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## Archivos de Zootecnia

*versión impresa* ISSN 0004-0592

#### Resumen

CRUZ, G.R.B.; RIBEIRO, M.N. y PIMENTA FILHO, E.C.. **Estimates of lactation curve parameters of cattle**.* Arch. zootec.* [online]. 2009, vol.58, n.224, pp.695-704.
ISSN 0004-0592.

The objective of this research was to identify the mathematical function that best fits the lactation curve of Guzerá and Sindi cattle. 840 lactations records (467-Guzerá, 373-Sindi) were used from animals raised at Carnauba ranch, in the town of Taperoá, Paraíba. Milk production control were taken every in 35 days, between years 1987 and 2004. Lactation records used contained a minimum of five and a maximum of ten controls. Six mathematical functions were fitted to the mean curve and individual lactations: polynomial inverse (PI), hyperbolic lineal (LH), gamma incomplete (GI), quadratic logarithmic (QL), lineal (L) and quadratic (Q) functions were fitted using an iteration process. Criteria used to verify fitting quality were: determination coefficient (R_{a}^{2}), percent of deviation between the total observed estimated productions, and percent of typical curves. Residual distribution graph were used only to evaluate fitting of mean curve. R_{a}^{2} for mean curve fitting were always larger than 0.93. Good fits were also obtained (R_{a}^{2}>0.80), in 61.4% and 66.7% of the lactations fitted by PI and GI functions, respectively, for Guzerá cattle. For Sindi cattle, these values were 57.2% and 50.0%. PI and GI, respectively, were closest to the production oscillations throughout lactation, even though estimated deviations between total productions were observed and estimated that were similar to the other functions. All studied functions fitted well means curve data. For individual lactations, however, PI and GI give better estimates of total milk yields.

**Palabras clave
:
**Lactation curves; Mathematical functions; Guzerá; Sindi.