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Factors affecting external and internal mammary morphology traits and assessment of their interrelationships with milk yield in Lori Bakhtiari breed ewes

S Sadeghi, S A Rafat, M Ghaderi Zefrei*, F Khaligh**, K H Rostami***, M Bohlouli, M R Bahrani Behzadi* and M Mohaghegh*

Department of Animal Science, University of Tabriz, Iran
* Department of Animal Science, University of Yasouj, Iran
** Department of Animal Science, Ferdowsi University of Mashhad, Iran
*** Department of Animal Science, Ramin Agriculture and Natural Recuses University, Ahvaz, Iran
Saadat Sadeghi, Department of Animal Science, University of Tabriz, Tabriz, Iran


Udder morphology traits were measured and subjectively assessed in 100 ewes of Lori Bakhtiari breed using linear scoring system. Ewes were recorded repeatedly within and between lactations. In total 300 sets of measurements and linear scores were collected. Udder measurements included: udder height, udder width, cistern height, teat length, teat angle, attachment width and udder circumference. The implementation of digital picture analysis was by Digimizer 3.6 software that allows the extraction and calculation of measurements from a digital picture. Linear scores were assessed for: udder depth, cistern depth, teat opening, teat size, udder attachment and udder shape. Milk yield recording was performed at 3 weeks, 2 months and 4 months of the lactation period.

Analysis of variance showed significant effect of stage of lactation in all traits measured and subjectively assessed except of teat opening and teat angles. Lori Bakhtiari ewes showed greater udder depth, teat opening and daily milk yield at 3 weeks than at 2 or 4 months over lactation period. Positive and significant phenotypic correlation coefficient (rp=0.332) was found between udder depth score and cistern depth score (P<0.01). Assessment of the teat length was highly correlated with measurement udder for teat angle (rp = 0.88; P<0.001). Subjectively assessed linear scores for udder depth, cistern depth, teat opening, teat size, udder attachment showed high correlations with actual measurements of the respective traits on udder in the Lori  Bakhtiari (rp = 0.87–0.98). For udder depth score more than 48% ewes had score 3. In conclusion, Lori Bakhtiari ewes showed udder measures and linear scores were correlated with milk yield. These results would provide significant information for udder characteristics of the Lori Bakhtiari, which is the most popular indigenous breed of sheep in Iran. Such information could be used as a basis for genetic improvement of Lori Bakhtiari breed. 

Keywords: cistern, teat, udder depth, udder measurements


Evaluation of udder morphology can be performed by direct measurements of the udder (Labussiere 1988) or by subjective assessment of udder traits using linear scales (De La Fuente et al 1996). Direct measurements provide objective information, but they are time consuming and laborious for applying on a large scale (De La Fuente et al 1996). On the other hand, linear traits are more useful for large scale evaluations, but rely on subjective information. A combination of both categories of traits, as carried out in the present study, is certainly the best approach in research projects, trying to identify correlations between traits and develop effective descriptors for large scale use. Inter-relationships among udder measurements and milk yield within sheep breeds have been demonstrated (Legarra and Ugarte 2005) yet not fully elucidated. In dairy sheep, the most important functional traits are those related to udder morphology, thus, there is a need to introduce improved udder traits into sheep breeding schemes (Gutierrez- Gil et al 2008). The morphological traits of sheep udder have been investigated in Mediterranean breeds, particularly in dairy sheep breeds, such as Churra (Fernandez et al 1995; De La Fuente et al 1996), Lacaune (Marie- Etancelin et al 2005) and Sarda (Casu et al 2010), but not in meat breeds. The study of udder morphological traits in meat breeds and its relationship with milk production should be of interest for rearing ability, and also for knowing dairy potential and yield of some breeds traditionally considered for meat purpose (Martinez et al 2010). This could be the case of Lori Bakhtiari sheep, an indigenous sheep breed in Iran. In this context, the study of mammary morphological traits and their effects in Lori Bakhtiari breed, could permit to understand its dairy potential and also would identify those mammary traits more suitable for specific breeding programs. The knowledge of the relationships between individual characteristics of udder morphology is important to be included into total selection indexes to construct partial selection indexes for udder morphology and to predict future correlated responses in milk-oriented selection schemes (Milerski et al 2006). The knowledge of these relationships is needed to optimize the udder linear score scheme for dairy sheep breeds in Iran.

