Methods of carcass classification based on subjective ...

Anima! Science 2003, 77: 383-393 © 2003 British Society of Animal Science

Methods of carcass classification based on subjective assessments of carcass fatness and of carcass conformation: effect of sex on the prediction of tissue composition in carcasses of sucking lambs E. MigueP, F. Ruiz de Huidobro1t, M. T. Díaz2, S. Velasco2, S. Lauzurica3, C. Pérez3, E. Onega\ B. Blázquez1 and V. Cañeque2 lInstituto Madrileño de Investigaci6n Agraria y Alimentaria, Apartado 127, 28800 Alcalá de Henares, Spain 2Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Apartado 8111, 28080 Madrid, Spain 3Universidad Complutense, Avenida Puerta de Hierro, s/n. 28040 Madrid, Spain t Corresponding author. E-mail address : felipe.ruí[email protected]

Abstract Forty-eight sucking lambs (26 males and 22 females) of the Manchega breed were used in this work. Lambs were slaughtered at 10, 12 and 14 kg líve weight. Carcass degree offatness was assessed by three assessors from colour photographs of the carcasses, using the European Uníon scale for light lambs (EU), the Colomer-Rocher method (CF) and another new scale developed by our group (sucking lambs scale, SL). Carcass conformatíon was assessed according to the Colomer-Rocher method (CC). Fatness and conformation scales were divided to give 0·25 points in each interval. Left half-carcasses were jointed and dissected into lean, fat and bone. Muscle proportíon, bone proportíon and whole fat proportion (obtaíned by addition of every fat depot: subcutaneous fat, intermuscular fat, inguinal fat and kidney knob and channel fat) were determined. Male and female carcasses showed a very different tissue composition: both groups had statistically significant differences (P < 0·05) in 20 out of 25 tissue composition variates. Males showed a higher number of variates that were well correlated with assessors' scoring than females. Correlation coefficients between most of the tissue composition variates and assessors' scores were higher in males. Furthermore, the number of variates that were significantly correlated with assessors' scores was lower in females. Therefore, subjective methods for the estimation of carcass degree of fatness and of carcass conformation are poor predictors of tissue composition in female sucking lamb carcasses. Keywords: carcasses, classification, sex, sheep, tissues. (estimated subjectively by assessors in the slaughterhouse). Usually, carcass conformation is only a secondary quality criterion, because it is implicitly considered when degree of fatness is evaluated. Of course, quality criteria taken into account in a given country reflect the criteria considered by consumers when buying in the market.

Introduction Any classifícation method must be able to group different units into classes, according to one or several quality criteria (Diestre, 1990). Carcass classification must be according to an elementary premise : to group a heterogeneous set of carcasses into homogeneous groups or classes that show similar tissue composition characteristics (Colomer­ Rocher and Kirton, 1975). According to these authors the success of a classification system depends on the extent of the difference between the characteristics of each class established according to the dassification system. Several factors can be considered when a carcass dassification system is introduced: carcass weight, animal age, animal sex (as objective criteria), . carcass degree of fatness and carcass conformation

In the European Uníon the system approved for

ovine carcass classification takes into account carcass weight, carcass degree of fatness and carcass conformation as quality criteria. Usually, animal sex and age are not taken into account, although the last criterion is indirectly considered when a specific sheepmeat production system is chosen. In Spain 383

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Miguel, Ruiz de Huidobro, Díaz, Velasco, Lauzurica, Pérez, Onega, Blázquez and Cañeque

several commercial classes are to be found (Boletín Oficial del Estado, 1975), two oi wruch are included in the light carcasses group oi the European Union (under 13 kg): sucking lamb (lambs that are only milk-ied and with a carcass weight under 8 kg), and 'ternasco' (lambs up to 4 months old, and with a carcass weight around 13 kg). In this work we evaluate the importance oi sex in carcass classification, using carcasses oí both sexes from animals slaughtered at the same live weight. Subjective assessment oi carcass degree of fatness using photographic standards as references is used in slaughterhouses as a cheap and quick method to predict carcass tissue composition. But actually there is not a common method used in all the slaughterhouses. The European Union has established a model (EU method) for light lamb carcasses under 13 kg (European Union, 1994a) using photographic standards (European Union, 1994b). In Spain another classification using either carcass degree of íatness (CF method) or carcass conformation (CC method) has also been used traditionally for research work (Colomer-Rocher et al., 1988). Besides, in our work group we have developed a new method of classification for sucking lambs (SL method) (Ruiz de Huidobro et al., 2000). Sex is one of the most important factors influencing carcass and meat quality. Sex and genotype effects tend to disappear as development increases (1hompson and Butterfield, 1987), but when animals are slaughtered at the same live weight, sex ís an important factor. In earlier works it was found that female lambs produced more subcutaneous fat (Molénat and Thériez, 1973) and that they showed a rugher degree of fatness than males (Crouse et al., 1978). At the same Uve weight, females have achieved a hígher percentage oi adult weíght, and a higher development stage (and therefore a higher degree oí iatness) because of their precocity (Butterfield, 1988; Cañeque et al., 1991). In the present work, 48 sucking lambs oi the Manchega breed were slaughtered at 10, 12 and 14 kg Uve weight.

The study tried to analyse the useiulness oí three methods ior the scoring oi carcass degree oi iatness (EU, CF and SL), and of one method ior carcass conformation scoring (CC) to predict tissue composítion in male and female sucking lamb carcasses, and in three main joints (shoulder, leg and best end neck plus loin).

