الفهرس 
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Abstract
400 individual quarter milk samples collected from 120 cows showing clinically sound udders secreting apparently looking normal milk. The animals were randomly selected from three dairy farms of Dakhlia Governorate (Shoha, el-Baramoun and El-Youssifia Farms) collected samples firstly subjected to California mastitis test as first screening test for detection of subclinical mastitis milk at the farm. The positive California mastitis test milk samples subjected immediately for confirmatory screening tests (catalase, direct microscopic somatic cell count
”D.M.S.C.C”) as well as microbiological examination for
detection and isolation of mycoplasmataceae and Acholeplasmataceae.
The obtained findings revealed that 150 (37.5%) out of 400 quarter milk samples proved to be suffering from
subclinical mastitis with different positive scores of California mastitis test. The correlation between positive California mastitis and microbiological positive results, in (1+) score the number of Acholeplasma positive samples were 2 (2.4%) of 85 milk samples, in (2+) score was one (2.9%) of 35 milk samples, while in (3+) scores were 22 (73.3%) of 30 milk samples. Therefore, California mastitis test with scores (3+) more sensitive and reliable than scores (1+) and (2+) for detection of subclinical mastitis. Regarding the correlation between different scores of positive catalase test and microbiological positive samples. It is clear that the quarter milk samples which liberated 2 ml oxygen by catalase test were Acholeplasma free and the correlation between catalase test and micro-biological results were 6.12% (3/49), 9.1% (6/66) and 80% (16/20) when catalase test was 2-3, 3-4 and >4 cc oxygen, respectively. Meanwhile, the catalase test with score (>4 cc oxygen) is considered as a decisive test for subclinical diagnosis. The correlation between direct microscopic somatic cell count test and the incidence of Acholeplasmas indicated that quarter milk samples showed somatic cell count less than 5x105 cells per ml of milk proved to be free from microorganisms, while most of milk samples which had somatic cell count more than 5x105 cells per ml of milk proved to be Acholeplasma positive. when direct microscopic somatic cell count was 5x105-106 and >106 cells per ml of milk, the number of Acholeplasma positive samples were 3 (8.1%) of 37 and 22 (84.6%) out of 26, respectively
Direct microscopic somatic cell count (>106 cells per ml of milk) strongly related with microbiologically positive samples (84.6%) followed by catalase test (80.0%) when the amount of oxygen >4.0 cc, while the California mastitis test (3+ score) revealed the comparatively least percentage (73.3%). It could be concluded that direct microscopic somatic cell count (>106) cells per ml of milk had the best screening test in comparison with Acholeplasma isolates used for detection of subclinical mastitis.
Acholeplasmas were recovered from’25 (16.7%) of 150 quarter milk samples showing subclinical mastitis. Acholeplasma laidlawii constituted the majority of the isolates 13 (8.7%) followed by Acholeplasma axanthum and untypable Acholeplasma each of them was 4% (6/150), mixed infection was not detected. Acholeplasma proved to be failed to recover laboratory pasteurization of artificially contaminated milk using laboratory pasteurizer and also it is considered as an acid intolerance during the manufacturing of yoghurt. Suggestion programmes for controling of mastitis among dairy animals by veterinarians are discussed.