# Dairy Herd Reproductive Efficiency: Metrics and Diagnostic Investigation ## Key Takeaways - Dairy herd reproductive inefficiency is systematically diagnosed by stratifying performance metrics to differentiate between detection failure (indicated by low service rate or prolonged days to first service) and conception failure (indicated by low conception rate). - Subclinical endometritis, diagnosed via endometrial cytology with a threshold of ≥5% polymorphonuclear cells between 21-62 days postpartum, significantly impairs conception rates and prolongs days open, necessitating targeted sampling and intervention. - Metabolic profiling via blood sampling for beta-hydroxybutyrate and non-esterified fatty acids in early lactation cows is crucial for identifying negative energy balance, subclinical ketosis, and hypocalcemia, which suppress luteinizing hormone pulse frequency and delay cyclicity. - Infectious agents like Bovine Viral Diarrhea Virus (BVDV) can cause widespread reproductive losses including reduced conception, embryonic death, and abortion; investigation requires screening for persistently infected animals and appropriate serological or antigen testing. - Stressors such as lameness or milk fever disrupt reproductive hormone release, leading to prolonged calving-to-conception intervals and increased inseminations per conception, necessitating assessment of cow comfort, body condition, and transition cow health. - Accurate record-keeping of calving dates, service dates, pregnancy diagnoses, and culling events is foundational, enabling the calculation of critical metrics like 21-day pregnancy rate, conception rate, and service rate, which guide the diagnostic pathway. --- This article provides a structured approach to evaluating and diagnosing reproductive inefficiency in dairy herds. It is written for practicing veterinarians who investigate herd-level fertility problems and advise on management change. The focus is on the diagnostic pathway from record analysis to targeted examination, not on treatment of individual cows. The clinical question addressed is direct: when a dairy herd underperforms reproductively, how does the veterinarian distinguish problems of detection, conception, and pregnancy loss, and which diagnostic tools resolve each category? The article covers the metrics that define normal and abnormal performance, the biological basis of reproductive failure, and a staged investigation protocol. ## At a Glance | Parameter | Definition | Typical target or decision point | |---|---|---| | 21-day pregnancy rate | Percentage of eligible cows becoming pregnant each 21-day cycle | Herd benchmark varies by region and system, trend matters more than a single value | | Conception rate | Pregnancies per 100 inseminations | Compare by parity, service number, and season | | Service rate | Inseminations per 100 eligible cows in 21 days | Low values indicate detection failure | | Days in milk at first service | Interval from calving to first insemination | Prolonged values suggest detection or voluntary waiting period issues | | Pregnancy loss rate | Proportion of confirmed pregnancies lost before term | Investigate if above expected herd baseline | | Calving interval | Interval between successive calvings | Rolling annual value reflects cumulative reproductive performance | | Submission rate | Cows inseminated within a defined postpartum window | Useful for monitoring detection efficiency | ## Defining Reproductive Efficiency in Dairy Herds Reproductive efficiency in dairy herds is a composite of three distinct biological processes: the resumption of ovarian cyclicity after calving, the expression and detection of estrus, and the establishment and maintenance of pregnancy. Failure at any point produces characteriztic changes in herd records. The diagnostic value of herd metrics lies in their ability to separate these failure points before physical examination begins. The 21-day pregnancy rate integrates both detection and conception into a single value. It is the product of service rate and conception rate, and it is the most useful single metric for monitoring herd performance over time. A decline in 21-day pregnancy rate demands decomposition into its components, because the corrective actions for detection failure differ completely from those for conception failure. Calving interval remains the traditional cumulative measure, but it is a lagging indicator. A full calving interval spans 12 to 14 months, so a herd problem may be present for several cycles before the interval reflects it. Rolling annual calving interval values are best used to confirm the magnitude of a problem identified by more current metrics. ## Physiology of the Postpartum Period The postpartum dairy cow must undergo uterine involution, resumption of ovarian follicular growth, and establishment of cyclic luteal