Study of Persistency of lactation and Survival of Iranian Holstein dairy cattle using Random Regression Model

The aim this paper is to investigate whether characteristics of the first lactation (FL) curve of Iranian Holstein cows is associated with survival. Cows with least 10 Test days of milk production in their FL were used. The persistency of lactation (PL) and survival were estimated using a Random Regression Model by REML with the ECHIDDNA software. We also used the Wood model to parameterize each individual lactation curve and then analyze various curve characteristics using an animal model. The EBV of the characteristics of the lactation curve of the cows from day 40-305 predicted. The EBV of the production range (PR) and the slope of line in increasing phase (m_(40,Peak)) of production curve of sires with higher survival EBV were lower than other sires (p˂0.05). The estimates of LP were independent of survival estimate. Therefore, the PR from 40th day after calving can be considered as a definition of PL. Because the lower the PR, the flatter is the milk production curve. Genetic evaluation of young bulls for survival needs the data of death or culling of their daughters. Therefore, the bulls can genetically be evaluated for survival according to the LP and m_(40,Peak) of FL information of their daughters.

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