Material and methods Forty-eight Manchega sucking lambs (26 males and 22 females) were used in this work. Lambs were slaughtered at 10,12 and 14 kg live weight. Carcasses

were held at 4°C ior 24 h and then photographs of the carcasses were taken. Cold carcass weight was measured and carcasses were split in two halves, and the left half-carcass was jointed according to a standard method (Boccard and Dumont, 1955; Colomer-Rocher et al., 1972) and dissected into lean, fat and bone (Colomer-Rocher et al., 1988). Muscle percentage, whole fat percentage (obtained from the addition of every fat depot: subcutaneous fat, intermuscular fat, inguinal fat and kidney knob and channel fat (KKCF» and bone percentage were determined. Carcass characteristics were assessed on colour photographs in three independent sessions, by three trained assessors, as has been described in previous work (Miguel et al., 2003). Carcass fatness was assessed from three different methods : the European Union scale for light lambs (EU), the Colomer-Rocher five-point scale (CF) (Colomer-Rocher et al., 1988) and a new four-point scale ior sucking lambs developed by our group (SL) (Ruiz de Huidobro et al., 2000; Miguel et al., 2002). Carcass conformation was subjectively assessed by using the Colomer scale of five points (CC) (Colomer-Rocher et al., 1988). CF, CC, UE and SL are methods based on colour photographs as standards ior each point. Intervals between points in CF, CC, UE and SL were divided into four subintervals oi a quarter oi point (i.e.l·00, 1·25, 1·50, 1·75, 2·00, etc. ). Subdivisions were made on the following basis : if a carcass was found to be placed between two points, 0·5 points were added to the lesser point. If carcass characteristics were slightly over a point, 0·25 points were added to that point. If carcass characteristics were slightly under a point, 0·25 points were subtracted from that point. In prior works (Ruiz de Huidobro et al., 2000) results obtained from carcass classification on colour photographs were not statistically different from on­ carcass results. A single panel oi assessors was used to assess carcass characteristics in all carcasses from both sexes, in a cross-classification design (every assessor evaluated a11 the carcasses). This permitted consideration oi assessors' effect in isolation (Lea et al., 1997). Assessors evaluated photographs in slaughter order (as if an on-line evaluation), in three independent sessions a week apart, by al! four methods in the following order : CF, CC, EU and SL. Each carcass photograph was thus assessed three times (three independent sessíons) by each assessor. We have estimated panel precision by analysing both assessor repeatability and panel repeatability between sessions. Assessor repeatability was expressed as the coeificient oi variation of the three mean scores (one from each session, a1148 carcasses' scores pooled). Panel repeatability was assessed as

the coefficient 4 assessors poolE

As carcass el¡¡ carcass charac sensory analys statistical anal] sensory anal}'1 classífication 1 scales, so one 1 1 and 2 refl, and 3. As methods ay, . ordinal data, eommon pra, Data were s statistical pa (Statsoft,l997.

Session eff, assessor eff, performed o: method and taking all randornIy people, and instrumento

Effect Method (M, fi Assessor (A, f Session (S, fixi MethodX (MXS) MethodXas: (MXA) AssessorX (AXS) Method X as: (MXAX

.

Male (no. = 2, Female(no.­ Significance

t CCW

COi

fat in carcass fat in carcass

Carcass dassification method and sex of lamb aphs of ht was es, and g to a , 1955; to lean, Muscle m the us fat, ob and were

the coefficient of variation of the mean scores with all assessors pooled. As carcass classification using assessors to assess carcass characteristics visuaHy is just a kind of sensory analysis (assessors assess using their eyes), statistical analysis has been made taking into account sensory analysis characteristics. Values of carcass classification have been obtained from interval scales, so one can assume that the difference between 1 and 2 reflects the same difference as that between 2 and 3. As there are more and easier statistical methods available for analysing interval data than ordinal data, treating sensory data as interval scale is common practice in the literature (Lea et al., 1997). Data were statistically analysed by means of the statistical package Statistica for Windows, r. 5·0 (Statsoft¡ 1997a).

385

work are not conclusions about the whole population of potential assessors (Lea et al., 1997), but just about the classification methods tested in this work. Tissue composition from male and female groups were compared by a fixed ANOVA (Statsoft, 1997b), taking assessors effect and sex effect as fixed effects. Correlation and regression analyses were also carried out. Correlation analysis was carried out between assessors' scores and the values of tissue composition variates. Regression analysis was a simple one¡ with tissue proportions in the carcass and in the joints as dependent variates, and assessors' mean scores with each cIassification method as independent variates (StatSoft, 1997b).

Results Repeatability of assessors' scoring

ormation er scale 988). CF, n colour Intervals divided (i.e.l·00, ere made d to be added to

) results n colour t from on­

was used sses from

gn (every permitted 'on (Lea et aphs in ), in three all four and SL. d three

Session effect, classification method effect and assessor effect were tested by means of a fixed A."10VA perfonned on the scores of each assessor with each method and in each session. The ANOVA was made taking aH effects as fixed because assessors were not randomly chosen; assessors were highly trained people, and they worked as a measurement instrumento Therefore¡ conclusions drawn from this

In the analysis of variance performed on all data

Table 1 Analysis of varianee of Bcores by each assessor with each method in each session

Table 2 Repeatabi/íty (between sessions) ofthe individual assessors and ofthe whole panel for each carcass classifícation methodt

Effect

d. f.