The objectives of this study were to evaluate the relationships between measurements of chosen udder dimensions or angles and subjective assessment of udder characteristics based on linear scoring system and their correlations with milk yield in Lori Bakhtiari breed.  

Material and Methods

Investigations were performed in five flocks in Iran. One hundred purebred Lori Bakhtiari ewes were included in the experiment. All ewes were in first and second parity and had one or two lambs per partum. Lambs were separated from their mothers for 12 hours before measurements and linear scores of morphological traits and milk yield were taken, to provide the appropriate period for milk secretion. In addition, milk yield was estimated in each test-day observation immediately after mammary morphology measurements and linear scores of ewes milked by hand. Three measurements and linear scores per lactation were taken from all ewes at 3 weeks, 2 and 4 months postpartum; therefore 300 sets of measurements and linear scores were collected in total.

Three pictures of the udder were analyzed: fore views of the whole udder and two particular views of the right and left teat. The implementation of digital picture analysis was by Digimizer 3.6 software that allows the extraction and calculation of measurements from a digital picture.

The direct measurements of seven traits, which were modifications of the standards initially described by Milerski et al (2006), included: udder circumference measured with a tape, udder width, udder height, cistern height, teat length, sum of two angles or teat opening and udder width.

Linear assessments were done subjectively by one experienced assessor using a nine-point scoring system. The linear assessment scheme contained six characteristics of udder and teats: udder depth (1-low, 9-high), cistern depth below the teat level (1-none, 9-high), teat placement or teat opening (1-vertical, 9-horizontal), teat size (1-short, 9-long), udder attachment (1-narrow, 9-wide), udder shape (1-bad, 9-ideal) described by De La Fuente et al (1996) Casu et al (2006) and Milerski et al (2006). Feeding of all animals was based on grazing on natural prairies, supplemented with 100 g oats grain at night.

Statistical analyses

Data were analyzed by least squares means techniques using the GLM procedure of SAS (2000). Phenotypic correlation coefficients between all traits were computed by the CORR procedure in SAS software. The factors studied for morphological traits and milk yield were the parity, the lamb number per partum and the stage of lactation. The statistical model used was:

Yijkl = μ + Pi + Nj+ Sk + eijkl

Where Yijkl = dependent variables studied; μ = mean; Pi = effect of parity (two levels); Nj= effect of lamb number per partum (two levels); Sk = effect of test-day number or stage of lactation (three levels: 3 weeks, 2 and 4 months postpartum); and eijkl = effect of residual error. The interactions were not significant (P > 0.05), therefore they were not included in the statistical model.

Results and Discussion

The distribution of the frequency of udder linear scores are showed in Figure 1. Udder depth showed lowest variation in the Lori Bakhtiari population, where 85% of ewes had score 2 and 3. Maximum variation was observed for teat opening score. Short udders (score<4) were more frequent in the Sarda× Lacaune backcross ewes (Casu et al 2010) according to our results. Contrary to the present study, the traits related to teat opening in Churra breed showed a tendency to move forward and horizontally (Fernandez et al 1995) probably due to the differences between animals.

Figure 1: Distribution of the most frequent score for udder in the Lori Bakhtiari ewes

The stage of lactation had important effect on the traits studied (Table 1). The traits defining udder size diminished throughout lactation, this reduction being particularly evident at 4 months postpartum. This udder size variation (decrease) was compatible with the reduction of milk yield, which diminished from 950 g/day (3 weeks postpartum) to 230 g/day (4 months postpartum). Establishing lactation curve can be of interest to study of the accuracy of the milk yield and lactational measures obtained from test day records. The maximum secretion potential of the ewes resulted at 3 weeks postpartum.

