Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 1997
Publication Date: N/A
Technical Abstract: Heritabilities for milk, fat, and protein yields were estimated from first lactation Ayrshire data used for USDA-DHIA genetic evaluations. Contemporary group assignments and standard deviations within herd-year (SD) were determined with the procedure used for national evaluations. Pedigree data were included for animals born since 1970; yield data were included for cows born since 1980. Lactation records were divided into four mutually exclusive data sets based on SD; data set 1 had the lowest SD, and data set 4 had the highest. The ranges for SD were chosen to result in data sets of approximately equal size: 11,486, 11,714, 10,484, and 11,330 records for milk and fat yields and 10,069, 10,545, 9,878, and 10,964 records for protein yield. The heritabilities were estimated with Method R using 25 different random samples of half of the data for each data set. Mean heritability estimates increased with SD and ranged from 0.22 to 0.46. The current heritabilities for USDA-DHIA genetic evaluations, which range from 0.20 to 0.30 with heritability increasing as SD increases, may be too low. Procedures developed with Ayrshire data are being applied for analysis of data from other dairy cattle breeds.