Incidence and relationships of black skin spots in the fleece area and pigmentation traits in commercial Corriedale flocks

Page 1

Small Ruminant Research 120 (2014) 64–70

Contents lists available at ScienceDirect

Small Ruminant Research

jou rn al h om epa ge : w ww.elsev ier .com/ locate /smal l rumres

Incidence and relationships of black skin spots in the fleecearea and pigmentation traits in commercial Corriedale flocks

J.I. Uriostea,∗, F. Penagaricanoa,b, R. López Correaa, H. Nayaa,c, R. Kremerd

a Departamento de Producción Animal y Pasturas, Facultad de Agronomía, UDELAR, 12900 Montevideo, Uruguayb Department of Animal Sciences, University of Wisconsin, Madison 53706, WI, USAc Unidad de Bioinformática, Institut Pasteur de Montevideo, 11400 Montevideo, Uruguayd Departamento de Ovinos, Lanas y Caprinos, Facultad de Veterinaria, UDELAR, 11300 Montevideo, Uruguay

a r t i c l e i n f o

Article history:Received 20 March 2013Received in revised form 5 May 2014Accepted 8 May 2014Available online 23 May 2014

Keywords:Black skin spotsWool pigmentationSheep

a b s t r a c t

The presence of pigmented fibres (PF) in the wool prevents access to high quality mar-kets. Pigmentation traits such as black spots in the fleece area and pigmentation scoresin non-fleece areas might be correlated with PF. The aim of this study was to assess theincidence and variation of black skin spots and pigmentation scores of nose, hooves andears of sheep, and their phenotypic relationships, in 13 randomly selected commercial Cor-riedale flocks. During 2006 and 2007, data from 2448 animals (10–15% of each flock) ofdifferent ages (1- to 5-years-old) and broad genetic origins (different studs) were collectedat shearing. Pigmentation in non-fleece areas was assessed using a subjective scale of 1(light) to 5 (black). Black skin spots were identified in fleece areas and percentage of PF onits surface was determined using a subjective scale of 0–5. Distribution of nose pigmenta-tion scores was symmetric and unimodal, whereas they were skewed towards a high scorein hooves and a low score in ears. Presence of spots increased with the age of animals. Innose and hooves, a reduction in pigmentation with age of animals was observed. Importantdifferences between flocks and animals were detected for all pigmentation traits. Spots

and pigmentation traits in non-fleece areas were phenotypically associated. This study onpigmentation traits of commercial Corriedale sheep indicated that there is a noticeablephenotypic variation among animals and flocks, suggesting the existence of an underlyinggenetic variation in these traits.

1. Introduction

Uruguay is traditionally a wool exporting country, witha current stock of about 7.7 million sheep and an export

value of US$ 252.4 million during 2012, 70.1% of total ovineexport (S.U.L., 2013). Within the sheep industry, the Cor-riedale breed is the most important in terms of number

∗ Corresponding author at: Departamento de Producción Animal y Pas-turas, Facultad de Agronomía, Av. Garzón 780, Montevideo, Uruguay.Tel.: +598 2355 9636; fax: +598 2354 3460.

E-mail address: [email protected] (J.I. Urioste).

http://dx.doi.org/10.1016/j.smallrumres.2014.05.0020921-4488/© 2014 Elsevier B.V. All rights reserved.

© 2014 Elsevier B.V. All rights reserved.

of breeders and volume of wool produced (Abella et al.,2010). Corriedale sheep are a dual purpose breed used bothin the production of white wool and meat, and interna-tionally farmed (Australia, New Zealand, the United Statesof America, several Latin American countries includingArgentina and Uruguay). In the breed standard, hoovesand nose are preferably black (Mason, 1996). The presenceof coloured fibres in Corriedale sheep is recognized as afault (Australian Corriedale Association Inc., 2013). Most

Uruguayan wool is exported as tops, where the best oppor-tunities are in markets with high standards and qualityparameters. Consequently, the presence of coloured fibreslimits the competitiveness of wool with other fibres and

Page 2

inant R

rbp

ticmelte

ds(sslcat1i6t(

im(rtsmaowctaeo

aaakssnflc

2

2

at

J.I. Urioste et al. / Small Rum

educes its value by 20% in quality markets when the num-er exceeds 300 fibres/kg top (F. Raquet and G. Ruvira 2013,ersonal communication).