Method (M, fixed) Assessor (A, fixed) Session (S, fixed) Method X session (MXS) Method X assessor (MXA) Assessor X session (AXS) Method X assessor (MXAXS)

MSerror

F

3 2 2

0·2194 242·6182 6·0077 0·2194 0·2194 0·9978

6

0·2194

0·2466

6

0·2194

9·8370

4 0·2194 X session 12 0·2194

0·1135 2·8364

pooled, using assessor and session as fixed effects (Table 1), no significant session effect was found, so assessors' repeatability was high, and aH pooled scores by each assessor have been analysed. Assessors' mean scoring (Table 2) for all the carcasses had coefficients of variation (CV) lower than 0·05 for the EU and SL scales. Higher values were obtained

Carcass dassification method~

Sígnificance

.. ... •••



- - _.._ - - - - - - - - - ­ Assessor 1 Assessor 2 Assessor3 Panel

EU

CF

CC

SL

4·02 1·93 3·33 3·18

5·24 9·87 5·49 1H2

11-52 10·18 0·88 642

4·14 4·98 2·92 7·67

t Results are expressed as the variation coefficient of mean

scores.

~ EU European Uníon scale for fatness¡ CF = Colomer scale

for fatness¡ CC = Colomer scale for conformation;

SL = sucking lamb scale.

Table 3 Mean earcass tissuet compositron in males and females

Male(no.

26)

Female(no. Significance

22)

Mean s. d. Mean s.d.

CCW

CM

CSF

CIF

KKCF

INF

CWF

CB

6·38 1·00 6·50 0·98

524·7 23·8 514·6 21·0

65·2 23·3 89·0 18·9

50·8 11·6 59·2 10·9

23·6 8·5 34·5 9·1

3·4 1·5 3·0 1·5

143·0 40·2 185-6 29·8

236·6 16·4 219-6 20·0

*

"

"

"

t CCW cold carcass weight (kg)¡ CM muscle in carcass (g/kg)¡ CSF subcutaneous fat in carcass (g/kg)¡CIF intennuscu1ar fatin carcass (g/kg)¡ KKCF = kidney knob and channel fat in carcass (g/kg)¡ INF inguinal fat in carcass (g/kg); CWF =whole fat in carcass (g/kg); CB = bone in carcass (g/kg).

386

Miguel, Ruiz de Huidobro, Díaz, Velasco, Lauzurica, Pérez, Onega, Blázquez and Cañeque

Table 4 Correlation coefficíents between variates ofcarcass tíssue composition (proportíons)t and carcass classification based on subjectíve scores ofdegree offatness and carcass conformation Carcass dassification method:j:

CCW CM CSF CIF KKCF INF CWF CH

Male Female Male Female Male Female Male Female Male Female Male Female MaIe Female Male Female

EU

CF

CC

SL

0·38 0·53' -0·58' 0·08 0·68' 0·38 0·65' 0·24 0·59' 0·00 0·08 -0·07 0·71' 0·32 -0-47* -0·63'

0·27 0·33 -0·59' 0·14 0·68' 0-41 0·59' 0·17 0·49' 0·01 0·00 -0·02 0·67* 0·33 -0·36 -0·59*

0-40' 0·40 -0-41' -0·24 0·52' 0·58* 0·46' -0·02 0·65* 0·42' 0·31 0·19 0·59'

0·27 0·59' -0·57' 0·11 0·65' 0·32 0·56' 0·15 0·51' 0·04 0·10 -0·10 0·65' 0·27 -0·38* -0·63'

O·SO· -0·40' -0·31

for CF and CC scales. As expected, assessors' repeatability between sessions was higher than panel repeatability with a11 assessors pooled. A very significant effect of carcass classification method (F = 242·62) and a significant assessor effect (F = 6·01) were detected. Differences in assessors' scoring for a carcass were mainly attributed to the classification method used and secondly to inter-assessor variability.

Careass tissue Carcass tissue composition in males and Jemales. Male and female carcasses were different (P < 0·05) in five carcass tissue proportions : subcutaneous fat, intermuscular fat, KKCF, whole fat and bone in the carcass. Male carcasses showed lower fat content and higher bone content than female carcasses. There were no significant differences (P < 0·05) in the amount of muscle in the carcass expressed as a proportion. Correlation analysis between assessors' seores and earcass tissue eomposition. In Table 4 correlation coefficients between varíates of carcass tissue composition and

t See TabIe 3 for abbreviations. :j: See Table 2 for abbrevíations.

of carcasa tissue composition (proportíons)t and carcass classificatíon based on subjective scores ofdegree offatness and carcass conformation

Table 5 Regression results between variates

Carcass classífication method:j: CF

EU

CM

R2 Residual s.d. Significance

CSF

R' Residual s.d. Significance

CIF

R' Residual s.d. Significance

KKCF

R' Residual s.d. Significance

INF

R' Residual s.d. Significance

CWF

R' Residual s.d. Significance

CB

R' Residual s.d. Significance

SL

CC

MaIe

Female

MaIe

Female

Male

Female

Male

Female

0·3319 1·9880

0·0664 2·1484

0·3509 1·9595

0·0187 2·1353

0·1678 2·2187

0·0557 2·0947

0·3224 2·0021

0·0112 2·1435

0·4634 1·7442

0·4615 1·7473

0·3372 1·5797

0·4239 1-8072

..

