UBC Theses and Dissertations

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UBC Theses and Dissertations

Sources of variation affecting an alternate a.m./p.m. testing plan for dairy cows Dunn, Lorne Kendall


The feasibility of an alternate A.M./P.M. sampling scheme for testing the milk, fat, protein and lactose production of dairy cows was investigated. It was found (Part I) that the contribution of testing, sampling and compositing variances to the variance of records based on alternate and 24 hour testing schemes did not differ significantly. In Part II, it was found that additive correction factors for estimating daily yields from a single A.M. or P.M. weight were sufficient correction for all yield variables over different seasons of calving, lactation numbers, stages of lactation and individuals, but that different factors were required for different milking intervals. In addition, it was found that lactation yield estimates could be calculated by extending the alternate single sample yields over the respective test intervals and summing the results, without any significant bias, for different intervals and for all yield variables.

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