Presence of coloured wool fibres is due to environmen-al (urine and chemicals) and genetic (presence of melaninn the fibre) factors. With adequate shearing techniques,oloured fibres from environmental sources can be mini-ized, but those of genetic origin still remain, and greatly

xceed the minimum required. Black skin spots and iso-ated pigmented fibres, randomly distributed throughouthe fleece, are the probable origin of these fibres (Cardellinot al., 1990; Fleet, 1985, 1996).

Previous research on this subject is scarce. An earlyescriptive study of pigmentation and presence of blackpots in Corriedale sheep was reported by Kremer et al.2003). These authors found, in two experimental Univer-ity flocks, that 70.8% of the ewes presented black skinpots. They also observed that pigmentation in the nose-ips was higher (p < 0.01) in spotted sheep, although nolear differences were apparent between the flocks. Innother local Uruguayan study, Pereira et al. (2003) foundhat 78% of animals presented a score 2 or less (on a scale of–5) for nose pigmentation, and 50 and 90% for external or

nternal ear surface, respectively. On the contrary, 54 and5% of animals presented scores 4 and 5 in hooves, respec-ively. Similar results were reported by Fleet and Stafford1989) in Australia.

The biology of pigmentation is complex. White coatn sheep may arise from improper melanoblast develop-

ent or survival, reflecting absence of mature melanocytesRenieri et al., 2008). In this sense, Fleet et al. (2004)eported the absence of melanocytes in the skin duringhe wool follicles growth in foetal development in Merinoheep, and this absence generally persists in the adult ani-al. However, and by yet unknown mechanisms, some

nimals are born with and/or develop over time, brownr black spots on the skin that can also produce pigmentedool fibres. Possibly, many genes are involved in this pro-

ess; accordingly, quantitative genetic tools could be usedo improve competiveness in the wool industry throughdequate breeding plans. Unfortunately, present nationalvaluation schemes only consider a subjective assessmentf pigmentation in the selection candidates.

Sampling in commercial flocks, on the other hand,llows a quick evaluation of approximate population levelsnd phenotypic variation in pigmentation and spot char-cteristics, and serves as a first step in generating newnowledge on new candidate traits. Thus, the aim of thistudy was twofold: (i) to assess the incidence of blackkin spots in the fleece area and pigmentation scores ofose, ears and hooves of sheep from commercial Corriedaleocks and (ii) quantify their phenotypic variation and asso-iations among variables through regression analysis.

. Materials and methods

.1. Data

Thirteen commercial Corriedale flocks raised at pasturend located in seven Municipalities scattered throughouthe country were randomly selected and visited between

esearch 120 (2014) 64–70 65

October and December 2006 and the same period in 2007.In total, records from 2448 animals of different ages weretaken. The average number of animals per flock was 188,with a range between 76 and 257. The general age structurewas as follows: 28.9% of 1-year-old animals, 22.6% for 2-years-old, 11.0% for 3-years-old, 30.1% for 4-years-old and7.4% for 5-years-old animals. An oral survey applied to eachfarmer confirmed that the rams used came from at least26 different studs. Strong regional representativeness oframs purchased by the farmers (seven regions with impor-tant presence of sheep husbandry) is expected; therefore,genetic ties among flocks are supposed to be weak, and inconsequence a fair representation of the whole Corriedalebreed in our sample was assumed.