0·1049 1-8357

0·3507 0·9569

0·1693 1·7685 § 0·0279 1-1060

0·2749 2·0275

0·4220 0·9028

0·1407 1-7987 § 0·0587 1·0883

0·2115 1·0545

0·0006 1-1214

0·3120 0·9850

0·2170 1·1095

0·3500 0·7030

0·0000 0·9292

0·2368 0·7617

0·0001 0·9291

0-4223 0·6627

0·2636 0·7482

0·0015 0·9285

0·0071 0·1538

0-0048 0·1523

0-0000 0·1543

0·0006 0·1526

0·0952 0·1468

0·1732 0·8449 § 0-0360 0·1499

0-0094 0·1536

0-0099 0·1519

0·5072 2·8797

0·1054 2·8835

0-4477 3·0486

..,

0·1063 2·8819

0·3450 3·3198

0·2474 2·6447

0-4258 3·1086

0·0718 2·9372

0·2167 1-4797

0·3998 1·5870

0-1266 1·5625 §

0·3447 1·6583

0·1614 1·5311

0·0937 1·9502

0-1475 1·5436 §

0·3935 1-5952

••

,., ,.,

••

••• •

••

t See Table 3 for abbreviations. :j: See Table 2 for abbreviations. § Tending towards significance (P < 0·1).

.,.

••

••

,.

•

••

,

., ••

•••

••

Carcas s classification method and sex of lamb

ue expected, was higher rs pooled. A tionmethod ect (F

6·01)

scoring for a c1assification

emales. Male 0·05) in five eous fat, bone in the t content and asses. There 0·05) in the ressed as a

SL Female 0·0112 2·1435 0·1049 1·8357

0·0099 0·1519 0·0718 2·9372 0·3935 1·5952

••

LSF

MaJe (no. = 26) Mean 604·8 21-1 s- d. Fernale (no. = 22) Mean 603·2 18·2 s. d. Significance

UF

CF

LWF

LB

52·6 19-6

27·6 6·1

15·1 6·4

95·2 27·0

237·1 15·6

67-4 15·1

32·3 7·5

20·9 120·6 9·7 24·7

221-4 11-3

•

•

•

t LM musde in leg (g/kg); LSF = subcutaneous fat in leg (g/kg); UF =intermuscular fat in leg (g/kg); CF =channel fat in leg (g/kg), LWF = whole fat in leg (g/kg); LB = bone in leg (g/kg).

assessors' scores can be seen. There was a significant correlation (P < 0·05) in male carcasses between assessors' scores (using any method) and the variates carcass musde, carcass subcutaneous fat, carcass intermuscular fat, KKCF and carcass whole fat, a11 of them expressed as proportions of the carcass. There was also a significant correlation for the amount of bone and every classiciation except with CE In the proportion of inguinal fat in the carcass there was no significant correlation with any classification method. rabie 4 also shows that in female carcasses there were no significant correIations (P < 0-05) between assessors' scores using any method and the proportion of muscle, intermuscular fat and inguinal fat. The proportions of subcutaneous fat and KKCF were only significantIy correlated with Ce. A significant correlation between proportion of bone in Table 7 Correlation coefficíents between variates of leg tissue

composition (proportions)t and carcass classification based on subjective scores ofdegree offatness and carcass conformatíon Carcass classification method*

0-2170 1-1095 0·0015 0·9285

the carcass and EU, SL, and CF classifications was found.

Table 6 Leg tissue compositíont in males and fema/es LM

LM LSF UF CF LWF LB

Male Female Male Fernale Male Female Male Fernale Male Fernale Male Fernale

EU

CF

CC

SL

-0·44' 0·18 0·59­ 0·37 0·24 -0·15 046' 0-18 0·59' 0·25 -0·36 -043'

-0·50' 0·12 0·53' 0·35 0·20 -0·02 0·35 0·19 0·51' 0·28 -0·26 -0·48­

-0·26 -0·06 0·49­ 0·54' 0·08 0·11 0·48­ 0·25 0-49' 0·46' -0·31 -0·20

-049­ 0·21 0·55' 0·38 0·24 -0·18 0·37 0·14 0·54' 0·23 -0·29 -0·36

t See Table 6 for abbreviations. * See Table 2 for abbreviations.

387

A comparative study between male and femaIe correlation coefficients between assessor's scores and carcass tissue composition varia tes was carried out. CorreIation coefficients were higher in male carcasses in every method and in every variate except proportion of subcutaneous fat (every method but CC showed higher correlation coefficients in male carcasses) and proportion of bone in the carcass (every method is a good predictor of female bone content but CC).

Regression analysis between carcass tissue composition and assessors' seores. TabIe 5 shows that every method was a better predictor of carcass tissue composition in males than in females. No method correctIy predicted inguinal fat proportion either in male nor in female carcasses. For the proportion of muscle, intermuscular fat and KKCF and of whole fat in the carcass, determination coefficients were higher in males, no matter which method was used. A11 the methods were good predictors of male subcutaneous fat proportion in the carcass, except Ce. Finally, every method but CC was a good predictor of female bone in the carcass.

Leg fissue Leg tissue composition in males and Jemales. Male and female carcasses were different (P < 0·05) in a11 the variates of leg tissue composition except in the proportion of muscle in the leg (Table 6). Male legs showed lower proportions of whole fat, subcutaneous fat, intermuscular fat, and channel fat, and a higher proportion of bone, than females legs.

