Reproductive failure is extremely costly for producers. However, the exact cause of loss is often very hard to determine as the problem is usually not identified until many months after the breeding season. Reproductive losses can occur as a result of a number of factors that limit the percentage of females that are cycling at the start of the breeding season or factors that interfere with conception or cause loss of the fetus.
The most commonly recognized causes for reproductive failure are poor cow nutrition (energy and micronutrients); venereal diseases, such as trichomoniasis (trich) and vibriosis (vibrio); other infectious diseases, such as BVDV, IBR, and leptospirosis; bull infertility, disease and injury; and changes to breeding season management (length of the breeding season, bull-to-cow ratios).
Reproductive failure is the most common reason associated with culling cows from the breeding herd. In addition to cows failing to become pregnant or aborting, other cows may take longer to become pregnant and calve late. Calves from these cows will have significantly lower weight gain on pasture. There is also greater chance a late calving cow won’t become pregnant the next year.
The expense of an open cow to a producer is not only the lost value of a calf, but also the cost of maintaining the cow for a year without a calf being produced. A cow that calves in the third cycle rather than the first cycle can produce a calf that is 50 lbs or lighter at weaning.
|If open rates are higher than 6% of cows and 8% of heifers talk to your veterinarian about solutions to reduce this in the future|
|Abortion rates greater than 3% for cows and 6% for heifers are cause for concern and should be investigated by your veterinarian|
|A good target is to have 60% of your cows bred in the first cycle|
|Nutrition is the most important factor in getting cows rebred. Maintaining cows at an adequate body condition score of 3 out of 5 will ensure they have the best chance of getting pregnant|
|Maintaining a year-round mineral program will help to ensure cows get bred early in the breeding season|
|Testing for venereal diseases in bulls is relatively easy and cheap and can help prevent reproductive wrecks|
|Vaccination for BVD can be effective at preventing reproductive losses|
|Monitoring bulls during the breeding season is important to help detect any injuries that may reduce performance|
Keeping good records is important to track changes in pregnancy and abortion rates in your herd over time. Producers who have a veterinarian pregnancy test the herd on a yearly basis are more likely to identify problems when it is still possible to determine a cause and potentially limit future losses.
Data from the Western Canadian Cow-Calf Surveillance Network (2014-2017) showed that 50% of herds had less than 6% of cows and 8% of heifers open at pregnancy testing. Producers should aim to have open rates at or below these benchmarks. Open rates greater than 13% for cows or 24% for heifers were reported less than 5% of the time and would be considered very unusual; if producers are experiencing these levels of open rates, they should contact their veterinarian. Breeding heifers two weeks before cows and feeding heifers separately from cows may help to reduce some of the problems associated with getting heifers bred on schedule.
While most herds periodically experience a few abortions, abortion rates greater than 3% for cows and 6% for heifers would also be considered cause for serious concern based on the surveillance network data. Most herds reported abortion rates of less than 1% per year.
The importance of maintaining momentum throughout the breeding season is well established. Numerous controlled studies show that there are economic benefits to having at least 60% of cows and heifers become pregnant during the first 21-day cycle. A good benchmark to target is 85% in total by the end of the 2nd cycle and 95% by the end of the 3rd cycle.
Nutrition is the most important factor for cow fertility. Cows with a diet that is deficient in energy and that have low body condition score and/or lose condition after calving are much less likely to be pregnant in the fall than cows in better condition.
Body condition score
Adequate winter nutrition is necessary to maintain an optimal cow body condition score (3.0 or 3.5 out of 5) in order to:
- minimize time to rebreeding and enhance pregnancy rates
- decrease the risk of abortion and calf death at or near birth
- encourage calving ease (very thin cows at highest risk of difficult calving)
- sustain adequate milk production
To ensure good reproductive success adequate body condition is required before calving and before breeding. However, it is also critical the cow does not lose a substantial amount of condition after calving or after the start of the breeding season. The loss of even a single condition score category can have a measurable impact particularly for cows that have a BCS of less than 3 out of 5.