The decreases of milk production between successive (1st and 2nd and 2nd and 3rd) test day observations were 51.6% and 50% respectively. Total milk yield calculated from lactation curve averaged 945, 892, 718 and 455 mL/day for Chilota and Suffolk Downewes in 15, 45, 75 and 105 d respectively (Martinez et al 2010). Stage of lactation had a significant effect on daily milk yield according to Rovai et al (1999).

As lactation continued the udder height diminished (P < 0.05) from 3 weeks (24.3 cm) to 4 months (15.3 cm) postpartum, but teat length increased (P < 0.05) at 4 months postpartum (3.25 cm) coinciding with the involution of mammary gland at end of lactation. All traits of udder morphology measurements and linear scores exception teat size (score) and teat length (measure) significantly diminished throughout lactation, although the stage of lactation did not affect (P > 0.05) the teat position (score and measure).

Rovai et al (1999) found average udder height 172 mm for Manchega and 178 mm for Lacaune breed. Milerski et al (2006) reported higher average linear score for teat position in Lacaune (5.8) than in Tsigai (4.3). Similar average teat angles 48.5° and 44.1° were reported in Lacaune ewes by Rovai et al (1999) and Marie- Etancelin et al (2003), respectively.

Mean teats length, udder circumference, udder depth at two weeks postpartum and two weeks post-weaning for Ghezel ewes were 3.3 and 3.6, 50.9 and 36.3 and  14.8 and 13.3 respectively (Izadifard and Zamiri, 1997). Fernandez et al (1995) observed teat size (length and width) tended to decrease between the 1st and 4th month of lactation.

Average udder depth, udder attachment, teat placement, teat size and udder shape scores in Churra breed ewes were 5.16, 5.14, 4.48, 4.78, and 4.76, respectively (De La Fuente et al 1996). In agreement to our result, De La Fuente et al (1996), found a reduction between months 1 and 5 of lactation for depth udder.

Generally, reduction of all udder traits exception teat length and teat size scores are associated with lower amount of milk production. Increased teat length and teat size scores during lactation period would suggest that sucking lambs and hand milking being influencing in their correlations with milk yield production.

Table 1: Least square means for udder morphology measurements, linear scores and milk yield studied based upon lactation stage in Lori Bakhtiari ewes.


Stage of lactation


3 weeks  (n=100)

2 months  (n=100)

4 months  (n=100)






Milk yield (g/day)





Linear udder assessment scores





Udder depth





Cistern depth





Teat opening





Teat size





Udder attachment





Udder shape





Udder measurements





Udder height (cm)





Udder width (cm)





Udder circumference (cm)





Cistern height (cm)





Teat length (cm)





Teat angle (ᵒ)





Attachment width (cm)





Means in the same row without common letter are different P<0.05

Phenotypic correlation coefficients between linear scores and milk yield are presented in Table 2. A significant correlation between all udder linear scores with daily milk yield was found, as udder depth was highly correlated with daily milk yield (rp = 0.56; P<0.001). Lori- Bakhtiari assessments of the udder shape were more dependent on the udder attachment, as correlation coefficient between linear score for udder shape and linear scores for udder depth was rp = 0.33. Linear scoring for teat size and teat opening were negatively correlated with udder shape, udder depth and cistern depth.

Udder attachment showed higher correlations with udder dimensions and cistern height in Slovak native sheep breeds than in Lacaune (Milerski et al 2006). Significant phenotypic correlations were found between udder shape with teat placement, teat size, udder depth and udder attachment (De La Fuente et al 1996). Teat opening was negatively and significantly (P <0.01) correlated with milk yield in the Istrian dairy crossbreeds (Dzidic et al 2004) according to our results.

Low correlations between some of aforementioned traits indicate some degree of independence from each other. This to some extent could dictate to include all of them in the udder evaluation system. The correlations of udder shape with udder attachment show a high dependency between them in order to define morphological aptitude of milking. 

