The industry’s current understanding of dairy cow mortality is reliant upon descriptions largely based on producer or veterinary assumptions regarding cause of death without the benefit of detailed postmortem evaluations, says Craig McConnel, DVM, MVCS, Colorado State University, in a paper published May 2009 in the Journal of Dairy Science. The paper, “A Necropsy-based Descriptive Study of Dairy Cow Deaths on a Colorado Dairy,” detailed a study that sought to describe dairy cow deaths on a Colorado dairy over a one-year period and explore classification systems for necropsy findings that might influence management changes to reduce mortality.
“Rising mortality levels on dairies have paralleled the increasingly complex structure of larger intensive dairies,” explains McConnel. “Facilities, nutrition, biosecurity, expansion and labor intricacies all combine into a complex management system. This system can be highly productive, but problems and management errors can result in numerous poor outcomes.” One result, adds McConnel, is that as the percentage of dead cows has increased, there are many potential reasons to which deaths can be attributed. “The difficulty is in documenting the deaths so that underlying causes can be defined and appropriately managed.”
McConnel believes a hindrance to establishing meaningful causes of death may be the perception that a certain level of death is inevitable with no particular standard to aim for and no obvious means for capturing useful information that would make a difference anyway. “In other words, there has been little impetus to identify legitimate causes of death when there is no clear use for that level of detail. The end result is that causes of deaths are based on best guesstimates without the benefit of a necropsy and recorded in a format that is not amenable to future monitoring or analysis.”
What the data found
The study included 2,067 cows, of which 94 cows died, resulting in a mortality risk of 6.4 deaths per 100 lactations at risk. McConnel says the distribution of deaths by parity was significantly different from the herd distribution at the end of the study with the largest percentage of death present in parity 4 and above. About 45% of the total deaths occurred within the first 30 days after calving and nearly half of those deaths occurred within the first six days of lactation.
McConnel says a producer’s perception of cause of death can be seriously flawed (45% incorrect overall), particularly when dealing with animals dying an unassisted death (63% incorrect). This study was founded on the premise that a detailed necropsy examination would provide the best information for establishing causes of death.
“The errors in the producer’s perceived causes of death relative to those established by necropsy examination were certainly interesting,” McConnel notes. “While it was expected that there would be discrepancies in the producer’s perception without a postmortem exam, the margin of error was impressive, particularly for those animals that died an unassisted death.” He says it was eye-opening how many specific proximate causes of death were represented on this single farm, “that 94 deaths could be broken into 29 separate specific causes speaks to the complexity of the issue of mortality.”
Each death was characterized by a proximate cause based upon a necropsy, and then was categorized. Review cate-gories included accidents, calving disorders, digestive disorders, locomotor disorders, metabolic disorders, udder/teat disorders, other known reasons and unknown reasons. The veterinary medical record scheme was based on the mnemonic acronym DAMN-IT.
Postmortem findings representing the proximate cause of death for the 94 cows included (ranked from highest to lowest) severe limb injury, GI ulceration, metritis, spinal injury, abdominal/liver abscess, toxic mastitis, digestive-infectious, lymphoma, pneumonia (chronic and aspiration), ruptured uterus, unknown, arthritis, joint infection, metabolic, nerve damage, acute pneumonia, post-surgical trauma, abdominal exsanguination, chronic inflammation, hardware, peritonitis, septicemia, thrombosis, choke, digestive-obstructive, lacerated milk vein, malignant edema and prolapsed uterus.
Recording cow deaths
While having a cause of death is an important first step in getting a handle on dairy cow mortality, the information gained from a necropsy examination must be recorded in a format that can be used for formulating management strategies. Because an individual death is often the end result along a continuum of failures, if only a single reason is documented it may be in error. McConnel says most record systems on U.S. dairies are focused on reproductive and milk production performance and are primarily used by producers to evaluate the current status and performance of animals as well as to generate “to-do” lists. The usefulness of these records for analyzing his-tory and cow death reasons leaves a lot to be desired.
Necropsying as many animals as possible would be ideal, but has the potential to overwhelm the veterinarian. McConnel’s study suggested that there are subsets of animals for which a necropsy really does not provide enough information to necessarily justify the time and expense. “It is unlikely that necropsying the majority of euthanized animals and/or animals that died due to accidents or locomotor disorders will provide enough additional information to warrant the effort,” he says.
“However, this does not mean that these deaths should not be documented along with those unexplained deaths for which a postmortem examination is imperative. All deaths should be recorded and the issue becomes one of effectively labeling and categorizing deaths so that they can be analyzed in total as a part of herd health monitoring.”
Establishing legitimate diagnoses through postmortem analyses, in tandem with recording those diagnoses such that they can be tracked effectively, is necessary if the cause and effect of management and operational vagaries are to be addressed, McConnel adds.
The DAMN-IT scheme
DAMN-IT (or DAMN-IT V) is a mnemonic acronym to help veterinarians develop a list of differentials. It has the following categories: Degenerative; Anomalous, autoimmune; Metabolic; Neoplastic, nutritional; Inflammatory (infectious or noninfectious), immune mediated, iatrogenic, idiopathic; Traumatic and toxic, and is often also followed with “V” for vascular.
Diagnostic acronym: the DAMN-IT V scheme
D = Degenerative
A = Anomaly
M = Metabolic
N = Neoplastic, nutritional
I = Inflammatory, infectious, immune mediated
T = Trauma, toxicity
V = Vascular
Mortality records: Making them make sense
Regardless of whether current record systems are modified or new systems are developed to more thoroughly address dairy health issues, it is important to have simplicity and consistency. “It can be difficult to piece together historical influences that ultimately lead to poor outcomes, and this difficultly is a limiting factor in current record systems,” says Craig McConnel, DVM, MVCS.
Nonetheless, data entry within even the most basic record systems can often be streamlined to allow for more effective analysis. Farms can individually tailor their data recording regardless of their record system such that like events and/or outcomes can be combined and monitored using simple, consistent terminology. “However, until record systems are made that integrate historical data with current outcomes it will remain difficult to thoroughly address dairy cow mortality,” McConnel says.
It is important to recognize that the final outcome of death is the end result along a continuum of failures, notes McConnel. “Incorporating a sense of those underlying issues that lead to a death within the categorization of that death provides an avenue for exploring preventive managerial alternatives. For instance, it is not necessarily enough to simply name a disease. Mitigation of losses requires that the cause of the disease is identified. Noting that a cow was euthanized as a downer is not as useful as noting why she was down, such as metabolic problems, calving trauma, or injury from falling on concrete.” Accounting for that level of detail within record systems that group similar underlying causes together is the first step toward pursuing preventive strategies.