Directory UMM :Data Elmu:jurnal:S:Small Ruminant Research:Vol36.Issue3.2000:

Variation of mohair quality over the body in Angora goats

H.R. Taddeo

*

, L. Duga, D. Almeida, P. Willems, R. Somlo

INTA, EstacioÂn Experimental Agropecuaria Bariloche, C.C 277-8400 S.C de Bariloche, Argentina

Accepted 26 August 1999

Abstract

Forty female Angora goats were selected at random from the experimental nucleus of the National Institute of Agricultural Technology (Pilcaniyeu, Argentina), with the aim of analyzing the variability of main ¯eece characteristics of the Angora goats and establishing an optimum sampling site. Samples were taken at the ®rst and second shearings (12 and 18 months of age) from the following parts of the ¯eece: neck, midrib, back, britch, belly and shoulder. For each sample the following determinations were made: oven-dry yield (YLD); average (AFD); standard deviation (SDAFD) and coef®cient of variation (CVAFD) of ®ber diameter; percentage of medullated ®bers (MFT); characterization of three types of medullated ®bers: continuous (MFC), interrupted (MFD) and kemp (KEMP) by estimating their proportion, average ®ber diameter, standard deviation and coef®cient of variation of ®ber diameter; wax (WAX); suint (SUINT); humidity (HMD); staple length (STAPLE); degree of brightness (Y) and degree of yellowness (Y±Z). All variables studied showed statistically signi®cant variability among to the sampling position (P< 0.05), except of Y±Z, proportion of FMC, average ®ber diameter of MFD and KEMP, and standard deviation of ®ber diameter of KEMP at 12 months of age, at 18 months old for STAPLE and standard deviation of ®ber diameter of MFD, and for CVAFD at the two ages of shearing (P> 0.05). The results showed that sampling from the midrib of Angora goats gave adequate representation for most of the ¯eece variables analyzed.#2000 Elsevier Science B.V. All rights reserved.

Keywords:Angora Goats; Mohair; Fleece sampling

1. Introduction

The nucleus of Angora goats at Experimental Field Station Pilcaniyeu (RõÂo Negro Province, Argentina) from the National Institute of Agricultural Technology (INTA), has a marked in¯uence on the genetic improvement rate in the commercial herds, since it is the main producer of bucks in the country.

According to Mueller (1990), the nucleus of Pilca-niyeu impacted on approximately 15% of the Angora population, a proportion that should have increased since then, given the constant incorporation of males from this nucleus to the commercial herds.

The objective of the genetic improvement program carried out on the nucleus considers variables that characterize the quantity (greasy and clean ¯eece weight) and the quality (average and variability of ®ber diameter, and proportion of medullated ®bers) of ¯eece in their selection objective.

In the short and medium term this objective should be broadened by incorporating variables of color, *_{Corresponding author. Tel.:‡54-2944-422731/429862/429863;}

fax:‡54-2944-424991/428141.

E-mail address: htaddeo@inta.gov.ar (H.R. Taddeo)

staple length, yield, types of medulla of medullated ®bers: interrupted, continuous and kemp (Lupton et al., 1991), and all other variables that allow char-acterization of ¯eeces with precision.

The objective evaluation of these variables is car-ried out by sampling ¯eece, from the ¯ank (mid-side) of animals, following procedures used for other spe-cies, especially sheep.

However, in Angora goats, there is evidence of ¯eece variation over the body of the animal (Engdahl and Bassett, 1971; Gifford, 1989). Basset (1986) showed that one of the main sources of variation in the determination of the proportion of kemp is the body location of the sample, concluding that the proportion of kemp estimate from midrib samples, underestimates the real value of the proportion of kemp in the ¯eece. Muller and Taddeo (1993) observed a low correlation in the average ®ber dia-meter and proportion of medullated ®bers, 0.01 and 0.31 respectively, when comparing measurements from back and midrib of adult animals.

The objective of the present work is to analyze the variability of different parts of the body of Angora goats in the main characteristics of ¯eece and to determine if the same is affected by age, in order to use the information to establish an optimum sampling site on the ¯eece.

2. Materials and methods

2.1. Experimental protocol

Forty female goats of approximately 12 months of age, were selected at random from females of the nucleus of Angora herd at the Pilcaniyeu Experimen-tal Field Station of INTA. Breeding conditions of Angora goats in Argentina were reviewed by Camp-bell (1983) and Taddeo et al. (1998). The goats were born in spring 1992, weaned at 3.5 months of age and received similar handling from birth onward.

