The practical application of age conversion factors to dairy cattle production (butterfat) records

Abstract

1. From an analysis of the records from 702 cattle of predominating Jersey type tested for at least six consecutive years under normal and average herd conditions in New Zealand, the authors have attempted a detailed study of the nature of the increase in production according to age.2. They are unable to find any evidence supporting the theory that increase in production for dairy cattle operates as a percentage addition from early age to maturity.3. The evidence secured from an analysis of 702 Jersey records of six consecutive lactations commencing at 2 years of age, strongly suggests that the increase in production according to age can be summarized neither by a percentage addition nor a constant addition alone, but is best represented by a regression formula of the nature X = aY + b, where X equals the maturity production and Y the immature production.4. The strict regression formula will probably change according to the interpretation of “maturity equivalent”, but in general its application should lose little of the simplicity of the ratio form of conversion.