Effects of udder traits on the milk yield of sheep

In order to determine the possible effects of udder traits on milk yield and milk composition a serial of experiments were carried out on five different sheep farms, between 1998-2000. Ten breeds and genotypes were included in these experiments: Merino, (Merino x Pleven Blackhead) F1, Pleven F1 x Black East Friesian, Lacaune, (Merino x Lacaune) F1, British Milksheep, (Merino x British Milksheep) F1, Awassi, (Merino x Awassi) F1, Milking Tsigai. The udder traits (type, size, teat size) were determined individually at the time of the first test milking, within two weeks after the weaning in each year. Milk yield was measured in every four weeks (morning and evening). Data collected were processed using LSLMW and MIXMDL (HARVEY, 1990) program. Differences among and within the genotypes in udder characteristics were summarised and presented in tables and figures.


Introduction
The udder characteristics do not belong to the most important traits of the milking sheep; however, they could have strong effects on the milk yield and composition (UGARTE and GABINA, 2004).On most of the farms the udder (apart from case when one side of the udder is lost) is not studied during the selection.On the contrary, the use of objective measurements for the characterization of the dairy sheep udder and for the study of the relations with milk yield or other productive traits has been undertaken by different authors since the development of machine milking.The target of this present study (apart of examinations of various sheep genotypes) was to compare the effects of udder characters on milk production based on several genotypes and over the period of three years.The ram effect on the udder traits, and the heritability of these characteristics were not in the aim of this study.

Material and methods
Ten different sheep genotypes were included in this three years long experiment to determine the milk production traits of the ewes belonging to the following populations /only minimum number of ewes was fallen out during the period of the study/: 1 The animals were milked on five different farms.Genotypes of no. 1, 4, 5 were kept on farm I., no. 2, 3 were kept on farm II., no.6 and 8 on farm III., no.7 on farm IV., no. 5 on farm V.The Milking Tsigai group was excluded from the experiment in 1999 because of short controlled milking period.In the year 2000, the Awassi-, and the Awassi F1 group were let out from the experiment as a consequence of changing identification system.The udder traits of the ewes between second and fourth lactation were studied between 1998 and 2000 using the system worked out by KUKOVICS and NAGY (1989) based on the results of LABUSSIÉRE (1988).The udder characters were classified by the same person at the occasion of the first test milking in every year using the same sheep populations on the farms.Ewes were grouped based on their udder type (I, II, III, IV), relative udder size and relative teat size (small, medium, big as 1, 2 , and 3) (Figures 1-3).The extreme measurements of udder-and teat size (4) were also observed in several cases.Milk production was measured four weekly, twice a day (morningevening).Data collected was processed using LSLMW and MIXMDL (HARVEY, 1990) program to calculate the relationships among the udder traits and milk yield.
The following model was used in the processing: In the case of Milking Tsigai, the year effect was taken out from the model, because this breed was a part of the experiment only in the first year.Data of this breed were evaluated separately.Results There were several differences found among the studied genotypes concerning the udder characteristics.
In general, studying the same flocks great differences could be observed within the various genotypes mainly as the effect of the year.The ratio of type, size or even the teat size could change a little bit year by year.In the case of Merinos the II.and the III.type was dominating, with small or medium udder size.The teat size was dominantly small or medium.They hardly had big udder or teat size.We could not find too many big udders in the case of Milking Tsigai either.The most dominating type was the II.and III., and only limited number of ewes was belonging to the type IV.The udder-and the teat size were mainly medium, but a good number of ewes had big or too big teats.The Pleven F 1 ewes had similar results than that of the Merinos, however, the big udder and big teat size quite often were observed.In the case of Pleven F 1 x BEF the udders were mainly belonging to type III and II, and several % of them to type IV.Only some % of the ewes had big udder, the dominating measurement was the medium in both udder and teat sizes.The udders of BMS ewes mainly belonged to type III and II, while that of the BMS F 1 -s to the II.and III type.The dominating size was the medium one in both cases, but in the purebred animals the big-, and in the crossbred group the small size was on the second rack in the order.The teat size was dominantly small (crossbred) and medium (purebred).Most of the Awassi ewes had II.type of udder, with medium or big size, and small or medium teats.In the case of Awassi crossbreds, the type III. and II.were almost equally dominating.Most ewes had medium or small udder with small or medium teats.At the same time, the most of the extremely big udder-and teat sizes were observed in these groups.In the case of Lacaune sheep (pure-and crossbred) type III was dominating with medium or small udders, and mainly small teats.

