Prediction of the nutritive value of lucerne hay in diets for growing rabbits

ANIMAL FEED SCIENCE AND TECHNOLOGY

E:LSEVIER Animal Feed Science and Technology 54 ( 1995) 33-44 -

Prediction of the nutritive value of lucerne hay in diets for growing rabbits

J. Garciaa, L. PCrez-Albab, C. Alvarez’, R. Rochaa, M. Ramosa, C. de Blas”y*

aDepartamento de Produccih Animal, ETS Ingenieros Agrhomos, Universidad Politkcnica, 28040 Madrid, Spain

bDepartamento de Produccih Animal, Facultad de Veterinaria, Universidad de Cbrdoba, 14005 Cdrdoba, Spain

“COREN SCL. Avda Juan XXIII, 37 32003 Orense, Spain

Received 6 July 1994; accepted 17 November 1994

Abstract

Fifty-one New Zealand WhiteXCalifomian rabbits were used to evaluate apparent in vivo dry matter (DM), organic matter (OM), energy, nitrogen (N), neutral detergent fibre (NDF) and amino acid digestibilities of five luceme hays varying in chemical composition. Hays were ground and pelleted and given as sole feeds throughout the experiment. In vitro DM, OM, NDF and N digestibilities of feed samples were also determined. A ruminal incubation trial was performed to determine NDF disappearance of luceme hays in nylon bags. The type of luceme hay had a large effect on its nutritive value. The range of variation for digestible energy (DE) and digestible crude protein (CP) contents and for NDF digestibility was 6.4-9.2 kJ g-‘, 114-164 g kg-’ and 0.204-0.276, respectively. The type of luceme hay also atTected lysine, methionine and threonine digestibilities. Stepwise regression analysis showed that the best single predictors for energy, CP, NDF and amino acid digestibilities were dietary NDF and non starch polysaccharide (NSP ) contents, rumifial NDF degradability after 48 h of incubation and CP digestibility, respectively. Regressions using only chemical components as independent variables were also calculated. The results of this study showed that in vitro methods and prediction equations determined for mixed diets and concentrated ingredients need to be adjusted to estimate nutritive value of forages in rabbits.

Keywords: Rabbit; Lucerne; Digestibility

* Corresponding author: Tel. 34-l-5497978; Fax. 34-l-5499763.

0377-8401/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved ssDI0377-8401(94)00759-4

34 J. Garcia et al. /Animal Feed Science and Technology 54 (1995) 33-44

1. Introduction

Lucerne hay is commonly a major ingredient in rabbit diets, accounting for around one-third of the commercial feeds. Chemical composition of luceme hay is variable because of differences in variety, maturity, climate and conservation technique. Coefficients of variation for dry matter (DM), crude protein (CP) and neutral detergent fibre (NDF) contents over 56 commercial samples were 13.6%, 9.096, and 14.0% (C. Alvarez, unpublished data, 1993). Significant vari- ations in nutritive value might also occur.

Methods for estimating the energy and protein value of complete diets for rabbits have been developed based on chemical composition (Maertens et al., 1988; de Blas et al., 1992) or in vitro techniques (Ramos et al., 1992). However, this information cannot be extrapolated to most feed ingredients, whose chemical composition lies outside the predictive range of these equations. The objective of this study was to determine in vivo the feeding value of five lucerne hays differing in chemical composition, and to develop methods of prediction for the main components of its nutritive value.

2. Materials and methods

2. I. Diets

Five luceme hays of cultivar ‘Aragon’, harvested at different stages of maturity, were selected in order to obtain the greatest variability in fibre and protein composition, and were named A, B, C, D and E in order of increasing NDF content. Hays were ground through a 4 mm screen and then pelleted (pellets 15 mm in length, 3 mm in diameter). Chemical analyses of these materials are shown in Table 1. The range of variation of the chemical compounds was 248-372 g kg- ’ DM for crude libre (CF), 387-550 g kg-’ for NDF, 295-402 g kg-’ for acid detergent fibre ( ADF) ,60-90 g kg- ’ for acid detergent lignin ( ADL), 220- 167 g kg-’ for CP, 2.0-2.3 g kg-’ for acid detergent insoluble nitrogen (ADIN) and 5.0-8.3 g kg-’ for neutral detergent insoluble nitrogen (NDIN).

Neutral sugar composition of non starch polysaccharides (NSP) of the live diets and amino acid contents of luceme hays A, C and E, are shown in Tables 2, and 3, respectively. The five samples of alfalfa hay were also analysed for DM, OM, NDF and CP digestibilities (Table 4 ) using an in vitro technique developed byRamosetal. (1992).