From each commercial Corriedale flock, a random sam-ple of animals, approximately 10–15% of the total shorn,was examined immediately after shearing, to avoid thatdust or other environmental conditions could impair theobservation in the freshly shorn fleece area. Each animalwas scored for number of black spots (minimum 1 mmdiameter, measured with a calliper) in the fleece area. Inaddition, the percentage of pigmented fibres (PF, brown orblack) within each spot was estimated, to further classifythe spots. For non-fleece areas, a subjective scale (1–5) wasused for pigmentation in nose, hooves and ears. This scalewas slightly adapted from Fleet and Stafford (1989).

Traits examined included:Black skin spots: total number of spots (TBS); number

of spots with up to 20% of the area with pigmented fibres(BS1); number of spots with 21–40% of the area (BS2); num-ber of spots with 41–60% of the area (BS3); number of spotswith 61–80% of the area (BS4), and number of spots with81–100% of the area covered with pigmented fibres (BS5).When pigmented fibres were not observed within the spotarea, the value 0 was assigned (BS0).

Pigmentation traits: The following subjective scale forobservations in the nose and hooves (all 4 feet) wasprimarily used: 1 = pigmented up to 20% of the totalarea, 2 = 21–40% pigmented of total area; 3 = 41–60% pig-mented of total area; 4 = 61–80% pigmented of total area;5 = 81–100% pigmented of total area. In the case of thehooves, the observed values of each feet were added intoa single value (range 4–20). Ears (internal and externalsurfaces) were classified as 1 to indicate absence of pig-mentation, and 2 otherwise.

2.2. Statistical analysis of phenotypic variability

For subsequent statistical analyses, spot traits werere-defined as binary (i.e. presence or absence) and werelabelled as BINTBS, BINBS0, etc. according to the totalscore of each response variable, where 0 means absenceof respective spot trait, at least one means presence. Forhooves, animals were subjectively grouped into 2 classesaccording with the total score of pigmentation (i.e. sum ofpigmentation in the four hooves, with maximum value of5 × 4 = 20): animals with “dark” hooves (total score: 19 or

20) or “light hooves” (total score less than 19). The obser-vations on ears were also organized into 2 classes: animalsthat had no pigmentation in either internal or external sur-faces of ear skin, or animals with any pigmented signs.

Page 3

66 J.I. Urioste et al. / Small Ruminant Research 120 (2014) 64–70

Table 1Percentage of animals according to different spots traits: overall mean, range of variation between flock averages and class of age at shearing.

Spot classa Mean (%) Range among flocks (%) Age (years)

1 2 3 4 5

TBS 62.2 43.3–81.6 28.8 52.4 78.9 88.9 88.9BS0 49.1 31.7–75.7 18.2 38.6 61.5 75.1 78.3BS1 30.7 16.3–41.2 5.5 19.8 37.0 53.5 60.0BS2 17.2 9.6–30.3 3.5 8.9 19.6 31.6 34.4BS3 11.1 7.3–18.0 1.7 3.8 12.6 21.4 26.1BS4 7.8 2.2–17.4 2.1 3.8 7.0 13.4 20.6BS5 8.3 3.7–17.4 4.0 3.3 8.9 14.0 17.2

a TBS, total number of black spots; BS0, number of black spots without pigmented fibres; BS1, number of spots with up to 20% of the area with pigmentedted fibred fibre

fibres; BS2, number of black spots with 21–40% of the area with pigmenfibres; BS4, number of black spots with 61–80% of the area with pigmentfibres.

In the case of the pigmentation scores of the nose, thedistribution was symmetrical and bell shaped, so a nor-mality assumption was subjectively assessed through anormal probability plot and considered appropriate; thus,untransformed scores were used, since earlier research(Penagaricano et al., 2011) showed no clear advantages ofusing more sophisticated models.

The other variables under study were not normallydistributed and therefore the analyses were based on gen-eralized linear models. The data were analyzed under amixed model implementation, with the GLIMMIX proce-dure of SAS (SAS Institute Inc., Cary, NC, USA), assuminga binomial distribution and using logit as a link function.All models included the random effect of flock and age asa linear covariate. Age was also tested as a classificationvariable, but the results were very similar to those obtainedusing the predictor as a linear covariable and therefore theywill not be reported here.

