24Background 25Understanding the effects of environment on livestock provides valuable information on how 26 farm animals express their production potential, and on their welfare. Ruminants are often 27 confronted with perturbations that affect their performance. Evaluating the effect of these 28 perturbations on animal performance could provide metrics to quantify how animals cope 29 with their environment and therefore better manage them. In dairy systems, milk production 30 records can be used to evaluate this effect because (1) they are easily accessible, (2) the 31 overall dynamics throughout the lactation process have been widely described, and (3) 32 perturbations often occur and cause milk loss. In this study, a lactation curve model with 33 explicit representation of perturbations was developed. 34 Methods 35The perturbed lactation model is composed of two components. The first one describes a 36 theoretical unperturbed lactation curve (unperturbed lactation model), and the second 37 describes deviations from the unperturbed lactation model. The model was fitted on 319 38 complete lactation data from 181 individual dairy goats allowing the characterization of 39 individual perturbations in terms of their starting date, intensity, and shape. 40 Results 41The fitting procedure detected a total of 2354 perturbations with an average of 7.40 42 perturbations per lactation. Loss of production due to perturbations varied between 2 % and 43 19 %. Results show that it is not the number of perturbations is not the major factor 44 explaining the loss in milk yield over the lactation, suggesting that there are different types of 45 animal response to disturbing factors. 46 Conclusions 47 * ( ) = • • − • 128where * ( ) is the unperturbed daily milk yield in kg, is the time in days after parturition 129 and , , are positive parameters that determine the shape of the lactation curve ( scales the 130 general level of the curve, controls the type and magnitude of the curvature of the function, 131 and regulates the rate of decrease in milk yield after the lactation peak). Values of these 132 parameters can be used to calculate some essential features of the lactation curve such as the 133 time of peak yield ( ⁄ , in days), the lactation persistency, i.e., the extent to which peak yield 134 is maintained (−( + 1) • ( ) in kg.d -1 ), or the peak yield ( • ( ⁄ ) • − in kg) [16]. 135Perturbation model 136