function before she can conceive. These processes occur concurrently with the onset of lactation, which imposes substantial metabolic demand. The interaction between energy balance and reproductive hormone secretion is central to herd fertility. Negative energy balance in early lactation suppresses luteinizing hormone pulse frequency, delaying first ovulation. Cows that lose excessive body condition or that fail to resume cyclicity by 60 days in milk have prolonged intervals to first service and reduced conception rates. The relationship between metabolic status and fertility is not limited to the pre-service period. High-producing cows have increased metabolic clearance of steroid hormones, which affects the endocrine environment around insemination and during early pregnancy. Uterine health is a second critical determinant of postpartum fertility. Endometritis, whether clinical or subclinical, impairs conception and extends days open. Subclinical endometritis is defined by endometrial cytology, typically using the cytobrush technique or low-volume uterine flushing, with polymorphonuclear cell thresholds that vary by days postpartum. A general threshold of 5 percent polymorphonuclear cells has been proposed for cows between 21 and 62 days postpartum. The condition reduces conception rates and prolongs both days to first service and days open, and it may affect embryo survival and quality. Sampling is minimally invasive and does not depress subsequent conception. ## Stress and Reproductive Performance Stress acts on reproduction through multiple endocrine pathways. Field data from dairy cows indicate that stressors such as milk fever or lameness extend the calving to conception interval by 13 to 14 days and add approximately 0.5 inseminations per conception. The mechanisms involve disruption of the precise timing of reproductive hormone release within the follicular phase, with alterations in gonadotropin secretion that impair follicular development and ovulation. The practical implication for herd investigation is that stressors must be identified and quantified. Lameness prevalence, body condition score distribution, and transition cow disease rates are all relevant inputs to a reproductive investigation. A herd with excellent metrics for detection and semen handling but with elevated lameness prevalence will show a characteriztic pattern of reduced conception instead of reduced service rate. ## Infectious Causes of Reproductive Failure Infectious agents can interrupt reproduction at any stage from conception to calving. Bovine viral diarrhea virus is notable for its capacity to cause reduced conception rates, early embryonic death, abortion, congenital defects, and the birth of weak calves. The birth of persistently infected calves perpetuates the virus within a herd and spreads it to other herds. Bulls acutely or persistently infected may shed virus through natural service or semen used in artificial insemination. Control depends on elimination of persistently infected animals, biosecurity, and strategic vaccination. The diagnostic approach to suspected infectious reproductive failure requires a defined protocol. Abortion submissions should include fetal tissues, placenta, and maternal blood where feasible. Serologic testing of paired samples from affected cows can identify recent exposure, but interpretation requires knowledge of vaccination history. For agents such as bovine viral diarrhea virus, the presence of persistently infected animals is the key finding that explains ongoing reproductive loss. ## Genetic and Management Contributions Genetic selection has changed the reproductive landscape of dairy herds. Genomic selection enables prediction of genetic merit from genome-wide markers and has been adopted by dairy industries worldwide. It is expected to double genetic gains for milk production and other traits. However, selection for production traits has historically been accompanied by declining fertility, and current breeding programs increasingly include fertility traits in selection indices. Herd investigation should consider whether genetic trends are working with or against reproductive management goals. Management factors that affect fertility include semen handling, insemination technique, timing of insemination relative to estrus, and the accuracy of estrus detection. Estrus confirmation at insemination is a critical determinant of conception. The delivery of an appropriate number of normal spermatozoa to the appropriate site at the appropriate time of estrus remains the fundamental requirement for successful artificial insemination. Errors in any of these steps produce conception problems that mimic biological infertility. ## Diagnostic Sequence for Herd-Level Reproductive Inefficiency A structured investigation begins with record analysis, proceeds through targeted physical