Connection of somatic cell count and milk yield as well as composition in dairy ewes

The aim of this study was to determine the effect of somatic cell count (SCC) on milk yield and composition using a threshold value of 250 ∙103 cells/ml in dairy ewes of line 05. A total of 1 512 milk samples from udder halves were collected throughout milking periods at monthly intervals. In the present study milk composition (from halves of the udder) and daily milk yield (from udders) was examined in terms of SCC in ewe milk in three groups: from both halves of the udder below 250 ∙103 cells/ml, from one halves of the udder below 250 ∙103 cells/ml and from second half udder above 250 ∙103 cells/ml and from both halves of the udder above 250 ∙103 cells/ml. Milk yield from udders, somatic cell count in milk samples from udder halves and milk composition depended on the level of SCC recorded for halves of the udder. Somatic cell counts in milk from one or both halves of udders exceeding 250 ∙103 cells/ ml resulted in a statistically significant (P<0.01) decrease in daily milk production of ewes, by approx. 15.89 and 30.22 %, respectively. The analysis of variance showed also a significant effect of parity and stage of lactation of ewes on somatic cell count (log SCC) and milk composition from udder halves below 250 ∙103 cells/ml.


Introduction
Breed, flock, parity, stage of lactation, type of birth, estrus, as well as diurnal, monthly and seasonal variations of somatic cell counts (SCC) contribute significantly to changes of SCC in milk of dairy sheep (GONZÀLEZ-RODRIGUEZ et al. 1995, FAHR et al. 2001, GONZALO et al. 2002, SCHULZ et al. 2004, Kukowivs et al. 2006, WÓJTOWSKI et al. 2006, RAYNAL-LJUTOVAC et al. 2007). However, BIANCHI et al. (2004) observed a significant increase of fat concentration in milk from infected udder halves in the Sarda breed.In relation to the effect of SCC on the percentage content of protein in ewe milk, many authors are of the opinion that a high level of SCC is related to a higher protein content in milk than a low SCC level (DIAZ et al. 1996, NUDDA et al. 2003, ALBENZIO et al. 2004, BIANCHI et al. 2004).In turn, other authors reported lower percentage content of protein at a high SCC (JAEGGI et al. 2003).PIRISI et al. (2000) and ALBENZIO et al. (2005) indicated nonsignificant differences in protein contents at high and low levels of SCC in ewe milk.
The aim of this study was to determine the effect of somatic cell count on milk yield and composition using a threshold value of 250 •10 3 cells/ml in dairy ewes of line 05.

Material and methods
The investigations were carried out in the years 2000-2002 at the Złotniki Experimental Farm belonging to the August Cieszkowski Agricultural University of Poznań.Experimental material consisted of dairy ewes line 05 (East-Friesian sheep 13/16 and Polish Merino 3/16).Ewes were machine milked for the period of 16 weeks in two calendar seasons: spring-summer (III-VI) and summer-autumn (VII-IX).Ewes with clinically healthy udders were milked two months after lambing (60 ± 22 days).Total in the years 2000-2002 examined 756 ewes.Milking performance of ewes was examined at monthly intervals and the yield of the udder was determined in ml from both morning and evening milking.At each milk recording before morning milking, after fore stripping, washing and drying of the teats, approx.50 ml of milk were collected from the udder halves in order to determine the percentage content of fat, total protein and lactose, as well as somatic cell counts (SCC).The basic milk composition was evaluated using a MilkoScan testing machine, while SCC -using a Fossomatic 90 apparatus.
Results received presented in this study for 3 groups of ewes in dependence from somatic cell counts in milk from udder halves.The first group of ewes has SCC in milk from left and right halves of the udder below 250 •10 3 cells/ml.Second group of ewes has SCC in milk from one halves of the udder below 250 •10 3 cells/ml and from second half udder above 250 •10 3 cells/ml.Third group of ewe‹s has SCC in milk from left and right halves of the udder above 250 •10 3 cells/ml.
The SCC value was transformed to a common logarithm (log SCC) in order to obtain the distribution close to normal (ALI and SHOOK 1980).The data were subjected to an analysis of variance, using the GLM procedure of the SAS software package (2000).The following linear models were applied in the calculations: where Yijk is the daily production of milk of the udder at milk recording (ml), somatic cell counts (log SCC), fat, protein and lactose contents (%) in milk from half udder, μ is the grand mean, Ai is the effect of parity, Bij is the effect of type of birth of ewes, Cijk is the effect of stage of lactation, and eijk is the effect of random error.

