The Role of the Lab in the Investigation of Herd Health Problems:
Intelligent Use of Lab DiagnosisIreland

[Although Grange does not test samples for the public now, the data in this paper will be useful background material  for professionals]

Workshop for Animal Health Professionals, 09-09-1999
Grange Research Centre, Dunsany, Co. Meath, Ireland

Phil Rogers MVB, MRCVS & Bernadette Earley PhD
philrogers@eircom.net & bearley@grange.teagasc.ie

INTRODUCTION
Farmer-perceived problems of herd health | Multifactorial aspects of herd health disorders | Need for good clinical diagnosis | Diagnosis is clinical skill | Definitive diagnosis | Nonclinical problems

INTELLIGENT USE OF LAB RESULTS
Previous history of supplementation | Appropriate blood samples | Appropriate animals | Sample problem group at problem time | Timing of blood samples | Trace-element check in healthy herds | What tests to request? | Which Labs to use? | Summary | Further reading

Introduction

Based on fictional stories of hospital- and medical- practice, popular TV programmes often give the impression that the Lab is crucial in the diagnosis of disease. After working with animal health problems and Lab results for >35 years, in my experience that impression is very misleading; life, and veterinary diagnosis, is not that easy.

The Internet [http://www.vet.cornell.edu/consultant/consult.asp] has a very useful piece of free diagnostic software, the Cornell Consultant. It allows users to input all the presenting clinical signs of a case. It then returns the diagnoses that fit those signs. If you have not used the package before, check it out! It will remove any illusions that casual Vets may have about their diagnostic ability - the ability to recall all the diseases which may present with a given set of clinical signs. However, the package is not perfect; for example, some of the common signs of trace-mineral deficiencies are omitted. Thus, some of the possible diagnoses, say for stillbirth, or calf mortality, are overlooked.

With or without the help of expert software, it is usually easier to diagnose herd problems than problems in individual animals. However, the history and clinical data usually are more important than the Lab data in both situations.

The Grange Laboratories can help little to diagnose problems in individual animals in a large herd. Having several hundred possible causes, a disorder in individual cattle is more complex, difficult, and prone to diagnostic error than a herd problem, or a problem common to a large group of cattle. Without a full history and clinical information from the practitioner who has seen the affected animals, diagnosis by Lab personnel (including vets) could be incorrect in many cases. Even with good background information and Lab results, the team (Lab staff and practitioner) may fail to solve the problem, in that it continues after implementation of an action programme based on the total history. That said, the Lab can help practitioners to confirm their clinical suspicions in many cases.

This paper will discuss the investigation of farmer-perceived problems of herd health, and the role of the Lab [especially the Grange Blood Lab] in helping the investigation. The following areas will be discussed:

1. Farmer-perceived problems of herd health

Table 1 shows typical bovine herd health problems for which farmers seek veterinary help. It also shows the "normal" background incidence, and incidences classed as slight, moderate and severe.

Table 1. Indices to assess the severity or otherwise of a reported problem of "herd infertility"

