Optimal Replacement Policies and Economic Value of Clinical Observations in Sow Herds Optimal Replacement Policies and Economic Value of Clinical Observations in Sow Herds 2 3

25 Even though several sow replacement models have been published, integrating 26 information about the health status of sows has not yet been handled satisfactorily. This 27 paper presents a framework for integrating a Weak Sow Index (WSI) into an existing 28 sow replacement model. The WSI, which is developed as part of this study, quantifies 29 various clinical signs into one numerical value representing the risk of a sow to be 30 involuntarily culled. The objective of the study is to investigate the effect of observing 31 clinical signs of sows on the optimal replacement policy. A second objective is to 32 estimate the economic value of observing clinical signs of individual sows. Bayesian 33 networks are used to develop the WSI models for lactating and pregnant sows, 34 respectively. The optimization of the replacement policy is done in a multi-level 35 hierarchical Markov decision process. To illustrate the behaviour of the model, the 36 effect of the WSI on the replacement policy, and the economic benefit of observing 37 clinical signs of individual sows are investigated in two fictitious herds with a high and 38 a low risk of involuntary culling of sows. In general, the value of the WSI has a high 39 influence on the optimal replacement policy, allowing for a better economic 40 classification of sows when taking information about the health status into account. It is 41 shown that the economic value of the WSI is higher in a high risk herd compared to a 42 low risk herd. Among the individual clinical signs, "unwillingness to stand" made the 43 lowest contribution to the economic value of the WSI. The highest contribution was 44 made by the clinical sign "vulva bite" in pregnant sows. 45 46 47