Effect of udder traits on milk production characteristics
The effect of the udder type on milk production was not always clean, and varied by the genotype and the year (Fig. 4 -6).The udder size had a strong and significant effect on the studied traits (Fig. 7 -9).As the size was increasing the quantity of the milk yield was growing in every genotype.The year had an effect on the quantity, but the tendency was not clean.Interesting picture was found in the case of teat size (Fig. 10 -12).In general, there was an increasing trend with the growing teats in most of the genotypes, but differences were also found.
In Awassi, Lacaune F 1 (1999) and BMS (1999) the quantity of milk declined with the growing teat size.
In the case of Milking Tsigai (Table 1), an increasing tendency was observed in all of the udder characteristics, only the ewes with ideal udder type broke the trend.The most expressed differences were found among the udder size categories.
In the case of other genotypes (Table 2) similar trends could be observed.Certainly the year and the genotype modified the average milk yield data.The udder size had the most distinct effect on milk yield, more than 20 litres were found between the measurement classes.Based on the result, the III.one was the most favourable udder type, because the ideal type (IV) was accompanied by a smaller quantity of milk.Similar observations were found in the case of teat size: the extra size of teat did not increase the milk yield, what's more, resulted reduced quantity.

Analysis of Variance
The results of analysis of variance confirmed the observations.In the case of Milking Tsigai only udder size had a strong and significant (P<0.001)effect on milk yield.In the other genotypes concerned every studied traits had significant effect on milk quantity.Besides genotype and year, udder type, udder size, and teat size strongly modified the yield data (P<0.001).Trying to establish the type of relationships between milk yield and udder traits we received two different results.In the case of Milking Tsigai breed, only the linear adjustment was significant.On the contrary, both linear and quadratic approaches were highly significant (P<0.001) in the case of other genotypes.

Discussion
The udder characteristics and their effects on the milk production traits were evaluated differently by the various authors.Many of them took the udder measurements concerning different sheep breeds from the udder using cm scale, which method needed time and extra labours.The method developed and used by us based on standard figures and the udder characteristics of certain ewes were classified comparing to these serial of figures.The continuous nature of the measurements increased the discriminating capacity of each variable and the significance of correlation with the productive traits.The methodology generally used corresponds to the standardized protocol of LABUSSIÈRE (1983) with small variations incorporated in some cases (GALLEGO et al., 1983;FERNÁNDEZ et al., 1983a,b, 1995, as well as KUKOVICS and NAGY, 1989).The repeatability of udder measurements made according to this methodology is low for udder dimensions (r= 0.17 to 0.18), medium for teat dimensions and teat position (r= 0.45 to 0.52), and high for teat angle (r= 0.65) and cistern height (r= 0.77), as calculated by FERNÁNDEZ et al. (1995) in the Churra dairy breed (CAJA et al, 2000).The udder type and size could be changed year by year (KUKOVICS et al., 1993) and their effect could also modify the milk yield data. Significant differences were found between breeds and crossbred sheep populations concerning udder type and size (LABUSSIÉRE et al., 1981;LABUSSIÉRE, 1988;KUKOVICS-NAGY, 1989;KUKOVICS et al., 1993KUKOVICS et al., , 1999)).In Sarda sheep the udder type and udder size had significant effect on milk production (CASU et al., 1989).Different correlations were found among the udder traits and milk production characters by CASU et al. (1989), KUKOVICS et al. (1993, 1998), SCHULZ et al. (2004) and VOLANIS et al. (2002); while the first one got only weak correlation, the latter one observed correlation with variable values and changing indications.CARTA et al. (1999) established that the udder type (teat placement) could have a role in improving milk production traits, especially machine milking ability of the sheep.The stage of lactation produced significant effects on all udder traits in accordance with GALLEGO et al. (1983), FERNANDEZ et al. (1983a,b, 1995) and FAHR et al. (2001).Nevertheless, despite the differences in milk yield, breed effects on udder length and distance between teats were non significant, and only showed a tendency in teat angle.Similar results were observed in regard to parity, where differences in teat angle and udder length were not significant.On the contrary, differences in teat dimensions (width and length) and udder height (depth and cistern height) were significant for breed and parity.These results agree with those obtained previously in different breeds (LABUSSIÈRE, 1988;FERNÁNDEZ et al., 1983aFERNÁNDEZ et al., ,b, 1995) ) although teat angle was affected by stage of lactation in other references (CASU et al., 1983;GALLEGO et al., 1983;LABUSSIÈRE et al., 1983a,b;FERNÁNDEZ et al., 1989aFERNÁNDEZ et al., , 1995)).Other authors indicated that udder length was not affected by the various factors analyzed (CAJA et al., 2000).
milk yield µ is the population mean for milk yield, i Year is the fixed effect of year, j Genotype is the fixed effect of genotype, k 1 T is the fixed effect of udder type, l 2 T is the fixed effect of udder size,

Table 2
Effects of udder characteristics on average milk production of the ewes belonging to different genotypes (Einfluss der Eutereigenschaften auf die Milchleistung der Mutterschafe unterschiedlicher Genotypen)