lo

ng-

term

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ther

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Jan

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Feb

ruary

Marc

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pri

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ay

Ju

ne

Ju

lyA

ugu

stS

ep

tem

ber

Octo

ber

No

vem

ber

Decem

ber

Rain

fall

(mm

)105

92

70

39

49

56

58

50

56

80

84

108

Pan

A

evapora

tion

(mm

)

166

139

132

95

67

48

54

74

106

136

151

178

Min

imu

m

tem

pera

ture

(°C

)

13á5

13á5

11á8

7á8

4á7

1á8

0á4

1á3

4á1

7á2

9á9

12á2

Maxim

um

tem

pera

ture

(°C

)

24á8

24á3

22á9

19á8

15á8

12á7

12á0

13á7

16á4

19á2

22á0

24á4

Inci

den

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(days)

00

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24

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(No.056013).

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(1910±97),

data

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252 J. F. Ayres et al.


(Allied Screen Fabrics, Hornsby, Australia). In each

period, bags containing the test feed (one per incuba-

tion time) were placed in the rumen of each sheep fed

the same feed as that of the test feed. Incubation times

were 2, 4, 8, 16, 24 and 48 h. The bags were

introduced into the rumen in reverse sequence and

removed at the same time. Immediately after removal

from the rumen, bags were immersed in cold water

then washed for 30 min in a washing machine set on

the cold rinse cycle. The value at time zero was

obtained by washing a bag containing the test feed in

the washing machine without placement in the

rumen. The bags and their contents were then dried

at 55°C for 48 h in a forced-draught oven. The residue

left in each bag at each incubation time was used for

the analysis of nitrogen.

Determination of degradability characteristics

The in sacco data for protein degradability were obtained

from four sheep for each batch of white clover and

®tted to the exponential equation derived by érskov

and McDonald (1979) of the form:

P � a� b�1± exp�±ct��

where a represents the soluble and rapidly degradable

protein, b is the slowly but potentially degradable

protein that disappears at a constant fractional rate c

per unit time, and P is the disappearance of protein at

time (t).

Determination of protein components andfermentable metabolizable energy

The following protein fractions were calculated ac-

cording to the Agricultural and Food Research Council

(AFRC) (1993): effective rumen degradable protein

(ERDP) ± the portion of rumen degradable protein

(RDP) captured and utilized by rumen microbes for

growth and synthesis; digestible undegradable protein

(DUP) ± the portion of rumen undegradable protein

(UDP) digested and absorbed in the lower intestine;

and metabolizable protein (MP) ± the total digestible

true protein available to the animal for metabolism

after digestion and absorption. Metabolizable energy

(ME) was calculated from in vivo digestibility according

to the Ministry of Agriculture, Fisheries and Food

(MAFF) (1984). Fermentable metabolizable energy

(FME) was calculated from AFRC (1993) according

to the relationship [FME] � [ME] ) [MEfat] )[MEfermentation].

Nutritive value records

The Glen Innes feeds laboratory retains a nutritive

value database with more than 10 000 records derived

from retrospective ®eld and glasshouse studies con-

ducted at Glen Innes. Records of 1225 white clover

samples were extracted. These records comprised:

organic matter (OM, g kg)1 DM), nitrogen (N, g kg)1

DM), in vitro OM digestibility (g g)1), NDF (g kg)1 DM)

and ADF (g kg)1 DM).

Statistical analysis

The data on nutritive value extracted from retrospective

records are reported as arithmetic means and standard

deviations based on variable numbers of records. Data

for in vivo digestibility and voluntary intake were

examined by analysis of variance for a completely

randomized design; least-squares means and LSDs are

reported for comparing dietary main effects. The in sacco

degradability data for protein for each feed were ®tted

to the exponential equation of érskov and MacDonald,

1979) to derive the degradation constants; the mean

degradation constants were then used to calculate

ERDP, DUP and MP.