2.2. Digestibility trial

A group of 5 1 male and female New Zealand White~Califomian rabbits (a minimum of eight animals per diet), from 45 to 60 days of age, and weighing from 1.3 to 1.8 kg, were allotted at random to the five diets. Animals were given ad libitum access to luceme hays as sole feeds throughout the experiment. Ani-

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Table 3 Mean amino acid contents (g kg-’ DM) of luceme hays fed to rabbits

Amino acid Lucerne hays

A C E

GUY ASP Thr Ser Glu Ala Val

Be Leu Tyr Phe LYS His Arg Pro

10.2 9.4 1.4 22.2 21.2 17.8

9.4 8.4 6.5 9.8 9.2 1.9

20.6 19.2 17.7 11.5 10.2 1.8 11.4 10.5 8.4 2.1 2.5 2.2 9.0 8.1 6.3

15.4 14.1 11.1 5.8 5.0 4.1

10.3 9.3 1.3 11.2 9.5 6.4

5.6 5.2 4.2 12.7 10.4 8.9 15.6 13.5 12.6

Table 4 Mean in vitro nutrient digestibility of luceme hays fed to rabbits

Lucerne hays SEM”

A B C D E

DM 0.619 0.544 0.555 0.530 0.492 0.004 OM 0.596 0.529 0.544 0.516 0.470 0.007 NDF 0.226 0.212 0.231 0.220 0.197 0.011 CP 0.819 0.781 0.803 0.833 0.813 0.003

%tandard error of means ( n = 3).

cubated during 2,4,8,16,24,48, and 72 h. Bags were made of nylon with a pore size of 46 p (nylon Blutex ref. 120, Tripette & Renauld, Paris). Dried samples (3 g) were milled through a 2 mm screen and introduced in each bag. Bags were heat sealed and tied to a stainless steel chain with an approximate weight of 250 g. All bags were washed after the incubation with cold water and were stored at - 20 “C. Bags were thawed and washed three times during 5 min with cold water in a turbine washing machine, then they were dried at 80°C for 48 h and the NDF disappearance was determined.

2.4. Analytical methods

Chemical analyses were made using the method of Robertson and Van Soest ( 1981) for NDF, Goering and Van Soest ( 1970) for ADF, ADL, ADIN and

J. Garcia et al. /Animal Feed Science and Technology 54 (1995) 33-44 37

NDIN, and the Association of Official Analytical Chemists ( 1984) for DM, ash, CP and CF. Gross energy was determined by adiabatic calorimetry. Amino acid contents were determined using high pressure liquid chromatography (Cohen et al., 1989). For sulphur amino acids, the samples were first oxidised with per- formic acid overnight at 0°C. The reaction was stopped with hydrogen bromide and the samples were dried and treated as for all other amino acids. Neutral sug- ars of non starch polysaccharides were measured by gas-liquid chromatography analysis of their alditol acetate derivatives (Harris et al., 1984). Uranic acids were determined calorimetrically by the m-phenyphenol method (Blumenkrantz and Asboe-Hansen, 1973 ) .

2.5. Statistical analysis

Statistical analyses were performed using the General Linear Model procedure of the Statistical Analysis System Institute Inc. ( 1985). If the treatment effect was significant, the differences among means were tested using the least significance difference (LSD) test. The effect of time of incubation was tested using a repeated measures analysis. A non linear procedure (NLIN) was used to fit regression curves between NDF degradability and incubation time. Stepwise regression analysis was employed for developing prediction equations using chemical and in vitro measurements as independent variables and in vivo digestibilities as dependent variables. The stepwise procedure introduced variables into the model only if they contributed to a significant improvement (PC 0.15 ) in the estimation of the dependent variables.

3. Results

3.1. In vivo digestibility trial

In vivo apparent digestibility coeffkients for DM, OM, energy, nitrogen and NDF of the five luceme hays are shown in Table 5. Feed intake was not signifi- cantlyaffectedby type ofdiet, averaging (mean?SE) 73.82 11.3 gday-I. Coef- ficients of variation of the digestibility determinations were on average 6% for DM, OM and energy, 3% for CP and 13% for NDF. Type of diet significantly affected all the digestibilities studied, which decreased linearly (P< 0.00 1) with NDF and inversely with crude protein content in the luceme hay. Digestible energy (DE) and crude protein digestible values derived from gross energy and crude protein contents and energy and nitrogen digestibilities were 9.2 kJ, 7.6 kJ, 7.5kJ,8.0kJand6.4kJg-‘DMand 164g, 163g, 15Og, 129gand 114gkg-’ DM, for alfalfa hays A, B, C, D and E, respectively.

