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Lactation Studies. IV. Accuracy of Different Methods of Estimating Lactation Yields^{1, 2,}

Department of Dairy Science, State College of Washington, Pullman

ABSTRACT

Previous papers in this series have described effects of gestation (6), estrus (7) and other causes of daily variation (8) in yields of dairy cows. These studies were felt necessary as a prelude to studying variations in estimating lactation yields by various methods.

Accepted methods for recording yields of cows have gradually changed over the years. The 7-day test was shown by Yapp (17) to be a poor indicator, while Gaines (9) later showed that 7-day tests conducted after 60 days in lactation were more indicative as an estimate of lactation yields. M'Candlish and M'Vicar (12) found that a 1-day test per month yielded results within 2 per cent of actual yield, and Dick (5) observed an average error of 2.32 per cent from actual when cows were tested at 28-day intervals. Houston (11) found that weekly test intervals gave estimated yields approximating actual, and that to keep errors within a range of 10 per cent the testing interval should not exceed 30 days.

¹ Scientific Paper no. 1133, Washington Agricultural Experiment Stations, Pullman. Project no. 1077.

² Acknowledgment is made to W. T. Southworth for assistance with the I.B.M. analyses of data used for this study.

³ On military leave of absence.