Bovine respiratory disease (BRD) is an ongoing and costly issue for the dairy industry. An early study on the incidence of this disease in Ontario dairy herds reported that 15% of heifer calves were treated for respiratory disease prior to weaning, with a case fatality rate of 5% (Waltner-Toews et al., Reference Waltner-Toews, Martin and Meek1986a). More recently, a Saskatchewan study reported 40% of calves less than 6 months of age were diagnosed with BRD by producers (Van Donkersgood et al., Reference Van Donkersgoed, Ribble, Boyer and Townsend1993). Researchers and producers continue to focus on prevention and early detection of this disease. The value of prevention cannot be overestimated, given that every case of BRD impacts the welfare of the affected calf and is costly for producers. However, the best practices do not guarantee elimination of this disease. Focusing on caring for animals affected with this disease presents an opportunity to minimize the associated animal welfare and economic costs.

During clinical disease, affected calves experience many symptoms which result in compromised welfare such as dyspnea, coughing, anorexia and depression (Mellor and Stafford, Reference Mellor and Stafford2004; Kahn, Reference Kahn2005). After the acute phase of BRD, calves may become chronically ill. These animals may have pulmonary abscesses or fibrinous pleuritis, which will result in prolonged suffering and may be severe enough to lead to death in the affected animal. All of these factors combined make BRD a critical welfare challenge on farms.

The cost of rearing replacement heifers is the second largest operating expense on Ontario farms and BRD can be a significant contributor (Rodenburg, Reference Rodenburg2000). The direct costs of treatment and prevention of this disease have been estimated at US$14.71 per calf per year for milk fed calves, US$1.95 per calf per year for replacement heifers and US$9.08 per cow per year over the entire herd (Kaneene and Hurd, Reference Kaneene and Hurd1990; Miller and Dorn, Reference Miller and Dorn1990). However, perhaps the most significant and underestimated cost of this disease is the long-term effect on the health and growth of calves. Some of these costs of respiratory disease in young calves include decreased growth (Donovan et al., Reference Donovan, Dohoo, Montgomery and Bennet1998), delayed time to first calving (Correa et al., Reference Correa, Curtis, Erb and White1988; Warnick et al., Reference Warnick, Erb and White1994) and increased risk of dystocia (Warnick et al., Reference Warnick, Erb and White1994). In addition, calves treated for BRD before 3 months of age are 2.5 times more likely to die after 90 days of age than calves not treated for BRD (Waltner-Toews et al., Reference Waltner-Toews, Martin and Meek1986b).

It is evident that dairy producers are willing to take steps to prevent BRD through management changes. However, there is a lack of guidelines and direction for appropriate changes. The importance of minimizing stress in order to prevent immune suppression is clear, but the practical methodology is not obvious (Carroll and Forsberg, Reference Carroll and Forsberg2007). For example, some dairy producers are attempting to minimize post-weaning stress by removing dividers between individual stalls in the nursery to form groups prior to movement to the heifer rearing barn. From economic and labor standpoints, most nursery barns are not designed to house weaned calves for extended periods of time. Thus, in order to adopt this practice, producers have to make important decisions with limited information. Currently, the benefits of grouping calves in the nursery 1 week prior to movement to a new facility are being investigated. However, this is only the first step towards creating practical science-based guidelines for producers. Factors such as the effective group size and the timing as to when calves should be grouped are unknown. Of equal importance is identifying simple indicators for detecting calves that fail to adapt to a new environment, and are at risk for the development of disease. These behavioral indicators of poor growth and subclinical disease are emerging (Todd et al., Reference Todd, McKnight, Millman, Duffield and Leslie2006; Todd, Reference Todd2007; Borderas et al., Reference Borderas, De Passillé and Rushen2008; Stanton et al., Reference Stanton, Leslie, Kelton, Dingwell, Widowski, LeBlanc and Millman2008a, Reference Stanton, Kelton, Leslie, LeBlanc and Millman2009a, Reference Stanton, Kelton, Leslie, LeBlanc, Hester and Millmanb). Yet, there is considerably more work to be completed in order to make this information practical for implementation by producers.

The extensive welfare and economic costs associated with BRD are daunting. However, it should be possible to manage and minimize these costs. Early identification of sick animals can reduce the number of re-treatments necessary, which will reduce both the treatment costs and the length of time calves are suffering from dyspnea (McGuirk, Reference McGuirk2008). The long-term effects of these diseases must be closely monitored. An easy system for long-term monitoring of BRD recovery is to chart growth to identify calves with poor performance (Stanton et al., Reference Stanton, LeBlanc, Dingwell, Kelton, Millman, Wormuth and Leslie2008b). Although this approach would require a change in the way many producers manage calves, there is a potential for many benefits. If calves are weighed at regular intervals, it is possible to identify calves that are not achieving appropriate weight gains. With this information, intervention could be undertaken. However, the appropriate interventions are not always clear. If a calf is not achieving acceptable rates of gain, due to an abscess or fibrinous pleuritis, this calf should be assessed to determine if further recovery is possible. If the damage to the lung is extensive, and the calf is suffering and unable to recover, euthanasia may be the most appropriate and humane solution. However, if there is only minimal lung damage, and the calf is gaining at lower rates due to increased energy demands or a lower dominance status that restricts its access to resources, moving affected animals to a less competitive environment may allow calves to recover and mitigate some of the long-term effects of this disease. The extended time period between diagnosis of BRD and some of its outcomes, such as dystocia, has the potential to be an economic drain. However, if this situation is identified early, there may be an opportunity to minimize or prevent these outcomes.