Results

Nutritive value records

Consistent seasonal patterns in the nutritive value data

were evident (Table 2). OM and N were consistently

high during the cool season (April±August) with OM

values ranging from 908 to 919 g kg)1 DM and N values

ranging from 37 to 43 g kg)1 DM. Structural ®bre (NDF,

ADF) was correspondingly low during May to August

(NDF: 359±389 g kg )1 DM; ADF: 244±261 g kg)1 DM)

and elevated structural ®bre values (NDF: 481 g kg)1

DM, ADF: 359 g kg)1 DM) were evident with onset of

maturity in November. In vitro OM digestibility was at a

maximum of 0á82 in October (mid-spring), declined

rapidly to 0á69 with onset of phenological maturity and

otherwise remained in the range of 0á64±0á75 during

the secondary regrowth phase in summer and cool-

season months of autumn and winter.

Phenological development

The white clover cultivar Haifa is a mid-season ¯ower-

ing cultivar as evidenced by initiation of ¯owering in

mid-spring; the phenology record for cv. Haifa shows

that full ¯owering occurs in early November and ripe

seed stage in mid-December (J. F. Ayres, personal



Tab

le2

The

nutr

itiv

eva

lue

(org

anic

mat

ter,

nitro

gen,n

eutr

al-d

eter

gent®b

re,a

cid-d

eter

gent®b

re,i

nvitro

OM

dig

estibility

)ofw

hite

clove

rhar

vest

edm

onth

ly;v

alues

from

1,2

25

white

clove

rre

cord

shel

dat

the

Gle

nIn

nes

feed

sla

bora

tory

dat

abas

e.

Jan

uary

Feb

ruary

Marc

hA

pri

lM

ay

Ju

ne

Ju

lyA

ugu

stS

ep

tem

ber

Octo

ber

No

vem

ber

Decem

ber

Org

an

icm

att

er

(gkg

)1

DM

)884

886

899

908

909

919

919

912

862

883

885

896

n15

36

49

910

652

1077

31

3

s.d.

48

55

810

611

10

39

26

50

5

Nit

rogen

(gkg)

1D

M)

31

35

32

37

43

42

39

39

23

30

32

34

n8

22

16

62

455

1058

25

1

s.d.

49

3±

33

12

57

5±

Neu

tral-

dete

rgen

t

®bre

(gkg)

1D

M)

455

365

446

440

369

359

389

367

469

398

481

±

n4

11

13

33

22

34

s.d.

51

±±

±60

23

22

20

818

43

Aci

d-d

ete

rgen

t

®bre

(gkg)

1D

M)

292

253

294

264

244

245

250

261

241

287

359

±

n4

11

13

32

22

34

s.d.

25

±±

±19

73

214

20

22

Invi

tro

OM

dig

est

ibil

ity

0á6

80á7

10á7

00á6

40á7

10á7

20á7

50á7

30á7

40á8

20á6

90á7

0

n15

36

49

910

66

1063

31

3

s.d.

0á0

50á0

10á0

60á0

30á0

70á0

30á0

20á0

20á0

20á0

40á0

80

n,

nu

mber

of

reco

rds;

s.d.,

stan

dard

devia

tion

.



communication). Major changes in the ®eld dry matter

content and plant fraction composition of the three

diets accompanied these phenological changes from

early ¯owering to ripe seed; ®eld dry matter increased

from 200 to 420 g kg)1 and leaf proportion (leaf +

petiole) declined from 0á99 to 0á52 (Table 3).

Chemical composition andin vivo digestibility

Changes in nutritive value with onset of maturity

were generally consistent with the pattern of changes

observed with the extensive data set; namely, reduc-

tion in in vitro OM digestibility and increase in

structural ®bre constituents (Table 4). From early-

¯owering to ripe seed stage, in vitro OM digestibility

declined from 0á74 to 0á65, N concentration declined

from 36 to 20 g kg)1 DM, NDF increased from 184 to

301 g kg)1 DM and lignin increased from 35 to

68 g kg)1 DM.

In vivo digestibility and voluntary intake

Onset of maturity from early-¯owering to ripe seed stage

was associated with a reduction in in vivo OM digestibil-

ity from 0á77 to 0á60 and a decline of voluntary intake

per LW0.75 from 75 to 61 g d)1 (Table 5).