2.3. Relationship between black skin spots andpigmentation traits

To explore and illustrate associations between spots andpigmentation traits, the presence (BINTBS) and number(TBS) of total black skin spots in the fleece were analyzedas response variables using different pigmentation traits.Four models were used with pigmentation score in nose,ears or hooves as predictor variables (models 1–3, respec-tively), and a full model including all three variables (model4). Binomial and Poisson distributions and logit or log linkfunctions were assumed for BINTBS and TBS, respectively.

All models included a linear predictor,�ijkl = � + ˇAgei + flockj + traitk, where �ijkl is a functionof the expected TBS or BINTBS in the fleece area of the ijklrecord; � is an intercept; Agei is the age at shearing, in

Table 2Average number of spots and range (minimum and maximum values) in all or sp

Spot classa BS0 BS1

All animals 2.17 0.65

Spotted animals 3.49 1.05

Range 0–65 0–17

a BS0, number of black spots without pigmented fibres; BS1, number of spots

spots with 21–40% of the area with pigmented fibres; BS3, number of black spospots with 61–80% of the area with pigmented fibres; BS5, number of black spots

es; BS3, number of black spots with 41–60% of the area with pigmenteds; BS5, number of black spots with 81–100% of the area with pigmented

years (i = 1, 2, . . ., 5), and is the linear regression coeffi-cient on age; flockj represents the random effect of the jthflock (j = 1, 2, . . ., 13) and traitk is the fixed pigmentationtrait (nose, ears or hooves) considered in the analysis.

3. Results

3.1. General description of the presence of black skinspots

Table 1 displays the overall mean and the range of vari-ation between flocks, and the age effect, for the percentageof animals showing different type of spots. For example,any kind of spots (TBS) were scored in nearly 62% of theanimals screened, with a range of variation between flocksranging from 43 to 82%.

Nearly half of the recorded animals displayed BS0 spots,some 20.0% of the animals presented only spots withoutfibres, and 57.8% (37.8% without spots plus 20% with spotsbut without fibres) did not present spots with pigmentedfibres. A 7.8% of the animals showed skin spots with 61–80%(BS4) and 8.3% had spots with more than 80% of PF (BS5).This initial characterization was differentially expressed byage (Table 1). The youngest category (1-year-old) was theone with lower spot incidence, most spots having no pig-mented fibres. With increasing age, especially from 3 yearsof age and onwards, there was an important presence ofspots (78.9–88.9% of animals). The increase in spots withfibres was especially remarkable: BS4 evolved from 3.8% at2 years of age to 20.6% at 5 years; similarly, 3.3% of animalshad BS5 at 2 years of age, and 17.2% at 5 years.

There was a noticeable variation in the presence andclass of spots between flocks. As reported in Table 1, theranges in the presence of spots ranged from 18.4 to 56.7%of animals without spots. When grouping in broader classes

otted animals (any kind of spots), by spot class.

BS2 BS3 BS4 BS5

0.27 0.20 0.12 0.180.43 0.32 0.20 0.290–10 0–9 0–8 0–45

with up to 20% of the area with pigmented fibres; BS2, number of blackts with 41–60% of the area with pigmented fibres; BS4, number of black

with 81–100% of the area with pigmented fibres.

Page 4

J.I. Urioste et al. / Small Ruminant Research 120 (2014) 64–70 67

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

1 2 3 4 5

Fre

quen

cy

ation s

1-year-old

2-year-old

3-year-old

4-year-old

5-year-old

1–5) in

oo1fiwbpfsaw

3

dwtothiweb2

aotmn

Pigment

Fig. 1. Distribution of pigmentation scores (

f spots with pigmented fibres, the ranges were13.2–28.8%f animals only with spots without pigmented fibres (BS0),0.7–34.2% of animals with less than 40% of pigmentedbres (BS1 and BS2), and 10.1–35.5% incidence for spotsith more than 40% of fibres (BS3–BS5). Average spot num-

ers and range, by individual animals and spot category, areresented in Table 2. Median values were 1 for TBS and 0or all other traits. However, 4.8% of individuals with spotshowed 10 spots or more. A few very extreme animals werelso found; that was the case, for example, of an animalith 74 spots.