1. PR% (Pregnancy Rate) to a given service is calculated separately for 1st, 2nd, 3rd, 4th services, or for all services as: (100 X number of dams pregnant (confirmed, or assumed) to that service / number of dams given that service). As a guide to herd fertility, the % pregnant to 1st service is most useful, as it may identify problems early on. If a PD was not made and if a dam has not been seen in heat by 56 days after the last service, she is assumed to be pregnant to that service. A PR based on veterinary PD by ultrasound or palpation per rectum is more accurate than a PR based on 56-day non-return rates, as some of the latter may not have conceived (and been subsequently missed, or become anoestrous), or they may have conceived, lost the pregnancy and then been missed.
2. S/C (Services/conception) for all served dams = (Total services / Total number of dams pregnant, or assumed pregnant on 56-day non-return). Data for any dams culled or dead within 56 days of last service, or before PD or subsequent calving, are excluded.
3. CFSI (Calving to First Service Interval) in days (Postpartum Interval): The mean interval is calculated for all calved dams which were served, including those sold or dead during the period of the analysis.
4. CCI (Calving to Conception Interval) in days (Days Open): The mean interval is calculated for all calved dams which were pregnant, or assumed pregnant (on 56-day non return), including those sold or dead after a positive PD.
5. SR% (Submission Rate) = (100 X number of dams served, or seen in heat but not served, in a 3-week period early in the breeding season / number of dams eligible for breeding in that period). Note: In this definition, "Eligible dams" = ALL CALVED DAMS, as in some herds, some dams may be served before 30 days postpartum; in Moorepark, 4% are served pre-30 days postpartum). Genuine anoestrus as well as poor heat detection can reduce this index.
6. NDO% (Non-Detected Oestrus) = (100 X number of dams calved 42 days or more but not served / number of dams calved 42 days or more). Genuine anoestrus as well as poor heat detection can increase this index.
7. HDR% (Heat Detection Rate) = (100 X number of services) / (number of services + number of missed heats). The number of missed heats is assumed as 1, 2 or 3 for each return interval of 36-53, 54-72 and 73-96 days respectively. This index can be reduced by embryonic loss or fertilisation failure, followed by genuine anoestrus.
8. Normal (18-24 day) returns: With good heat detection, 60-65% of returns should be 18-24 days. A high % repeats at intervals <18 days, with a low % at 18-24 day repeats, suggests poor heat detection and presentation for service of dams that are not in heat. A high % of long repeats (>24 days), with a low % <18 days suggests over cautious heat detection and failure to inseminate dams which are actually in heat (but are missed). A high % of long repeats can also occur with loss of the embryo due to infection etc, or with anoestrus (after one or more normal heats).
9. Culling of pregnant dams!: 8-12% of dams culled as empty are pregnant at slaughter. All dams should be pregnancy-tested early. At the very least, dams should be pregnancy-tested before culling to ensure that they are empty.

More recent statistical analysis of cow fertility in Ireland (O'Farrell KJ & Harrington D (1999) Reproductive performance targets: the effect of herd size. Irish Vet J 52(8):440-441) show that the indices of suspicion of, and for intervention to solve, herd fertility problems relate to herd size. Coincidental or random events in one or two cows in smaller herds greatly increase the error factor in deciding if there is a herd problem or not. The next table shows the "Cut-off" Points (?) and Intervention Levels (I) above or below which a fertility problem may exist (at 95% confidence level) for different herd sizes:

CSI = Calving to service interval; CCI = Calving to conception interval; HDE = Heat detection efficiency;
¹Same for 18-24 day repeats;
²Same for heat detection rate (%);
³Same for non-detected oestrus (%)

Fertilisation rate and embryonic/foetal/calf loss: Fertilisation rate to AI averages about 90% but the calving rate to a single service averages about 50%, i.e. about 10% of services and 45% of conceptions and do not progress to a viable pregnancy. National calf losses (embryos + foetuses + neonates) are about 47+5% of fertilised ova.

Estimates of the timing and % of embryonic, foetal and calf losses and total losses are:

Table 2. "Normal" background incidence (% of group at risk) of calf mortality (conception to c. 3 weeks of age.

* CALF LOSSES: Calves can die in-utero, at birth, or in the days or weeks after birth. "Acceptable losses" for abortion, stillbirth and neonatal calf deaths are 2, 3 and 2% respectively, or a total calf mortality of up to 7%. Teagasc investigation of farmer-complaints is unlikely to reduce losses significantly if total calf loss is <7%. Unless herd incidence exceeds these figures, herd investigation is not warranted. The higher the incidence, the more important it is to establish the causal factors, and to plan effective control measures.

Table 3. "Normal" background incidence (% of group at risk) of other common bovine disorders

* Unless herd incidence exceeds these figures, herd investigation is not warranted. The higher the incidence, the more important it is to establish the causal factors, and to plan effective control measures.
** Routine precautions are advised to prevent these conditions. With good control measures, the herd incidence should be zero to negligible.

Farmer-perceived problems of herd health may be "real" or "imagined". The first task of the vet practitioner is to establish which is the case, i.e.:

1. to qualify the problem (establish its nature, timing, duration, signs, symptoms and effects on health and productivity; what types of animals, ages, stage of pregnancy, lactation etc are affected) and
2. to quantify its extent (what % of the group(s) are affected - 1, 5, 10, 20, 40% etc).

