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Variation in cell wall digestibility of perennial ryegrass at heading stage

Frederik van Parijs

Introduction

Frederik van Parijs, Chris Van Waes, Erik Van Bockstaele, Geert Haesaert, Isabel Roldán-Ruiz, Hilde Muylle

HEADINGVEGETATIVE FLOWERING SHEATHBLADE STEM

Material and methods

Results and discussion

Why improving total digestibility?Increase dry matter intake

Increase energy release during digestionReduce release of nitrogen into the environment

Improve milk production and quality

Why improving cell wall digestibility (NDFD)?Less environmental variation than WSC

High concentration of WSC leads to acidosis

How to increase selection response?Assess individual genotypes

Harvest at heading stageSeparate organs

Plant material13 diverse diploid genotypes

Harvested at heading (3 spikes) in spring 2011Organs separated and weighed

Wet-chemical analysisNDFD with ruminal fluid (Goering & Van Soest 1970)

NIRSSeparate calibration model for blade and sheath/stem

Statistical analysisPlant values calculated from organ fractions

ANOVA and MLR (fixed effects)Post-hoc: Tukey

Inter-genotypic variation in NDFDMore variation in NDFD for sheath and stem than for plant

Plant level: significant genotype effects (R² = 68%)Organ level: significant genotype effects (R² = 76-80%)

=> More variance explained by separating organs

Difference in blade, sheath and stem NDFDOn average: blade NDFD > sheath NDFD > stem NDFD

But: significant genotype-by-organ interaction=> Selecting higher blade fractions is another option to

increase plant NDFD

Variation in weight fractions of blade, sheath and stemBlade: 58%, significant genotype effects (R² = 83%)

Sheath: 26%, significant genotype effects (R² = 83%)Stem: 12%, significant genotype effects (R² = 68%)

High correlation between sheath and stem fractions

Strategies to increase plant NDFD1) Increase blade fraction? No (small effect)

2) Increase NDFD for blade? No (not enough variation)3) Increase NDFD for sheath/stem? Yes (large effect)

Table 1. Summary table of genotype means and variation. “95% range” is the range within which 95% of genotypes lie, assuming a normal distribution (2*1.96*SD).

Table 1. Summary table of genotype means and variation. “95% range” is the range within which 95% of genotypes lie, assuming a normal distribution (2*1.96*SD).

Heading /

harvest date

NDFD (%) Weight fraction (%)

Plant Blade Sheath Stem

Blade Sheath Stem Stem

+ sheath

Mean 01/06

75.8 78.6 71.7 67.9

57.9 25.8 12.2 38.1

Min. 16/05

72.8 75.7 66.1 59.4

47.2 13.7 4.7 19.4

Max. 14/06

79.4 80.9 78.2 76.6

77.6 33.2 18.2 47.0

95% range 35,1

7.8 6.2 14.2 18.6

39.1 24.2 17.8 36.7

0102030405060708090

100

Aber

zest

_291

Bara

ta_1

9510

370_

22O

rant

as_2

58Ca

rillo

n_91

Aber

zest

_299

5297

Mel

way

s_32

Bara

ta_1

98M

elon

i_16

0ba

1299

0_6

Siba

sa_2

35As

turio

n_12

3

Wei

ght f

racti

on (

%)

55

60

65

70

75

80

85

Aber

zest

_291

Bara

ta_1

9510

370_

22O

rant

as_2

58Ca

rillo

n_91

Aber

zest

_299

5297

Mel

way

s_32

Bara

ta_1

98M

elon

i_16

0ba

1299

0_6

Siba

sa_2

35As

turio

n_12

3

NDF

D (%

)

Blade

Sheath

Stem

Plant

Table 1. Multiple linear regression model. Average plant NDFD is estimated by NDFD of each organ and the blade fraction (which is complementary to sheath and stem fraction). The intercept is the expected NDFD of a plant with an average blade fraction and average organ NDFDs. Variation inflation is limited as shown by the VIF factors (<3).

estimate SE 95% C.I. p-value VIF

(Intercept) 75.7769 0.1827 75.36 to 76.20 <0.0001 Blade NDFD 0.3856 0.1758 -0.02 to 0.78 0.0596 2.14

Sheath NDFD 0.3456 0.0626 0.20 to 0.49 0.0006 1.42

Stem NDFD 0.1618 0.0446 0.06 to 0.26 0.0068 1.25

Blade fraction 0.0778 0.0230 0.02 to 0.13 0.0096 1.45