The type of luceme hay affected both content (Table 3 ) and digestibility (Ta- ble 6) of most amino acids, although no significant differences were found for glutamic acid, valine, leucine, tyrosine and arginine digestibilities. Digestible lysine, methionine and threonine contents, the amino acids usually limiting in rab-

38 J. Garcia et al. /Animal Feed Science and Technology 54 (I 995) 33-44

Table 5 Effect of type of luceme hay on apparent nutrient digestibility by rabbits

Lucerne hays SEM” Pb

A B C D E

DM 0.547a( 11) 0.477b( 13) 0.464b(9) 0.47Ob( 10) 0.407c(8) 0.007 OM 0.524a( 11) 0.455b( 13) 0.438b(9) 0.455b( 10) 0.377c( 8) 0.008 Energy 0.512a(ll) 0.425b(12) 0.42Ob(9) 0.437b( 10) 0.359c(S) 0.009 Nitrogen 0.744a( 11) 0.736ab(S) 0.716b(8) 0.727ab(S) 0.674c(8) 0.010 NDF 0.276a( 9) 0.259ab( 8) 0.249ab(S) 0.227bc(S) 0.204c(8) 0.012

‘Standard error of means. bProbability of significant differences among treatment means. Means in the same row that not followed by a common letter differ (PC 0.05 ) . Numbers in parentheses indicate number of determinations per diet.

0.001 0.001 0.001 0.001 0.001

Table 6 Effect of type of luceme hay on apparent faecal amino acid digestibility by rabbits

Amino acid Lucerne hays SEM” Pb

A C E

GUY 0.738a 0.692b 0.634~ 0.01 0.001 Asp 0.830a 0.79Ob 0.758b 0.01 0.006 Thr 0.774a 0.722b 0.670~ 0.02 0.001 Ser 0.744a 0.698ab 0.664b 0.01 0.009 Glu 0.794 0.758 0.742 0.01 0.053 Ala 0.778a 0.736a 0.688b 0.01 0.004 Val 0.774 0.744 0.708 0.02 0.073 Met 0.798a 0.726b 0.726b 0.02 0.012 Be 0.81 la 0.753b 0.746b 0.01 0.007 Lell 0.816 0.778 0.760 0.01 0.056 TF 0.832 0.802 0.802 0.01 0.247 Phe 0.810a 0.748b 0.7541, 0.01 0.007 LYS 0.814a 0.76Ob 0.672~ 0.02 0.001 His 0.774a 0.718b 0.7OOb 0.01 0.00 1 Arg 0.884 0.856 0.854 0.01 0.210 Pro 0.866a 0.82Ob 0.816b 0.01 0.001

aStandard error of means ( n = 5 ) . bProbability of significant differences among treatment means. Means in the same row not followed by a common letter differ (PC 0.05).


bitfeeds,were9.1g,7.2g,4.3g;2.1g, 1.8g, 1.6g;7.3g,6.1gand4.3gkg-‘DM for alfalfa hays A, C and E, respectively.

3.2. Ruminal incubation in situ trial

Both type of luceme hay (P<O.OOl), time of incubation (P<O.OOl) and its interaction (PC 0.001) had a significant influence on NDF degradation. The differences between luceme hays A and E were larger when time of incubation increased (Table 7 ) . Ruminal degradability of NDF ( RNDFd ) increased curvilin- early with incubation time (t, h). The best adjustments were obtained when following the model proposed by Orskov and McDonald ( 1979)

RNDFd=a+b( 1 -e-“)

where a, b and c are constants which can be interpreted as the rapidly soluble fraction, the fraction potentially degradable and the rate of degradation, respectively. The regression equations obtained in this study for each luceme hay were (n= IS) as follows:

Lucerne A

RNDFd=0.036( +_0.022)+0.635( kO.025) (1 _e-O.OWfO.OW~) R~=-JJCJ

Lucerne B

RNDFd=0.034( +0.027)+0.543( 20.034)

(l-e -0.049(+0.0093)1) ~2~0.97

Lucerne C

RNDFd=0.015( -+0.018)+0.558( 20.024)

Table 7 Effect of incubation time (b) and type of luceme hay on in situ ruminal NDF degradability

Incubation time Lucerne hays SEM” Pb

A B

2 0.116 4 0.129 8 0.268a 6 0.441a

24 0.474a 48 0.610a 72 0.670a

0.103 0.128 0.197b 0.284b 0.463a 0.531b 0.542b

C D E

0.068 0.097 0.18Ob 0.253b 0.391ab 0.520b 0.530bc

0.088 0.084 0.01 0.10 0.108 0.092 0.01 0.16 0.202b 0.156b 0.02 0.001 0.262b 0.240b 0.02 0.001 0.362b 0.335b 0.03 0.01 0.486b 0.427~ 0.02 0.001 0.536b 0.478~ 0.02 0.001

“Standard error of means ( n = 3 ) . bProbability of significant differences among treatment means. Means in the same row not followed by a common letter differ (PC 0.05).