assessment, and concludes with a prioritized action plan. The sequence is iterative: findings at any stage may redirect the investigation. ### Step 1: Define the Problem from Records Calculate the key metrics described in Part 1 for the affected cohort and compare them with the herd's own historical baselines and regional benchmarks. Separate the analysis by parity, calving season, and service sire. A problem confined to first-lactation animals suggests a different aetiology than one affecting the entire herd. The first decision point is whether the deficit lies in service submission or conception. Submission problems present as prolonged days to first service with acceptable conception rates. Conception problems present as low conception rates with acceptable submission patterns. Mixed patterns occur and require separate analysis. ### Step 2: Physical Assessment of the Herd and Environment Walk the housing, feeding, and handling facilities during a routine milking or feeding period. Assess cow comfort, stocking density, stall dimensions, and footing. Observe oestrus detection aids and their placement. Review the ration as fed, not as formulated, and collect representative samples for analysis if a nutritional component is suspected. Body condition scoring of the milking herd and the dry cow group provides immediate information about energy balance. Target body condition score at dry-off, calving, and peak lactation should be compared with the herd's actual distribution. [The relationship between stress and reproductive failure](https://pubmed.ncbi.nlm.nih.gov/10844239/) is well documented, and poor body condition represents a chronic metabolic stressor that delays cyclicity and reduces conception. ### Step 3: Targeted Diagnostic Testing Selection of diagnostic tests follows the record analysis. A herd with normal submission and poor conception warrants investigation of semen handling, insemination technique, and uterine health. A herd with poor submission warrants investigation of oestrus detection efficiency, anovulation, and periparturient disease. **Uterine health assessment.** Cytological evaluation of the endometrium identifies subclinical endometritis, which reduces conception rates and prolongs days open. [The cytobrush technique and low-volume uterine flushing](https://pubmed.ncbi.nlm.nih.gov/28407857/) are minimally invasive and do not impair subsequent conception. A threshold of 5% polymorphonuclear cells is applicable for cows between 21 and 62 days postpartum. Sample a minimum of 10 to 15 cows per parity group within the at-risk window. **Metabolic profiling.** Blood sampling from a representative group of cows at defined lactation stages detects subclinical ketosis, hypocalcemia, and negative energy balance. Sample 8 to 12 cows per group at 7 to 21 days in milk for beta-hydroxybutyrate and non-esterified fatty acids. Interpretation requires comparison with laboratory reference intervals and consideration of sampling timing relative to feeding. **Infectious disease screening.** [Bovine viral diarrhea virus affects all phases of reproduction](https://pubmed.ncbi.nlm.nih.gov/15062471/), from conception through fetal development. Screening for persistently infected animals is indicated when early embryonic death, abortion, or poor conception occurs in the absence of management explanations. Bulk milk antibody testing and individual antigen testing of calves and youngstock identify viral circulation. ### Step 4: Prioritize Findings and Implement Changes Rank identified problems by their contribution to the overall reproductive deficit and by the feasibility of correction. A single dominant problem, such as anovulation from overconditioning at dry-off, may explain most of the deficit. Multiple smaller problems often coexist and require simultaneous correction. ## Monitoring Parameters and Their Interpretation The following table summarizes monitoring parameters, the abnormality each detects, and the diagnostic action triggered. | Monitoring parameter | Target or threshold | Abnormality detected | Diagnostic action | | --- | --- | --- | --- | | 21-day pregnancy rate | Herd-specific, typically 15 to 25% | Combined submission and conception deficit | Separate into submission rate and conception rate | | Submission rate (oestrus detection) | 60 to 70% of eligible cows per 21 days | Poor oestrus detection, anovulation, silent oestrus | Review detection aids, assess cyclicity, check periparturient disease | | Conception rate at first service | 35 to 45% for lactating cows | Uterine disease, semen handling, timing of insemination | Uterine cytology, semen evaluation, insemination technique audit | | Days to first service | 60 to 75 days | Delayed cyclicity, poor detection, extended voluntary waiting period | Metabolic profile, body condition scoring, detection audit | | Calving interval | 12 