.2. General description of pigmentation traits

Fig. 1 illustrates the variation found for nose scores. Theistribution of observations was approximately normal,ith high frequency in an intermediate degree of pigmen-

ation (score of 3.0) and lower frequencies to either sidef the mean. Nose pigmentation analyzed by age also hadhe same distribution, except for the oldest category whichad a higher frequency of less pigmented noses. An eas-

ly observable variation among flocks (data not shown)as also detected: there were 6 flocks with average values

xceeding 3.0, other 6 flocks displayed score mean valuesetween 2.5 and 3.0, and one flock had a mean value below.5.

Fig. 2 shows the frequency for hooves pigmentationccording to age classes. An asymmetric distribution was

bserved, unlike what was observed with pigmentation inhe nose. The youngest animals (1-year-old) had highly pig-

ented hooves; with increasing age, there were a higherumber of animals with light hooves.

core

nose by age at shearing (1- to 5-years-old).

As observed for pigmentation on the nose, there weremarked differences between commercial flocks. For exam-ple, in one flock, there was a significant presence of animalswith fully pigmented hooves, while another flock wascharacterized by the presence of animals with slightly pig-mented hooves. It is important to remark that this flock alsopresented animals with very light pigmented nose.

The phenotypic variation observed in the degree of pig-mentation in ears was very low, 93–94% of the observationson the external surface of the ears and 99% of the observa-tions on the inner surface corresponded to the lowest scorein the pigmentation scale.

3.3. Phenotypic variability for black skin spots

Under the present mixed model implementation, flockswere assumed sampled from a population of Corriedaleflocks and we focused on determining the percentage of thetotal variation in measures of spots explained by the flockeffect. This effect could be probably interpreted in terms ofboth genetic and management components; the results areshown in Table 3.

The percentage of total variation explained by the flockcomponent in various measures of black skin spots rangedfrom 7 to 22%. Most of the variation was then explainedby differences between animals. Importantly, all the BINBSvariables increased significantly (p < 0.001) with the age ofthe animal.

3.4. Phenotypic variability for pigmentation traits

The analyses for pigmentation traits are also presentedin Table 3. Pigmentation traits were taken as the response

Page 5

68 J.I. Urioste et al. / Small Ruminant Research 120 (2014) 64–70

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

4-6 7-8 9-10 11-12 13-14 15-16 17-18 19-20

Fre

quen

cy

Pigmentation score

1-year-old

2-year-old

3-year-old

4-year-old

5-year-old

d rear h

Fig. 2. Distribution of total hooves pigmentation scores (sum of front anto 5-years-old).

variables and the significance of the effects of the modelwere assessed. The effects of flock and age were highly rel-evant in explaining the variation in all variables analyzed. Inthis case, the overall effect of the age was negative, i.e. ani-mals were classified as less pigmented with increasing age.For pigmentation in the ears, a general blackening effect(“burned ears”) that the sun produces on them probablyprevented more adequate recording.

Table 3Variation between (�2

flock) and within (�2

e ) flocks, percentage of variationexplained by the flock effect (% �2

flock) and age effect (regression coefficient

in the corresponding scale) for the presence or absence of different typesof spots, and pigmentation score in nose, hooves (classified as light ordark) and ears (classified as clean or stained).