40 J. Garcia et al. I Animal Feed Science and Technology 54 (I 995) 33-44

(l- e-0.042"0.0058)t) R2=0_g8

Lucerne D

RNDFd=0.050( +-0.019)+0.539( 20.034) (l_e -0.033(f0.0060)1) ~2~0 98

Lucerne E

RNDFd=0.034( +0.019)+0.470( 20.028)

(l-e- 0.039(+0.0070)1) R2=0*97

According to these results, the soluble fraction was not significantly different from zero for any of the hays studied, whereas both the fraction potentially degradable and the rate of NDF degradation tended to decrease when luceme tibre content increased.

3.3. Prediction of nutritive value of lucerne hays

The results of the stepwise regression analyses for predicting energy, CP, NDF, lysine, methionine, and threonine digestibilities, and DE content of luceme hays from their chemical composition and in vitro digestibility are shown in Table 8. Ruminal degradability of NDF at the different incubation times studied, and in vivo CP digestibility were included as independent variables for predicting NDF and amino acid digestibilities, respectively.

The best single predictor for gross energy digestibility (GEd) and DE content was dietary concentration of NDF (%, DM basis). Prediction of GEd improved when in vitro DM digestibility was added to the model (see Table 8). Good correlations were also obtained when using gross energy content (GE, kJ g- ’ ) as a second independent variable, both for DE content (see Table 8 ) and GEd

GEd= - 0.0409 ( 2 0.544) - 0.0092 ( + 0.00079)NDF

+0.051 (kO.03O)GE R2=0.742 P<O.OOl

The best prediction equation for NDF digestibility (NDFd) was obtained from RNDFd after 48 h of incubation (Table 8)) although absolute values of NDFd were intermediate among NDF degradabilities after 8 and 16 h of incubation. In vitro NDF digestibility was poorly related to NDFd ( t= 0.43 ) . When excluding ruminal fermentation data from the analysis, the stepwise method selected a mul- tiple regression model, choosing NDF and CP dietary contents (%, DM basis) as independent variables

NDFd=O.205( +0.128)-0.00214( kO.OO14)NDF

+0.00704( +-0.0034)CP R2=0.382 P<O.OOl

The highest correlations of NDFd with neutral sugar composition of NSP were

Tabl

e 8

Estim

atio

n of

in

vivo

app

aren

t nu

trien

t di

gest

ibili

ty

of l

ucem

e ha

ys b

y th

e st

epw

ise

met

hod

( n =

40)

(n

umbe

rs

in p

aren

thes

es

indi

cate

SE

)

Reg

ress

ion

equa

tion

R2

P

GE

dige

stib

ility

St

ep

1:0.

868

(f0.

038)

-0.0

0913

(+

O.O

OO

Sl)N

DF

0.72

7 to

.001

St

ep 2

: 1.

27 (

f0.2

1)-0

.012

4 (k

O.0

018)

N

DF-

0.46

2(

kO.2

33)

IVD

MD

0.

748

<O.O

Ol

Dig

estib

le

ener

gy

Step

1:

15.

6 (k

O.7

1)-0

.164

(k

O.0

15)

ND

F 0.

719

tO.O

O1

(kJg

-‘D

M)

Step

2:

-9.6

8 (_

+9.5

9)-0

.166

(_

+0.0

14)N

DF+

1.41

(k

O.5

3)

GE

0.75

5 <0

.001

N

DF

dige

stib

ility

St

ep

1: 0

.031

( T

O.0

46)

+0.4

10

( 20.

087)

R

ND

Fd48

0.

361

<O.O

Ol

CP

dige

stib

ility

St

ep

1: 0

.969

(+_

0.04

3)-0

.007

1 (+

0.00

12)

NSP

0.

443

<O.o

ol

Lysi

ne d

iges

tibili

ty

Step

1:

-0.2

87

(kO

.OS9

)+1.

44

(kO

.124

) C

Pd

0.91

2 to

.001

Th

reon

ine

dige

stib

ility

St

ep

1: -0

.084

(+

0.05

7)+1

.125

(k

O.0

80)

CPd

0.

