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A Comparison of the Different Methods of Calculating Yearly Milk and Butterfat Records

Ohio State University
Louisiana State University

ABSTRACT

1. One hundred yearly Holstein and Jersey records were computed by various present-day methods of estimating their actual amounts. The standard records used for comparisons were based on actual daily milk weights and forty-eight butterfat tests during the year.
   
2. Centering-the-testing-day method showed only slight advantages over the monthly method (testing date not centered) in mean differences from the standard and its records failed in all comparisons to be as highly correlated with the standard as were the monthly records.
   
3. A systematic irregularity in testing dates tended to overcome some of the bias shown with regular testing dates and did not lower the correlation with standard records.
   
4. The use of daily milk weights tended to reduce the variability of the records when compared to the standard.
   
5. Bi-monthly tests and the use of daily milk weights resulted in records which were practically as accurate as were records from monthly and centering methods not utilizing daily milk weights.
   
6. Results of the study show only small differences between the accuracy of various methods now used by breed associations, agricultural colleges, and the Bureau of Dairy Industry, and indicate that uniform testing rules could be profitably adopted by all parties concerned.
   

^* The authors are indebted to C. C. Hayden and C. F. Monroe of the Ohio Agricultural Experiment Station for supplying the records for this problem, to C. H. Staples of Louisiana State University for his help during the course of the study, and to W. G. Cochran and J. L. Lush of Iowa State College for aid in statistical interpretations.