| Clinical mastitis (CM) is a production limiting disease affecting dairy cattle worldwide. Cows suffering from CM may experience a loss in milk production, reduction in rate of conception an increased risk of mortality and culling. Dairy farmers are often faced with the decision of what to do with their diseased cows; whether to keep or replace with a younger heifer. The economic model developed to assist dairy farmers with these decisions is based on dynamic programming. It was necessary to develop a pathogen specific model for several reasons: (1) The previous framework did not separate CM into the different pathogens that are causative, hence, in the past, the effects of pathogen specific CM were pooled while decisions may be pathogen specific and (2) Discarded milk due to treatment after adjusting for the loss of milk from disease was not accounted. Further, the previous framework did not have the flexibility to include additional pathogens easily. In developing this model, we estimated the effects of pathogen specific CM for inclusion in the model (i.e., risk of pathogen specific CM and risk of mortality (and culling)). Further, prior to developing a pathogen specific model, we expanded an existing generic CM model (i.e., where all CM pathogens were combined) to study the cost of 3 different types of CM i.e., gram-positive, gram-negative and other CM. Cows with more cases of CM in the previous lactation were at greater risk of bacteria specific CM in the current lactation, e.g., among multiparous cows in wim ≥ 3, cows were 2.2 times more at risk of a first case of E. coli if they had 2 cases of CM (of any type) in the previous lactation compared with no cases in the previous lactation. Among multiparous cows, cows were at greater risk of a recurrent case within the first month after the previous case of CM, unlike primipara, where these cows were at greater risk of a recurrent case within 2 months of the previous case. Among first lactation cows, the presence of a first CM case generally exposed cows to a greater risk of mortality in the current month (compared with the absence of a first case). This was especially acute with a first case of Klebsiella, where cows were 4.57 (exp(1.52)= 4.57 [95% CI (2.75, 7.61)]) times more at risk of mortality, and with a first case of E. coli with cows 3.32 times more at risk (i.e., relative risk = exp(1.20)= 3.32, [95% CI (2.46, 4.48)]. In general the presence of a first or second case resulted in cows in parity ≥2 with a greater risk of mortality (compared with cows with no first or second case of bacteria specific CM in the current month in milk). In first parity cows, the risk of culling generally increased with the presence of a case of bacteria specific CM. Among cows of parity ≥2, when a cow contracted a case of Streptococcus spp., she was more likely to be culled one month after the case of CM (regardless of whether it was a first, second or third case of Streptococcus spp.). The average costs per case (USD) of gram-positive, gram-negative and other CM were 133.73, 211.03 and 95.31, respectively. This model provided a more informed decision making process in CM management for optimal economic profitability and determined that 93.1% of gram-positive CM cases, 93.1% of gram-negative CM cases and 94.6% of other CM cases should be treated. The main contributor to the total cost per case of gram-positive CM was treatment cost (51.5% of the total cost per case), milk loss for gram-negative CM (72.4%) and treatment cost for other CM (49.2%). From the pathogen specific economic model, we determined the net returns per cow and year, with an incidence of CM (cases per 100-cow years) of 35.5 was 500 US... |