It is important to establish these at the outset, because serious problems warrant serious investigation. In contrast, minor or merely aesthetic problems warrant little investigation and have less chance of success as regards control or future prevention.

For example, the owner of a 75-cow herd may ask for investigation of herd infertility when 3 of his best cows return for service for the fourth time. On inspection of the fertility data, the vet may find that the overall herd conception rate to a given service is 65%. In that case, a detailed herd investigation is not warranted, but individual treatment of affected cows may be worthwhile.

"Imagined" problems (i.e. those at or below "normal" background incidence) do not warrant detailed investigation, or corrective actions that may put significant expense on the farmer. There are exceptions to that guideline:

• The essentials for life and optimal health are high quality air, water, food and shelter, in that order of priority.
• High animal productivity demands high standards of nutrition, management and husbandry.
• It is essential that calves receive 2 litres of high quality colostrum within one hour of birth and a second 2 litres at 4 to 6 hours later. Friesian X Holstein calves should be helped to suckle, tubed, or hand-fed 4 litres of colostrum in two feeds within 6 hours of birth.
• Routine vigilance and prophylaxis are needed to control infectious, toxic and parasitic diseases.
• High levels of herd fertility demand high standards of nutrition, heat-detection and management.
• It is wise to take routine precautions to prevent common disorders such as milk fever, grass tetany, mastitis, lameness, etc.
• It is wise to provide high-quality minerals routinely to bulling heifers close to breeding, and to cows for 1 month prepartum (Dry Cow Minerals) and 4 months postpartum (Lactation Minerals - usually in dairy rations - while indoors, and Tetany-Control Minerals while grazing in the tetany-risk periods), and to weanlings and finishers in winter.

"Real" problems may be relatively unimportant (causing no to slight economic loss or no to minimal animal suffering, or of aesthetic importance only) or important (causing moderate to severe economic loss or animal suffering).

Examples of real but unimportant "herd problems" are (a) pica, (b) non-clinical ketonaemia or uraemia, and (c) rough, patchy, discoloured haircoats.

1. Pica: Many farmers ask for herd investigation if their cows or other cattle show signs of pica (urine- or slurry- drinking indoors in winter, or bark- or soil- ingestion at pasture). Although pica can be a sign of mineral imbalance and other conditions, and it can possibly cause ingestion of infection or toxins, it usually is harmless and of aesthetic interest only.
2. Non-clinical ketonaemia or uraemia: Routine milk-, urine- or blood- test may show high levels of ketones in high-yielding dairy herds in early lactation indoors. Milk- or blood- tests in cows, especially in the first few months after turnout to heavily fertilised pasture, may show (in fact usually show) high levels of urea.
3. Rough, patchy, discoloured haircoats: Although anomalies of the haircoat may be a sign of many chronic disorders (deficiency of P, Cu and Co, Se toxicity, parasitism, chronic infection, undernutrition etc), healthy and thriving animals can have rough, patchy, discoloured haircoats, especially in the first few months after turnout to pasture.

In those examples, provided all other indices of health and productivity are normal, detailed investigation and corrective action are not needed. In the case of pica, most attempts at corrective action fail as long as the animals have access to the "desired" material. In a herd with poor coats, the hair may improve some weeks after administration of a CuO bolus, but the improvement may be coincidental only (i.e. unrelated to Cu status) unless some animals were left untreated for comparative purposes. If, however, in the examples above, OTHER indices of health and productivity are subnormal, a detailed herd investigation may be justified, in which case the emphasis should be placed on the OTHER indices.

2. Multifactorial aspects of herd health disorders

Most serious herd health disorders are multifactorial; they seldom arise from a single cause. These can include genetic, nutritional (water-, energy-, protein-, mineral-, vitamin-, metabolic-, toxic-), infectious-, parasitic-, allergic-, environmental/climatic-, managemental- and stress-related-, and many other factors. Thus, the most successful control measures must address many, if not all, of the causal factors.

3. Need for good clinical diagnosis of clinical or subclinical herd illhealth

"Real" problems of clinical or subclinical herd health need good clinical diagnosis - accurate identification of the nature and extent of the problem, and its main causal factors. Good diagnosis is the basis for the best specific corrective actions to treat, control and prevent the problems.