At ®rst and second shearing (12 and 18 months of age average) ¯eece samples of approximately 60 g were taken from animals on each of the following sites (Fig. 1): neck (NEC), midrib (RIB), back (BAC), britch (BRI), belly (BEL) and shoulder (SHO). On the other ¯ank, each one of the parts was de®ned with chalk, shorn and weighed.

2.2. Variables

Determinations carried out on each sample were: over-dry yield (YLD); average (AFD), standard devia-tion (SDAFD) and coef®cient of variadevia-tion (CVAFD) of ®ber diameter, and percentage of medullated ®bers (MFT) by means of projection microscope according to the norm IWTO No 8-89 (E); characterization of the three types of medullated ®bers: continuous (MFC), interrupted (MFD) and kemp (KEMP) by estimating proportion, average ®ber diameter, and standard deviation of ®ber diameter according to the norm IWTO 8-89 (E); determination of wax (WAX) by means of extraction with Soxhlet, suint (SUINT) by means of watery extraction; humidity (HMD); staple length (STAPLE); grade of brightness (Y) and grade of yellowness (Y±Z) according to the norm IWTO 14-88 (E).

Proportions of the several type of ®bers (MFC, MFD and KEMP) and average ®ber diameter were carried out on 600 ®bers for each sample using projection microscope. The analysis were done by the Textile Laboratory for Animal Fibers from INTA (Bariloche, Argentina).

2.3. Statistical analysis

The model used for analysis corresponded to a split plot design, treating the animal as the principal plot

and the several parts of the body like subplots, accord-ing to the followaccord-ing expression (Timm, 1975):

yijkˆm‡ai‡e…i†j‡bk‡dik‡ei…jk†; (1)

wherem is the population mean, ai the effect of ith

season of shearing (iˆ1,2),E(i)jrandom error of the

principal plot,bkthe effect of thekth body locations of

samples (kˆ1,2,_{. . .},6), dik the interaction between

season of shearing and body locations of samples and E(i)jkthe random error of subplots. In order to achieve

normality the variables corresponding to proportions of the several types of medullated ®bers (MFT, MFC, MFD and KEMP) were transformed according to

log(x‡0.5), wherexrepresents a proportion.

The analysis was carried out with statistical package SAS (1988) by means of the GLM procedure. The hypotheses were tested with a signi®cance level of 5%.

3. Results and discussion

The average contribution (and standard deviation) of each ¯eece sample in relation to total ¯eece weight for the two shearing is shown in Table 1. Homogeneity is evidenced when comparing contributions of each part of the ¯eece between shearings except for the belly (4.5% vs. 8.1% spring shearing and autumn shearing, respectively). The ventral zone of animals is shorn normally only at the beginning of the winter season. This produces a shorter staple for the belly at

the spring shearing (9.3 vs. 14.3 cm of staple length for the belly and the weighed average of the ¯eece, respectively) (Table 2).

The analysis of variance of model (I) showed that the interaction between shearing season and sampling positions was statistically signi®cant (P< 0.05). Thus, sampling positions within each one of the two differ-ent shearing seasons were compared.

All variables showed statistically signi®cant differ-ences between means of different sampling positions

(P< 0.05), except for Y±Z and STAPLE in shearing at

12 and 18 months old, respectively, and the CVAFD in

the two ages of shearing (P> 0.05). This analysis

showed the homogeneity between sampling sites for this set of variables, however, the conformation of homogeneous group for WAX and MFT for the two shearings, and for Y±Z for second shearing are mark-edly in¯uenced for the high variability of these char-acters. The averages (standard deviation) and conformation of homogeneous group for sampling positions are shown in Table 2.

A similar pattern of variation according to sampling position of ¯eece in the two shearing occasions is shown for AFD, even when a difference is observed

due to age (22.4 vs. 33.0mm, for shearing at 12 and 18

months old, respectively). Fleece diameter declined from neck to britch and from belly to back. Mohair from neck was signi®cantly coarser than the other ®ve sampling positions. Stapleton (1976) and Gifford (1989) reported similar results, concluding that in Australian Angoras the neck mohair is coarser than that from midrib or shoulder positions.

SDAFD showed a similar tendency between shear-ing and between samplshear-ing positions, explainshear-ing that results for CVAFD are not signi®cant.

