Has the disease changed?

BRD is a disease complex that results from the interaction of numerous pathogens that combine in varied manners in all cattle production sectors (Taylor et al., Reference Taylor, Fulton, Lehenbauer, Step and Confer2010). One possibility is that the disease (one or some of the specific pathogens) has changed in terms of prevalence, incidence, or virulence in one or more cattle production sectors. This could be due to the natural evolution of the pathogen(s) or due to some novel expression of the pathogens resulting from new combinations or changes in the timing of pathogen exposure. Certainly, this is a question for animal health professionals and is beyond the scope and theme of this paper but is a possibility that must be considered in this discussion.

Have cattle production practices changed?

Cattle weights continue to increase over time as a result of genetic improvement, feeding technology, and management changes. Rapid change in cattle genetics in the past two decades allows cattle to grow rapidly and longer thus resulting in larger cattle. Cattle have been getting bigger for many years but the pace of increase has been faster recently. For example, steer carcass weights have increased an average of 4.3 pounds year⁻¹ in the 50 years from 1969 to 2018. This is an increase from about 680 to 883 pounds, an increase of 30% from the beginning to the end of the period. In the past 25 years, average steer carcass weights have increased 5.3 pounds year⁻¹. Heifer carcasses have increased somewhat faster than steers, increasing an average of 5.2 pounds year⁻¹ in the past 50 years, from about 574 to 814 pounds, a 42% increase. Heifer carcass weights have increased an average of 5.3 pounds year⁻¹ in the last 25 years (Drouillard, Reference Drouillard2018).

Facilitated by genetics, much of the continued growth in cattle size has resulted from the implementation of feeding technologies. Aggressive use of growth promotants, ionophores, and β agonists have accounted for much of the increased cattle performance in the past 25–30 years (Drouillard, Reference Drouillard2018). It has been noted anecdotally that some ‘high-performance’ cattle seem to be at higher risk of health wrecks during backgrounding and feeding, but confirmational research is not currently available. Is it possible that increasingly intensive cattle production systems are responsible for increased health challenges in cattle?

Management factors and environmental conditions are well known to contribute to BRD incidence and impacts. Weaning, commingling, crowding, shipping, and processing are all stressors that increase the likelihood of BRD impacts. Inclement and variable weather, both heat and cold, diurnal temperature changes, wet, dusty, or other weather conditions often aggravate or exaggerate disease impacts (Taylor et al., Reference Taylor, Fulton, Lehenbauer, Step and Confer2010). While weather conditions are beyond control, changes in management practices could result in changes in observed BRD impacts. However, no broad-based changes in the industry's use of these practices are apparent at this time.

Cattle demographics can impact the observed general cattle health situation. On average, feedlot steers have lower morbidity and mortality compared to heifers (Stehle et al., Reference Stehle, Peel and Riley2018). Lighter weight animals placed in feedlots typically have higher morbidity and mortality (Stehle et al., Reference Stehle, Peel and Riley2018). Because of the nature of annual cattle production, there is a normal seasonal pattern of cattle age and gender demographics each year. Additionally, cattle numbers and changes have longer term cyclical or trend impacts on the demographics and composition of cattle flow across sectors (Drouillard, Reference Drouillard2018). The beef cattle industry has experienced herd growth since 2014, the first significant expansion in cattle numbers in 20–25 years. The dynamics of cattle cycles have numerous implications on cattle demographics and the average animal health situation.

Heifer retention to support herd expansion in recent years resulted in significant reductions in heifer flows through stocker and feedlot production (Peel, Reference Peel2018). This resulted in the heifer percentage of total yearling slaughter in 2016 at the lowest levels since 1974. Overall cattle numbers also impact the age demographics of cattle production flows. With increasingly limited cattle supplies prior to 2014, feedlots were often forced to utilize younger and smaller animals, which often meant increased cattle morbidity and mortality (Peel, Reference Peel2018). Growing feeder cattle supplies in recent years allows feedlots to focus more on preferred cattle in terms of weight, age, and management background. Normal seasonal and particularly cyclical herd dynamics impact herd demographics and the observed average health status of the industry at any point in time.

Has overall cattle health changed?

Is it possible that overall cattle health has changed over time? While there is no definitive evidence to support such a conclusion, there are indications that merit consideration. For example, research on fetal programming has shown that cow nutrition during gestation has post-natal impacts on calf health and productivity (Summers and Funston, Reference Summers and Funston2013). That, combined with the fact that cow weights have increased over time, raises at least the possibility of increased nutritional stress on cows during gestation in some or many situations with subsequent impacts on overall cattle health.

