Some Factors Affecting Test-Day Visual Milk Somatic Cell Concentration and Milk Yield in Holstein Friesian Cows Raised in Egypt

To assess the relationship between sample test-day milk yield (TDM) and milk somatic cell concentration of Holstein Friesian cows raised under Egyptian conditions, the effects of cow source, farm, season and year of calving, parity and age at calving were investigated. Data on a total number of 2811 cows were collected from four dairy farms located in different areas (Al-Salhia and Dunia in Ismailia region, and Delta Misr farm 1 and 2 in Monofia governorate). Milk somatic cell concentration was examined using visualized linear score (VLSSCC) ranging from 0 to 3 digits. VLSSCC was converted to expected somatic cell count (ESCC), which in turn was expressed as expected somatic cell score (ESCS) in statistical analysis. The results showed that the direct animal random effect was responsible for a remarkable variability in TDM and partially for ESCS. These findings refer to the presence of genetic variability of these traits and indicate the possibility of genetic improvement of general udder health and milk yield through appropriate genetic improvement strategies. Overall least square means (LSM) of TDM and ESCC ranged from 10.1 to 27.9 Kg/day and from 575,000 to 1,404,000 cells per ml milk, respectively. The highest LSMTDM was 21.7+4.47 Kg/day at the third parity. Estimates of LSM for ESCC ranged from 575,000 to 957,000 and 851,000 to 1,404,000 cells per ml milk for the two groups representing low and high level of ESCC, respectively. Age at calving and parity are generally the second most affecting factor on TDM and ESCS. Changes in TDM and ESCC were computed at different levels of VLSSCC. In general, TDM decreased with advancing level of ESCC indicating a negative relationship. The average overall reduction in TDM was 4.01 Kg/day and the corresponding increase of ESCC was 418,670 cells per ml milk. Prediction of milk SCC was based on daily milk yield (DYKg), days in milk (DIMdays) and order of lactation (Pr). The general form is: milk SCC = 2119 -59.94*DY - 9.56*DIM - 19.43*Pr. The equation could be used for prediction under the prevailing conditions of local Holstein Friesian dairy farms. Accuracies of all suggested SCC prediction equations ranged from 57.4% to 84.8%.