Gamma-Gompertz mixture model with cure fraction to analyze data on Anglo-Nubian goats with positive EPG

Abstract

The exposure of small ruminants to gastrointestinal endoparasites is one of the main factors limiting their production, by compromising the herd’s performance because of delayed growth and mortality, among other factors. But with advancements in the treatments, an increase in the life expectancy this ruminants under-going new treatments is expected. In this paper, we present a study experimental goat herd belonging to the Agrarian Sciences Center of Federal University of Piaui (UFPI) diagnosed with positive EPG. The objective of this study was to use the approach of cure fraction models. The proposed modeling is based on the gamma-Gompertz mixture model with cure fraction model in which the frailty variable assumes the Gamma distribution and the basis risk function is Gompertz. The model proposed was suitable for this type of analysis, because besides enabling quantifying the heterogeneity not observed due to hard-to-measure factors, it was possible to identify evidence of long-term survival for some subgroups of animals while in others the survival curve approached zero with increase of useful life.