to 13 months | Prolonged days open, extended service period | Review all preceding metrics | | Prevalence of subclinical endometritis | Less than 10 to 15% of sampled cows | Uterine inflammation, poor uterine involution | Cytobrush sampling, review calving management | | Persistently infected cattle with BVDV | Zero | Active viral circulation | Antigen screening, biosecurity review | ## Equipment and Consumable Choices The cytobrush technique requires commercially available cytobrushes, a protective sheath, glass slides, and a staining kit. Low-volume flushing requires a sterile catheter, syringe, and collection vessel. Both methods require a microscope with a 400x objective for polymorphonuclear cell counting. Metabolic profiling requires serum or plasma tubes, a centrifuge, and access to a diagnostic laboratory. Point-of-care ketone meters provide immediate beta-hydroxybutyrate results but have higher per-sample cost than laboratory analysis. Ultrasonography with a 5 to 7.5 MHz linear or convex transducer is required for pregnancy diagnosis and ovarian assessment. Doppler capability, as described in [the review of noninfectious factors affecting fertility](https://pubmed.ncbi.nlm.nih.gov/22153267/), permits evaluation of luteal blood flow and may improve early pregnancy diagnosis, but adds cost and requires additional training. ## Documentation and Record Keeping Record all findings in a format that permits longitudinal comparison. For each investigation, document the cohort sampled, sampling dates, laboratory results, and the specific metrics calculated. Photographic records of body condition scoring and cytology slides support consistency across examinations. The herd record system must capture the events needed for metric calculation: calving dates, service dates, pregnancy diagnosis results, and culling dates. [Dairy herd data management systems](https://www.msdvetmanual.com/) vary in sophistication, but the minimum requirement is accurate event recording with dates. Without reliable event data, none of the diagnostic steps described here can be performed. ## System-Specific Considerations The diagnostic approach differs between confinement and pasture-based systems. Pasture-based herds often have seasonal calving patterns that concentrate reproductive events, making submission rate the dominant constraint. Confinement herds with year-round calving can address conception problems with less seasonal pressure. Herd size changes the feasibility of diagnostic testing. Cytobrush sampling of 30 cows is practical in a 200-cow herd but may be impractical in a 2,000-cow herd where a larger sample is needed for statistical confidence. In large herds, consider sequential sampling of smaller groups over time instead of one large sample. Regional disease status affects the infectious disease investigation. [International animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) and national surveillance programs determine which diseases warrant routine screening. Consult [USDA APHIS animal health information](https://www.aphis.usda.gov/livestock-poultry-disease) for current disease status and control program requirements in the United States. Genomic information adds a further layer to the investigation. [Genomic selection has doubled genetic gains for production traits](https://pubmed.ncbi.nlm.nih.gov/23261029/) and can identify cows with low predicted fertility. When herd-level management problems are excluded, genetic variation in fertility may explain residual differences between cows. ## Recognized Complications and Failure Modes Herd-level reproductive investigations fail most often when the diagnostic endpoint is mis-specified. A herd with a 35% conception rate at first service may be labelled a "conception problem" when the actual deficit lies in oestrus detection intensity, semen handling, or insemination timing. Each failure mode leaves a distinct record signature, and the discriminating check is usually a cross-tabulation of parity, service number, and days in milk at service. Early embryonic death presents as a rising proportion of cows returning to oestrus at 25 to 35 days after service, instead of the expected 18 to 24 day interval. Pregnancy-associated glycoprotein measurements can confirm fetal loss when performed at the appropriate post-insemination window, but the clinician must first exclude inaccurate pregnancy diagnosis dates as the cause of apparent late returns. Subclinical endometritis, defined by endometrial cytology thresholds of 5% to 18% polymorphonuclear cells depending on days postpartum, reduces conception rates and prolongs days open without producing visible discharge [Wagener et al., institutional publication](https://pubmed.ncbi.nlm.nih.gov/28407857/). The cytobrush technique is minimally invasive and does not depress subsequent conception, making it a practical