Copper is a critical mineral when it comes to reproduction. Copper deficiencies can result in
- increased number of open cows
- poor growth
- changes in hair colour
Blood samples collected in 2014 indicate that up to 43% of cows in Western Canada may be copper deficient (< 0.5 ppm). More than 85% of herds have at least one deficient animal. Cows with blood copper levels below 0.4 ppm prior to breeding are at increased risk of not becoming pregnant, particularly young cows.
Mineral supplementation is one way that producers can help to combat copper deficiencies. While most producers will provide free choice trace mineral supplements, not all cows consume enough to maintain adequate levels. This suggests a need for further field research to identify cost-effect trace mineral supplementation programs to improve fertility of beef cows.
Maintaining a year-round mineral program is recommended to ensure that mineral requirements are met and don’t negatively impact pregnancy rates. Trace mineral supplementation should be undertaken carefully following product recommendations. All trace minerals, including copper, have the potential to be toxic at very high levels of intake. Annual testing is highly recommended, as mineral levels can vary from year to year even in the same water source, pasture, or hayfield. Surface water sources (such as dugouts) are particularly vulnerable to changes in sulfate levels (which can tie up copper) and total dissolved solids (decrease mineral intake).
Most beef herds in Canada continue to use bulls to breed their females, and therefore, are susceptible to sexually transmitted diseases. The most commonly reported venereal diseases of cattle include trichomoniasis (trich) and vibrio. Although these diseases occur infrequently, the results of infection can be very devastating.
- Trich is caused by a protozoan parasite called Tritrichomonas foetus (T. foetus).
- Vibrio is caused by bacteria called Campylobacter fetus subsp. venerealis.
Both trich and vibrio are transmitted through physical contact when a bull breeds a cow. Once a cow is infected they act as a source of infection for other non-infected bulls within the herd which then spread the disease(s) to other cows. Cows that are in that breeding pasture but become pregnant and calve successfully are unlikely to carry the infection.
If a bull tests positive for either disease they will most likely remain infected for life.
Low pregnancy rates in bull-bred beef herds can be caused by venereal diseases.
Neither disease causes noticeable swelling or other clinical signs in the bull. The semen of affected bulls will also appear normal on a breeding soundness examination.
Herds infected with trich or vibrio will typically have:
Low or very low pregnancy rates due to early embryonic death
High numbers of open cows at calving in herds that do not pregnancy test
Extended breeding season, with cows that conceive much later than expected (i.e. cows can lose their first pregnancy and rebreed later in the breeding season)
Newly infected cows may still conceive, but their resulting pregnancy is commonly absorbed between 40 and 70 days after breeding. Cows that have aborted will typically start to cycle again, but experience temporary infertility for 1 to 5 months as they clear the infection.
Testing for Trich
Producers should test and cull infected bulls for slaughter, not resale to another producer.
Assuming the bulls are still available for testing, a scrape sample should be collected from their sheath. For trich, the scrape sample is flushed into a pouch with a culture broth to grow the parasite. Traditionally these pouches were incubated and examined with a microscope on days 3, 5 and 7 after collection for the presence of the trich organism.
More recently, polymerase chain reaction (PCR) tests that identify a specific gene sequence from the organism have been developed. These PCR tests are able to identify a smaller number of trich organisms and are considered more specific to T. foetus. Occasionally bulls may have trich-like organisms found on culture as a result of manure contamination, but PCR tests are able to differentiate between these trich-like organisms and disease-causing organisms.
Herds with suspected or confirmed trichomoniasis should test their bulls 3 times at weekly intervals with either culture or PCR before considering them negative. For routine screening of larger bull batteries with low risk of disease, using PCR on pooled samples made from up to 5 individual bulls has been found to identify a positive bull greater than 90% of the time1. This is comparable to the detection rate of a single culture or PCR test on an individual bull.
