Abstract: The present study confirmed a significant (p<0.01) decrease in total milk yield in mastitis-infected cows compared to healthy ones, during first lactation. Moreover, during the second lactation, the previously infected cows showed a significant decrease (p<0.05) in milk yield, compared to the healthy and newly infected cows. Similarly, the newly infected cows in the third lactation revealed a significant (p<0.05) decrease in total milk yield compared to those from cows infected during the three successive lactations. However, they showed a significant increase (p<0.05) compared to cows infected during, both the first and third lactations. The newly infected cows in the third lactation showed a significant decrease (p<0.05) for milk yield on 305 days compared to cows infected during first and third lactations and cows infected during the three successive lactations. The lactation length showed a significant increase (p<0.05) only, when comparing cows infected during both the first and third lactations to those infected during both second and third lactation. The peak yield, although decreased due to infection, it only showed a significant decrease (p<0.05) during the second lactation, when comparing healthy and newly infected cows with those infected previously during, both the first and second lactations. In conclusion, mastitis reduces the production performance of the cows hence attention should be directed to the control of this costly disease.