Degradability characteristics of protein

The rapidly soluble fraction of protein (aPROT) of

white clover at the ripe seed stage of growth was

greater than at other stages of growth, and aPROT was

less at the early-¯owering stage than at the full-

¯owering stage (Table 6). The slowly degradable frac-

tion of protein (bPROT) was highest at the early-

¯owering stage and lowest at the ripe seed stage. The

ranking of the fractional rate of degradation of protein

(cPROT) was ripe seed > full ¯owering > early

¯owering.

Table 3 The ®eld characteristics

of white clover harvested at three

stages of maturity

Field dry matter Proportion Proportion of

Harvest date Stage of maturity (g kg±1) of leaf in¯orescence

18 October Early ¯owering 198 0á999 0á002

8 November Full ¯owering 223 0á595 0á351

12 December Ripe seed 421 0á523 0á432

Table 4 The nutritive value of white clover harvested at three stages of maturity in the spring primary growth phase

Early Full Ripe

¯owering ¯owering seed

Nitrogen (g kg)1 DM) 36 25 20

Acid-detergent insoluble nitrogen (g kg)1 DM) 2á21 3á10 3á62

Organic matter (g kg)1 DM) 867 736 864

Cell wall organic matter (g kg)1 DM) 271 319 415

Neutral-detergent ®bre (g kg)1 DM) 184 225 301

Cellulose (g kg)1 DM) 149 178 233

Hemicellulose (g kg)1 DM) 87 94 113

Lignin (g kg)1 DM) 35 47 68

Fat (g kg )1 DM) 49á4 29á0 31á6

In vitro OM digestibility 0á738 0á677 0á647

Table 5 The voluntary intake and

in vivo organic matter digestibility of

white clover harvested at three

stages of maturity in the primary

growth phase in spring

Early Full Ripe

¯owering ¯owering seed LSD

Voluntary intake (g d)1) 1175 1048 931 72á5

Intake per LW0á75 (g d)1) 75 67 61 4á6

Organic matter digestibility 0á771 0á689 0á595 0á014



Concentration of protein componentsand fermentable metabolizable energy

The ranking of ME, FME, ERDP, DUP and MP concen-

trations of the white clover batches was early ¯owering

> full ¯owering > ripe seed (Table 6). The concentration

of ERDP of the early-¯owering and full-¯owering white

clover was in excess, and the available FME was

limiting; therefore, the calculation of MP was based

on FME in accordance with AFRC (1993). For the full-

¯owering and the ripe seed stages of white clover, ERDP

were not limiting relative to FME, therefore calculation

of MP was based on the concentration of ERDP in

accordance with AFRC (1993).

Discussion

Examination of the extensive data set of nutritive value

of white clover (Table 2) provides information on

seasonal changes of key constituents. The data were

drawn from a number of ®eld and glasshouse experi-

ments and aggregates results (as means) across cult-

ivars, years and growing conditions. Some values

reported are based on many records (e.g. 1058 records

for N in October), but some are based on very few

records (e.g. two records for NDF in August). Caution

with interpretation is necessary because the nutritive

value of a pasture plant at the time of harvest relates to

in situ growing conditions and aggregated nutritive

value data needs to be interpreted in relative rather

than absolute terms (Sullivan, 1973). The strengths and

weaknesses of this data set are those that apply

generally to feed composition tables (e.g. Ostrowski-

Meissner, 1987): namely, too few records representing

a diversity of growing conditions. The usefulness of the

present data, however, is that it is a large data set for a

single species grown in a limited geographical area and

the results provide indicative trends of underlying

seasonal patterns. The broad seasonal pattern evident

from the data set is one of high nutritive value during

cool-season months in autumn and winter, progressive

decline through the period corresponding to the pri-

mary growth phase in spring and lower but relatively

uniform nutritive value through summer.