For HMD, the autumn ¯eece in relation to spring, has a higher humidity content (8.8% vs. 10.5% for shearing of spring and autumn, respectively), and the distribution on the body is in¯uenced by the position, where the least humid position of ¯eece in the two shearings is back. In contrast, a major percentage of humidity is observed in belly and neck for spring shearing, and in belly, neck and shoulder for autumn shearing.

WAX and SUINT behave similarly, with major percentages for shearing at 12 months of age (spring) in relation to the shearing carried out at 18 months of age (autumn), 6.8% vs. 3.9% for WAX and 2.7% vs.

Table 1

Percentage of contribution (standard deviation) of each one of sampling position to the total weight of the ¯eece for shearing at 12 (September/spring) and 18 (March/autumn) months old in Angora goats

Location Age

12 months 18 months

Belly 4.5 (0.02) 8.1 (0.04)

Neck 16.1 (0.06) 15.1 (0.04)

Midrib 24.7 (0.07) 22.3 (0.06)

Britch 21.7 (0.07) 22.7 (0.04)

Back 14.6 (0.05) 15.8 (0.04)

Shoulder 18.4 (0.05) 16.0 (0.03)

1.7% for SUINT, respectively. The sampling positions that showed larger value of these variables is belly for shearing at 12 months of age, and midrib, although jointly with britch, back and shoulder showed simi-larity in WAX, and the same sampling positions plus belly are similar in SUINT for shearing at 18 months old. Similar variability for WAX measured at 12 month of age on females was reported by Delport (1987).

MFT showed little difference between shearings (3.4% vs. 3.1% for shearing at 12 and 18 months old, respectively), but a major difference can be observed among sampling positions. At 12 months

of age at sampling sites with major presence of medullated ®bers are britch and back, while at 18 months the distribution of medullated ®bers is more uniform, since except for neck with a 2.3%, the other sampling positions are similar with more than 3% of medullated ®bers. High variability was also observed by Gifford (1989), with coef®cients of variation higher than 40% for the different types of medullated ®bers.

Staple length showed a marked difference between shearing (14.3 vs. 12.0 cm for shearing at 12 and 18 months of age, respectively), due to fundamentally different period of growth, since shearing at 12 months

Table 2

Average (standard deviation) of ¯eece traits of Angora goats measured at 12 and 18 months of age in different sampling position

Belly Neck Midrib Britch Back Shoulder Total

Age 12 months

HMD (%) 9.1a(0.7) 9.3a(0.7) 8.7b(0.6) 9.2a(0.6) 7.7c(0.9) 9.0ab(0.6) 8.8 (0.9)

WAX (%) 8.7a(3.0) 6.0d(2.2) 7.8b(2.3) 5.9d(1.8) 5.4d(2.0) 6.9c(2.3) 6.8 (2.5)

SUINT (%) 3.8a(1.3) 2.5b(0.6) 2.7b(0.7) 2.7b(0.7) 2.4b(0.6) 2.7b(0.6) 2.8 (0.9)

STAPLEe(cm) 9.3d(3.7) 15.8a(4.6) 14.3bc(3.2) 13.3c(2.2) 14.3bc(2.8) 15.4ab(4.3) 13.7 (4.1)

YLDf_{(%) 77.3}cd_{(5.4) 83.0}a_{(4.7) 79.0}bc_{(5.4) 79.8}b_{(4.6) 76.1}d_{(6.0) 82.2}a_{(4.8) 79.4 (5.7)}

Yg _58.8a_{(3.0) 56.2}b_{(3.4) 57.2}ab_{(3.3) 58.2}a_{(3.4) 53.6}c_{(2.8) 56.8}b_{(2.7) 56.5 (3.5)}

Y±Zh _5.0a_{(0.8) 5.8}a_{(1.0) 5.2 (1.0) 6.2}a_{(0.9) 7.0}a_{(1.0) 5.8}a_{(0.9) 5.9 (1.1)}

MFTi_{(%) 2.6}c_{(2.0) 2.8}c_{(3.0) 3.3}bc_{(3.1) 4.0}ab_{(2.5) 4.6}a_{(2.8) 2.5}c_{(2.3) 3.3 (2.7)}

AFDj₍

mm) 22.6b(2.8) 24.4a(2.8) 21.7bc(2.1) 22.1bc(2.4) 21.1c(2.3) 22.9b(2.2) 22.5 (2.6)

