Effects of Level of Herd Environment. I. Relationship between Yield and Age

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Abstract
Milk records in herds producing at high, medium, and low levels were analyzed for biases in adjustments for age at freshening. A highly significant relationship between age of cow and yeild remained in the age-corrected records at all levels of environment. The bias appeared to be less marked in the high-environment herds for milk production but not for fat production. However, this apparent change in the yield-age relationship with increasing herd environment was not statistically significant. A method for predicting first-lactation from herd yield at older ages to minimize this bias and, at the same time, to provide a more efficient use of 1st lactation records for sire evaluation in small herds is described.