title: On the analysis of Canadian Holstein dairy cow lactation curves using standard growth functions.
abstract: Six classical growth functions (monomolecular, Schumacher, Gompertz, logistic, Richards, and Morgan) were fitted to individual and average (by parity) cumulative milk production curves of Canadian Holstein dairy cows. The data analyzed consisted of approximately 91,000 daily milk yield records corresponding to 122 first, 99 second, and 92 third parity individual lactation curves. The functions were fitted using nonlinear regression procedures, and their performance was assessed using goodness-of-fit statistics (coefficient of determination, residual mean squares, Akaike information criterion, and the correlation and concordance coefficients between observed and adjusted milk yields at several days in milk). Overall, all the growth functions evaluated showed an acceptable fit to the cumulative milk production curves, with the Richards equation ranking first (smallest Akaike information criterion) followed by the Morgan equation. Differences among the functions in their goodness-of-fit were enlarged when fitted to average curves by parity, where the sigmoidal functions with a variable point of inflection (Richards and Morgan) outperformed the other 4 equations. All the functions provided satisfactory predictions of milk yield (calculated from the first derivative of the functions) at different lactation stages, from early to late lactation. The Richards and Morgan equations provided the most accurate estimates of peak yield and total milk production per 305-d lactation, whereas the least accurate estimates were obtained with the logistic equation. In conclusion, classical growth functions (especially sigmoidal functions with a variable point of inflection) proved to be feasible alternatives to fit cumulative milk production curves of dairy cows, resulting in suitable statistical performance and accurate estimates of lactation traits.
authors: Instituto de Ganadería de Montaña (CSIC-ULE), Departamento de Producción Animal, Universidad de León, 24071 León, Spain. Electronic address: s.lopez@unileon.es.
authors: S
authors: S
authors: López
authors: Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors: J
authors: J
authors: France
authors: Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors: N E
authors: NE
authors: Odongo
authors: Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors: R A
authors: RA
authors: McBride
authors: Department of Animal Science, University of California, Davis 95616.
authors: E
authors: E
authors: Kebreab
authors: Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors: O
authors: O
authors: AlZahal
authors: Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors: B W
authors: BW
authors: McBride
authors: Animal Nutrition Group, Wageningen Institute of Animal Sciences, Wageningen University, Marijkeweg 40, 6709 PG Wageningen, the Netherlands.
authors: J
authors: J
authors: Dijkstra
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000502:physiology*; D008954:Models, Biological; D010298:Parity; D011247:Pregnancy; D012044:Regression Analysis
keywords: dairy cow; growth function; lactation curve; lactation trait