SDAFDk₍

mm) 5.4ab(1.1) 5.6a(1.0) 5.1b(1.0) 5.0b(0.8) 5.0b(0.8) 5.4ab(1.0) 5.2 (1.0)

CVAFDl_{(%) 23.9}a_{(4.6) 23.3}a_{(4.0) 23.5}a_{(4.7) 22.6}a_{(3.6) 23.9}a_{(3.6) 23.6}a_{(4.6) 23.5 (4.2)}

Age 18 months

HMD (%) 11.1ab(0.73) 11.2a(0.8) 10.1d(0.9) 10.5c(1.0) 9.9d(1.1) 10.8bc(0.9) 10.6 (1.0)

WAX (%) 3.3c (1.78) 3.5bc_{(2.1) 4.4}a_{(2.2) 4.3}ab_{(2.5) 3.6}abc_{(2.4) 3.7}abc_{(2.2) 3.8 (2.2)}

SUINT (%) 1.8ab_{(0.51) 1.5}b_{(0.4) 1.9}a_{(0.6) 1.8}ab_{(0.5) 1.6}ab_{(0.4) 1.6}ab_{(0.4) 1.7 (0.5)}

STAPLE (cm) 11.6a_{(1.12) 12.4}a_{(1.2) 12.2}a_{(0.9) 11.4}a_{(1.1) 11.9}a_{(0.9) 12.4}a_{(0.8) 12.0 (1.1)}

YLD (%) 89.8a_{(4.20) 90.4}a_{(5.1) 83.9}b_{(4.9) 84.1}b_{(4.1) 81.8}c_{(6.2) 88.6}a_{(4.6) 86.4 (5.8)}

Y 63.2ab_{(2.60) 61.7}bc_{(2.8) 61.7}bc_{(2.9) 63.5}a_{(3.2) 58.5}d_{(2.6) 61.6}c_{(2.8) 61.7 (3.3)}

Y±Z 7.8b_{(1.30) 9.2}ab_{(1.7) 8.7}b_{(1.4) 7.8}b_{(1.2) 8.8}b_{(1.6) 10.9}a_{(0.5) 8.9 (4.2)}

MFT (%) 3.4a_{(1.86) 2.3}b_{(3.8) 3.0}a_{(1.8) 3.1}a_{(1.5) 3.2}a_{(1.6) 3.7}a_{(5.0) 3.1 (2.9)}

AFD (mm) 35.3b(3.48) 37.3a(5.0) 31.9d(3.1) 31.2d(3.4) 31.3d(2.7) 33.8c(3.7) 33.5 (4.2)

SDAFD (mm) 7.2ab(1.41) 8.1a(2.1) 6.6b(1.3) 6.5b(1.5) 6.4b(1.4) 6.9b(1.5) 7.0 (1.6)

CVAFD (%) 20.6a_{(4.01) 21.8}a_{(5.2) 20.8}a_{(3.9) 20.9}a_{(4.0) 20.4}a_{(4.0) 20.5}a_{(4.3) 20.8 (4.2)}

a.b.c.d_{Within each variable and age, means followed by a common letter do not differ signi®cantly (P> 0.05).}

e_{STAPLE, staple length.}

f_{YLD, oven-dry yield.}

g_{Y, grade of brightness.}

h_{Y±Z, grade of yellowness.}

i_{MFT, percentage of medullated ®bers.}

j_{AFD, average.}

k_{SDAFD, standard deviation.}

of age represents the ®rst shearing of animals. On the other hand, while at second shearing the staples are of more uniform length across the several sampling sites, at ®rst shearing the belly showed a lower average length than the other sampling sites, as explained above. This result is different from those of Stapleton (1976) and Gifford (1989), which showed that staple length declined signi®cantly from the neck to the shoulder positions.

The mohair produced at 18 months old shearing showed a higher average brightness (Y) than the ¯eece produced at 12 months of age (61.7 vs. 56.6, respec-tively), while among positions the back is the one that showed the lower average brightness in the two shearings.

The grade of yellowness (Y±Z) is higher at 18 months old (5.9 vs. 8.9 for shearings at 12 and 18 months old, respectively). Neck and shoulder are the sampling positions with higher grade of yellow-ness at second shearing. At 12 months of age this variable could be considered homogeneous for the whole body.

