|Wright, Janice - Jan|
Submitted to: American Dairy Science Association Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/27/1999
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: A method with best prediction (BP) properties that condenses information from many test days into lactation measures of yield and persistency has been proposed as a possible replacement for the test interval method (TIM), which currently is used in the US to estimate lactation yield. Milk weights from monthly (MO), a.m.-p.m. (AP), and trimonthly (TRI) test plans, which represent extreme differences in sampling methods, were examined to compare the effectiveness of BP and TIM for estimation of lactation yield. Individual weights were from 658 Canadian Holstein cows in 17 herds. Testing intervals were from 97,878 to 99,185 US Holstein cows enrolled in traditional MO test plans. Individual milk weights or daily yields of the Canadian cows were selected to correspond to test intervals of the US cows. For estimation of AP credits, the initial milk weight for the lactation was selected randomly from the morning or evening milking and alternated thereafter on the designated test day. For TRI credits, one of the first three designated test day weights was selected randomly, and each third designated test day weight was used thereafter. Correlations between actual and TIM-estimated 305-day lactation yields were .97, .96, and .93 for MO, AP, and TRI testing, respectively. Corresponding correlations for BP were .97, .97, and .93. Standard deviation of difference between estimated and actual lactation yields for MO, AP, and TRI testing were 388, 425, and 606 kg for TIM and 373, 400, and 546 kg for BP. Thus, BP had 4, 6, and 10% greater accuracy. Advantage of BP over TIM is minimal if two milk weights are recorded monthly but is substantial if testing is less frequent. Organizations that estimate lactation yield should consider replacing TIM with a more accurate procedure.