Abstract
OBJECTIVE To develop a partial budget analysis of direct costs associated with bovine respiratory disease (BRD) in preweaned calves on US beef cow–calf operations and identify factors that strongly influence those costs.
DESIGN Risk analysis model.
ANIMALS US preweaned beef calf inventory from 2011 through 2015.
PROCEDURES A stochastic simulation model was developed by use of a computer spreadsheet and add-in software. Input data were obtained from the USDA, peer-reviewed literature, and a survey of beef cow–calf producers. A simulation consisting of 10,000 iterations was used to account for either uncertainty or variability in model inputs. The median (90% confidence interval) was reported for each output variable. Global and local sensitivity analyses were performed to identify the most influential factors and quantitatively evaluate the effects of inputs on the estimated costs.
RESULTS From 2011 through 2015, BRD in preweaned calves cost the US beef cow–calf industry approximately $165 million annually, of which costs associated with the death, treatment, and decreased weaning weight of BRD-affected calves were approximately $126, $25, and $15 million, respectively.
CONCLUSIONS AND CLINICAL RELEVANCE Although BRD in preweaned calves may have a fairly small effect on the total gross income for the US beef cow–calf industry as a whole, it can have a substantial adverse effect on the net profit of BRD-affected herds. The model developed provided important information regarding the cost of BRD in preweaned calves on US beef cow–calf operations and identified factors that had an import effect on those costs.
Bovine respiratory disease, sometimes called shipping fever or pneumonia, continues to be one of the leading causes of morbidity and death in beef cattle and calves in the United States.1,2 Results of a 2013 study3 indicate that the mean ± SD percentage of calves affected by BRD between birth and weaning on US beef cow-calf operations is 3.0 ± 71% The high SD of that measure suggests that the risk of BRD in preweaned beef calves is highly variable, and the BRD morbidity rate in preweaned calves may be high in some herds and low or 0% in others. In herds with a BRD problem, the mean annual incidence rate of BRD in preweaned calves can exceed 10%.4,5 In a USDA survey2 conducted in 2007 and 2008, death was attributed to BRD for 31 ± 4% of all beef calves that died between 3 weeks of age and weaning, and BRD was the leading cause of death for calves in that age category.
For the beef cow–calf industry, direct costs associated with BRD include cattle deaths, expense of medicine and labor to treat affected cattle, and decreased growth or performance of affected cattle that recover.6 Over 33% of the US beef cow–calf producers who participated in the 2007–2008 USDA survey2 agreed (20.5%) or strongly agreed (13.4%) that BRD had a substantial economic impact on their operations. However, only a few reports7–9,a have described costs associated with BRD specifically for the cow-calf segment of the beef industry. Thirty years ago, the annual costs associated with the prevention and treatment of respiratory tract disease on beef cow–calf operations in 3 states were estimated.7–9 In 2000, costs (medicines, weaning weight loss, and death loss) associated with BRD in preweaned calves were estimated at $50.46/affected calf for 1 large beef cow–calf operationa; however, that estimate did not include labor costs associated with treating BRD-affected calves.
Risk analysis allows for evaluation of the probability and consequences (ie, biological, social, and economic) of events or actions and is conducted by either qualitative or quantitative methods.10,11 Quantitative risk analysis is conducted by use of deterministic or stochastic modeling. Deterministic risk analysis models produce single estimates, which are determined by a single value for each input variable, and the amount of uncertainty or variation around that value is not considered.12,13 Alternately, stochastic risk analysis models use probability distributions estimated from historical data or deduced from expert opinion to indicate uncertainty and variation in factors that limit the outcome.14,15 Each estimated output is a range or statistical distribution, which may provide decision-makers more information under uncertain situations.13 Several stochastic models have been developed to study the cost of BRD in dairy cattle16,17 and feedlot cattle18,19 on a specific farm or in countries other than the United States. However, to our knowledge, similar models to investigate the cost of BRD in preweaned calves on US beef cow–calf operations have not been developed. Therefore, the objective of the study reported here was to stochastically model a partial budget analysis of the direct costs associated with BRD in preweaned calves on US beef cow–calf operations and identify the factors that most strongly influence those costs.