Disease characteristics

The fact that BRD is a complex involving numerous pathogens, interacting in a variety of ways, in a wide range of environmental and management conditions and across multiple production sectors, significantly increases the challenges of understanding the many manifestations of the disease. There appears to be little agreement about the relative role and contributions of various pathogens and as a result, little agreement on the priority of pathogen-specific control.

Bovine viral diarrhea virus (BVDV) has undoubtedly received the most individual attention and for good reason. BVDV is known to originate at the cow–calf level and has the singular characteristic of producing persistently infected (PI) animals that act as a reservoir of virus exposure across all production sectors. BVDV is usually not the ultimate cause of mortality in cattle but the immunosuppressive impact of BVDV increases the likelihood and severity of infections by other BRD organisms (Taylor et al., Reference Taylor, Fulton, Lehenbauer, Step and Confer2010). However, there is little consensus regarding how much, if any, overall BRD impacts would be reduced if enhanced BVDV control could be achieved.

Complex industry structure adds to the challenge

The inherent complexity of the beef industry, as previously noted, contributes significantly to the management needs that represent significant sources of stress for cattle. Dispersed cow–calf production and the subsequent assembly, shipping, and commingling of cattle into larger management groups in other regions of the country for stocker/backgrounding and feedlot production is an inevitable consequence of the industry structure and function in the USA.

The challenge of enhanced BRD control is significantly more difficult because of the wide range of animal health and management histories across individual operations and sectors and the frequent lack of information transfer across multiple cattle owners. The result is duplicative and, worse, inevitable gaps in health management at times. The complex structure of the beef industry greatly increases the difficulty and cost of coordinated and comprehensive BRD control efforts.

Failure to recognize BRD disease/impacts

In some cases, it appears that BRD disease and impacts are not always recognized, at least for some pathogens in certain circumstances. This is arguably most true for the cow–calf sector. For instance, BVDV, which occurs with low incidence and prevalence, may be present in low levels in some cow herds without the impacts being recognized. BVDV is, on the one hand, a reproductive disease, causing lower calving percentages resulting from reduced breeding rates and abortions; and is also a calf health disease, causing increased calf mortality and further reducing weaning rates (Newcomer et al., Reference Newcomer, Chamorro and Walz2017). At low levels, BVDV is often not suspected or recognized and the impacts are viewed as within the normal range of production parameters, i.e. slightly lower pregnancy/calving rates, slightly higher calf mortality/lower weaning rates (Taylor et al., Reference Taylor, Fulton, Lehenbauer, Step and Confer2010). Only when BVDV reaches higher levels are the impacts obvious and attributed to the disease. Failure to recognize the disease and impacts contributes to suboptimal health management. In the cow–calf sector, respiratory vaccines are used on about one-third of calves and 25–28% of cows (NAHMS, 2009).

In other cases, stocker and feedlot producers may also be accepting low levels of BRD impacts which are accepted as baseline levels of morbidity and mortality. This could account, for example, for feedlots perceiving that testing for PI animals is not worth the cost. They are perhaps correct given that it is not known the extent to which PI animals contribute to observed levels of BRD in feedlot animals and that much of the impact of BVDV exposure has already happened prior to or at arrival in the feedlot.

Market failure and economic incentives for BRD control

Notwithstanding the complexities of the BRD and the challenges inherent in the structure of the beef industry and even in cases where BRD impacts are known, there may be a fundamental reason for less than optimal levels of BRD control: producers in the various production sectors may simply not have the proper economic incentives to invest in additional BRD control. Any economic situation where individual decisions do not result in an overall optimal outcome is known as market failure.

Market failure is, simply put, a situation where private decisions do not collectively lead to an aggregate (socially) optimal or efficient solution (Pettinger, Reference Pettinger2019). This is usually the result of positive or negative externalities, which are positive or negative factors not accounted for in individual decisions. There are many examples, large and small, of market failure. A firm that does not bear the cost of the pollution resulting from production activities will produce more pollution than it would if all costs were internalized into the firm's decision-making. Public education is subsidized because the value to society of an educated populace is greater than the amount of education individuals would invest in on their own. A weed control district is more effective and cost-effective than if individuals were acting independently without a coordinated effort.

The last example is similar to the situation for BRD. The collective benefits to the industry of better BRD control very probably outweigh the total costs of enhanced control across sectors but individual producers do not capture enough benefits to warrant additional investment in BRD control. In other words, the costs and benefits of enhanced BRD control are not properly distributed across production sectors.

