Lactation yield: Interval level comparison of milk records for genetic improvement in Friesian vs Arsi crossbred cows in the highlands of south eastern Ethiopia
Milk recording intervals was studied by analysing 1220 lactation records of Friesian x Arsi crossbred cows kept in south eastern highlands of Ethiopia. Milk Recording Intervals (MRI) comparison was made at 15, 30 and 45 day's length. Accuracy was measured in terms of percentage difference between actual and estimated yield, Root Mean Square Error (RMSE) and coefficient of determination (R2). The study revealed that 15, 30 and 45-day MRI can estimate lactation yield accurately to extent of less than five percent error. Lactation yield estimated by 15-day MRI was marginally more accurate with higher R2 (99.6%) and lower RMSE (34.8) values compared to 30 and 45-day MRI. Simple regression analysis indicated that yield of 9th period (121-135 days) in 15-day; the 5th period (121-150 days) in 30-day and the 3rd period (91-135) in 45-day time interval provided reliable estimate of 305-day yield. The step-wise regression analysis showed that combination of more than three records did not result in increasing the accuracy of estimates. Thus 30 and 45-day MRI can be used in the estimation of lactation yield in Friesian x Arsi crossbred cows.
Keywords: Accuracy, Lactation yield, Interval comparison, Test day