screening tool for cows 21 to 62 days postpartum. Anovulatory or cystic ovarian conditions produce prolonged inter-oestrus intervals and are confirmed by ultrasonographic examination of ovarian structures across repeated examinations. Stress-mediated suppression of reproductive hormone release can mimic these findings, since stressors such as lameness or milk fever extend the calving to conception interval by 13 to 14 days and add approximately 0.5 inseminations per conception [Dobson and Smith, institutional publication](https://pubmed.ncbi.nlm.nih.gov/10844239/). The distinction matters because treatment differs: ovarian cysts may respond to hormonal therapy, whereas stress-induced anovulation requires correction of the underlying environmental or health insult. | Observation | Likely cause | Discriminating check | |---|---|---| | Returns clustered at 18 to 24 days | Oestrus detection failure or insemination timing error | Compare service records with activity monitoring or heat detection aids | | Returns at 25 to 35 days | Early embryonic death | Pregnancy-associated glycoprotein testing or ultrasonography at 28 to 35 days | | Long intervals over 40 days | Anovulation, cystic ovarian disease, or missed oestrus | Serial ultrasonography of ovaries at 7 to 10 day intervals | | Low conception in primiparous cows only | Transition or milking pressure effects on young cows | Stratify conception rate by parity and review fresh cow health records | | Seasonal deterioration | Heat stress or photoperiod effects | Overlay conception rate against temperature-humidity index data | ## Common Diagnostic Errors The most frequent error is interpreting herd averages without stratifying by parity, service number, or season. A herd-level conception rate of 40% can conceal a primiparous cow conception rate of 55% and a multiparous rate of 30%, which directs investigation toward transition cow management instead of semen or insemination technique. Less experienced clinicians also tend to over-weight infectious causes. Bovine viral diarrhea virus can produce reduced conception, early embryonic death, abortion, and persistently infected calves, but the investigation should confirm viral involvement through antigen or antibody testing before committing to a control program [Grooms, institutional publication](https://pubmed.ncbi.nlm.nih.gov/15062471/). Testing every aborting cow for every agent is inefficient, the diagnostic plan should follow the record-defined problem. A second common error is sampling too few cows for cytology or bacteriology. Subclinical endometritis prevalence estimates are unreliable when fewer than 15 to 20 cows per risk group are sampled, and the sampling window matters because PMN thresholds vary with days postpartum [Wagener et al., institutional publication](https://pubmed.ncbi.nlm.nih.gov/28407857/). A third error is failing to verify that records are complete before drawing conclusions. If service dates are missing for 10% of cows, the calculated conception rate is biased and the investigation proceeds on faulty premises. ## Evidence Limitations and Divergent Expert Opinion The evidence base for herd-level reproductive diagnostics contains genuine gaps. The definition of subclinical endometritis remains debated, with threshold values varying from 5% to 18% PMN depending on the study and the postpartum interval [Wagener et al., institutional publication](https://pubmed.ncbi.nlm.nih.gov/28407857/). Some studies report no negative effect of subclinical endometritis on reproductive performance, which complicates interpretation of cytology results in herds where other limiting factors are present. Expert opinion also diverges on the relative contribution of stress versus infectious disease in herds with multifactorial infertility. The endocrine pathways by which stress disrupts reproductive hormone release are well characterized in experimental settings, but field quantification of stress effects remains imprecise [Dobson and Smith, institutional publication](https://pubmed.ncbi.nlm.nih.gov/10844239/). Genomic selection offers a pathway to improve fertility traits, with predicted doubling of genetic gains for production traits, but the realised response for fertility traits in commercial herds is slower and more variable [Hayes et al., institutional publication](https://pubmed.ncbi.nlm.nih.gov/23261029/). Clinicians should present genetic improvement as a long-term strategy that complements, instead of replaces, management corrections. ## Referral and Regulatory Considerations Most herd-level reproductive investigations can be completed in practice with ultrasonography, cytology, and routine blood or milk sampling. Referral to a veterinary teaching hospital or diagnostic laboratory is warranted when the investigation requires specialised testing such as fetal pathology, viral isolation, or