Journal of Dairy Science, Vol 78, Issue 8 1855-1861, Copyright
© 1995 by American Dairy Science Association
Age and seasonal effects on Holstein yield for four regions of the United
States over time
H. D. Norman, T. R. Meinert, M. M. Schutz and J. R. Wright
Animal Improvement Programs Laboratory, Agricultural
Research Service, USDA, Beltsville, MD 20705-2350, USA.
Multiplicative factors to adjust Holstein yield for age and season of
calving were calculated and analyzed from 20 data files for region
and time. Regions were 1) California, 2) Minnesota and Wisconsin, 3)
New York and Pennsylvania, and 4) six southern states (Texas,
Louisiana, Mississippi, Alabama, Georgia, and Florida). Time periods
were calving years of 1964 to 1968, 1971 to 1975, 1976 to 1980, 1981
to 1985, and 1986 to 1990. The same statistical model was used that
had been used to derive current USDA factors from 1964 to 1968 data.
The number of lactation records for each data file ranged from 81,394
to 2,238,201 and increased with time. Effect of calving season on
milk yield generally decreased with time; the largest decrease was
for the southern region. Effect of calving age also generally
decreased for recent data, and the largest decreases were for
California. Updated factors to adjust yield for calving age and
season are indicated for some regions.