Assessing the correlation structure in cow udder quarter infection times through extensions of the correlated frailty model
Résumé
The association between infection times of the udder quarters of a dairy cow is essential information for control of udder infections in a dairy cow herd. Extensions of the correlated frailty model are proposed to investigate and compare di erent correlation structures amongst the four udder quarter infection times of clustered within a cow. Such complex frailty models can be tted with the SAEM-MCMC algorithm. It is demonstrated that substantial correlation exists between the udder quarter infection times, with the correlation within front and rear udder quarters being larger than between front and rear udder quarters. This signi es that an infected udder quarter is a risk factor for the other udder quarters, especially when the udder quarter is in the same region, i.e., front or rear.