Survival analysis of Simmental cows was depending on the year of birth

Abstract

Longevity of cows is the most economically important characteristic in dairy cattle breeding, so studies aimed at an earlier assessment of the productive life expectancy of dairy cattle are relevant. The total population of Simmental cows was 23 587 animals, the study period covered 1999–2017. Survival analysis was carried out using the Survival Kit v6.1 program, using the Cox regression model. It has been established that the greatest impact on the survival of Simmental cows is exerted by the level of milk productivity, and its increase above the median values, that is, more than 6362 kg of milk in the period 2011–2017, increases the risk of Simmental cows leaving. In the general population has seen an increase in productivity — from 3865 kg of milk in the period before 2004 to 6362 kg in the period 2011–2017. Analyzing the survival graphs of Simmental cows in different time periods, it was found that in each subsequent generation, the survival of cows increases by an average of 19.1–21.0% or from 713 to 1029 days. This is due to an increase in the level of feeding, housing conditions and better work of the veterinary service. The studies conducted to analyze survival to assess the productive longevity of Simmental cows are being conducted in Russia for the first time and are of an exploratory nature. The use of the Cox regression method simplifies calculations and facilitates genetic and non-genetic studies of longevity in dairy cows, which will subsequently allow this indicator to be included in the general selection index.