Sampling sites that showed a higher YLD at 12 months of age are neck and shoulder (83.0% and 82.2%, respectively), while at 18 months old belly is added (90.4%, 88.6% and 89.8%, respectively). Gifford (1989) showed at 12 months of age that YLD of ¯eece samples were signi®cantly higher at neck than at midrib or shoulder positions.

The correlation between each variable and the total ¯eece, for each sampling position for both shearing, are given in Table 3. The total for each variable is a weighed average, the weight being given by the con-tribution of each sampling site to the total ¯eece weight. The results indicated that for the shearing at 12 months of age, the samples obtained from midrib would represent the ¯eece appropriately where the correlations estimated at midrib are the highest ones, or close to them (Table 3), except for the grade of yellowness. For Y±Z samples obtained from shoulder represent a marked improvement in the estimate (correlations of 0.68 vs. 0.81 for midrib and shoulder, respectively). For second shearing shoulder showed the highest number of the highest correlations (Table 3).

Due to a signi®cant interaction (P< 0.05) between season of shearing and different sampling sites varia-bility between sampling positions of proportion, aver-age ®ber diameter and standard deviation of averaver-age ®ber diameter of three components of medullated ®bers (interrupted, continuous and KEMP) was ana-lyzed within each season shearing.

At ®rst shearing only KEMP showed variation

between sampling positions (P< 0.05), back and

britch with 2.0% and 1.5%, respectively being the regions with greater values (Table 4). Similar results and patterns were reported by Stapleton (1976) and Gifford (1989). At 18 months, KEMP showed

sig-Table 3

Correlations estimated between the different sampling areas and the total weighed, for ¯eece traits in Angora goats measured at 12 and 18 months old

12 months of age 18 months of age

Belly Neck Midrib Britch Back Shoulder Belly Neck Midrib Britch Back Shoulder

HMD (%) 0.69 0.79 0.86a 0.76 0.75 0.82 0.62 0.80 0.77 0.77 0.66 0.84

WAX (%) 0.75 0.76 0.85 0.80 0.78 0.82 0.85 0.96 0.94 0.92 0.92 0.94

SUINT (%) 0.64 0.63 0.81 0.68 0.78 0.67 0.46 0.78 0.67 0.76 0.77 0.79

STAPLE 0.54 0.75 0.79 0.45 0.73 0.82 0.61 0.70 0.79 0.80 0.76 0.66

YLD (%) 0.48 0.74 0.91 0.87 0.74 0.76 0.89 0.93 0.92 0.91 0.91 0.94

Y 0.37 0.60 0.78 0.50 0.45 0.79 0.78 0.77 0.83 0.82 0.48 0.60

Y±Z 0.46 0.37 0.68 0.70 ÿ0.07b _{0.81 0.22}b _{0.35 0.34 0.45 0.36 0.92}

MFT (%) 0.37 0.69 0.82 0.69 0.62 0.81 0.61 0.74 0.77 0.73 0.74 0.75

AFD (mm) 0.62 0.80 0.76 0.77 0.82 0.81 0.65 0.74 0.90 0.83 0.84 0.86

a_{Numbers in italics means the highest correlation coef®cient by trait and by class of age.}

ni®cant variation (P< 0.05), where back and britch, shoulder and belly had KEMP values of 1.2%, 1.3% and 1.3%, respectively. Concerning the other two components of medullated ®bers, only the continuous medullated ®ber at second shearing showed signi®cant variation (P< 0.05).

Analyzing the average ®ber diameter of the three components, at ®rst shearing only the continuous medullated ®bers showed a variation in their ®neness due to the sampling positions, with ®bers obtained from britch, belly and back showing larger diameters,

with 42.7, 41.0 and 42.2mm, respectively (Table 4).

For the 18 months shearing, the three components showed statistically signi®cant variation (P< 0.05), with different patterns of distribution. Continuous

medullalted ®bers at belly with 55.9mm is the region

of larger diameter, the coarser interrupted medullated

®bers are at neck and belly with 50.3 and 48.1mm

respectively, while the coarser KEMP is distributed

throughout midrib, shoulder and back with diameters

larger than 82mm.

The variability of ®ber diameter of three types of medullated ®bers is shown in Table 4. At ®rst shearing only MFD showed signi®cant variability, neck being the region with the least variability, while at 18 months of age only KEMP showed differences in the variance of ®ber diameter being the belly the region with minor variability.

4. Conclusions

The results found in this work showed that the majority of the analyzed variables are adequately represented by the sample obtained from the midrib of the animal. This is a convenient result since most Angora breeders are familiar with the recommenda-tion of midrib sampling.

