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

item Norman, H

Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/5/2009
Publication Date: 7/12/2009
Citation: Schutz, M.M., Bewley, J.M., Norman, H.D. 2009. Derivation of factors to estimate daily fat, protein, and somatic cell score from one milking of cows milked twice daily. Journal of Dairy Science. 92(E-Suppl. 1):209(abstr. T37).

Interpretive Summary:

Technical Abstract: The objective was to derive factors to predict daily fat (F) and protein (P) yield or somatic cell score (SCS) when milk is sampled once for cows milked twice per d. Milk samples were collected for each milking on test-day by Dairy Herd Improvement personnel from herds recording milking times and milk weights automatically. Following edits, 2190 records of 1869 first lactation (L1) cows and 3363 records of 2931 later lactation (L2) cows in 25 2x herds 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, 3 methods were compared to estimate factors or equations to predict daily F and P. Factors were estimated as the ratio of the sum of daily yield to the sum of partial yield within a parity-MINT class (24 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 am and pm milking. Method 3 resulted in consistently stronger correlations between estimated and actual yields, smallest variance of estimates, and smallest root mean squared error (rMSE) for all traits in both milkings in L1 and L2. Method 3 resulted in rMSE of 0.12 (F, L1), 0.17 (F, L2), 0.07 (P, L1), and 0.10 (P, L2) kg for am milkings; compared to rMSE of 0.15, 0.20, 0.08, and 0.11 kg from current factors for the same traits in L1and L2. Differences were similar for F and P for the pm milkings and for SCS for both 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.