Many previous studies have reported the changes in

nutritive value for other pasture plants, especially

temperate grasses that occur in the primary growth

phase, in particular those changes that accompany

onset of maturity (e.g. Sullivan, 1973; Jones and

Wilson, 1987). However, no other extensive data set

for white clover is known to the authors that compre-

hensively contrasts chemical composition across the

different growth phases (cool-season vegetative growth,

winter quiescence, spring primary growth and summer

regrowth). Givens et al. (1993) compared the chemical

composition and ME concentration of spring primary

growth, summer regrowth and autumn regrowth of

temperate perennial grass swards (Lolium perenne,

L. multi¯orum) and found that, although the differences

between years were not consistent, there was a trend

for summer regrowth to be relatively high in NDF and

lignin and low in crude protein. Also, the ME concen-

tration of spring herbage was greater than summer and

autumn regrowth owing to the very high ME concen-

tration (ME > 11á9 MJ kg)1 DM) of ®rst-cut spring

herbage. However, the ME content of spring herbage

declined at a greater rate with advancing maturity.

The large effects of advancing maturity on the

constituents of nutritive value in the present study

(Table 4) dispute the contention of previous workers

that the effects of onset of maturity for pasture legumes

are of lesser magnitude than for pasture grasses (Sul-

livan, 1973; Jones and Wilson, 1987). The present data

for white clover in this environment show substantial

changes in the constituents of nutritive value: increase

in structural ®bre, decline in N and in vitro OM

digestibility. These compositional changes were accom-

panied by differences in feeding value, decline in in vivo

OM digestibility and reduced intake (Table 5). Similar

effects were reported by Mulholland et al. (1996) for the

annual pasture legume subterranean clover (Trifolium

subterraneum); onset of maturity from the vegetative

Table 6 Degradability characteristics and proportions of protein (aProt, rapidly soluble protein; bProt, slowly degradable protein; cProt, rate of

degradation of fraction b) and calculated values of effective rumen degradable protein (ERDP), digestible undegradable protein (DUP), metabolizable

protein (MP), metabolizable energy (ME) and fermentable metabolizable energy (FME) of white clover at three stages of maturity in the primary

growth phase in spring

ERDP DUP MP ME FME

Growth stage a Prot b Prot

c Prot

(h)1)

(g kg)1

DM)

(g kg)1

DM)

(g kg)1

DM)

(MJ kg)1

DM)

(MJ kg)1

DM)

Early ¯owering 0á118 0á788 0á062 119 78 144 12á1 10á4

Full ¯owering 0á133 0á633 0á110 85 44 97 10á8 9á8

Ripe seed 0á285 0á449 0á148 70 22 67 9á3 8á2



stage to the end of ¯owering was associated with a

progressive increase in structural ®bre components and

decline in in vitro digestibility from 0á77 to 0á68. The

post-¯owering period saw an abrupt decline in in vitro

digestibility to between 0á40 and 0á50 depending on

cultivar. This decline in nutritive value through ¯ow-

ering and into senescence with subterranean clover was

accompanied by a substantial decline in lamb growth

rate and wool growth.

It is especially noteworthy that the rate of decline of in

vivo OM digestibility of white clover from early-¯ower-

ing to ripe seed stage was 0á0032 per day. This is com-

parable with the rate of decline of 0á0020± 0á0035 per

day for the grasses L. perenne, L. multi¯orum and Festuca

arundinaceae reported by Givens et al. (1989) and the

rate of decline 0á005 per day for L. perenne and Dactylis

glomerata reported by Minson et al. (1960) but is greater

than the values of 0á0015 and 0á0017 per day for white

clover during spring growth reported by Harkess (1963)

and Davies et al. (1966) respectively. However, the

results of Harkess (1963) and Davies et al. (1966) are

based on an in vitro DM digestibility assay. By compar-

ison, the rate of decline in in vitro OM digestibility for the

white clover diets in the present study from early-

¯owering to ripe seed stage was 0á0016 d)1 (decline from

0á738 to 0á647 over 55 days; Table 4). Clearly, the

change in nutritive value of white clover with advancing

maturity based on in vitro digestibility determinations in

contrast to in vivo digestibility measurements under-

states the nutritional signi®cance of onset of phenolog-

ical maturity. The perception that `¼white clover

maintains its nutrition value at a high level, with slight

fall with advance in maturity¼' (Davies et al., 1966) and

again `¼white clover has been unique in its general high

level of digestibility, and in its slow fall in digestibility

with maturity' (Thomson and Raymond, 1969) accord-

ingly needs to be interpreted with caution, at least for

Australian dryland (non-irrigated) conditions.