Spot classa �2flock

�2e % �2

flockAge

BINTBS 0.191 1.011 15.89 0.967BINBS0 0.251 0.989 20.25 0.829BINBS1 0.097 0.944 9.30 0.843BINBS2 0.160 0.927 14.69 0.728BINBS3 0.068 0.928 6.79 0.801BINBS4 0.275 1.001 21.56 0.644BINBS5 0.187 0.986 15.95 0.509Nose 0.080 0.841 8.69 −0.037Hooves 0.272 0.996 21.5 −0.387Ears 0.232 0.971 19.3 −0.167

a BINTBS, presence/absence of total number of black spots; BINBS0,presence/absence of black spots without fibres; BINBS1, presence/absenceof spots with up to 20% of the area with pigmented fibres; BINBS2,presence/absence of black spots with 21–40% of the area; BINBS3,presence/absence of black spots with 41–60% of the area; BINBS4,presence/absence of black spots with 61–80% of the area; BINBS5, pres-ence/absence of black spots with 81–100% of the area.

ooves, from 4 to 20, grouped in two-score classes) by age at shearing (1-

3.5. Relationships between black skin spots andpigmentation traits

Relationships between the pigmentation traits (nose,ears and hooves) and TBS or BINTBS were tested throughfour models that incorporate the pigmentation traits indi-vidually or all together as explanatory variables (Table 4).As in the previous analyses, the positive effect of age onresponse variable was highly significant. A marked effectof nose pigmentation on TBS and BINTBS was found (mod-els 1 and 4), with increasing values of BINTBS and TBS with

nose score. Fig. 3 illustrates results found using Model 4. Inconclusion, a positive association between nose pigmenta-tion and number and presence of black skin spots in thefleece was detected.

Table 4Linear regression of age and statistical significance of the age effect andthe fixed effects of pigmentation scores on the presence of black spots(BINBS) and the total number of black spots (TBS).

Modelsa BINTBS TBS

Model 1Age coefficient 0.99 (p < 0.001) 0.78 (p < 0.001)Nose score p < 0.001 p = 0.008

Model 2Age coefficient 0.98 (p < 0.001) 0.77 (p < 0.001)Hooves score p = 0.1204 p = 0.3340

Model 3Age coefficient 0.98 (p < 0.001) 0.78 (p < 0.001)Ear score p = 0.0178 p = 0.0255

Model 4Age coefficient 0.997 (p < 0.001)a 0.77 (p < 0.001)Nose score p < 0.001 p = 0.0031Hooves score p = 0.8321 p = 0.0282Ear score p = 0.0488 p = 0.0553

a The flock effect is not reported.

Page 6

J.I. Urioste et al. / Small Ruminant Research 120 (2014) 64–70 69

●●

●●

●●

●●

0.0

0.5

1.0

1.5

2.0

Nose

Spots

B2 P2 B3 P3 B4 P4 B5 P5

Fig. 3. Association of nose pigmentation score (1–5) with total number of spots (full circles), assuming a Poisson distribution and presence/absence ofs a scale rP

lBias

4

awtrai(Pimomrcfi(

pots (full triangles), assuming a binomial distribution. Score 1 is used as

(Poisson scale) or B (binomial scale).

Hoof pigmentation (defined as binary variable, dark oright hooves) did not appear to be associated with TBS orINTBS when considered alone. Finally, the pigmentation

n ears (“stained” or “clean”) was positively (but weakly)ssociated with the presence or the total number of blackpots in the fleece area.

. Discussion

High quality levels in wool are of economic importance,nd selection against presence of pigmented fibres is oneay of improvement. However, the information needed

o establish a breeding plan in the Corriedale breed foreducing the number of genetically pigmented fibres, i.e.dditive genetic variability and genetic correlations withndicator traits acting as indirect selection criteria, is scarcee.g. Fleet, 1996; Enns and Nicoll, 2002; Naya et al., 2008;enagaricano et al., 2011). Presently, evaluation schemesn Uruguay only consider a subjective assessment of pig-

entation in the selection candidates. Therefore, the mainbjective of this study was to acquire knowledge about pig-entation traits using commercial data, which could be

elated with presence of coloured fibres. Potential short-omings in the data analyzed include lack of records onbre faults, lack of information on the pedigree of animalsthe data are not suitable for direct genetic analyses), and

eference in both cases; nose pigmentation scores are preceded by letters

biases produced by management practices with respectto pigmentation that are difficult to account for. Thesedisadvantages are counteracted by the fact that it comesfrom a significant number of animals with different geneticorigins, and provide for initial phenotypic measures of vari-ation and relationships among variables thought to be usedas indicator traits. Given the paucity of national and inter-national information regarding pigmentation-related traitsin sheep, the analysis conducted provided some primaryinsight into the attributes of various traits as suitable vari-ables for future selection purposes.