Materials and Methods
Model description
A stochastic partial budget analysis model was developed by use of commercially available spreadsheet programb and add-in softwarec to estimate the costs of BRD in preweaned beef calves. The model (Figure 1; Appendices 1 and 2) consisted of 3 parts: cost of BRD-associated deaths in preweaned calves, cost to treat BRD-affected preweaned calves, and economic losses associated with decreased weaning weights of BRD-affected calves. The settings used for the model were selected to represent the entire US beef cow–calf system. The number of beef calves born each year from 2011 through 2015 was simulated on the basis of the USDA beef cow inventories20–24 for January 2012 through January 2016 because the January inventory for each year reports the number of primiparous and multiparous cows that calved in the previous year. The USDA estimates for the percentage of beef cows that calved25 and percentage of beef calves born alive26 were used to estimate the number of calves born alive each year. Although disease incidence is not static from year to year, particularly within a production unit, we assumed that BRD morbidity and mortality rates for the national beef cow–calf herd remained constant within a defined level of uncertainty from 2011 through 2015 and that responses in the USDA Beef 2007–08 survey2 remained relevant. Deaths caused by BRD were estimated for calves < 3 weeks old as well as calves between 3 weeks of age and weaning to be consistent with how the USDA stratified calf age when it reported the probability of calf death caused by BRD in the Beef 2007–08 survey.2 Among calves that were born alive and died before weaning, death occurred at < 24 hours old, 1 day to 3 weeks old, and ≥ 3 weeks old for 31.3%, 35.0%, and 33.7%, respectively.2 For calves that died < 3 weeks of age and between 3 weeks of age and weaning, the mean ± SE percentage of deaths caused by BRD was 8.2 ± 1.4% and 31.4 ± 3.9%, respectively.2 For each calf that died prior to weaning, regardless of its age at death, we assumed its economic value was equal to that of a calf weaned at 227 to 250 kg (500 to 550 lb). Therefore, the cost of deaths attributed to BRD was estimated by multiplying the number of preweaned calves that died because of BRD each year by the value of a weaned calf for that year, which was calculated by multiplying the mean weaning weight of calves by the mean price per kilogram received by producers for weaned calves (weight, 227 to 250 kg) for each year between 2011 and 2015.27 We used that approach to approximate foregone revenue because beef cow–calf producers expect that each calf weaned and marketed will weigh enough to more than recover the fixed and variable costs associated with maintaining its dam and raising it to weaning (ie, maintaining a cow-calf pair). Most costs associated with maintaining a cow-calf pair are incurred before the calf is born.
Schematic illustration of the framework for a stochastic simulation model developed to perform a partial budget analysis of the direct costs associated with BRD in preweaned calves on US beef cow–calf operations from 2011 through 2015. Variables in ovals represent the starting point (preweaned beef calf inventory) or main outputs. Variables in parallelograms represent inputs. Variables in rectangles represent intermediate calculations. See Appendices 1 and 2 for descriptions of the commands, distributions, and sources for model inputs and calculations for intermediate and main model outputs.
Citation: Journal of the American Veterinary Medical Association 253, 5; 10.2460/javma.253.5.624
The estimated cost for treatment of BRD-affected calves included the cost of both medicine and labor. We assumed all affected calves were treated. Therefore, the cost to treat BRD was calculated by multiplying the number of BRD-affected preweaned calves by the cost of medicine and labor required to treat a BRD-affected calf, which included a factor of uncertainty.
For BRD-affected calves that survived and were weaned, the decrease in weaning weight was calculated by multiplying the number of such calves by the mean loss of weaning weight attributed to BRD (6.76 kg/calf) reported by investigators of another study5 with a factor of uncertainty included. The number of BRD-affected calves that survived to weaning was calculated as the number of preweaned calves that developed BRD minus the number of those calves that died because of BRD or some other cause before weaning.
