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Title: Derivation of factors to estimate daily, fat, protein, and somatic cell score from one milking of cows milked three times daily

Author
item SCHUTZ, MIKE - Purdue University
item Norman, H

Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/8/2010
Publication Date: 6/24/2010
Citation: Schutz, M., Norman, H.D. 2010. Derivation of factors to estimate daily, fat, protein, and somatic cell score from one milking of cows milked three times daily. Journal of Dairy Science. 93(E-Suppl. 1):595(abstr. W31).

Interpretive Summary:

Technical Abstract: The objective was to derive factors to predict daily fat (F) and protein (P) yield and somatic cell score (SCS) when milk is sampled once per d for cows milked three times (3x) per d. Daily milk weights were recorded automatically and samples were collected from 8 herds for each milking on test-day by Dairy Herd Improvement personnel. Following edits, 1721 records of 1236 first lactation (L1) cows and 2704 records of 1940 later lactation (L2) cows remained. Factors currently in use to adjust single milking F and P for milking interval (MINT) were applied. No adjustments are currently in use for SCS. Also, 2 methods were compared to estimate factors or equations to predict daily F, P, and SCS. Factors were estimated as the ratio of the sum of daily yield to the sum of partial yield within a parity-MINT class (13 intervals in 2 parities) [Method 1] or as the sum of the ratios of daily yield to partial daily yield for each cow-day divided by the number of cow-days within parity-MINT class [Method 2]. Resulting factors from both methods were smoothed, applied to data, and residuals were regressed on days in milk (DIM). Regression equations (n=112) were also developed within parity-MINT-DIM classes (2x7x8) [Method 3] to jointly account for MINT and DIM. Separate factors were derived for milking 1, 2, and 3 for each trait in L1 and L2. Method 3 resulted in consistently stronger correlations between estimated and actual yields, and smallest variances of estimates, and root mean squared errors (rMSE) for all components in milkings 1, 2, and 3 in L1 and L2. Method 3 resulted in rMSE of 0.14 (F, L1), 0.22 (F, L2), 0.09 (P, L1), and 0.14 (P, L2) kg for milking 1; compared to rMSE of 0.18, 0.27, 0.12, and 0.16 kg from current factors for the same traits in L1 and L2. Differences in rMSE were similar for F and P for milking 2 and 3 and for SCS for all milkings. Work is ongoing to determine whether equations from Method 3 will allow accurate estimation of daily milk, F, P, and SCS when applied to other herds.