Cox-Gompertz model for analysis of the time of stay in an Anglo-Nubian goat herd

Abstract

Anglo-Nubian goats are hardy animals able to adapt to tropical environments, where their farming is usually held on pasture. However, climatic conditions in this environment also favor endoparasitism, which implies a negative aspect if sensitivity to worm infections interferes by reducing the reproductive lifespan of females, as their stay in the herd is a trait of great importance for efficient goat farming. In this respect, this study proposes to use the survival analysis methodology with the Cox-Gompertz proportional hazards model to assess the length of stay in the herd by relating the removal of females due to death with worm infection being the main cause to other forms of culling, using information from 101 Anglo-Nubian goats born from 2009 to 2013 in an experimental herd from Teresina - PI, Brazil. The Cox-Gompertz proportional hazards model chose body condition score, birth weight and birth season as important covariates (p-value ≤ 10%). Body condition score showed to be a favorable factor for the longer stay of the goats in the herd. Eggs per gram, age at first kidding, birth type and dam age were not significant. The Cox-Gompertz proportional hazards model is suitable for fitting the statistical model to estimate the length of stay in the herd, with censoring related to endoparasitism in Anglo-Nubian goats.