Correlation analysis between assessors' scores and leg tissue composition. Leg tissue composition in males was significantly correlated (P < 0·05) to assessors' scoring with any method (TabIe 7). lt was also significantly correlated to the proportions of subcutaneous fat and whole fat in the carcass. The proportions of intermuscular fat and bone were not significantly correlated with classification by any method used in this work. The proportion of channel fat in the leg, was significantly correlated to classification with EU and CC methods, and that of musde in the leg to that with EU, CF, and SL methods. In females, no significant correlation was observed (P > 0·05) between assessors' scores using any method and the proportions of muscle, intermuscular fat and channel fat in the lego The amount of subcutaneous fat was only significantly

388

Miguel, Ruiz de Huidobro, Díaz, Velasco, Lauzurica, Pérez, Onega, Blázquez and Cañeque

Table 8 Regression results between variates ofleg tissue composítion (proportíons)t and carcass classifícation based on subjectíve scores of degree offatness and carcass conformatíon Carcass classification rnethod:j: EU

LM

R2 Residual s. d. Significance

LSF

R2

Residual s. d_ Significance UF

R2

Residual s. d. Significance CF

R2

Residual s. d. Significance LWF

R2

Residual s. d. Significance LB

R2

Residual s. d. Significance

CF

CC

SL

Male

Fernale

Male

Fernale

Male

Fernale

Male

Fernale

0-1912 1·9361

0-0313 1-8318

0-2510 1·8631

0·0132 1·8488

0·0679 2·0785

0-0031 1·8583

0·2357 1·8821

0·0451 1·8187

0·2831 1-6942

0·1214 1-4515

0-2419 1·7422

0-2897 1-3052

0·3000 1-6740

**

**

0-0588 0·6083

0·1397 1-4363 § 0-0229 0·7646

0·2128 0·5751

0·0315 0·9817

* 0·3519 1-6108

**

0·3534 2·2152

0·0633 2·4499

** 0·1278 1-4831 §

*

** ** 0·0381 0·6149

0·0054 0·7734

0-0071 0·6247

0-0120 0·7689

0·0594 0·6081

0·0320 0·7611

0·1260 0·6060 § 0·2643 2-3627

0·0356 0·9796

0·2319 0·5681

0·0631 0·9656

0·0205 0·9873

0·0657 1·5350

*

0·2402 2·4012

0·2128 2·2459

0·1342 0·6031 § 0·2912 2-3192

*

*

**

0·0971 1·5090

0·0402 1-1336

0-0851 1·5190

* 0·0781 2·4304

** 0·1833 1·0456

0-0451 1·8187

0·2330 1·0133

*

0·0533 2·4629 0·1309 1·0787 §

I

BENLM BENLSF BENLIF

I

KK

I

t See

BENLWF BENLB

:j: See

t See Table 6 for abbreviatíons. :j: See Table 2 for abbreviatíons. § Tending towards significance (P < 0·1).

I correlated with the CC classification. As was the case with the proportion of whole fat in the carcass, whole fat in the leg was only significantIy correlated with the CC score. The proportion of bone in the leg was well correlated using EU and CF methods. Correlation analysis suggests that all methods gave poor correlations with female leg tissue composition. In the proportions of muscle, channel fat and whole fat in the leg, the highest correlation coefficíents with every method were found in males. In all the varia tes, except subcutaneous fat and bone in the leg,

the highest correlation coefficients were obtained in males (CC was better correlated to subcutaneous fat proportion in the legs of females, and showed higher correlation coefficients in females).

Regression analysís between leg tíssue compositíon and assessors' Bcores. Regression analysis (Table 8) showed that no one method was accurate for predicting the proportion of intermuscular fat in the leg. Muscle, channel fat and whole fat proportions in the leg were better predicted in the case of all methods in males. As in the carcass, all methods gave good predictions

26)

Fernale (no. = 22) Significance

Mean s. d. Mean s. d.

BENLM l' F 5 BENLSF J F

~

BENLIF J I KK

Table 9 Best end neck and loin tissue compositiont in males and females

Male(no.

ru

Tablell subjective SIl

J

1

BENLM

BENLSF

BENLIF

KK

BENLWF

BENLB

457·1 41-4 442·1 37·0

73·9 32·2 109-4 22·2

49·6 18·0 53·9 12·6

90·7 29·3 124·1 30·2 *

214·2 69·9 287·4 46·3 *

196·7 31-1 171-1 23·8

t BENLM = rnusde in the best end neck and loin (g/kg); BENLSF subcutaneous fat in the best end neck and loin (g/kg); BENUF = intermuscular fat in the best end neck and loin (g/kg); KK = kidney knob in the best end neck and loin (g/kg); BENLWF whole fat in the best end neck and loin (g/kg); BENLB bone in the best end neck and loin (g/kg).

BENLWF 1 I BENLB

t SeeTablE :j: SeeTablE § Tending

389

Carcass classification method and sex of lamb scores of

Table 10 Correlafion coefficíents between variates ofbest end neck

and loin tissue compositíon (proportions)t and carcass classification based on subjective scores of degree of fatnesa and carcass conformation Carcass classification method:j:

SL Female 0·0451 1·8187 0·0451 1·8187 0·0320 0·7611 0·0205 0·9873 0·0533 2·4629 0·1309 1·0787

§

BENLM

Male Female BENL5F Male Female BENLlF Male Female Male KK Female BENLWF Male Female Male BENLB Female

EU

CF

CC

5L

-0·59­ 0·05 0·71­ 0·42 0·56' 0·27 0·57* -0·08 0·71' 0·22 -0·49­ ...{J·53°

-0·58* 0·11 0·70* 0·43' 0·56' 0·21 0·46' -0·06 0·66* 0·23 -0·45' ...{J·58°

-0·44* -0·26 0·57' 0·25 0·38 0·15 0·67* 0·39 0·64' 0·42 -0·43' -0·19

-0·56* 0·03 0·66' 0·38 0·47" 0·19 0·52' -0·04 0·64' 0·21 -0·44* ...{J·5!'

