Nonlactating cows transitioning from pregnancy to high milk production are subjected to stressors, including depressed feed intake1,2 and diminished immune function.1 As a consequence, half of postpartum cows may have at least 1 infectious or metabolic disease,3 which includes uterine diseases and RFM, that in turn can negatively impact reproductive performance. Retained fetal membranes have been defined as fetal membranes observed outside the vulva or present in the vagina or uterus as determined by vaginal examination > 24 hours after calving.4 The median incidence of RFM in dairy cattle is 8.6%,4 which has not changed appreciably in recent years. Older age, dystocia, abortion, and increased prepartum serum concentrations of nonesterified fatty acids are among the risk factors associated with development of RFM.5,6 Cows with RFM produce less milk (753 kg [1,657 lb] less) than unaffected cows during an entire lactation, with an additional reduction of 259 kg (570 lb) of milk if metritis develops subsequently.7 In addition, cows with RFM are at a higher risk than cows without RFM of developing other clinical diseases such as metritis (OR, 6.3),8 DA (OR, 2.2),9 or mastitis (OR, 2.1)10 or of being culled during early lactation (OR, 1.3).11 Moreover, cows with RFM have a longer interval until pregnancy12,13 and a relative reduction of 14% in the odds of pregnancy after the first insemination.5
The cost of a case of RFM has been estimated. Investigators of 1 study14 estimated the cost was £298 ($489) in English dairy herds,14 whereas the cost of a case of RFM in Dutch herds was £71 ($164) in another study.15 Although these estimates included costs of reductions in milk yield and increases in culling rates, calving interval, and treatment costs, they were based on outdated market prices and values. In a recent study,16 the mean ± SD cost of a case of RFM estimated by use of a stochastic model was $232 ± 58. A stochastic model is one that assigns an input a probability distribution and then varies the value of that input during numerous iterations by sampling from the distribution to generate the outcome; thus, each time the model is run, different values will be obtained, which results in a summary value (eg, mean) and measures of variability around that summary value. On the other hand for a deterministic model, a fixed or determined value for input variables is used to generate the outcome. A sensitivity analysis then varies input values to describe their relative influence on model estimates. The objective of the study reported here was to use a deterministic economic model to estimate the cost of a case of RFM in a US dairy cow and to compare results with those obtained for previous models.
Materials and Methods
Sample
Inputs were obtained from published studies and reports as well as from personal communications. These sources were selected on the basis that they were peer-reviewed information, published by the government (ie, USDA), or presentations at industry conferences. Personal communications were with experts in the field of veterinary economics.
Procedures
Inputs were used for calculations7,8,17–23,a (Table 1). A deterministic economic model was developed in a spreadsheetb and used to estimate the cost of a case of RFM in dairy cattle. Economic losses attributable to RFM were direct (attributable to a reduction in milk yield and impaired reproductive performance) and indirect (attributable to an increased risk of developing clinical disease and increased culling risk as a result of RFM). Dairy efficiency is the kilograms (pounds) of milk produced as a result of a cow consuming 1 additional kilogram (2.2 additional pounds) of dry matter above maintenance requirements.17 Dairy efficiency used in calculating milk loss attributable to RFM accounted for only the energy required to produce marginal milk by use of a net energy of lactation of 0.75 Mcal/kg (0.34 Mcal/lb) for milk with 4% fat and 1.73 Mcal/kg of feed (0.79 Mcal/lb of feed) on a dry-matter basis.18 Treatment costs were not included in calculations because the value of treating RFM is questionable as determined on the basis of published reports.24–26
Inputs used in a deterministic model to calculate the cost of a case of RFM in a dairy cow in the United States.
| Item | Value | Reference |
|---|---|---|
| Dairy efficiency (kg of milk/kg of additional feed)* | 2.3 | 17, 18 |
| Herd incidence of RFM (%) | 7.5 | 19 |
| Mean milk price/L ($)† | 0.39 | 20 |
| Milk reduction for RFM cases (kg) | 753 | 7 |
| Milk reduction for RFM cases that progress to metritis (kg) | 1,012 | 7 |
| RFM cases that progress to metritis (%) | 33 | 8 |
| Cost of 1 kg of total mixed ration on a dry-matter basis ($) | 0.29 | 2I |
| Cost of pregnant replacement heifer ($)‡,§ | 1,700 | 20 |
| Cull cow value ($)§,∥ | 980 | 20 |
| Annual herd turnover rate (%) | 35 | 22 |
| Cost of 1 day not pregnant between 90 and 120 DIM ($) | 5.20 | 23 |
To convert cost of 1 kg of total mixed ration to cost of 2.2 lb of total mixed ration, multiply value by 2.2.