Equivalent results are scarce in the literature. Theresults of the present study (Tables 1 and 3) are in generalaccordance to early national data from two research flockspresented by Kremer et al. (2003), with minor differencesin the incidence of spots BS3 and BS5.

Contrary to our findings, Pereira et al. (2003), workingwith a single Corriedale flock, reported that most animalshad low pigmentation in the nose and high pigmentationin hooves. They detected no association between pigmen-tation levels and age of the animal. Fleet and Lush (1997)also reported a great variety of pigmentation traits in a Cor-

riedale flock. In their study, all sheep had darkened hooves,and most sheep had pigmented skin.

A marked effect of the age of animals, particularly inthe spots variables, was detected. Forrest and Fleet (1986)

Page 7

inant R

70 J.I. Urioste et al. / Small Rum

found that the number of dark spots increased with ani-mals’ age, were mainly located in the back and wereprobably induced by ultraviolet rays after shearing. In theMerino breed in Australia, this is not a problem until 6 yearsof age (Fleet et al., 1991). To our knowledge, changes innose, ear or hoof pigmentation have not reported before.

An important finding in this study is that phenotypicvariation exists between animals for all measured traits(with the exception of pigmentation in ears), and betweenflocks. In the latter case, it was not possible to distinguishwhether the causes of variation are largely attributable togenetic or management reasons. Additionally, differencesin age structure may mask (or increase) the differencesbetween flocks. We hypothesize that the genetic aspectsof between-flock variability could be of importance, sinceflocks are thought not being genetically connected. The dif-ferences between individuals of the same flock can be alsoassumed to have a genetic component. Given the scien-tific evidence of genetic components in some of these traits(e.g. Fleet, 1996; Fleet and Lush, 1997; Naya et al., 2008;Penagaricano et al., 2011), these results suggest presenceof additive genetic variance in the Uruguayan Corriedalepopulation in the traits analyzed, which will be furtheraddressed in complementary studies. Another factor thatmay be influencing the differences between flocks is thespecific farm management; a few farmers discarded ani-mals with very visible spots at first shearing.

A distinguishable phenotypic relationship was detectedamong spot and pigmentation variables. Applying regres-sion techniques and taking into account the binary natureof the traits, we have shown that presence and number ofblack spots are phenotypically associated with pigmenta-tion traits. Australian research (Fleet and Lush, 1997; Fleetand Stafford, 1989) has also reported positive phenotypiccorrelations among pigmentation traits. Importantly, in ourstudy the presence and number of black skin spots werepositively associated with the pigmentation in the nose.Therefore, a high emphasis on selecting animals with darknose, following the Corriedale breed standard, may con-tribute to the increased presence of black skin spots andhence with the presence of pigmented fibres in the fleece.

5. Conclusions

This study of pigmentation traits and presence of blackspots in commercial flocks of Corriedale enabled us toobserve a high incidence of spots, and among them, spotswith the presence of pigmented fibres. Important phe-notypic variation was observed. A marked effect of theage of animals, particularly in the spots variables, wasalso detected. In any case, the existence of an underly-ing genetic variation, which could be exploited throughadequate breeding programmes, is a standing hypothesis.

The implication of this research is that it suggests somealternative traits that can be further examined for theirgenetic variation, using appropriate data structure. There-fore, the next step should be to study these traits further

esearch 120 (2014) 64–70

using well-designed data, for obtaining estimates of geneticparameters.

Conflict of interests

The authors declare that there is no conflict of interestswith farmers involved in this research.