Data sources
Information regarding commands, distributions, and sources for model inputs were summarized (Appendix 1). Input data were obtained from USDA surveys2,25–27 or reports,20–24,28 peer-reviewed articles,3,5 and a beef cow–calf producer survey.29 Morbidity and mortality rate data were obtained from the USDA Beef 2007–08 survey.2,3 Auction market data, which consisted of 189,747 weekly weighted market prices for feeder bulls, steers, and heifers with weights between 227 and 250 kg, were collected from USDA market reports.28 Because some market reports included data of sales on a per-animal basis or sales of weaned calves, data were removed if the lowest animal weight category for which the price was reported was > 318 kg (700 lb), comments included “price per head”, “replacement”, or “yearling”, or the mean reported price/45.5 kg (100 lb) was < $50 or > $500. The mean ± SE price was calculated from a total of 188,652 auction reports representing 4,805,690 feeder cattle by use of statistical software.d
Most model inputs other than BRD treatment costs and decreased weight gain were obtained at the national level. Treatment costs (including medicine and labor) were obtained from results of a survey29 of 43 beef cow–calf producers from Nebraska, North Dakota, and South Dakota whose operations had a history of BRD in preweaned calves. Because the producers who participated in that survey29 represented a nonrandom subset of producers from a 3-state region of the United States, the BRD treatment costs used for the model might have been affected by selection bias; however, those values represented the most recent estimates of BRD treatment costs for preweaned calves. The mean decrease in weaning weight for BRD-affected beef calves varies among published studies.5,30,31 For modeling purposes, we used the estimated decrease in weaning weight attributed to BRD reported by investigators of a study5 of 31,243 calves over a 20-year period.
Model simulation
A simulation was used to account for either uncertainty or variability in model inputs. Parametric distributions used for input variables included normal, lognormal, and discrete. The normal distribution was used for variables that were normally distributed and included 2 parameters (mean and SE). Lognormal distributions were used for variables that could not have negative values, and those variables were described by 2 parameters (mean and SE of the logarithm). Variables with discrete distributions were described by 2 parameters (possible values and their corresponding probabilities).32
Each iteration of the simulation began by random selection of the year to trigger the simulated beef cow inventory and market price. The values for each input variable were randomly generated simultaneously in accordance with their respective probability distributions. The outcomes of each iteration varied, and the overall results were updated on the basis of each iteration. The simulation consisted of 10,000 iterations. The probability distributions of outputs were calculatedc for the simulation, and the medians and corresponding 90% CIs for those outputs were reported.
The percentages of calves that were born alive and died within 24 hours after birth, between 1 day and < 3 weeks of age, and between 3 weeks of age and weaning were reported such that the sum of those 3 percentages totaled 100%.2 A discrete distribution was used to generate a random number to trigger the simulation of those 3 inputs at equal probability. During each iteration, only 2 of those 3 inputs were simulated on the basis of their distributions, whereas the third input was determined by subtracting the sum for the 2 simulated inputs from 100%.
Convergence tolerance was set at 1% (with 95% confidence), and tests were performed to estimate median costs associated with BRD. Latin hypercube sampling with 10,000 iterations was conducted to meet the convergence criteria (ie, the change in the median of main outputs will converge at ≤ 1.0%). Those outputs included death (deaths at < 3 weeks and deaths ≥ 3 weeks of age to weaning) and treatment (medicine and labor) costs and decrease in weaning weight attributed to BRD.
Sensitivity analysis
Global and local sensitivity analysis methods were performed to identify the most influential factors and quantitatively evaluate the effects of inputs on the economic cost of BRD in preweaned beef calves. Global sensitivity analysis was conducted to investigate the effect of changes to all input variables simultaneously by calculation of Spearman rank correlation coefficients (ρ). Local sensitivity analysis was used to assess how uncertainty in 1 factor influenced the model output when other factors were maintained at their expected values.33 Six variables (probability of BRD-related death in calves < 3 weeks of age, probability of BRD-related death in calves between 3 weeks of age and weaning, probability of calves developing BRD before weaning, cost of medicine and labor required to treat BRD-affected calves, and economic loss associated with the BRD-related decrease in weaning weight) directly associated with BRD were included. A tornado graph was created to show the percentage change in the median cost of BRD in preweaned calves as each input varied ± 1 SD from the median of its distribution while the expected distributions of all other input variables were held constant.