Kilograms of milk produced as a result of a cow consuming 1 additional kilogram of dry matter above maintenance requirements17; this calculation accounted only for the energy required to produce marginal milk by use of a net energy of lactation of 0.75 Mcal/kg (0.34 Mcal/lb) for milk with 4% fat and 1.73 Mcal/kg (0.79 Mcal/lb) of feed on a dry-matter basis.18
Mean milk price between November 2015 and November 2016. To convert value to $/gallon, multiply value by 3.79.
Price as of October 2016.
Loss attributed to premature culling was calculated by use of a depreciation model.a Data on when cows with RFM were culled are lacking; therefore, we assumed a midpoint in the linear depreciation of a cow through the 1 lactation included in the model. Depreciation of the value of the cow by the time she was culled = $1,700 – $980 = $720. Mean depreciation of the value of a cow by the time she was culled = $720/2 = $360. Mean value of a culled cow = $1,700 – $360 = $1,340. Loss attributable to premature culling = $1,340 – $980 = $360.
Cull cow value was based on a mean weight of 636 kg (1,399 lb) and $70/cwt (hundredweight) = 14 cwt × $70/cwt = $980.
It is estimated that milk production decreases by 753 kg for an uncomplicated case of RFM.7 In addition, one-third of cows with RFM develop metritis,8 and these complicated cases are expected to lose a total of 1,012 kg (2,226 lb) of milk production/lactation.7 These estimates were used because they were reported for a large multiherd study,7 which was one of only a few studies that explicitly partitioned milk losses between RFM and metritis. Marginal milk cost was calculated by subtracting the cost of feed (dry-matter basis) not consumed as a result of reduction in milk yield attributable to RFM from the total loss resulting from the reduction in milk yield attributable to RFM.
The mean increase in time from calving to pregnancy for cows with RFM (ie, 14 days) was the mean value for previous reports.12,13,27–29 The cost of 1 day not pregnant was $5.20.23 These values were multiplied to obtain the total cost of an increased number of nonpregnant days for cows with RFM.
Cows with RFM are more likely to develop metritis (OR, 6.3),8 DA (OR, 2.2),9 and mastitis (OR, 2.1).10 The cost of clinical diseases was used in calculations8–11,19,21,30,31 (Table 2). The herd incidence risk for each of these 3 diseases was obtained from other reports,19,31 and the basal risk of developing each clinical disease (ie, risk of developing each clinical disease for cows without RFM) was calculated by use of the following equation:
Herd incidence of a clinical disease or culling = (Herd incidence [percentage] of RFM × increased risk of developing that clinical disease or premature culling × x) + (cows without RFM × x)
where x is the risk of developing that disease or of premature culling for cows not affected with RFM. The attributable risk of developing each clinical disease as a result of RFM (ie, percentage of each clinical disease attributed to the fact a cow had RFM) was calculated by subtracting the basal risk from the herd incidence. Finally, the cost of each clinical disease attributable to RFM was the value for the risk of each clinical disease attributable to RFM multiplied by its respective cost.
Losses attributable to clinical diseases and inputs and calculations of epidemiological estimates of the contribution of RFM to subsequent clinical diseases used to calculate the cost of a case of RFM in a dairy cow in the United States.
| Factor | Metritis | DA | Mastitis | Culling |
|---|---|---|---|---|
| Total loss ($) | 39621 | 70721 | 44730 | 360 |
| Losses excluding milk loss ($)* | 287 | 651 | 332 | 360 |
| OR for increased risk attributable to RFM | 6.258 | 2.29 | 2.110 | 1.311 |
| Herd incidence (%) | 16.719 | 4.819 | 35.631 | 7.53† |
| Basal risk (%)‡ | 12.0 | 4.4 | 32.9 | 7.36 |
| Attributable risk (%)§ | 4.7 | 0.4 | 2.7 | 0.17 |
| Cost of disease or premature culling ($)∥ | 13.5 | 2.6 | 9.0 | 0.60 |
Milk losses were excluded to avoid double counting.
Proportion of cows with RFM culled by 60 DIM multiplied by annual herd turnover rate = 21.5 × 35% = 7.53%.
Disease or premature culling for cows not affected with RFM, which was calculated as follows: herd incidence of a clinical disease or premature culling = (Herd incidence of RFM [%] × increased risk of developing that clinical disease or premature culling × x) + (cows without RFM [%] × x), where x is the risk of developing that disease or premature culling for cows not affected with RFM.
Calculated by subtracting basal risk from herd incidence.
Cost of increased incidence of disease or premature culling attributable to RFM was a function of the cost of a disease or cost of premature culling and the attributable risk (eg, cost of increased metritis attributable to RFM = $287 × 4.7% = $13.5).