Testing for vibrio usually involves the collection and culture of a scrape sample from the sheath of a bull. However, the bacteria causing vibrio are very temperature sensitive and commonly die on route to the diagnostic laboratory if transport of more than 24 hours is required. PCR tests have been developed and recently evaluated. PCR tests for vibrio are 85% accurate at identifying positive and negative bulls when sampled in the field. While not perfect, it is an improvement over what has traditionally been available to practicing veterinarians. This test is currently most recommended for use when investigating poor reproductive performance, rather than screening low risk bulls, and is best interpreted when other causes have been ruled out.
If the bulls are unavailable for testing, a diagnosis of either trich or vibrio can be made from aborted fetuses or even the vaginal mucous of carrier females. However, finding an aborted fetus with either disease is uncommon and the short duration of infection in females can make finding infections difficult. Collecting samples for testing from females with obvious reproductive tract infections (pyometra) is most likely to provide useful information.
Prevention and Containment
Vaccinate cows and bulls for vibrio before going to communal grazing pastures for breeding.
Infected animals should be culled for slaughter. Identifying and replacing positive bulls with virgin bulls remains the cornerstone of controlling both venereal diseases. Cows that are open or which conceived late in the breeding season should also be removed from the herd. Only cows that have their calf at foot should be allowed to be a part of the breeding herd.
Vaccinations for vibrio are available. However, there is a need for more research on the best choice of vaccine and recommended dosing schedule. A vaccine for trich is available in the US. However, the evidence suggests that it provides some protection against fetal loss but does not effectively prevent infection.
Initiating a timed artificial insemination program is great method to prevent disease, but will still require either heat detection or a bull for “clean up”.
Other Infectious Causes of Reproductive Losses
Infectious diseases, including venereal diseases described above, present the greatest risk to herds that are rapidly expanding and bringing in cows from a number of sources and herds that pasture where there is contact with other herds, such as community pastures.
Bovine viral diarrhea virus (BVD) and Infectious Bovine Rhinotracheitis virus (IBR)
BVD infection can lead to poor conception rates and both BVD and IBR can cause abortions in cattle. Blood tests show exposure to these diseases is common in unvaccinated herds.
There is good evidence from a number of experimental trials that these vaccines are effective. For BVD vaccination, an average decrease of 85% has been reported for fetal infection and 45% for abortions. On average, studies reported a 5% increase in pregnancy rates in vaccinated herds2. The IBR vaccine has been reported to reduce the risk of abortion by 60% on average3. Field studies in Western Canada have shown a significant improvement in pregnancy rates and decrease in abortion rates for vaccinated compared to unvaccinated cows on community pastures4,5 .
BVD and IBR was the most common type of vaccination reported in mature cows and bulls in a recent survey that was part of the Western Canadian Cow-Calf Surveillance Network. While most producers are vaccinating their cow herd, many producers are not yet vaccinating their bulls. Bull vaccination presents an important opportunity to decrease the risk of reproductive failure. For example, the testicular tissue of bulls can potentially remain infected with BVD for prolonged periods and provide a source of the virus to susceptible cows and heifers6.
In herds where BVD is suspected, testing and culling of persistently infected carrier animals can be considered as an additional management tool.
Infection with leptospirosis can lead to poor conception rates and abortions in cattle. Producers should consult with their veterinarians to determine the risk of infection in their geographic area and what, if any, vaccine strategy is appropriate for their herd.
Neospora caninum is a protozoal parasite of canids such as coyotes and dogs that can be passed to a number of species including cattle. It is a very common cause of abortions in dairy herds but has also been responsible for significant losses in some beef herds. Blood tests have shown that the level of infection has stayed relatively stable over the past 20 years. On average slightly more than 1 in every 20 cows have been exposed to the parasite at some time. The infection can be transmitted from the cow to her unborn calf. Not all exposed cows will abort. There is no effective vaccine or treatment for neosporosis. Careful dead stock management might help to minimize contact with coyotes in some areas.