Results
Economic costs
The total direct economic cost of BRD in preweaned beef calves on US beef cow–calf operations between 2011 and 2015 was estimated at $165 million (90% CI, $129 to $246 million; Figure 2). The distribution of that cost for the 10,000-trial simulation was bimodal with one peak at approximately $140 to $170 million and the other at approximately $210 to $230 million. The feeder cattle market prices and calf values were clustered by year with low values during 2011 through 2013 and high values for 2014 and 2015. For example, the mean market price for 227-to 250-kg weaned calves varied from $2.79 to $3.24/kg between 2011 and 2013 and was $4.73/kg in 2014 and $4.81/kg in 2015. The distributions for the market price and value of weaned calves contributed to the bimodal distribution observed for the total direct costs of BRD in preweaned calves (Figure 3). Model outputs estimated on a national and per-cow basis were summarized (Table 1).
Frequency distribution of the total cost of BRD in preweaned calves on US beef cow–calf operations from 2011 through 2015 as determined for each of 10,000 iterations of the stochastic simulation model described in Figure 1. The solid vertical line represents the median ($165 million) and the dashed vertical lines delimit the 90% CI ($129 to $246 million).
Citation: Journal of the American Veterinary Medical Association 253, 5; 10.2460/javma.253.5.624
Frequency distribution of the weaned calf market price (A) and value (B) used as inputs for each of 10,000 iterations of the stochastic simulation model described in Figure 1.
Citation: Journal of the American Veterinary Medical Association 253, 5; 10.2460/javma.253.5.624
Outputs for a stochastic simulation model developed to perform a partial budget analysis of the direct costs associated with BRD in preweaned calves on US beef cow–calf operations from 2011 through 2015.
| Output | National estimate (× $1 million)* | Cost per cow ($)† |
|---|---|---|
| Total cost of all BRD-related deaths | 126 (92–200) | 4.30 (3.08–6.70) |
| Cost of BRD-related deaths in calves < 3 wk of age | 44 (29–72) | 1.48 (0.96–2.42) |
| Cost of BRD-related deaths in calves between 3 wk of age and weaning | 84 (57–138) | 2.87 (1.93–4.65) |
| Total cost associated with treatment of BRD-affected calves | 25 (20–32) | 0.86 (0.67–1.09) |
| Cost of medicine to treat BRD-affected calves | 10 (8–13) | 0.34 (0.27–0.43) |
| Cost of labor to treat BRD-affected calves | 15 (11–20) | 0.51 (0.37–0.69) |
| Income loss associated with decreased weaning weight of BRD-affected calves | 15 (9–25) | 0.50 (0.31–0.83) |
| Total cost of BRD in preweaned beef calves | 165 (129–246) | 5.63 (4.33–8.26) |
Values represent the median (90% CI).
National estimates are for the respective costs associated with BRD for the US beef cow–calf industry in its entirety.
Cost per cow was calculated by dividing the national estimate by the annual US beef cow inventory, which was randomly generated by the model.
Sensitivity analysis
The factor with the greatest effect on the cost of BRD in preweaned beef calves was year (ρ = 0.80). Of the 6 variables directly associated with BRD, calves that died because of BRD between 3 weeks of age and weaning was the most influential factor. A 10% increase in the number of BRD-related deaths in calves between 3 weeks of age and weaning (eg, from 31.4% to 34.5%), resulted in a 4.9% increase in the median of cost of BRD for preweaned calves (Figure 4).
Tornado graph of the results of a 1-way sensitivity analysis for each of 6 input variables associated with the cost of BRD in preweaned calves on US beef cow–calf operations used in the stochastic simulation model described in Figure 1. Each bar represents the percentage change in the median estimated cost of BRD in preweaned calves when that input varied ± 1 SD from the median of its distribution while the expected distributions of all other input variables were held constant. For each variable, the value in parentheses represents the median of the expected distribution for that variable. CLabor/sick = Cost of labor required to treat BRD-affected calves. CMedicine/sick = Cost of medicine required to treat BRD-affected calves. PDeathBRD<3w = Among all calves that were born alive and died before weaning, the percentage that died because of BRD at < 3 weeks of age. PDeathBRD≥3w = Among all calves that were born alive and died before weaning, the percentage that died because of BRD between 3 weeks of age and weaning. PMorbidityBRD = Percentage of calves that developed BRD before weaning. WLossBRD = Decrease in weaning weight attributed to BRD for affected calves. See Appendix 1 for further description of input variables.
