Modeling Extended Lactations of Dairy Cows

Abstract

Nine mathematical models were compared for their ability to predict daily milk yields (n = 294,986) in standard 305-d and extended lactations of dairy cows of Costa Rica. Lactations were classified by parity (first and later), lactation length (9 to 10, 11 to 12, 13 to 14, 15 to 16, and 16 to 17 mo), and calving to conception interval (1 to 2, 3 to 4, 5 to 6, 7 to 8, and 9 to 10 mo). Of the nine models, the diphasic model and lactation persistency model resulted in the best goodness of fit as measured by adjusted coefficient of determination, residual standard deviation, and Durbin-Watson coefficient. All other models showed less accuracy and positively correlated residuals. In extended lactations, models were also fitted using only test-day records before 305 d, which resulted in a different ranking. The diphasic model showed the best prediction of milk yield in standard and extended lactations. We concluded that the diphasic model provided accurate estimates of milk yield for standard and extended lactations. Interpretation of parameters deserves further attention because of the large variation observed. As expected, the calving to conception interval was found to have a negative effect on milk yield for cows with a standard lactation length. In extended lactations, these negative effects of pregnancy on milk yield were not observed.

Analysis of lactation shapes in extended lactations

“…However, a marked difference in persistency can be observed between 200 and 305 DIM, especially for MY. Such a difference, reported by several authors (Bertilsson et al, 1997;Vargas et al, 2000;Dematawewa et al, 2007) may be explained by the effect of pregnancy on milk production, that results in a reduction of yield and in a change of milk composition around the 6th month of gestation (Bertilsson et al, 1997;Brotherstone et al, 2004).…”

“…For example, more than 55% of US Holsteins have lactations longer than 305 days and about 25% of cows in Costa Rica are dried off after 330 days of lactation (Vargas et al, 2000). An overall increase of lactation length of 30 days for the last decade has been estimated by Gonzalez-Recio et al, (2004).…”

“…Till the early 2000s, most literature dealing with lactation curve modelling was focused on the standard length and models have been basically conceived to fit 305-day lactation patterns. Vargas et al (2000) fitted some of the most popular functions to extended lactations, obtaining the best performances for the diphasic model. Grossman and Koops (2003) further developed the multiphasic approach.…”

Utilização de funções matemáticas no estudo da curva de lactação em caprinos

“…Diversos autores têm estudado essas funções, principalmente em bovinos (Cobby & Le Du, 1978;Shanks et al, 1981;Papajcsik & Bodero, 1988;Sherchand et al, 1995;Freitas et al, 1997;Bueno et al, 1998;Oliveira, 1999;Cobuci et al, 2000;Vargas et al, 2000).…”

“…Os resultados deste estudo podem ser usados em modelos bioeconômicos, para determinação de estratégias de acasalamento tanto para cabras quanto para vacas (Vargas et al, 2000).…”