Three random regression test day models, using Wilmink's function, first and second order Legendre polynomials, were used to fit lactation curves of the Tropical Milking Criollo (CLT) cattle. 9968 test-day records from 299 CLT cows located in the tropical low lands of the Gulf Coast of Mexico were analysed. Cows were fed mostly on grazing pastures, and milked manually once a day with the calf presence. Estimated heritabilities ranged between 0.27 and 0.48 and repeatabilities between 0.39 and 0.63 from 6 to 400 days in lactation. A high variation in genetic parameters was detected in the peripheral parts of the lactation curve. The second order Legendre polynomials model seemed to fit the data better based on residual variance and Akaike information criterion.

E. Santellano-Estrada, J. de Alba, Y. M Chang, Daniel Gianola, R. Ramirez-Valverde, C. M Becerril-Perez

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume , , 16.17, 2006
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