Citation: Journal of the American Veterinary Medical Association 253, 5; 10.2460/javma.253.5.624
Discussion
In the present study, a stochastic partial budget simulation model was developed to estimate the costs associated with BRD in preweaned beef calves on US beef cow–calf operations for the years of 2011 through 2015. The model included estimates of costs associated with the death and treatment of BRD-affected calves as well as production (weaning weight) losses for BRD-affected calves that survived to weaning. The cost of BRD vaccination was not included in the model because that is considered an investment in BRD prevention rather than a direct cost of the disease.
Results of the present study suggested that, when spread across the entire US beef cow inventory, BRD in preweaned calves cost cow-calf producers a median of $5.63/cow/y during the study period. However, that cost was primarily borne by the approximately 20% of beef cow–calf producers whose herds are affected by BRD annually,34 and for BRD-affected herds, the estimated cost of BRD in preweaned calves was approximately $28/cow/y. For US beef cow–calf producers during the period of 2011 to 2015, the median annual gross and net profits were $729/cow and $108/cow, respectively.35 Therefore, although BRD in preweaned calves may appear to have a small economic effect on the total beef cow–calf industry annual gross income per cow, it can have a substantial effect on the profitability of affected herds.
Results of the global sensitivity analysis indicated that year had the greatest effect on the cost of BRD in preweaned beef calves, likely because both cow-calf inventory and market price were modeled (ie, determined) on an annual basis. Other influential factors were BRD morbidity and mortality rates in preweaned calves, and the values used in the model for those inputs were obtained from reliable national estimates.2,3,20–24,28 Therefore, we believe that the input data and probability distributions were well estimated and representative of the system modeled.
The model developed in the present study was designed strictly as a partial budget analysis of the direct costs associated with BRD in preweaned calves on US beef cow–calf operations. It did not consider factors such as drought, grain and corn prices, consumer demand, or events occurring in other livestock industries that might affect the demand for or value of beef feeder cattle. The model also did not account for costs that would be recouped by the beef cow–calf industry if BRD in preweaned calves was eliminated. It would be inappropriate to assume that feeder cattle market prices would remain the same if BRD in preweaned calves was eradicated. The US cattle inventory and feeder cattle price typically move in opposite directions, which reflects responses to supply and demand.36 Theoretically, if it was assumed that feeder cattle demand remained constant and BRD in preweaned calves was eliminated, whereby calves did not die or have decreased performance because of the disease, then the feeder cattle market price would be expected to decrease in response to the additional supply of calves reaching the market.
In the United States, the feeder cattle market price is currently dictated, in part, by the weight of all weaned calves (those that were and were not affected by BRD) marketed. The mean weight of calves marketed from herds not affected by BRD is greater than that for calves marketed from herds affected by BRD. Therefore, cow-calf producers whose herds are not affected by BRD benefit by marketing more calves that, on average, weigh more than the calves marketed by producers of BRD-affected herds. Moreover, producers of BRD-affected herds also bear the medicine and labor costs associated with the treatment of diseased calves. The direct costs estimated in our model reflect those differences.
Results of the stochastic partial budget model developed in the present study suggested that BRD in preweaned calves was a substantial problem for the US beef cow–calf industry and cost producers approximately $165 million annually during the period from 2011 through 2015. The majority ($126 million/$176 million [76%]) of that cost was attributed to the lost economic value of calves that died because of BRD. Although BRD in preweaned calves may have a fairly small effect on the total gross income for the US beef cow–calf industry as a whole, it can have a substantial adverse effect on the net profit of BRD-affected herds. The model developed in this study provided important new information about the costs of BRD in preweaned calves on US beef cow–calf operations and identified factors that had an important effect on those costs.
Acknowledgments
This research was a contribution of the Beef Cattle Population Health and Reproduction Program at Mississippi State University and supported by the Mikell and Mary Cheek Hall Davis Endowment for Beef Cattle Health and Reproduction.
The authors declare that there were no conflicts of interest.
Presented in part as an oral presentation at the 14th International Symposium of Veterinary Epidemiology and Economics, Merida, Yucatan, Mexico, November 2015; and World Buiatrics Congress, Dublin, Ireland, July 2016.
