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Comparison of parametric, orthogonal, and spline functions to model individual lactation curves for milk yield in Canadian Holsteins

Macciotta, Nicolò Pietro Paolo and Miglior, Filippo and Dimauro, Corrado and Schaeffer, Lawrence R. (2010) Comparison of parametric, orthogonal, and spline functions to model individual lactation curves for milk yield in Canadian Holsteins. Italian Journal of Animal Science, Vol. 9 (4), p. 460-464. eISSN 1828-051X. Article.

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DOI: 10.4081/ijas.2010.e87


Test day records for milk yield of 57,390 first lactation Canadian Holsteins were analyzed with a linear model that included the fixed effects of herd-test date and days in milk (DIM) interval nested within age and calving season. Residuals from this model were analyzed as a new variable and fitted with a five parameter model, fourth-order Legendre polynomials, with linear, quadratic and cubic spline models with three knots. The fit of the models was rather poor, with about 30%-40% of the curves showing an adjusted R-square lower than 0.20 across all models. Results underline a great difficulty in modelling individual deviations around the mean curve for milk yield. However, the Ali and Schaeffer (5 parameter) model and the fourth-order Legendre polynomials were able to detect two basic shapes of individual deviations among the mean curve. Quadratic and, especially, cubic spline functions had better fitting performances but a poor predictive ability due to their great flexibility that results in an abrupt change of the estimated curve when data are missing. Parametric and orthogonal polynomials seem to be robust and affordable under this standpoint.

Item Type:Article
ID Code:5700
Uncontrolled Keywords:Test day model, residuals, legendre, polynomials, splines
Subjects:Area 07 - Scienze agrarie e veterinarie > AGR/17 Zootecnica generale e miglioramento genetico
Area 07 - Scienze agrarie e veterinarie > AGR/19 Zootecnica speciale
Divisions:001 Università di Sassari > 01 Dipartimenti > Scienze zootecniche
Copyright Holders:© Nicolò P. P. Macciotta et al., 2010 Licensee PAGEPress, Italy
Deposited On:07 Mar 2011 11:05

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