Effect of Aetiological Agents of Mastitis on Milk Composition and Milk Yield of Friesian Cattle in Sudan

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Ibtisam EL Yas Mohamed, EL Zubeir
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A monthly comparison of clinical and subclinical mastitis to the total incidence (July 1990-June 1992) was carried out. California Mastitis Test (CMT) score and bacteriological analysis were used for the evaluation of the incidence of mastitis among 99 diseased cows (49 cows during summer and 50 cows during winter) and ten healthy cows. During the period of 12 months the incidence of subclinical mastitis increased as compared to the clinical form of the disease. In winter, the subclinical mastitis recorded higher incidence while in summer clinical mastitis was the predominant form. Most of these incidences were found as mixed infection, with the predominant organisms being S.aureus (23.56%), S. epidermidis (14.37%), Actinomyces pyogenes (9.77%), Escherichia coli and K. aerogenes (8.62%) which were isolated only during summer. Other isolated organisms were micrococci (12.64%), Acinetobacter antratus (7.47%), B. cereus (6.90%), B. subtilis (4.60%), B. spp. (2.30%) and yeasts (3.45%). When the composition of mastitic cow's milk was compared with that from normal cows, highly significant changes were obtained (P<000l) in total solids, caseins, ash, chloride, lactose and casein number. There was a significant decrease in fat (P<0.0l) and total proteins (P<0.05) contents. There was a slight change in Koestler value (P<0.05). The differences between maximum, minimum, and mean values of healthy and mastitic cows were demonstrated for these parameters. The types of bacteria isolated showed significant change only with lactose (P<0.0l) and acidity (P<0.05). There was a non-significant effect on chloride (P<0.05). The severity (level) of disease as measured by CMT had a significant effect on caseins (P<0.0l), lactose (P<0.00l), total solids (P<0.0l), chloride (P<0.00l), Koestler value (P<0.0l) and ash (P<0.0l). Similarly, the variation of season affected caseins, whey proteins and ash (P<0.00l), total protein (P<0.05) and fat percent (P<0.05) of mastitic cow's milk. The interaction of types of bacteria and CMT score had a significant effect on chloride (P<0.00l) and lactose (P<0.05). The interaction of bacterial types and season affected caseins, and whey proteins (P<0.00l), acidity (P<0.0l) and fat percent (P<0.05). A total of 99 mastitis infected cows were studied and from the records, their weekly milk yield before, after and during infection were evaluated. The milk yield of ten mastitis free cows (according to CMT and microbiological analysis) was compared with that of infected cows. A significant reduction of milk yield (P<0.00l) was observed as a result of mastitis. Milk production never returned to the pre-infection level. The amount of reduced milk yield was found to be dependent on the stage of lactation in which infection occurred. It was concluded that, the earlier the cows contracted the infection during lactation, the greater the loss in milk yield. The cost of discarded milk (a total of 54543 litres), the cost of drugs used during the study (422812.121 Sudanese pounds) and the total number of animals being culled because of mastitis (36%) were determined; also the fate of the individual examined cows was reported. In another trial, milk and blood serum samples from clinically infected cows, sub clinically-infected cows and healthy cows (15 cows each) were evaluated for total bacterial counts, minerals and enzymes levels. The sub clinical mastitis showed significant effects on viable counts (P<0.05) and potassium and sodium levels (P<0.0l). The clinical form of the disease showed similar changes of viable bacterial counts and calcium (P<0.0l) and contents of sodium, potassium and magnesium. In normal milk samples the significant changes were in potassium (P<0.0l) initially and after three weeks of the first collection. Potassium and zinc changed (P<0.05) in sub clinically- infected cow's serum, in the clinically-infected blood serum samples calcium and phosphorus changed (P<0.0l) and zinc also changed (P<0.05). When comparing normal milk samples to those with subclinical mastitis, the changes were in sodium, calcium and magnesium (P<0.00l), potassium and zinc (P<0.0l), and copper (P<0.05). Comparison between normal and clinical mastitis' milk samples revealed non-significant changes (P>0.05) in phosphorus and copper, while that of subclinical and clinical mastitis revealed highly significant changes in calcium (P<0.00l), sodium (P<0.0l) and potassium, copper and zinc (P<0.05). The coefficient of variation for Glutamate oxaloacetate (GOT) and Lactate dehydrogenase (LDH) obtained during the present study, increased in values with intensity of infection, while the coefficient of variation for alkaline phosphatase (AP) was higher in subclinical mastitis cases compared with the clinical ones. Correlations between minerals and enzymes levels in both milk and blood serum of normal, subclinical and clinically infected cows were presented.
Aetiological Agents,Mastitis, Milk Composition,Milk