Results and discussion
The mean daily milk yield was 956.51 ml.The mean log SCC was 5.19 and the mean percentage content of fat, protein and lactose in milk was 5.45, 6.12, and 4.92, respectively.The means for milk yield, log SCC, fat, protein and lactose contents were similar to those recorded for other dairy sheep breeds (EL-SAIED et al. 1998, FAHR et al. 2001, SCHULZ et al. 2004, RIGGIO et al. 2007).
Results for mean daily milk yield and somatic cell counts in milk (log SCC) depending on SCC from udder halves are given in Table 1.The results show that SCC had a significant effect on daily milk production of ewes.Somatic cell counts in milk from one or both halves of udders above 250 •10 3 cells/ml had a statistically significant effect on a decrease in daily milk production of ewes, by about 15.89 and 30.22 %, respectively.The stage of lactation of ewes was statistically different (P<0.01) in milk production in all groups of sheep, but parity only in the third groups (SCC in milk from both udder halves above 250 •10 3 cells/ml).Numerous studies indicate a relationship between an increase in SCC and a decrease in milk yield.EL-SAIED et al. (1999) andFAHR et al. (2001) found a negative phenotypic correlation of SCC with milk yield (−0.16) for 2 379 ewes belonging to 10 flocks of the Spanish Churra breed.Similar results were reported by GONZALO et al. (1994) for ewes of that breed and by PELLEGRINI et al. (1997) for Lacune ewes.OTHOMANE et al. (2002) for ewes in eight Churra dairy flocks found a decrease of milk yield related to an increase in SCC.
Changes in milk composition depending on the level SCC from the udder half are presented in Table 2.The results show that SCC in milk below and above 250 •10 3 cells/ml had a significant effect on milk composition.An increase of somatic cell counts in milk from udder halves above 250 •10 3 cells/ml resulted in a significant increase of fat and protein content at a simultaneous significant decrease in lactose content.Group 1 SCC in milk from left and right halves of the udder below 250 •10 3 cells/ml, Group 2 SCC in milk from one halves of the udder below 250 •10 3 cells/ml and from second half udder above 250 •10 3 cells/ml, Group 3 SCC in milk from left and right halves of the udder above 250 •10 3 cells/ml, a,b,c means in the same column followed by different letters are different at P<0.01.*P<0.05,**P<0.01,ns not significant The increase in SCC results from the transfer of white blood cells from blood to milk (PIRISI et al., 2000).This increase is related to changes in milk composition, which may have two main explanations: injury of udder cells which reduces the synthesis of milk constituents in the udder (e.g.lactose), and changes in permeability of membranes and interstitial spaces, that increase the passage of components from blood to milk (SCHULTZ 1977).
The stage of lactation in ewes in all groups had a significant effect on milk composition (P<0.01).The type of birth of ewes in all groups did not have a significant effect on fat, protein and lactose content (P<0.01) in milk from both halves of the udder (except for lactose content in milk from left udder halves in the first and third groups of ewes).Parity had a significant effect on fat content in milk in the first and second groups of ewes, but on protein content only in the third group of ewes.Parity had a significant effect on lactose content in milk from both udder halves in the first group of ewes (SCC in milk from both udder halves below 250 •10 3 cells/ml).
Several authors showed that SCC did not affect fat content of ewe milk (PIRISI et al. 2000).In contrast, BIANCHI et al. (2004) observed a significant decrease of milk fat content in milk of infected ewes.Fat and protein contents in milk were not influenced by SCC and both increased with the advancement of lactation (ALBENZIO et al. 2005).EL-SAIED et al. (1999), NUDDA et al. (2003), ALBENZIO et al. (2004) andBIANCHI et al. (2004) reported that ewe milk with a high SCC contains more total protein than milk with a low SCC.In contrast, JAEGGI et al. (2003) found that the total protein content was lowest in milk with the highest SCC levels.PIRISI et al. (2000) and ALBENZIO et al. (2004) showed no significant differences between protein content of milk with high or low SCCs.The pH value increased and lactose concentration decreased with an increase in SCC of ewe milk (PIRISI et al. 2000, NUDDA et al. 2003, VIVAR-QUINTANA et al. 2006).
It is concluded that in milk of dairy ewes of line 05 fat and protein contents increased and lactose concentration decreased with an increase of SCC above 250 •10 3 cells/ml.Milk yield from udders, somatic cells count in milk samples from udder halves and milk composition depended on the level of SCC recorded in milk from halves of the udder.Somatic cell counts in milk from one or both udder halves exceeding 250 •10 3 cells/ml resulted in a statistically significant (P<0.01)decrease in daily milk production of ewes, by about 15.89 and 30.22 %, respectively.

Table 1
Means of milk yield and somatic cell counts (log SCC) depending on SCC from the udder half Die durchschnittliche Milchleistung und die Zahl der somatischen Zellen (log SCC) abhängig von SCC aus den Euterhälften

Table 2
Changes in milk composition depending on SCC from the udder half Die Veränderungen der Milchzusammensetzung in Abhängigkeit von SCC aus den Euterhälften SCC in milk from left and right halves of the udder below 250 •10 3 cells/ml, Group 2 SCC in milk from one halves of the udder below 250 •10 3 cells/ml and from second half udder above 250 •10 3 cells/ml, Group 3 SCC in milk from left and right halves of the udder above 250 •10 3 cells/ml, a,b,c Means in the same column followed by different letters are different at P<0.01.*P<0.05,**P<0.01,ns not significant