toxicology screening, or when the herd problem persists despite implementation of recommended changes. Consultation with a theriogenology specialist is appropriate for herds with complex multifactorial infertility where the clinician lacks confidence in prioritizing multiple concurrent findings. Regulatory reporting obligations vary by jurisdiction. Abortion storms, defined as an abortion rate exceeding a threshold set by local authorities, may trigger mandatory reporting to the relevant animal health agency. The World Organization for Animal Health provides international standards for notifiable disease surveillance and reporting, and veterinarians should consult these standards together with their national veterinary authority when a herd outbreak involves a listed pathogen [WOAH terrestrial animal health code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/). The USDA Animal and Plant Health Inspection Service provides comparable national program information for the United States [USDA APHIS animal health information](https://www.aphis.usda.gov/livestock-poultry-disease). Clinicians should confirm current local requirements before initiating any reporting process, since regulations differ between countries and regions. ## Frequently Asked Questions ### How Much Time Should a Herd-Level Reproductive Investigation Take, and How Do I Prioritize When Time Is Limited? A full investigation can span several visits over one or more estrous cycles. When time is constrained, begin with the records-based definition of the problem, then perform a targeted physical assessment of cows in the voluntary waiting period and at the time of expected breeding. Prioritize conditions with the largest expected impact on the herd's primary metric gap. For example, if submission rate is the deficit, focus on estrus detection and postpartum health. If conception rate is the deficit, prioritize semen handling, insemination technique, and uterine health sampling. Reserve advanced diagnostics such as cytology or pathogen testing for cases where the records and physical examination do not yield a clear direction. Document what was deferred so subsequent visits can address it. ### What Can I Do When Cytobrush or Low-Volume Uterine Flushing Equipment Is Not Available? Endometrial cytology is the reference method for diagnosing subclinical endometritis, but when sampling equipment is unavailable, rely on a combination of vaginal examination, ultrasonography for uterine luminal fluid, and white blood cell counts from a uterine lavage if basic supplies exist. The threshold for polymorphonuclear cells varies with days postpartum, and a general threshold of 5% is considered applicable between 21 and 62 days in milk, so interpret any surrogate findings with that timing in mind. Palpation per rectum for uterine wall thickness and symmetry remains useful. If you cannot sample, state the diagnostic limitation explicitly in the herd report and recommend that cytology be performed when supplies are obtained. Do not substitute milk or blood biomarkers for endometrial cytology without acknowledging their weaker correlation with the condition. ### How Should I Present Findings to a Producer Who Is Reluctant to Invest in Further Diagnostics? Frame the discussion around the cost of delayed intervention instead of the cost of testing. Use the herd's own records to calculate the financial effect of the current calving interval, culling rate, and semen expense per pregnancy. Explain that stressors such as lameness and milk fever can extend the calving to conception interval by roughly two weeks and add about half an insemination per conception, which gives the producer a tangible basis for comparing diagnostic costs against avoidable losses. Offer a staged plan that begins with low-cost changes such as estrus detection aids and insemination timing, then progresses to laboratory testing only if the response is inadequate. Provide a written summary with the expected decision point for each stage. ### How Does This Investigation Differ for Seasonal Calving Herds Compared with Year-Round Calving Herds? Seasonal systems compress the breeding period, so the diagnostic emphasis shifts from rolling 21-day pregnancy rates to the proportion of the herd pregnant within the first 6 weeks of the breeding season. A missed estrus in a seasonal herd costs a full year of production, whereas in a year-round herd it costs roughly one estrous cycle. This changes the priority ranking of findings. Estrus detection accuracy becomes the dominant concern in seasonal herds, and the investigation should examine bull management if natural service is used, including bull fertility and venereal disease risk. In year-round herds, postpartum disease and its effect on submission rate may carry more weight. The same diagnostic sequence applies, but the interpretation of