cows are 8 to 9 years of age, a slight reduction in the
amount of milk produced occurs and the reduction
continues till their death. However, some variation
existed among breeds.
Although milk yield increased with lactation
length, yet it did not seem advantageous to have
lactation length exceeding one year. The increase in
service period also resulted in increased lactation milk
yield which may be attributed to the prolonged lactation
persistency due to absence of pregnancy stress up to
210 days in imported and 150 days in farm born
Holstein cows