Abstract

The objective was to estimate genetic parameters and fit lactation curves for cows treated or not treated with bovine somatotropin (bST) and fit specific lactation curves for each animal for both random genetic and permanent environmental components from individual test-day milk, fat, and protein yields with a cubic spline model. A total of 70,752 test-day observations for first lactation Holstein cows recorded as treated bST and 73,387 test-day observations for untreated cows that calved between 1994 and early 1999 were obtained from Dairy Records Management Systems in Raleigh, North Carolina. The model included herd test-day, age at first calving, bST treatment, and days in lactation when test-day yield was recorded as fixed effects. Cubic splines were fitted for the overall lactation curve, additive genetic effects, and permanent environmental effects. The cubic splines used five predetermined intervals between days 0, 50, 135,220, and 305. Estimates of the (co)variances for the random components of cubic spline model with five knots were obtained with REML. Estimates of genetic parameters were calculated for the average test day model within each of the ten 30-d test day intervals. The estimates of heritability for milk, fat, and protein yields ranged from 0.09 to 0.15, 0.06 to 0.10, and 0.08 to 0.15 for test-day one to test-day ten. Estimates of genetic correlations between testdays ranged from 0.99 to 0.34 for milk yield, 0.99 to 0.49 for fat yield, and 0.99 to 0.36 for protein yield. Estimates of phenotypic correlations between test-days ranged from 0.67 to 0.27 for milk yield, 0.52 to 0.16 for fat yield, and 0.60 to 0.19 for protein yield. Differences between bST treated and untreated cows of 2 to 4 kg and 0.10 to 0.16 kg for milk and fat yields (smaller for protein yield) at day 90 were maintained until about day 305 of lactation.

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Apr 27th, 11:30 AM

CUBIC SPLINES FOR ESTIMATING LACTATION CURVES AND GENETIC PARAMETERS OF FIRST LACTATION HOLSTEIN COWS TREATED WITH BOVINE SOMATOTROPIN

The objective was to estimate genetic parameters and fit lactation curves for cows treated or not treated with bovine somatotropin (bST) and fit specific lactation curves for each animal for both random genetic and permanent environmental components from individual test-day milk, fat, and protein yields with a cubic spline model. A total of 70,752 test-day observations for first lactation Holstein cows recorded as treated bST and 73,387 test-day observations for untreated cows that calved between 1994 and early 1999 were obtained from Dairy Records Management Systems in Raleigh, North Carolina. The model included herd test-day, age at first calving, bST treatment, and days in lactation when test-day yield was recorded as fixed effects. Cubic splines were fitted for the overall lactation curve, additive genetic effects, and permanent environmental effects. The cubic splines used five predetermined intervals between days 0, 50, 135,220, and 305. Estimates of the (co)variances for the random components of cubic spline model with five knots were obtained with REML. Estimates of genetic parameters were calculated for the average test day model within each of the ten 30-d test day intervals. The estimates of heritability for milk, fat, and protein yields ranged from 0.09 to 0.15, 0.06 to 0.10, and 0.08 to 0.15 for test-day one to test-day ten. Estimates of genetic correlations between testdays ranged from 0.99 to 0.34 for milk yield, 0.99 to 0.49 for fat yield, and 0.99 to 0.36 for protein yield. Estimates of phenotypic correlations between test-days ranged from 0.67 to 0.27 for milk yield, 0.52 to 0.16 for fat yield, and 0.60 to 0.19 for protein yield. Differences between bST treated and untreated cows of 2 to 4 kg and 0.10 to 0.16 kg for milk and fat yields (smaller for protein yield) at day 90 were maintained until about day 305 of lactation.