The authors thank Kathleen Barton for technical assistance.
ABBREVIATIONS
| BRD | Bovine respiratory disease |
| CI | Confidence interval |
Footnotes
Dewell G, Keen J, Dewell R, et al. Production and financial losses associated with pre-weaning disease in beef cattle (abstr), in Proceedings. 83rd Conf Res Workers in Anim Dis 2002;31.
Excel, version 2013, Microsoft Corp, Redmond, Wash.
@risk, version 7.5.0, Palisade Corp, Ithaca, NY.
SAS, version 9.4, SAS Institute Inc, Cary, NC.
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Appendix 1
Description of commands, distributions, and sources for inputs of a stochastic simulation model developed to perform a partial budget analysis of the direct costs associated with BRD in preweaned calves on US beef cow–calf operations from 2011 through 2015.
| Input | Notation | Command and distribution | Source (reference No.) |
|---|---|---|---|
| Year | Year | RiskDiscrete ([2011, 2012, 2013, 2014, 2015], [0.2, 0.2, 0.2, 0.2, 0.2])* | — |
| US beef cow inventory in January 2012–2016 (No. of cattle) | NCowInventory | IF (Year = 2011, 30157900, IF [Year = 2012, 29297300, IF [Year = 2013, 29085400, IF [Year = 2014, 29302100, IF [Year = 2015, 30165800]]]])† | 20–24 |
| Calving percentage | PCalving | 1 – RiskLognorm (0.085, 0.006) | 25 |
| Percentage of calves born alive | PCalfAlive | 1 – RiskLognorm (0.029, 0.007)‡ | 26 |
| Percentage of calves born alive that died or were lost before weaning | PDeathPrewean | RiskLognorm (0.036, 0.002) | 2 |
| Random number | RNum | RiskDiscrete ([1, 2, 3], [0.333, 0.333, 0.333])§ | — |
| Of calves that were born alive and died before weaning, percentage that died < 24 h old | PDeath<24h | IF (RandNum = or (1, 2), RiskLognorm (0.313, 0.026), 1 – PDeath24h-3w –PDeath≥3w)§ | 2 |
| Of calves that were born alive and died before weaning, percentage that died between 1 day and 3 wk of age | PDeath24h-3w | IF (RandNum = or (2, 3), RiskLognorm (0.35, 0.028), 1 – PDeath<24h – PDeath≥3w)§ | 2 |
| Of calves that were born alive and died before weaning, percentage that died ≥ 3 wk of age | PDeath>3w | IF (RandNum = or (1, 3), RiskLognorm (0.337, 0.026), 1 – PDeath<24h – PDeath24h-3w)§ | 2 |
| Of all preweaned calves that died or were lost, percentage that died because of BRD at < 3 wk of age | PDeathBRD<3w | RiskLognorm (0.082, 0.014) | 2 |
| Of all preweaned calves that died or were lost, percentage that died because of BRD at ≥ 3 wk of age | PDeathBRD>3w | RiskLognorm (0.314, 0.039) | 2 |
| Weaning weight of calves (kg/calf) | WWeaning | RiskNormal (240.404, 0.907) | 27 |
| Mean market price for weaned calves (weight, 227–250 kg) in 2011–2015 ($/kg) | CCalf/kg | IF (Year = 2011, RiskNormal [2.79, 0.0018], IF [Year = 2012, RiskNormal [3.24, 0.0024], IF [Year = 2013, RiskNormal [3.21, 0.0024], IF [Year = 2014, RiskNormal [4.73, 0.0040], IF [Year = 2015, RiskNormal [4.81,0.0044]]]]])| | 28 |
| BRD morbidity rate for preweaned beef calves (%) | PMorbidityBRD | RiskLognorm (0.03, 0.003373) | 3 |
| Cost of medicine to treat BRD-affected calves ($/sick calf) | CMedicine/sick | RiskNormal (13.00, 1.24)¶ | 29 |
| Cost of labor to treat BRD-affected calves ($/sick calf) | CLabor/sick | RiskNormal (19.45, 2.94)¶ | 29 |
| Decreased weaning weight associated with BRD in affected calves (kg/sick calf) | WLossBRD | RiskNormal (6.76, 1.02)# | 5 |
Random generation of year triggers specific simulations in NCowInventory and CCalf/kg.