Best end neck plus loin tissue Best end neck plus loin tissue composition in males and Jemales. Males and females were significantly different (P < 0·05) in subcutaneous fat, kidney knob and in whole fat and bone proportion. No significant differences in muscle or in intermuscular fat proportions were detected between sexes (Table 9). Correlation analysis between assessors' scores and best end neck and loin tissue composition. For male best end neck and loin a significant correlation (Table 10) was detected (P < 0·05) between assessors' scores using all methods and the musc1e, subcutaneous fat, whole fat, kidney knob and bone proportions. For intermuscular fat there was a significant correlation coefficient with every method but Ce.

t See Table 9 for abbreviations. :j: See Table 2 for abbreviations. of whole subcutaneous fat in male Iegs, CC excepted. FinalIy, all methods were good predictors of female bone content in the Ieg, but Ce.

No significant correlation was to be seen in female carcasses with muscle, intermuscular fat, kidney knob or whole fat proportions in the best end neck and loin. Subcutaneous fat only shows a significant correlation coefficient with CF method. A significant correlation coefficient was obtained between the proportion of bone and classification with the EU and SL and CF methods (Table 10).

Table 11 Regression resulta between variates ofbest end neck and loin tissue composition (proportíons)t and carcasa classification based on

subjective scores of degree offatness and carcass conformation Carcass dassification method:j: EU

BENLB 196·7 31-1 171-1 23·8 loin (g/kg); loin (g/kg);

BENLM R2 Residual s. d. 5ignificance BENLSF R2 Residual s. d. 5ignificance BENLIF R2 Residual s. d. 5ignificance R2 KK Residual s. d. 5ignificance BENLWF R2 Residual s. d. 5ignificance BENLB R2 Residual s. d. 5ignificance

CF

CC

5L

Male

Female

Male

Female

Male

Female

Male

Female

0·3489 3·4067 00 0·5081 2·3060 000

0·0021 3·7837

0·3315 3-4519 •0

0-0115 3·7660

0·1976 3·7819

0·0695 3·6538

0·3148 3·4947

0·0011 3·7856

0·1748 2·0706

0·4964 2·3331

0·1828 2·0605

0·3279 2·6955

0·0647 2·2044

0·4354 2-4704

o

'o

0·3141 1·5233 00 0·3196 2-4648

0·0732 1·2407

0·3181 1·5189 *0 0·2139 2·6494

0·0454 1·2592

0·1415 1-7043

0·0237 1·2735

0·2199 1-6246

0·0032 3·0897

0·4437 2·2287

0·1503 2·8527

0·2678 2·5569

oo •

••

0·5037 5·0267 .0. 0·2376 2·7706

§

0·0060 3·0854

•

'o

'"

0·1446 H081

§ 0·0352 1·2659

o

§

0·0012 3·0928

§

o.

0·0501 4·6213

0·4405 5·3369

0·0513 4·6185

0-4093 5·4837

0·1739 4·3097

0·4117 5·4725

§

.,.

0·0444 4·6351

0·2817 2·0629

0·1981 2·8415

0·3362 1·9832 *0

0·1848 2·8650

0·0380 2·3874

0·1973 2·8430

0·2555 Hool

o

t See Table 9 for abbreviations. :t: See Table 2 for abbrevíations. § Tending towards significance (P < 0·1).

'n

•

390

Miguel, Ruiz de Huidobro, Díaz, Velasco, Lauzurica, Pérez, Onega, Blázquez and Cañeque Table 13 Correlation coefficients between variates ofshoulder tissue

Table 12 Shoulder tissue composition in males and females

Male (no. = 26) Mean s. d. Female(no. 22) Mean s. d. Significance

SM

SSF

SIF

SWF

SB

586·1 18·6

66·5 34·4

29·8 16·3

96·3 37·7

256-4 15·8

571-8 20·6

90·7 28·4 *

44·3 25·5

135·0 29·1

244·1 14-4

composition (proportions)t and of degree of fatness and carcass conformation Carcass conforrnation method:\:

SM

..

SSF

SM musc1e in the shoulder (g/kg); SSF = subcutaneous fat in the shoulder (g/kg); SIF = intermuscular fat in the shoulder (g/kg); SWF = whole fat in the shoulder (g/kg); SB = bone in the shoulder (g/kg).

SIF SWF SB

Comparing correlation coefficients values in males and in females, the former were the highest with every method for all variates except bone. Every method was a good predictor of female bone content, CC excepted.

Regression analysis between best end neck and loin tissue composition and assessors' scores. Regression analysis suggests (Table 11) that every method was a good predictor of muscle, subcutaneous fat, intermuscular fat, kidney knob fat and whole fat proportions but more so in males than in females. For bone proportion, every method but CC predicted females better than males.

Male Female Male Female Male Female Male Female Male Female

EU

CF

CC

SL

-0-41* -0·11 0·53* 0·19 0·30 0·23 0·61' 0·39 -0-45* -0-41

-0·41* -0·16 0·58' 0·29 0·24 0·27 0·63' 0·52' -0·38 -0·41

-0·38 -0·27 0·39 0·39 0·18 0·08 0·43* 0-45' -0·46' -0·27

-0·37 -0·16 0·50* 0·14 0·23 0·23 0·55* 0·34 -0·35 -0·39

t See Table 12 for abbreviations.

Regression and asses.

:\: See Table 2 for abbreviations.