Superscript numbers are the references used to provide inputs.
The cost of premature culling was calculated on the basis of a comprehensive depreciation model.a The first step was to calculate loss attributable to premature culling that resulted from the difference between the mean value of a cull cow and the actual price for which a cull cow was sold (Table 1). The next step was to calculate the incidence of culling by 60 DIM for an assumed typical herd turnover rate of 35%,22 of which 21.5% occurred during the first 60 DIM.32,33 Finally, basal and attributable risk of culling attributable to RFM were calculated (Table 2). The cost of culling attributable to RFM was calculated as the risk of culling attributable to RFM multiplied by the cost of premature culling.
Sensitivity analysis was performed to evaluate the change in 1 input at a time on the overall cost of 1 case of RFM. For all variables included in the sensitivity analysis, the base value used to estimate the cost of RFM was changed by adding or subtracting 50% from that base value.
Results
Default inputs were used in the economic model and yielded an estimated cost of $386 for 1 case of RFM. This loss comprised a reduction in milk yield of $287 ($199 was attributable to marginal milk loss from uncomplicated cases of RFM, and $88 was attributable to marginal milk loss of RFM cases complicated with metritis), increased interval until pregnancy of $73 (14 additional days not pregnant at $5.20/d), increased disease risk of $25 ($13.50, $2.50, and $9.00 for increased risk of metritis, DA, and mastitis, respectively), and increased culling risk of $1 ($360 for mean depreciation of a cow multiplied by an attributable risk of 0.17% for culling attributable to RFM). Sensitivity analysis was performed (Figure 1). The estimated cost of a case of RFM was most sensitive to milk and feed prices. Varying the incidences for the various clinical diseases and culling inputs (replacement heifer price, cull cow price, and turnover rate) resulted in a minimal change in the estimated cost of a case of RFM ($374 to $390) when compared with the default value ($386).
Tornado diagram of the results of sensitivity analysis for inputs used to estimate the cost of a case of RFM in a dairy cow in the United States. The diagram shows the change in the estimated cost of a case of RFM that results from a change in the value of a single input. Values in parentheses are base values used in the original model, whereas values on each side of the vertical line in the middle of the diagram are the minimum (white bars) and maximum (black bars) cost of 1 case of RFM after decreasing and increasing the base value by 50%, respectively. The vertical line in the middle of the diagram that separates minimum from maximum values is the calculated estimate of a case of RFM for the original model ($386). To convert milk price /L to milk price /gallon, multiply value by 3.79. To convert feed price /kg to feed price /lb, divide value by 2.2.
Citation: Journal of the American Veterinary Medical Association 252, 12; 10.2460/javma.252.12.1485
Tornado diagram of the results of sensitivity analysis for inputs used to estimate the cost of a case of RFM in a dairy cow in the United States. The diagram shows the change in the estimated cost of a case of RFM that results from a change in the value of a single input. Values in parentheses are base values used in the original model, whereas values on each side of the vertical line in the middle of the diagram are the minimum (white bars) and maximum (black bars) cost of 1 case of RFM after decreasing and increasing the base value by 50%, respectively. The vertical line in the middle of the diagram that separates minimum from maximum values is the calculated estimate of a case of RFM for the original model ($386). To convert milk price /L to milk price /gallon, multiply value by 3.79. To convert feed price /kg to feed price /lb, divide value by 2.2.
Citation: Journal of the American Veterinary Medical Association 252, 12; 10.2460/javma.252.12.1485
Tornado diagram of the results of sensitivity analysis for inputs used to estimate the cost of a case of RFM in a dairy cow in the United States. The diagram shows the change in the estimated cost of a case of RFM that results from a change in the value of a single input. Values in parentheses are base values used in the original model, whereas values on each side of the vertical line in the middle of the diagram are the minimum (white bars) and maximum (black bars) cost of 1 case of RFM after decreasing and increasing the base value by 50%, respectively. The vertical line in the middle of the diagram that separates minimum from maximum values is the calculated estimate of a case of RFM for the original model ($386). To convert milk price /L to milk price /gallon, multiply value by 3.79. To convert feed price /kg to feed price /lb, divide value by 2.2.