every metric must be anchored to the herd's calving pattern. ### What Records Should I Ask For Before the First Herd Visit? Request the last 12 months of individual cow records including calving dates, disease events, all insemination dates, pregnancy diagnoses, culling dates and reasons, and milk production data. Also request the herd's breeding calendar, semen inventory and handling logs, and any records of bull use. If the herd uses a commercial dairy software platform, ask for the standard reproductive reports instead of raw data exports, as these often include calculated intervals and rates. Verify that the records distinguish between observed estrus, timed inseminations, and natural service. In herds with incomplete records, state which metrics cannot be calculated reliably and base the investigation on the parameters that are supported by data. Cross-check records against the physical herd during the visit. ### How Should I Handle a Herd Where the Problem Appears to Be Pregnancy Loss instead of Failure to Conceive? Separate early embryonic loss from late embryonic and fetal loss using pregnancy diagnosis timing. If the herd uses transrectal ultrasonography, record the presence of a heartbeat at each examination and compare pregnancy rates between consecutive examinations. Late embryonic and early fetal loss is a critical step in pregnancy maintenance, and its investigation should include a review of stress events, nutritional management, and infectious causes. Bovine viral diarrhea virus can produce losses at all reproductive stages, so include herd vaccination status, biosecurity practices, and testing of persistently infected animals in the workup. If the pattern suggests a specific gestational window, target diagnostic testing to that period. The [USDA APHIS animal health information](https://www.aphis.usda.gov/livestock-poultry-disease) and [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) provide guidance on surveillance and reporting for notifiable causes of reproductive loss. ## Related Clinical & Scientific Guides * [Rumen Health Assessment in Dairy Cows: Clinical and Subclinical Indicators](/knowledge/veterinary-medicine/food-animal-medicine/rumen-health-assessment-dairy-cows-clinical-subclinical-indicators) * [Mastitis Control Programs in Dairy Herds: Monitoring and Prevention](/knowledge/veterinary-medicine/food-animal-medicine/mastitis-control-programs-dairy-herds-monitoring-prevention) * [Swine Nutrition and Health: Feed-Related Disease Diagnosis](/knowledge/veterinary-medicine/food-animal-medicine/swine-nutrition-health-feed-related-disease-diagnosis) ## References and Further Reading - [A review of the ongoing discussion about definition, diagnosis and pathomechanism of subclinical endometritis in dairy cows.](https://pubmed.ncbi.nlm.nih.gov/28407857/). 2017. - [Factors of a noninfectious nature affecting fertility after artificial insemination in lactating dairy cows. A review.](https://pubmed.ncbi.nlm.nih.gov/22153267/). 2012. - [What is stress, and how does it affect reproduction?](https://pubmed.ncbi.nlm.nih.gov/10844239/). 2000. - [The future of livestock breeding: genomic selection for efficiency, reduced emissions intensity, and adaptation.](https://pubmed.ncbi.nlm.nih.gov/23261029/). 2013. - [Reproductive consequences of infection with bovine viral diarrhea virus.](https://pubmed.ncbi.nlm.nih.gov/15062471/). 2004. - [Current situation and future trends for beef production in the United States of America - A review.](https://pubmed.ncbi.nlm.nih.gov/29973030/). 2018. - [USDA APHIS Animal Health Information](https://www.aphis.usda.gov/livestock-poultry-disease). USDA APHIS. - [FAO Animal Production and Health](https://www.fao.org/animal-production/en/). FAO. - [MSD Veterinary Manual, Professional Edition](https://www.msdvetmanual.com/). MSD Veterinary Manual. ## Related Articles - [Beef Herd Reproductive Diagnostics: Pregnancy Detection and Problem Investigation](/knowledge/veterinary-medicine/food-animal-medicine/beef-herd-reproductive-diagnostics-pregnancy-detection-problem-investigation) - [Diagnostic Approach to Mastitis in Dairy Cows: Pathogen Identification and Herd Patterns](/knowledge/veterinary-medicine/food-animal-medicine/diagnostic-approach-mastitis-dairy-cows-pathogen-identification) - [Dairy Herd Data Management: Using Records for Health Decisions](/knowledge/veterinary-medicine/food-animal-medicine/dairy-herd-data-management-using-records-health-decisions) - [Dairy Herd Health Certification: Standards and Veterinary Audit](/knowledge/veterinary-medicine/food-animal-medicine/dairy-herd-health-certification-standards) - [Dairy Calf Health: Diagnostic Approach to Neonatal Diarrhea](/knowledge/veterinary-medicine/food-animal-medicine/dairy-calf-health-diagnostic-approach-neonatal-diarrhea) > This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.