4. Diagnosis is a clinical skill

Diagnosis of animal health problems is a clinical skill, best done by experienced vets who know the problems of the local herds. When asked to investigate a "real" clinical or subclinical problem of herd health, the vet must try to define the nature, timing, duration and extent of the problem. These data help the vet to qualify and quantify the problem, and to decide if additional help or Lab investigation is needed to confirm the clinical suspicions.

5. Definitive diagnosis

A clinical diagnosis is confirmed only when a specific set of corrective actions in a properly randomised set of affected cattle clearly improves their status relative to that of untreated (control) cattle in the same peer-groups over the same time period. Thus, few diagnoses of herd illhealth are definitive. This is because properly randomised comparisons seldom are used in practice, and vix naturae, or changing circumstances, resolve many conditions in time.

6. "Nonclinical problems"

Severe imbalance of mineral-, metabolite-, enzyme-, vitamin- levels in bovine blood and tissues, and of minerals in soil and forage, are commonplace in the absence of any detectable animal health problem. Examples of abnormal Lab results which often arise in apparently healthy herds, and correction of which may not significantly improve animal productivity, are:

For example, >80% of Irish herds that are unsupplemented with iodine (I) in the days before blood test are low to very low in I on a plasma inorganic iodine (PII) test. However, most of these herds have no detectable health- or productivity- problems. Supplementation of those herds with 60 mg I/cow/d predictably restores PII to the mid-normal range within hours, but no improvement in health or productivity follows because the herds have no pre-existing clinical or subclinical problems.

Similarly, high levels of GLDH, GPx or pepsinogen in blood may suggest liver-stress, Se-toxicity or abomasal / intestinal parasitism, respectively. However, the sampled animals may have no detectable signs of these conditions. Also, cattle may be exposed to infection or toxic agents (as detected by Lab tests), yet show no detectable adverse effects.

That said, intelligent use of the test results can support (or refute) a vet's clinical suspicions, but abnormal (or normal) Lab tests should NOT be used as a substitute for a clinical diagnosis, and the diagnosis is not confirmed until the conditions in (5), above, are met.

7. Intelligent use of Lab results

An accompanying paper (Rogers et al., 1999: "Biochemical variables and trace element analyses") will discuss breakpoints used at Grange to assess the "normality" or otherwise of samples, and the interpretation of the results in relation to the clinical- and health- history of the herd.

Depending on the reason(s) for sampling, and the background history of supplementation and feeding etc, intelligent use of Lab results implies intelligent collection of the appropriate type of samples from the appropriate group(s) of animals, at the appropriate time. With the above in mind, practitioners should note the following:

Previous history of supplementation and feeding: Before any samples are taken, it is most important to do a "paper exercise" on the nutrition and supplementation of any herd under investigation for a herd problem. Vets should try to quantify the intake of water, energy, protein, minerals and minerals in relation to the requirements of the herd. If a mineral-imbalance is suspected, the "paper-exercise" may eliminate that suspicion immediately, and save the farmer the cost of unnecessary Lab fees.

For example, if a farmer or vet suspects Mg or I deficiency as a cause of reduced feed intake or cow infertility, estimation of the I intake from supplements may show that the cows are getting 2 kg of Summer Feed, containing 18 g Mg and 30 mg I/kg. The supplementary Mg and I intake in that case would be 36 g and 60 mg/cow/d, respectively. These would be generous amounts! Assuming that the feed actually supplied those amounts, the chances of hypomagnesaemia, or of I deficiency, occurring in that herd at that time would be very low.

When blood samples are submitted in connection with suspect nutritional or metabolic disorders, it is most important that a brief history of the problem, and of the feeding and supplements used, be sent with the samples. Failure to do that may compromise the interpretation of the Lab tests.

Appropriate type of blood samples: The type of sample is discussed in the accompanying paper (Rogers et al 1999).

Appropriate group(s) of animals: Vets who submit samples from insufficient numbers, or from the incorrect animal type can expect misleading Lab results. For consistent results, it is advisable to sample 8-10 animals from a problem herd. If more than one group is involved (say bulling heifers and cows in milk), 5-6 samples should be sent from each group.

