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Effects of Level of Herd Environment. I. Relationship between Yield and Age¹

Canada Department of Agriculture, Ottawa, Ontario

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 yield 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 first-lactation records for sire evaluation in small herds is described.

¹ Contribution No. 105, Animal Research Institute, Ottawa, Ontario, Canada.