Table 4

Average (standard deviation) of proportion, average ®ber diameter and standard deviation of average ®ber diameter of three components of medullated ®bers (continuous, interrupted and kemp) on each sampling positions for shearings at 12 and 18 months of age

12 months of age 18 months of age

MFCd MFDe KEMP MFC MFD KEMP

Proportion of medullated fibers(%)

Belly 1.5a_{(1.4) 0.8}a_{(0.6) 0.3}c_{(0.5) 1.7}a_{(1.2) 0.6}a_{(0.8) 1.1}ab_(1.0)

Neck 1.7a_{(2.1) 0.9}a_{(1.0) 0.3}c_{(0.4) 1.1}b_{(1.9) 0.6}a_{(1.0) 0.7}b_(1.1)

Midrib 1.5a_{(1.9) 0.7}a_{(1.2) 1.1}b_{(1.2) 1.5}ab_{(1.3) 0.5}a_{(0.4) 1.0}ab_(0.8)

Britch 1.8a_{(1.6) 0.8}a_{(1.1) 1.5}ab_{(1.4) 1.3}ab_{(0.9) 0.5}a_{(0.7) 1.3}a_(0.9)

Back 1.9a_{(1.5) 0.7}a_{(0.9) 2.0}a_{(1.8) 1.5}a_{(1.2) 0.4}a_{(0.5) 1.2}a_(0.9)

Shoulder 1.4a_{(1.4) 0.6}a_{(0.7) 0.5}c_{(0.8) 2.0}a_{(2.7) 0.4}a_{(0.6) 1.3}a_(2.1)

Average of fiber diameter(mm)

Belly 42.2ab_{(6.3) 35.8}a_{(7.2) 54.9}a_{(10.4) 55.9}a_{(4.8) 48.1}ab_{(6.3) 76.6}b_(9.9)

Neck 38.6c_{(6.2) 33.2}a_{(6.8) 58.2}a_{(12.3) 51.9}b_{(7.2) 50.3}a_{(7.8) 75.0}b_(12.4)

Midrib 38.8bc_{(6.1) 33.0}a_{(7.0) 60.9}a_{(13.2) 49.8}bc_{(4.3) 43.8}b_{(5.2) 82.8}ab_(12.7)

Britch 42.7a_{(7.9) 37.9}a_{(7.5) 62.2}a_{(11.8) 50.0}bc_{(4.1) 45.2}b_{(6.4) 85.1}a_(9.9)

Back 41.0abc_{(5.5) 35.6}a_{(7.3) 61.5}a_{(10.1) 50.1}bc_{(3.6) 45.0}b_{(7.0) 85.0}ab_(11.5)

Shoulder 38.6c_{(5.2) 33.9}a_{(7.4) 59.8}a_{(12.1) 47.8}c_{(4.0) 44.6}b_{(8.4) 77.7}ab_(10.6)

Standard deviation of average fiber diameter(mm)

Belly 5.7a_{(2.5) 6.1}ab_{(3.7) 8.4}a_{(5.3) 7.4}a_{(2.6) 7.3}a_{(4.6) 10.8}b_(6.2)

Neck 6.4a_{(2.2) 5.6}b_{(4.0) 10.6}a_{(8.3) 7.0}a_{(4.8) 7.2}a_{(3.8) 13.5}ab_(8.6)

Midrib 7.2a_{(4.1) 7.3}ab_{(4.3) 11.5}a_{(6.2) 6.4}a_{(3.6) 5.6}a_{(3.0) 16.5}a_(8.5)

Britch 6.5a_{(2.4) 7.5}ab_{(4.3) 11.3}a_{(4.0) 7.5}a_{(3.5) 8.0}a_{(3.9) 15.6}ab_(5.9)

Back 7.4a_{(2.5) 8.5}ab_{(4.3) 13.1}a_{(6.0) 6.7}a_{(3.4) 4.6}a_{(3.6) 16.6}a_(7.7)

Shoulder 7.3a_{(5.0) 9.3}a_{(6.1) 12.6}a_{(5.6) 6.3}a_{(2.2) 6.4}a_{(4.0) 13.0}ab_(4.9)

a,b,c_{Within each trait and age, means followed by a common letter do not differ signi®cantly (P> 0.05).}

d_{MFC, continuous medullated ®bers.}

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