Effect of Sub-clinical Mastitis on Milk Yield and Composition of Dairy Goats in Tanzania

Production of dairy goats is on the increase in East African countries. As in cows, prevalence of mastitis in dairy goats appears to be high but studies on the influence of this disease on milk yield and composition are scarce. This study was, therefore, carried out to determine the effect of sub-clinical mastitis on milk yield and composition in dairy goats of Magadu dairy farm in Morogoro, Tanzania. Does were screened for mastitis using the California Mastitis Test (CMT), milk yield was recorded and 80 ml samples collected for laboratory analyses. A total of 184 quarter milk yield samples were available for analyses. Milk samples were analysed for butterfat (BF) by the Gerber method, crude protein (CP) by the Kjeldahl method, lactose by IDF Standard No.28 method and chloride by titration using silver nitrate solution. Data were analysed using least squares analysis of variance based on General Linear models procedures. The fixed effects considered were CMT score, parity, stage of lactation, sampling occasion and quarter of the udder. Sub-clinical mastitis had a significant negative effect on quarter milk yield (P<0.001). Up to 29.4% milk reduction due to mastitis was recorded. Mastitis had a significant (P<0.05) effect on quarter crude protein, butter fat and chloride percentages but not on lactose content. There was a tendency for CP and chloride percentages to increase with increase in CMT scores. However, the mean chloride value obtained in this study of 0.244 was higher than expected. Further, mastitis significantly reduced BF content of milk from 6.32 in non-mastitic does to 4.91% among those with highest CMT score. The mean lactose percentage was 3.83. Sub-clinical mastitis had no significant influence on lactose content but there was a tendency for a decrease in this component with increase in severity of mastitis. It is recommended that further studies involving a bigger number of does with clinical mastitis be carried out to substantiate the present findings. Economic losses resulting from mastitis in goats also need to be assessed.