Two other reports of the effects of advancing maturity

during primary growth of white clover are known to

the authors. Firstly, Fleming (1973) reported for cv.

Ladino that nitrogen, phosphorus and potassium con-

sistently declined with advancing maturity (as did

copper, cobalt and iron), zinc increased and calcium,

sodium and manganese ¯uctuated inconsistently. Sec-

ondly, Wilman et al. (1994) reported the direct effects of

ageing of the leaf of white clover cv. Menna; the

concentration of nitrogen declined by »0á20, phospho-

rus and potassium declined by »0á50, manganese

declined by »0á15, whereas calcium increased ®vefold

and sodium increased by »0á15. The in¯uence of

maturation on nutritive value cannot therefore be

interpreted as an outcome exclusively of morphological

changes (namely decline in leaf:stem ratio); Wilman

et al. (1994) interpreted these changes of nutrient

composition with ageing as an expression of transloca-

tion of mobile nutrients to support phenological devel-

opment elsewhere in the plant.

In the present study, decline in N concentration from

early-¯owering to ripe seed stage (Table 4) was also

accompanied by a progressive decline (Table 6) in ERDP

(119±70 g kg)1 DM), DUP (78±22 g kg)1 DM) and MP

(144±67 g kg)1 DM). This is consistent with the effects

of advancing maturity on protein and energy composi-

tion reported for subterranean clover by Mulholland

et al. (1996). It is noteworthy that white clover at the

ripe seed stage was high in soluble protein (aPROT) and

high in fractional degradation of protein (cPROT), yet

relatively low in ERDP. This apparent con¯ict re¯ects

the low initial protein content of white clover at the ripe

seed stage that strongly in¯uenced the magnitude of the

derived values. For white clover in the present study,

the concentration of ERDP at the early-¯owering stage

was greater (relative to the available FME) than that

required for microbial protein synthesis, DUP was high

and MP status was theoretically adequate to support a

high level of lamb liveweight gain (AFRC, 1993). By

contrast, at both full-¯ower and ripe seed stages, FME

declined to levels (relative to the available ERDP) likely

to be limiting for microbial protein synthesis. Moreover,

DUP of white clover at the ripe seed stage was low and

the resultant MP value of 67 g kg)1 DM is less than the

requirement for maintenance for this class and live

weight of sheep (AFRC, 1993).

Conclusions

These data bring into question the contention based on

European pasture conditions that white clover remains

uniformly high in nutritive value throughout its growth

cycle. The data show that for this dryland summer

rainfall environment in Australia, white clover, as

occurs with other temperate pasture species, undergoes

substantial changes in nutritive value in conjunction

with phenological development during the primary

growth phase in spring. Notwithstanding the caution

that must be exercised in extrapolating results from pen

feeding trials to pasture grazing (McDonald, 1968) due

to preferential grazing phenomena (Curll, 1982), the

magnitude of this decline in quality provides explana-

tion for the declining performance of grazing animals

commonly observed in this environment in late spring/

early summer in the presence of ad libitum levels of

green pasture biomass. Future work needs to examine

the nutritive value of white clover-based pastures

during the regrowth phase over summer and determine

the forms of supplementary feeding required to avert

nitrogen wastage and dietary insuf®ciency for the high

levels of animal performance sought from intensive

sheep and cattle enterprises.



Acknowledgments

The authors are grateful to Mrs P. Newsome for word

processing and to Dr H. Lloyd Davies for helpful

comments on the manuscript.

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Documents

A study of the nutritive value of white clover (Trifolium repens L.) in relation to different stages of phenological maturity in the primary growth phase in spring