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Genetic and environmental aspects of the linear hyperbolic lactation curve

Evaristo Bianchini-Sobrinho^I; Francisco A. Moura Duarte^II

^IDepartamento de Ciências Exatas, Faculdade de Ciências Agrárias e Veterinárias de Jaboticabal, UNESP, 14870 Jaboticabal, SP, Brasil. Send correspondence to E.B.-S.
^IIDepartamento de Genética, Faculdade de Medicina de Ribeirão Preto, USP, 14049 Ribeirão Preto, SP, Brasil

ABSTRACT

The linear hyperbolic lactation curve was used to describe 1084 lactations of Gyr cows. Of the curves traced for each cow, 487 showed that production peaked during the first control and behaved in a practically linear manner. The asymptotes of the other curves gave an estimate of maximum total mean production for each lactation. The parameters of the curve were affected by calving season and number of milkings. The heritabilities of the characteristics of the linear hyperbolic lactation curve were of small magnitude, except for those estimated for production peak, g,, peak day and coefficient of determination. It is possible to establish a selection criterion for the highest peak value and for the lowest ßt value in order to increase total milk yield in a lactation.

Keywords: genetic; environmental; hyperbolic; lactation.

REFERENCES

Bianchini-Sobrinho, E. (1984). Estudo da curva de lactação de vacas da raça Gir. Doctoral Thesis. Faculdade de Medicina de Ribeirão Preto, USP.

Harvey, W.R. (1977). User's Guide for LSML-76: Mixed Model Least Squares and Maximum Likelihood Computer Program. Ohio State University, 76 pp.

Wood, P.D.P. (1967). Algebraic models of the lactation curve in cattle. Nature 216: 164-165.