VARIATION IN SOMATIC-CELL COUNTS IN EWES MILK DURING LACTATION

Determination of somatic cell counts (SCC) becomes more and more impor tant also for ewe's milk. SCC can be a useful indicator of milk qualit y for milk processors while it can be a mastitis indicator for sheep k eepers and an important selection criterion for breeders when ewe popu lations more resistant to mastitis are produced. As hardly any informa tion about individual variability of SCC in dairy breeds of sheep kept in Slovakia is in fact available, we formulated the objective of our study to acquire basic information about factors influencing SCC varia bility, namely in lambing ewes of the Tsigai (C) and Improved Valachia n (ZV) breeds. Somatic cell counts (SCC) were determined in 866 milk s amples of lambing ewes of the C and ZV breeds in 1993 and 1994, during lamb sucking and during milking period. An instrument Fossomatic 90 ( Foss Electric, Denmark) was used for analysis. The ewes were housed an d kept in identical conditions. Milk samples were taken in current ope rational conditions after milking of the particular lambing ewes, with oxytocin applications during lamb sucking and from hand milking durin g milking period. Nine and/or ten control samplings were done in 1993 and/or 1994 (4 and/or 5 samplings during lamb sucking, 5 during milkin g period). To evaluate the acquired data on SCC basic variation-statis tical methods and analysis of variance were used as well as a package of mathematico-statistical programs STATGRAPHIC. As the distribution o f basic data on SCC was asymmetric, the data were transformed by means of decadic logarithm (log(10) SCC) before their use in the analysis o f variance. Tab. I shows the basic variation-statistica1 data on somat ic cell counts. Figs. 1 and 2 indicate the relation of SCC and lactati on stage in 1993 and 1994. Average SCC varied from 270 to 1,897 thous. /ml during lamb sucking and from 268 to 2,139 thous./ml during milking period. As seen in Tab. II, the differences between the control sampl ing were statistically significant only in 1994 (P < 0.001). A trend o f increase in SCC was observed at the end of both sucking and milking periods (Figs. 1 and 2). An overall evaluation of lactation (Tab. I) b rought about the average SCC at 364 thous./ml in 1993 (log(10) SCC - 2 .25) and at 1,091 thous./ml in 1994 (log(10) SCC - 2.68). The indicato r log(10) was significantly influenced by breed (P < 0.001) only in 19 94 (C - 2.61; ZV - 2.75). The effect of lactation number and number of sucking lambs did not have any significant influence on SCC (Tab. II) .