Table 2: Phenotypic correlation coefficients between subjectively assessed linear scores of udder traits and its relationship with daily milk in Lori Bakhtiari ewes.


Udder shape

Udder depth

Cistern depth

Udder attachment

Teat opening

Teat size

Daily milk







Udder shape



0.0121 NS


-0.0932 NS

-0.100 NS

Udder depth





-0.192 NS

-0.0512 NS

Cistern depth




-0.0236 NS



Udder attachment





0.000 NS

-0.158 NS

Teat opening







*P < 0.05; **P < 0.01; ***P < 0.001; NS: non-significant.

Correlation coefficients between udder measurements are shown in Table 3. Udder width was positively and highly correlated with udder height (rp = 0.72).

Izadifard and Zamiri (1997) found in Ghezel breed ewes at two weeks post-lambing that several udder measurements were highly correlated to their lactation production. They found  the higher correlation in depth (rp = 0.75) and circumference (rp = 0.72) of the udder. Correlation coefficients for udder measurements and linear scores suggested that animals with higher cisterns tended to have more horizontally placed teats according to Milerski et al (2006). According to Izadifard and Zamiri (1997), correlations between udder’s measurements and milk yield could be helpful in cross breeding projects. Contrary to our results, no significant correlation was observed between teat length and milk production (Dzidic et al 2004). Positive correlations were observed between daily milk yield and udder depth in our study which showed an agreement with Labussiere (1988) results. 

Table 3: Correlation coefficients between direct measurements of udder traits and its relationship with daily milk in Lori Bakhtiari ewes.


Udder width

Attachment width

 Udder height

Udder circumference

Cistern height

Teat length

Teat angle

Milk yield





0.265 *



Udder width





0.134 NS



Attachment width





-0.010 NS

-0.155 NS


Udder height








Udder circumference






0.157 NS

0.189 NS

Cistern height








Teat length








*P < 0.05; **P < 0.01; ***P < 0.001; NS: non-significant.

Phenotypic correlation coefficients between linear udder traits and direct udder measurements are summarized in Table 4. Subjectively assessed linear scores for udder depth, cistern depth, teat placement, teat size, udder attachment showed high correlations with actual measurements of the respective traits on udder in the Lori Bakhtiari (rp = 0.87–0.98). A favorable correspondence was found between external udder dimensions and linear score for udder depth.

Correlation coefficients between the linear score for udder depth and the direct measurements of the same trait on udder were rp = 0.78 for Tsigai and rp = 0.76 for Lacaune breed (Milerski et al 2006). Marie- Etancelin et al (2003) after adjusting their data for main source of variation, found phenotypic correlations of rp = –0.60 between aforementioned traits in Lacaune ewes. They used an opposite scale for linear assessment of udder height so our findings are in agreement with them. The relationships between linear scores and ultrasonic measurements of cistern cross-section areas have been almost significantly positive in all examined dairy sheep breeds.

The linear scores are influenced by the same effects as traits measured on the biological scale; for example, teat size was correlated with teat length. Moreover, it is useful to be cited that most of the traits are expressed with greater variability on the linear scale, leading to a better description of the differences between animals.

Table 4: Correlation coefficients between subjectively assessed linear scores and measurements of characteristics of udder morphology in Lori Bakhtiari ewes.


Linear score

Udder measurements

Udder depth

Length teat

Teat position

Udder shape

Cistern depth

Udder attachment

Width udder


0.020 NS

-0.171 NS




Attachment width


0.0601 NS

0.010 NS


0.092 NS


Udder height


-0.196 *





Udder circumference


0.124 NS

-0.155 NS




Cistern height






0.0710 NS

Teat angle


0.095 NS


-0.133 NS


0.0306 NS

Teat length



0.112 NS

-0.125 NS


0.0608 NS

*P < 0.05; **P < 0.01; ***P < 0.001; NS: non significant.



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Received 15 November 2012; Accepted 31 January 2013; Published 1 March 2013

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