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

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 (r_p=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 (r_p = 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 (r_p = 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.

Introduction

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.

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:

Where Y_ijkl = dependent variables studied; μ = mean; P_i = effect of parity (two levels); N_j= effect of lamb number per partum (two levels); S_k = effect of test-day number or stage of lactation (three levels: 3 weeks, 2 and 4 months postpartum); and e_ijkl = 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.

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 (1^stand 2^nd and 2^nd and 3^rd) 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
Traits	3 weeks (n=100)	2 months (n=100)	4 months (n=100)
	Mean	Mean	Mean	SEM
Milk yield (g/day)	950^a	460^b	230^c	68.3
Linear udder assessment scores
Udder depth	3.43^a	2.61^b	2.16^b	0.332
Cistern depth	3.02^a	2.32^ab	2.15^b	0.260
Teat opening	5.63	5.34	5.21	0.171
Teat size	3.07^a	4.44^b	4.96^b	0.294
Udder attachment	4.75^a	4.02^b	3.48^b	0.313
Udder shape	3.24^a	2.53^ab	2.25^a	0.326
Udder measurements
Udder height (cm)	24.3^a	17.2^b	15.3^c	3.07
Udder width (cm)	18.4^a	16.2^b	15.1^b	2.13
Udder circumference (cm)	49.2^a	43.4^b	31.9^c	7.24
Cistern height (cm)	3.23^a	2.67^a	1.63^b	0.281
Teat length (cm)	2.32^a	2.69^b	3.25^c	0.364
Teat angle (ᵒ)	109	102	97.3	1.98
Attachment width (cm)	14.2^a	11.5^b	10.8^b	1.07
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 (r_p = 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 r_p = 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	0.452**	0.564***	0.376**	0.213*	-0.376**	-0.204*
Udder shape		0.274*	0.0121^NS	0.434**	-0.0932^NS	-0.100^NS
Udder depth			0.332**	0.306*	-0.192^NS	-0.0512^NS
Cistern depth				-0.0236^NS	-0.335**	-0.173^NS
Udder attachment					0.000^NS	-0.158^NS
Teat opening						0.292*
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 (r_p = 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 (r_p = 0.75) and circumference (r_p = 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.
Traits	Udder width	Attachment width	Udder height	Udder circumference	Cistern height	Teat length	Teat angle
Milk yield	0.333^**	0.248^*	0.389^**	0.393^**	0.265^*	-0.291^*	-0.303^*
Udder width		0.660^***	0.723^***	0.494^***	0.134^NS	-0.177	-0.186
Attachment width			0.414^**	0.209^*	-0.010^NS	-0.155^NS	-0.051^NS
Udder height				0.574^***	0.408^**	-0.224^*	-0.248^*
Udder circumference					0.161^NS	0.157^NS	0.189^NS
Cistern height						-0.228^*	-0.234^*
Teat length							0.883^***
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 (r_p = 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 r_p = 0.78 for Tsigai and r_p = 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 r_p= –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	0.632***	0.020^NS	-0.171^NS	0.503***	0.276*	0.674***
Attachment width	0.293*	0.0601^NS	0.010^NS	0.336**	0.092^NS	0.972***
Udder height	0.923***	-0.196^*	-0.214*	0.377**	0.420**	0.416**
Udder circumference	0.545***	0.124^NS	-0.155^NS	0.418**	0.347**	0.232*
Cistern height	0.320*	-0.222*	-0.321*	0.19*	0.964***	0.0710^NS
Teat angle	-0.233*	0.095^NS	0.980***	-0.133^NS	-0.364**	0.0306^NS
Teat length	-0.246*	0.874***	0.112^NS	-0.125^NS	-0.286*	0.0608^NS
P < 0.05; P < 0.01; **P < 0.001; NS: non significant.

Conclusion

References

De La Fuente L F, Fernandez G and San Primitivo F 1996 A linear evaluation system for udder traits of dairy ewes. Livestock Production Science 45: 171- 178. http://dx.doi.org/10.1016/0301-6226(96)00003-6

Labussiere J 1988 Review of physiological and anatomical factors influencing the milking ability of ewes and the organization of milking. Livestock Production Science 18:253–274. http://dx.doi.org/10.1016/0301-6226(88)90035-8

Marie- Etancelin C, Casu S, Aurel M R, Barillet F, Carta A, Deiana S, Jacquin M, Pailler F, Porte D and Tolu S 2003 New tools to appraise udder morphology and milkability in dairy sheep. CIHEAM-Options Mediterannes 55: 71–80. http://ressources.ciheam.org/om/pdf/a55/03600065.pdf

Martinez M E, Calderon C, De La Barra R, De La Fuente L F and Gonzalo C 2010 Udder morphological traits and milk yield of Chilota and Suffolk down sheep breeds Chilean. Journal of Agricultural Research 71: 90-95. http://www.bioline.org.br/request?cj11011

Milerski M, Margetin M, Capistrak A, Apolen D, Spanik J and Oravcova M 2006 Relationships between external and internal udder measurements and the linear scores for udder morphology traits in dairy sheep. Czech Journal of Animal Science 51: 383–390. http://www.agriculturejournals.cz/publicFiles/52323.pdf

Rovai M, Such X, Piedrafita J, Caja G and Pujol M R 1999 Evolution of mammary morphology traits during lactation and its relationship with milk yield in Manchega and Lacaune dairy sheep. Wageningen Pers, Wageningen, EAAP Publication 95: 107–109. http://phd.ke.hu/fajlok/1350480490-phd_nzs.pdf

SAS/STAT, 2000. User’s Guide, Release 8.2. SAS Institute Inc, Cary, NC, USA.

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*

Abstract

Introduction

Material and Methods

Results and Discussion

Conclusion

References

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*

Abstract

Introduction

Material and Methods

Results and Discussion

Conclusion

References

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