Sample the problem group at the problem time! To investigate milk fever, bloods should be taken within 1 day of calving, because blood Ca is remarkably normal for most of the year, except at that time. To investigate problems around the time of parturition (perinatal calf death, lazy calves, low calf immunity, retained placenta etc), dry cows are the best ones to sample. Calved cows in the same herd may have a totally different mineral profile because of supplementation after calving. To investigate a problem of herd infertility, sample the problem group close to breeding, or during breeding.

Timing of blood samples: There is little point in testing blood in September for a problem, which began in May. See the previous paragraph as regards testing of problem herds. However, one may also use blood tests to monitor for normality [to confirm effective control measures]. In that case, sample the animals while they are on the supplement.

Sampling to check trace-element status in apparently healthy herds: In recent years, many farmers have asked their vets to check the blood trace-element status of unsupplemented cows or yearlings in the late autumn. That is the best time for a routine check. If Cu and Se status are normal in that case, it is unlikely that they have been, or will be, a problem in that farm. However, Mg and I fall rapidly in periods of shortage, and one can expect >80% of unsupplemented cattle to be low in I at that time.

What tests to request depends on the problem, or the reason for sampling. Grange can help in the investigation of mineral- metabolic- nutritional problems, and in some infectious problems. However, in the detailed investigation of problems of infectious disease, poisoning, parasitosis etc, other tests may be needed from other Labs. If in doubt, practitioners should consult with the Lab before submitting samples.

Which Labs to use?

Grange Labs: The accompanying paper (Rogers et al 1999) lists the tests available at Grange, under the headings of milk tests, blood major elements and trace elements, liver Cu tests, nutritional and metabolic variables, antibody tests and haematology.

Veterinary Research Lab (Abbotstown) & RVLs: These Labs offer detailed microbiology, serology, faecal examination and postmortem examination etc, in infections, poisoning, parasitosis and serious diseases.

Other Teagasc- & commercial- Labs: Occasionally, vets may need specific feed analyses [for nutritional value, essential major- and trace- minerals], or soil analyses [soil fertility, Co/Mn, heavy metals]. These can be done in the Teagasc Labs at Johnstown Castle, Wexford, or in some Commercial Labs in the State.

Quality Control can be slack in commercial Labs. Any "Lab-in-a-garage" can issue a report, and, because of desktop publishing software, a report can "look well" but be worthless. Vets should ensure that the Labs that service their needs are accredited, or at least are involved in "Ring Tests" with reputable national and international Labs of high quality. They should also ensure that the Lab issues guide values for each test.

Medical and Toxicology Labs: Beaumount Hospital (Dublin, Tel: 01-837-9964) runs the Poisons' Information centre, and the Beaumount Toxicology Lab (Dublin, Tel: 01-809-2673, or 01-809-2675) can assay for specific toxins. By special arrangement, if vets suspect specific poisons or toxins as causes of disease, samples may be sent for analysis to that, or other, specialist medical Labs.

Out of State Labs: Certain tests, for example assay for antibiotic contamination, some vitamins (A, E), or fungal toxins in cattle feed, are unavailable, or difficult to obtain, within the State. Samples for such tests may have to be sent, by prior arrangement, to Labs outside of the State. Similarly, assay of soil or feed for industrial toxins such as dioxins etc may be very expensive and can be done only in specialist labs, usually abroad.

As discussed above, Lab tests should be used to support or refute a clinical diagnosis. As severe anomalies on blood- and other- tests often are found in otherwise healthy and thriving herds (see (6) above), "abnormal" Lab tests should be discounted unless there is clinical justification to take note of, and act on, them.

Further reading on the investigation and control of ruminant health problems

If you are not already on e-mail, I encourage you to "get wired" as soon as possible. E-mail and the WWW are essential parts of modern communications and information technology. Without access to these facilities, professionals will not be able to keep pace with, or filter, the information explosion that is happening now. Meanwhile, for those not using the Internet, because printing, copying and faxing or posting are time-consuming and expensive, I can send the notes only as e-mail attachments to a friend or colleague whom you nominate. For any or all of these notes, send an e-mail <philrogers@eircom.net> and indicate the title(s) of interest.

Condensed notes on the topics listed below are on the WWW (Internet) at tecnotes.htm and can be downloaded from there.

Technical notes for Vets & Nutritional Consultants

Technical Notes are available online. Click on the one(s) of interest to retrieve the text from the Internet.