938

<O.o

Ol

Met

hion

ine

dige

stib

ility

St

ep

1: 0

.260

(+0

.158

)+0.

684

(20.

220)

C

Pd

0.45

2 <O

.OO

l

ND

F,

neut

ral

dete

rgen

t tib

re

(%,

DM

bas

is);

IVD

MD

, in

vitr

o dr

y m

atte

r di

gest

ibili

ty;

GE,

gro

ss e

nerg

y (k

J g-

’ D

M);

RN

DFd

48,

rum

inal

N

DF

degr

adab

ility

af

ter

48 h

; N

SP,

non-

star

ch

poly

sacc

harid

es

(%,

DM

bas

is);

CPd

, in

viv

o cr

ude

prot

ein

dige

stib

ility

.


obtained for arabinose, galactose, glucose and uranic acid contents (g kg - ’ NSP ) : 0.44,0.53, -0.31 and 0.50, respectively.

The independent variable better correlated with in vivo CP digestibility (CPd) was dietary concentration of NSP (Table 8). No other variables met the 15% significance level to enter into the model. High single correlations were also obtained for NDF (%, DM basis) and ADIN (% total N) dietary contents

CPd=0.901(+0.041)-0.0038( +O.O0086)NDF R*=0.32 P<O.OOl

CPd=0.868( +0.034)-0.022( ?O.O05O)ADIN R2=0.32 P<O.OOl

In vitro CP digestibility was, however, poorly related (r=0.032, NS) to CPd in vivo of lucerne hays.

Amino acid digestibilities were highly correlated with CPd (Table 8). When including only chemical analyses (%, DM basis) in the model, the stepwise method calculated the following regression equations for lysine (LYSd), threonine (THRd) and methionine (METd) digestibilities

LYSd=l.121(?0.073)-0.0114(?0.0023)NDF

+0.272( 50.16)NDIN R2=0.75 P<O.OOl

THRd= 1.021(+0.061)-0.0063( +O.O013)NDF R2=0.65 P<O.OOl

METd=0.974( +0.069)-0.0047( +O.O014)NDF R2=0.45 P<O.OOl

4. Discussion

In vivo apparent nutrient digestibilities were greatly affected by the type of luceme hay. Values for DM, OM, energy and NDF digestibilities for luceme A were approximately 30% higher than for luceme E. Smaller differences ( 10%) were found for CP digestibility, although digestible crude protein content was 44% higher in luceme A than in luceme E.

Energy digestibilities were lower (from - 5 to - 17%) than those predicted for each luceme hay according to the equation proposed by Wiseman et al. ( 1992) for concentrated single feeds. This result confirms that more work is needed to develop a general equation for feed ingredients extrapolable to fibrous feeds. The values fit well, however, with the equation proposed by De Blas et al. ( 1992) for mixed diets ( + 4%). They are also in agreement with the value (0.42) reported by Maertens and De Groote ( 198 1) for luceme hay containing 27.5% CF on DM. The relatively high values obtained for CP digestibility (0.67-0.74) show the capability of rabbits to digest forage protein through microbial caecal fermentation and caecotrophy. However, relatively low NDF digestibilities (0.20-0.28) agree with previous reports (Gidenne, 1990) and are explained by the mecha- nisms of separation of fibrous particles at the ileo-caecal junction, avoiding the entry of large amounts of fibre into the caecum, and by the short caecal fermen-


tation time (6.9 h for a diet containing 76.5% of lucerne hay; Gidenne et al., 1991).

The type of lucerne hay had a variable effect on amino acid digestibility. The effect was higher for lysine ( 17.5% of difference between lucemes A and E), and threonine ( 13.5%), than for the average of all amino acids ( 10%). This result emphasizes the need of using digestible rather than crude units to express both animal requirements and amino acid content of feeds in rabbits.

Considering all the data together, the best single predictor for the digestibilities studied was dietary NDF content. Significant improvements were observed when including in vitro DM digestibility, GE, NSP, CPd and ruminal degradability of NDF after 48 h of fermentation in the prediction model of GEd, DE, CPd, amino acid digestibilities and NDFd, especially in the last two cases. For practical pur- poses, equations based on simple chemical predictors (NDF, CP, NDIN, ADIN) are also provided for the assessment of the nutritive value for rabbits of luceme hays. The results of this study also show that in vitro laboratory methods de- signed for mixed diets and concentrated ingredients, need some adjustments to be applied for predicting CP and NDF digestibilities of forages in rabbits.

Acknowledgement

This research was supported by CICYT (AGF93-0870) and CDTI-EUREKA Program (EU-6 19).

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Prediction of the nutritive value of lucerne hay in diets for growing rabbits

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