The BVDV example

BVDV provides a very clear example of market failure as shown in research by Hurt (Reference Hurt2018). BVDV originates at the cow–calf sector but occurs with low incidence and relatively low prevalence. The majority of cow–calf producers do not have BVDV and would incur a net cost to test and verify the absence of BVDV in the herd. BVDV-infected herds, even with low levels of the disease that may not be recognized, are experiencing losses in reproductive performance and calf morbidity and mortality. These herds would ultimately benefit from diagnosing and eliminating BVDV but would incur initial losses from the testing and indemnity of infected animals. In order to positively impact overall cattle health in the industry, it is imperative PI cattle be identified and depopulated from herds prior to leaving the ranch of origin.

PI-BVDV calves originate at the cow–calf level but those that survive move into stocker and feedlot production. A high percentage of PI calves either die or become chronics and thus represent direct losses to the stocker or feedlot operation. The bigger problem is that PI cattle provide a reservoir of continual exposure of all animals that have direct and indirect contact (Peel, Reference Peel2020). One PI animal may expose 200–300 other animals or more during shipping, in auctions, in commingling in stocker and feedlot operations, and through fence-line contact at every step. It is not known exactly how much this exposure contributes to subsequent BRD problems. However, feedlot data clearly show that feeder cattle sourced in auctions have increased respiratory disease morbidity and mortality compared to country-sourced cattle (Taylor et al., Reference Taylor, Fulton, Lehenbauer, Step and Confer2010). The estimates used by Hurt (Reference Hurt2018) suggest that there is sufficient industry value from reduced BVDV at the stocker and feedlot levels to compensate the cow–calf sector for the net additional costs of reducing BVDV and testing to verify the status of uninfected herds. There is not, however, any consistent market mechanism for such a reallocation of benefits to result in improved levels of BVDV control. For the stocker or feedlot operation, merely reducing the number of PI calves may not have much value because even a small number of PI calves remaining in the system result in continued exposure of many cattle.

A comprehensive industry approach is needed

The previous discussions highlight the need for a comprehensive multi-sector approach to respiratory disease management. While the beef industry structure divides production into different sectors, animal health must be considered and managed over the lifetime of the animal. Sector-specific efforts have been limited in effectiveness and will remain so.

Such a comprehensive approach takes the challenge beyond the decisions of individuals or even what markets in aggregate can coordinate. Management and coordination of comprehensive animal health programs must occur at the industry level and suggest that either the industry as a whole or perhaps the government will be needed to implement and manage such a program. The situation is similar to previous efforts for Brucellosis and Tuberculosis management.

Education

Current technology for BRD control is underutilized in the industry, particularly in the cow–calf sector. Only about 25–30% of cows and calves are vaccinated for respiratory disease. Biosecurity management is absent or minimal in most cow–calf operations allowing the introduction of outside animals and commingling without quarantine and testing, thus increasing disease threats. Continued and enhanced educational efforts can pay dividends in increased awareness, increased and more consistent use of vaccines and better animal health management.

Continued research

Despite the fact that current technology is underutilized, there is clearly a need for additional research and continued improvement/development of animal health technology. This includes continued efforts to understand the interactions of pathogens in the BRD complex and especially across production sectors. For example, just how much would enhanced BVDV control reduce BRD impacts in the industry? A better understanding of health and nutritional management on lifetime health (i.e. fetal programming) will be important, not only with respect to respiratory disease, but more broadly in the context of managing cattle generally to reduce health problems and reduce the use of antimicrobials.

Improved economic incentives

As noted previously, the imbalance of economic benefits and costs among cattle production sectors is a significant hindrance to improved BRD control. There are no consistent market mechanisms to address this imbalance. While premiums for PI-free calves have been observed, the use of such incentives is sporadic, minimal, and generally ineffective. However, preconditioning programs, which emphasize health management of weaned calves, are increasingly consistent in providing net benefits to cow–calf producers.

One option for improved BRD control could be a mandatory, government-imposed BRD control program. Such a program could require the use of vaccines, testing for BVDV, depopulation of PI animals and could be done with or without compensation. The industry would likely prefer an industry-driven and managed program which would require some mechanism to ensure that beneficiaries of improved BRD control compensate the costs of improved control. Such an approach would, at least conceptually, result in improved BRD control and leave the industry as a whole better off. That said, the structure and implementation of such an industry-based program would be challenging. The costs are immediate and some benefits would accrue more slowly over time.