Submitted to: NCDHIP Handbook
Publication Type: Other
Publication Acceptance Date: June 8, 1999
Publication Date: N/A
Interpretive Summary: Standardized lactation averages of cows are useful for indicating trends in production efficiency and describing cow populations. Numbers and standardized yields for lactation records started in 1997 and eligible for use in calculating national genetic evaluations were documented by State and breed. Numbers of records generally decreased over the years for all breeds. Average yields for milk, fat, and protein were at all-time highs for all seven breeds (Ayrshire, Brown Swiss, Guernsey, Holstein, Jersey, Milking Shorthorn, and Red and White) following calvings in 1997. Jerseys were the highest for percentages of fat and protein but also showed the largest declines since 1990. For the first time, this report includes lactation records computed with the best prediction method, an improved procedure that uses test-day data to predict lactation yield, instead of cumulative yield and projection factors. This report also marks the beginning of annual rather than biennial reporting and the phasing in of new adjustment factors for milking frequency. These statistics provide an important reference for comparison of State production levels and trends, and their use will aid in maintaining the competitive position of the U.S. dairy cattle population worldwide.
Technical Abstract: Means for dairy cow lactation data used in national genetic evaluations and other USDA research are useful for indicating trends and describing cow populations. Breed lactation means are on a 305-day, twice daily milking, mature-equivalent basis from cows contributing to genetic evaluations. This report includes lactation production estimated with the best prediction method for the first time. This improved procedure uses test-day data to predict lactation yield. Beginning with this report, statistics will be available each year instead of biennially. New adjustments for milking frequency are being phased in, and only a third of the difference in factors was implemented for 1997 calvings. Component percentages were computed from mean standardized milk and component yields; protein testing is at or near 100% except in California. Only information for a cow's first five lactations was included, but first-lactation data were required for any other information to be included. Numbers and mean standardized yields initiated in 1997 and eligible to contribute to genetic evaluations were documented by State and breed. Numbers of records generally decreased over time but yields for milk, fat, and protein were at all-time highs for all breeds. Component percentages relative to 1990 tended to be similar for fat and lower for protein. Jerseys remained the highest for both component percentages but also showed the largest declines since 1990.