14) that

Shoulder tissue Shoulder tissue composition in males and Jemales. The sexes differed in shoulder tissue composition (Table 12). Males had both higher muscle and higher bone but lower subcutaneous, intermuscular and whole fat proportions than females.

malemu fat propo: method proportio by all m predicted EUandC

Correlation analysis between assessors' acores and shoulder tissue composition. In males, whole fat proportion was the only variable of shoulder tissue

Table 14 Regression results between variates ofshoulder fissue composition (proportions)t and carcass classification based on subjective

scores ofdegree offatness and carcass conformation

Assessors' Jemales wit, Table 15 s female differenCi which of conforma statisticaU

Carcass classification method:\: EU

SM SSF SIF SWF SB

CF

CC

SL

Male

Female

Male

Female

Male

Female

Male

Female

0·1704 Residual s. d. 1·7305 • Signilicance R2 0·2772 Residual s. d. 2·9384 •• Significance R' 0·0914 Residual s. d. 1·5864 Significance 0·3730 R' Residual s. d. 3·0478 Signilicance 0·2033 R' Residual s. d. 1-4373 Significance

0·0110 2·1033

0·1715 1·7293

0·0243 2·0892

0·1421 1·7598

0·0714 2·0382

0·1379 1·7641

0·0262 2·0872

0·0374 2·8555

0·0816 2·7890

0·1497 3·2358

0·1549 2·6754

0·2509 3·0372

§

§

..

0·0203 2·8806

0·0529 2·5458

0·3339 2·8640 ** 0·0555 1·6175

0·0724 2·5194

0·0320 1-6375

0·0063 2·6076

0·0514 1-6210

0·0540 2·5443

0·0633 2·4499

0·3953 2·9932

0·0781 2-4304

0·1850 3·4750

0·2128 2·2459

0·0533 2·4629

0·1833 1·0456

0·1408 1-4926

0·2330 1·0133

0·2160 1-4258

0·0402 1·1336

0·3077 3·2027 .* 0·1251 1·5063

§

§

R2

... ..

§

t See Table 12 for abbreviations. :\: See Table 2 for abbreviations. § Tending towards significance (P < 0·1).

§

§

0·1309 1-0787

Table15

females usin'

Male (no. = Female(no

t See Tab. differences

Carcass classification method and sex of lamb composition that showed a significant correlation with every c1assification method studied. No significant correlation was detected between intermuscular fat proportion and classification under any method. The rest of the variates were well correlated with one method or another (Table 13). ~37

In females, no significant correlation was to be seen

~16

between scores under any method with any variate (Table 13) except whole fat which was well correlated with classification under both CF and CC methods.

~50' ~14

1·23 ~23

¡·ss' ~34

'·35 '·39

~

,. The [rabIe ibone

whole

~ and

le

fat ltissue I

I

~jective

~

r­ emale

0·0262 2·0872 0·0203 2·8806 0.0540 2·5443

Correlation coefficients for most varia tes and with most methods of classification were higher in males than in females.

Regression analysis between shoulder tissue composition and assessors' scores. Regression analysis shows (Table 14) that EU and CF methods were good predictors of male muscle proportion. 5ubcutaneous fat and whole fat proportions were well predicted using every method of degree of fatness evaluation. The proportion of intermuscular fat was poorIy predicted by all methods while that of bone was better predicted by EU and CC methods in males and by EU and CF methods in females. Assessors' mean careass classification seores in males and Jemales with each classification method Table 15 shows mean assessors' scores for male and female carcasses. No statistically significant differences were seen between sexes irrespective of which of the carcas s fatness methods or carcass conformation method assessors used. Although no statistically significant differences were detected, mean carcass c1assification scores based on degree of fatness were higher in females than in males. However, male and female carcasses showed a very different tissue composition: the two groups were statistically significant different in 20 out of the 25 variates studied in this work. No significant sex differences were detected in the proportion of muscle in the carcass, leg or best end neck and loin, or in the Table 15 Assessors' mean carcass classification scores in males and jemales using each method

Carcass classification methodt

10.0533 12-4629 0·1309 1-0787 §

= 26)

Mean s. d. Female (no. = 22) Mean s. d. Male (no.

EU

CF

CC

SL

1-49 0·37 1·57 0·30

1·33 0-43 1·42 0·38

1·10

1·88 0·61 2·00 0-46

0·15 1·08 0·14

t See Table 2 for abbreviations. There were no significant differences (P > 0·05) between fue sexes wifu any method.

391

proportion of intermuscular fat in the best end neck and loin or inguinal fat in the carcass.

Discussion Authors use three subjective scales for the classification of carcass degree of fatness and one scale for carcass conformation. The utility of these classification methods as predictors of carcass tissue composition has been studied in previous work by the same authors (Miguel et al., 2003; Ruiz de Huidobro et al., 2004). Sex effect on carcass tissue composition and on joint tissue composition have been well known for a long time. There are differences in tissue allometric coefficients between male and female. Males develop muscle and bone at a higher rate, and fat at a lower rate, than females. So at the same Uve weight males have a greater muscle percentage, a greater bone percentage, and a lower fat percentage, than females (Fouríe et al., 1970; Bénévent, 1971). Muscle development is higher in males, but muscle to bone ratio is lower because of their higher bone development (Hammond, 1932). Results here showed a tissue composition very different between male and female carcasses. Male carcass shows a higher amount of bone, and a lower amount of subcutaneous fat, intermuscular fat, KKCF and whole fat than female carcass. There were also significant differences in tissue composition among the three main joints: leg, shoulder, and best end neck plus loin. The fítness of the carcass classification methodologies studied in this work have been analysed. Performance of a measure instrument (in this manuscript the measure instrument is a panel of assessors, not individual assessors themselves) is usually assessed by means of the following four parameters (MacLeod and Sztrygler, 1990). (a) Fitness or suitability: the mean of the measures provided by the instrument should be very c10se to the actual value of the parameter (in this work we cannot know which this value is). (b) Accuracy: all individual measures should be very close to the actual value of the parameter (which is unknown for us).