Acknowledgements

This research was supported by Grant PDT 35-02 fromPrograma de Desarrollo Tecnológico (Uruguay). Farmersparticipating in the survey and field staff are greatlyacknowledged.

References

Abella, I., Cardellino, R.C., Mueller, J., Cardellino, R.A., Benítez, D., Lira,R., 2010. South American sheep and wool industries. In: Cottle, D.J.(Ed.), International Sheep and Wool Handbook. Nottingham Univer-sity Press, pp. 85–94, 2010.

Australian Corriedale Association Inc., 2013. http://www.corriedale.org.au/Page.asp? =Breed%20Information (retrieved 19.03.13).

Cardellino, R., Guillamón, B.E., Severi, J.F., 1990. Origen de las fibras col-oreadas en tops de lana uruguaya. Producción Ovina 3, 81–83.

Enns, R.M., Nicoll, G.B., 2002. Incidence and heritability of black spots inRomney sheep. N. Z. J. Agric. Res. 45, 67–70.

Fleet, M.R., 1985. Pigmented fibres in white wool. Wool Technol. SheepBreed. 33, 5–13.

Fleet, M.R., 1996. Pigmentation types – understanding the heritability andimportance. Wool Technol. Sheep Breed. 44, 264–280.

Fleet, M.R., Lush, B., 1997. Sire effects on visible pigmentation in a Cor-riedale flock. Wool Technol. Sheep Breed. 45, 167–173.

Fleet, M.R., Stafford, J.E., 1989. The association between non-fleece pig-mentation and fleece pigmentation in Corriedale sheep. Anim. Prod.49, 241–247.

Fleet, M.R., Smith, D.H., Pourbeik, T., 1991. Age related changes in pig-mentation traits in Merino sheep. Wool Technol. Sheep Breed. 39,26–36.

Fleet, M.R., Forrest, J.W., Walker, S.K., Rogers, G.E., 2004. Foetal develop-ment of melanocyte populations in Merino wool-bearing skin. WoolTechnol. Sheep Breed. 52, 101–123.

Forrest, J.W., Fleet, M.R., 1986. Pigmented spots in the wool-bearing skininduced by ultraviolet light. Aust. J Biol. Sci. 39, 123–136.

Kremer, R., Urioste, J.I., Naya, H., Rosés, L., Rista, L., López-Mazz, C., 2003.Incidence of skin spots and pigmentation in corriedale sheep. In:IX World Conference on Animal Production, Porto Alegre, RS, Brazil,October 26–31.

Mason, I.L., 1996. A World Dictionary of Livestock Breeds, Types and Vari-eties, fourth ed. C.A.B. International, 273 pp.

Naya, H., Urioste, J.I., Chang, Y.M., Rodrigues-Motta, M., Kremer, R.,Gianola, D., 2008. A comparison between Poisson and Zero-inflatedPoisson regression models with an application to number of blackspots in Corriedale sheep. Genet. Sel. Evol. 40, 379–394.

Penagaricano, F., Urioste, J.I., Naya, H., de los Campos, G., Gianola, D., 2011.Assessment of Poisson, Probit and linear models for genetic analysisof presence and number of black spots in Corriedale sheep. J. Anim.Breed. Genet. 128, 105–113.

Pereira, G.I., de Miquelerena, J., Urioste, J.I., Naya, H., López-Mazz, C.,Surraco, L., 2003. Presencia de Fibras Pigmentadas en una majadaexperimental Corriedale. In: 12◦ Corriedale World Congress. CD-ROM,Montevideo, Uruguay. September 1–10.

Renieri, C., Valbonesi, A., La Manna, V., Antonini, M., Lauvergne, J.J., 2008.Inheritance of coat color in Merino sheep. Small Rumin. Res. 74,23–29.

Secretariado Uruguayo de la Lana, S.U.L., 2013. Boletín exportaciones delrubro ovino enero 2013. http://www.sul.org.uy (accessed 19.03.13).