الفهرس 
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Abstract
In our study, we evaluated the bacteriological findings before dry therapy were very high as Staphylococcus aureus was the most common bacteria in examined groups as it was isolated from 31 cows, followed by Streptococcus spp. as it was isolated from 30 cows then E. coli isolated from 23 cows while coagulase negative staphylococci could be detected in 9 cows. The non lactating (dry) phase of the dairy cow is specific period between active lactating phases when the mammary gland changes dynamically both in structure and function. During dry period, elimination of infection is more likely than during lactation as the drug is not milked out and higher and more uniform concentration of antibiotic is maintained in the udder in addition there are no economical losses due to discarding of antibiotic in milk. This study found that there was a difference between the four different dry cow treatments (DCT) and their effectiveness in reducing intramammary infections (IMI). First three treatments were applied during dry period only to eliminate microbial population causing mastitis such as Staphylococcus spp. and Streptococcus spp. Dry cow therapy continues to lower significantly the rate of new dry period intramammary infection in herds with elevated somatic cell counts and a high prevalence of infection. The most effective treatment was applied in group 4 which showed decrease in infection rate, decrease in occurrence of clinical mastitis next lactating season, increased in milk production and this point is important from the economic view of dairy farms. This increase in milk production is due to decrease of infection rateand decrease of clinical mastitis which lead to improve udder tissue thus increasing its ability to produce milk. On the basis of these finding, spiramycin is indicated for the treatment of gram positive bacteria especially staph. aureus in subclinical mastitic cows at dry period as shown in our results in 1st , 3rd and 4th group. Spiramycin remain effective against staph. Aureus by inducing rapid breakdown of polyribosomes, an effect which has formerly been interpreted as occurring by normal ribosomal run-off followed by an antibiotic–induced block at or shortly after initiation of a new peptide. Comparing to the different regiems of dry cow therapy in our study reflect to us that the lowest results for cure rate and level of milk production moreover the appearance of new infected quarters for the same treated cows in next milking season were in the first group which treated with spiramycin only as two injection, 24 hours interval due to that the level of spiramycin in the milk was 125, 111.6, 68.2 and 25.2 in 4, 7, 14 and 21 respectivelly in mastitic cows and these level are under the MIC of staph. aureus (>32 mg/L) and strept spp. (0.125- 1 mg/ml). So spiramycin be more effective in first 6-24 hrs, however spiramycin injection has synergistic effect with ceftifure as intramammry to obtain more recovery rate, more milk production and sure less new clinical cases in the next milking season. Spiramycin at this high concentration act as bactericidal so it has a synergistic effect with ceftiofur which inhibit the formation of the cell wall of the bacteria, therefore, the most recovered animal and more increasing in the milk production in the 3rd and 4th group.