Citation: Journal of the American Veterinary Medical Association 252, 12; 10.2460/javma.252.12.1485
Discussion
The overall cost of $386 for a case of RFM obtained for the study reported here is comparable to the total mean ± SD cost of $313 ± 65 for older cows but higher than the cost of $150 ± 51 estimated for primiparous cows.16 There were differences in the approach used to estimate the cost of a case of RFM between the model of the present study and the model used in that other study,16 apart from the fact the model in the present study was deterministic and the model in that other study was stochastic. Because there is no clear benefit of treating cows with RFM,24–26 we decided not to include a treatment cost for RFM. A review of published evidence25 revealed no benefit in the use of hormones or administration of calcium to prevent RFM or for treatment of cows with RFM by use of hormones or antimicrobials to reduce the risk of other diseases or to enhance reproduction. Similarly, authors of other reviews24,26 concluded that the use of antimicrobials to treat RFM provided inconsistent results. Another difference is that the model of the present study considered the association between RFM and an increased risk of other diseases, which added to the accuracy of the calculated estimate. In the study reported here, we factored in the cost of culling (estimated to be only $1), which is consistent with results for not including the cost of culling in the calculations for that other study.16
The authors of 1 study14 estimated that the cost of a case of RFM is £298 ($489), which is higher than that estimated in the present study. The approach used to calculate the loss attributable to premature culling in that other study14 may have led to an overestimation of its value because the authors used a high culling risk for cows with RFM (18.6%) and because they also multiplied that risk directly by the actual cull cow cost of £770 ($1,263), which resulted in a loss attributable to culling of £143 ($235). That calculation did not account for the overall herd culling rate, increased risk of culling attributable to RFM, and culling attributable to RFM in the first 60 days after calving, which were accounted for in the study reported here. Other differences are that the authors of the previous study14 used a lower value of milk production losses (385 kg [847 lb]) and accounted only for the risk of an increase in metritis and not the risk of developing other clinical diseases. On the other hand, authors of another study15 estimated the cost of a case of RFM was £71 ($164). In that study,15 the authors used a cost of £0.6 ($0.96) for a day not pregnant after calving, did not account for an increased risk of other clinical disease (except for treating cases of metritis), used a lower value for milk production losses (207 kg [455 lb]), and multiplied culling attributable to RFM (7.9%) directly by a cull cow cost of £172.5 ($283).
To minimize double counting in the model reported here, the cost of clinical diseases used in calculations excluded losses attributable to reduction in milk yield because that was accounted for separately in the cost of a case of RFM. However, because no treatment costs were calculated specifically for RFM, the costs of veterinary fees and drugs were retained in the total cost of other clinical diseases. In the present study, the change in herd incidence of RFM was not associated with a change in herd incidence of other clinical diseases (metritis, DA, and mastitis). However, a change in the incidence of RFM resulted in a change of the basal and attributable risks of other clinical diseases, which in turn impacted the cost of a case of RFM.
Although deterministic models do not allow for variation of inputs while calculating an estimate, which is in contrast to stochastic models, sensitivity analysis offsets this drawback. Similar to results of another study,16 milk and feed prices in the present study were the most influential inputs, with higher milk prices and lower feed prices increasing the cost of a case of RFM (Figure 1). The reason that milk and feed prices are the most influential inputs is the large reduction in milk yield (753 kg for uncomplicated cases of RFM and 1,012 kg for RFM cases complicated with metritis).
One finding worthy of mention was that if a decrease in milk production by cows that had RFM complicated with metritis was excluded from the analysis, the cost of a case of RFM would have been $297, of which $199 (67%) was attributable to marginal milk loss and $73 (25%) was attributable to an increase in the number of days not pregnant after calving. This finding emphasized that most of the losses resulted from uncomplicated cases of RFM, so preventive measures to minimize the incidence of RFM warrant consideration by veterinarians and producers. Results of the study reported here can be used as part of a farm-specific estimation of the financial merit of actions to prevent RFM. Because most diseases of transition cows are interrelated, a preventative program targeting 1 disease will plausibly result in reducing the incidence of other diseases, but results for the present study underscored the cost for uncomplicated cases of RFM, which we hope will serve to motivate attention to prevention of RFM.
Retention of fetal membranes is a costly disease, which is comparable in cost per case to other well-characterized health disorders of transition dairy cows.21 Measures to prevent RFM (eg, provision of proper nutrition to minimize negative energy balance and enhance immune function, provision of pregnant nonlactating cows with sufficient bunk space to reduce social displacements and ensure feed intake, and parenteral administration or dietary supplementation of vitamin E) during the nonlactating period merit attention in herd health programs.
Acknowledgments
Dr. Gohary was supported by a postdoctoral scholarship funded by DeLaval-Canada and Mitacs.
The authors declare that there were no conflicts of interest.
Funding sources did not have any involvement in the study design, data analysis and interpretation, or writing and publication of the manuscript.
ABBREVIATIONS
| DA | Displaced abomasum |
| DIM | Days in milk |
| RFM | Retained fetal membranes |
Footnotes
Fetrow JF. Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul, Minn: Personal communication, 2013.
Excel, Microsoft Office 2010, Microsoft Corp, Redmond, Wash.
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