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Data consisted of 11 type appraisal traits for 51,044 Holstein first calf heif- ers with age at classification from 25 to 36 me. Effects of 10 rounds, 12 monthly ages at classification, 12 monthly stages of lactation, and 12 months (season) of classification were analyzed by least- squares. Effects of these four environ- mental factors were signifi...
Lactation records completed by 104 Holstein and 51 Ayrshire cows in the University of Guelph herd, in 1955 to 1965 inclusive, revealed a steady improvement in each breed for milk and fat yield. Maximum likelihood constants for environmental change indicated an annual increase of 3.9 and 4.0 breed age-class average (BCA) points for milk, and 2.2 and...
Age-corrected milk records of 40,374 Holstein cows tested in 1,073 herds in Ontario were studied to determine if the level of herd production had an effect on the genetic expression of milk production. Heritability of milk production was estimated from paternal half-sib correlations at each of seven levels of herd production. The estimates obtained...
The effect of days dry and days open on first, second and later lactation production was examined by intra-sire-herd-season regression. Neither variation in days dry nor days open accounted for more than 1% of the within-sire variance in fat test. Variation in preceding days dry accounted for 4.8% of the within-sire variance in milk production in s...