The respective updated beef cow inventories for January 2012 through 2016 were released by the USDA in January 2013 through 2017 and were adjusted to correspond to the model year (2011 through 2015) when calves were born (eg, Year = 2011 corresponds to the beef cow inventory in January 2012 released by the USDA in January 2013).
The mean value used in the distribution was obtained from the cited USDA report, whereas the SE was calculated by the author (MW) from available data.
The PDeath<24h, PDeath24h-3w, and PDeathBRD≥3w should sum to 100%; a random number was generated to control which 2 variables would be simulated in each iteration, with the remaining variable calculated.
The randomly generated year determined the simulated market price of weaned calves, which was calculated by use of statistical softwared on the basis of information obtained from USDA auction market reports.
The mean and SE were used to calculate national estimates (ie, the cost of BRD in preweaned calves for the US beef cow–calf industry in its entirety).
The mean value was obtained from the cited reference, whereas the SE was calculated from data simulated on the basis of information presented in the cited reference.
— = Not applicable.
Appendix 2
Description of intermediate and main outputs for the stochastic simulation model described in Appendix 1
| Output | Notation | Calculation |
|---|---|---|
| Intermediate outputs | ||
| No. of calves born | NCalfBorn | NCowInventory × PCalving |
| No. of calves born alive | NCalfAlive | NCalfBorn × PCalfAlive |
| No. of calves born alive that died or were lost before weaning | NDeathPrewean | NCalfAlive × PDeathPrewean |
| No. of calves born alive that died at < 24 h of age | NDeath<24h | NDeathPrewean × PDeath<24h |
| No. of calves born alive that died between 1 day and 3 wk of age | NDeath24h–3w | NDeathPrewean × PDeath24h-3w |
| No. of calves born alive that died between 3 wk of age and weaning | NDeath≥3w | NDeathPreweaning × PDeath≥3w |
| No. of calves that died because of BRD at < 3 wk of age | NDeathBRD<3w | (NDeath<24h + NDeath24h-3w) × PDeathBRD<3w |
| No. of calves that died because of BRD between 3 wk of age and weaning | NDeathBRD≥3w | NDeath≥3w × PDeathBRD≥3w |
| Among all calves that were born alive and died before weaning, the percentage that died for reasons other than BRD | PDeathOther | 1 – (PDeath<24h + PDeath24h-3w) × PDeathBRD<3w – PDeath≥3w × PDeathBRD≥3w |
| Value of a weaned calf ($) | VCalf | WWeaning × CCalf/kg |
| No. of preweaned calves affected by BRD | NBRD | NCalfAlive × PMorbidityBRD |
| No. of BRD-affected preweaned calves that recovered from the disease | NBRDRecover | NBRD – NDeathBRD<3w – NDeathBRD≥3w |
| No. of BRD-affected calves that survived to weaning | NBRDSurvWean | NBRDRecover × (1- PDeathPrewean × PDeathOther) |
| Main Outputs | ||
| Cost of BRD-related deaths in preweaned calves < 3 wk of age ($) | CDeathBRD<3w | NDeathBRD<3w × Vcalf |
| Cost of BRD-related deaths in preweaned calves between 3 wk of age and weaning ($) | CDeathBRD≥3w | NDeathBRD≥3w × Vcalf |
| Cost of all BRD-related deaths in preweaned calves ($) | CMortalityBRD | CDeathBRD<3w + CDeathBRD≥3w |
| Cost of medicine to treat BRD-affected preweaned calves ($) | CMedineBRD | NBRD × CMedicine/sick |
| Cost of labor to treat BRD-affected preweaned calves ($) | CLaborBRD | NBRD × CLabor/sick |
| Total cost to treat BRD-affected preweaned calves ($) | CTreatBRD | CMedineBRD + CLaborBRD |
| Income loss associated with decreased weaning weight of BRD-affected calves ($) | CLossWtBRD | NBRDSurvWean × WLossBRD × CCalf/kg |
| Total direct cost of BRD in preweaned beef calves ($) | CTotalCostBRD | CMortalityBRD + CTreatBRD + CLossWtBRD |
See Appendix 1 for remainder of key.