(c) Sensibility: expressed by the answer increase ratio shown by the instrument when an increase in the incoming signal occurs (it is of no use here as we do not know the actual value of the incoming signal). (d) Precision: the instrument's capacity to give similar measures when the same incoming signal

392

Miguel, Ruiz de Huidobro, Díaz, Velasco, Lauzurica, Pérez, Onega, Blázquez and Cañeque

arrives under the same conditions of use. Precision is based on lwo qualities : repeatabílity and reproducibility. Repeatability occurs when the instrument gives similar answers under the same experimental conditions (same operator, same sample, ete.). Reproducibility occurs when the instrument gives similar answers under different experimental conditions (another operator, etc.). CVs in intra-assessor scoring with EU and SL were less than 0·05i with CF less than O-lO; and with CC method were less than 0·12. Mean scores were 1·53 (EU method), 1·37 (CF), 1·09 (CC), and 1·93 (SL). CVs were 0·0318 (EU), 0·1142 (CF), 0·0642 (CC) and 0·0767 (SL) for the panel. CVs up to 0·10 mean differences in carcass fatness or in conformation of 0·20 points, which are less than the scales' intervals (0·25 points). In sensory analysis CV values up to 0·25 were considered use fuI and even better than instrumental analysis results (Touraille et al., 1990). Correlation and regression analyses belween assessors' scores and tissue composition varia tes were carried out. Every method was a good predictor of carcass and of main joint tissue composition in males. Higher correlation coefficients and higher determination coefficients belween assessors' scores and tissue composition variates were obtained for males. Besides, a higher number of variates showed a significant correlation (P < 0·05) with assessors' scores in males. It is remarkable that in female carcasses the methods based on estimation of fatness were better predictors of bone content than of fat content in the carcass, no matter which fat depot was considered. Carcass conformation is onIy a secondary quality criterion in a carcass classification system because it is implicitly considered when degree of fatness is evaluated. Nevertheless, this work suggests that it should be used, specially in male carcass. Furthermore, the only method that showed a significant correlation belween assessors' scores and female whole fat content in the carcass is Ce. In female carcasses this method was a better predictor of carcass fat content than any subjective degree of fatness estimation method. Despite tissue composition differences found belween male and female carcasses, assessors assessing carcass degree of fatness or carcass conformation were not able to detect differences. They onIy detected significant differences in the amount of KKCF. Working in four lamb carcass groups established by means of a cluster analysis (Miguel et al., 2002) the authors found that despite actual differences in tissue composition belween

groups, statistically significant differences belween assessors' scores onIy showed belween classification group 1 and the rest. There were no statistically significant differences belween scores in groups 2, 3 and 4. Using these same classification methods, assessors were only able to discrimina te belween low-fat carcasses (fat proportion less than 0·140) and high-fat carcasses. However it seems difficult for the assessors to discriminate belween carcasses with a high degree of fatness but different tissue compositions. This fact could explain why tissue composition in males carcass is better predicted than in females' (male carcasses only showed 0·143 total fat and female carcasses showed 0·186 total fat).

Conc/usions Assessors were not able lo detect differences in carcass degree of fatness and in carcass cOnformation belween male and female carcasses, in spite of different tissue compositions in both groups. Every classification method studied was a better predictor of male carcass tissue composition and of male joint tissue composition than of female. In males, a greater number of varia tes and of classification methods showing a significant correlation with each other were detected. Besides, correlation and determination coefficients were higher in the males, in most of the variates and of the methods. The Colomer-Rocher method for carcass conformation was a better predictor of whole fat and subcutaneous fat in female carcasses than any other method used in this work. Methods based on assessment of carcass degree of fatness in this work onIy showed a significant correlation with the amount of bone in the female carcass. The method based on the estimation of carcass conformation showed a significant correlation with the amount of whole fat and of subcutaneous fat in the carcass. Sex seerns to be an important factor for classification methods for carcasses of sucking lambs, at least when animals of similar live weight are taken into account. The lower degree of fatness in male carcasses results in tissue composition in male carcasses and in male main joints being well predicted by carcass classification methods, in contrast to that in females.

Acknowledgements This work has been made possible by financial help from

both Spanish Instítutions MCYT (project AGF98-0278-C02) and INIA (Project SC99-016-C2). 80th E. Onega and B. Blázquez have doctorate grants from IMlA (Regional

Carcass dassification method and sex of lamb between

Government of Madrid). S. Yelasco has a postdoctorate grant from INIA (Spanish Government).

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84-94-703-E5-D. Publishing Bureau of the European Cornmunities, L-2985 Luxembourg. Fourie, P. D., Kirton, A. H. and Jury, K. E. 1970. Growth and development of sheep. II. The effect of breed and sex on the growth and carcass composition of the Southdown and Romney and their crosses. New Zealand Journal of Agricultural Research 13: 753-770. Hammond, J. 1932. Growth and development of mutton qualities in the sheep. Oliver and Boyd, Edinburgh. Lea, P., N