Bull Fertility, Disease, and Injury
Breeding Soundness Evaluations
Depending on the survey, approximately 50 to 60% of cow-calf producers, who work with veterinarians, have reported having their bulls’ semen tested before the breeding season. Veterinarians will check scrotal circumference, the reproductive tract for any signs of abnormalities, and the semen for motility and defects. There is good evidence7 from field studies in Western Canada regarding the association between scrotal circumference and pregnancy rates. A breeding soundness evaluation also provides assurance that there have been no changes in semen quality from one year to the next due to disease, trauma or frostbite in bulls that might otherwise appear normal.
Reducing the risk of poor fertility
Bulls should be monitored for excessive weight loss and illness. Heat detection, breeding attempts, and semen quality can be reduced in bulls that are under-conditioned or sick. Lameness due to footrot can be an important cause of poor pregnancy rates on pasture as bulls are less likely to seek out cows in heat. A commercial vaccine is available for footrot and its use in bulls was reported by approximately 40% of producers in a recent survey.
Clostridial vaccines are also important for protection of valuable breeding stock. Bulls are sometimes overlooked when the rest of the mature herd is revaccinated.
Rapid detection of injuries reducing bull performance
Frequent observation of bulls during the breeding season is important to detect any lameness, inability to mount or successfully breed that might be caused by injuries to the bull’s legs, back or penis. This is particularly vital in single bull breeding pastures. Injured bulls if detected can be replaced before too much time is lost from the breeding season.
Breeding Season Management
Changes to breeding season management can result in substantial changes to pregnancy rates. Producers should not rule out issues such as appropriate bull to cow ratios for the bull age, pasture size, and terrain type. Other issues to consider include the potential for any reductions to the length of the time when the cows were exposed to the bulls or changes in the time the cows had to recover and start cycling again from calving to the start of the next breeding season. The average length of time from calving to fertile estrus is 50 to 80 days in most beef herds but it takes closer to 70 to 100 days for 90% of mature cows to return to estrus after calving8. Cows calving late one year due to a reproductive problem are significantly more likely to be open the next4 .
Heifers need to gain sufficiently and reach puberty so that they calve before 24 months of age. The objective is to get heifers pregnant fast enough that after calving they have enough time (80-100 days) to resume estrus and have 3 full estrus cycles to become pregnant after their first calf. To ensure first calf heifers calve near the front of the herd heifers should be bred before the rest of the mature cows. View Page
Read more on how different producers manage their first calf and replacement heifers to ensure they are ready for the breeding season:
Preventing Calving Difficulties
Cows that have problems at calving are less likely to rebreed during the next calving season. Selection of bulls with low birth weight or high calving ease EPD’s to minimize calving difficulties has the added benefit of minimizing later impacts on fertility. Cows where fetal manipulation due to a malpresentation or a Caesarean section was performed are less likely to be pregnant the following year4. Similarly cows that abort or lose their calf at birth or within the first few hours of birth are more likely to be open after the subsequent breeding season4. Thin or excessively overconditioned cows are also more likely to have problems at calving.
Exposure to various types of toxins can also impact reproductive performance. One of the most common areas of concern in Western Canada following a few more wet than average growing seasons was an increase in the amount of ergot. Ergot has a number of effects on cattle including an increased risk of abortions. Fusarium mycotoxins have also been identified more frequently in grains in recent years. The wide variety of mycotoxins produced by Fusarium have also been linked to infertility and abortion.
- Kennedy JA, Pearl D, Tomky L, Carman J (2008) Pooled Polymerase Chain Reaction to Detect Tritrichomonas Foetus in Beef Bulls. Journal of Veterinary Diagnostic Investigation. Volume: 20 issue: 1, page(s): 97-99.
- Newcomer BW, Chamorro MF, Walz PH. (2017) Vaccination of cattle against bovine viral diarrhea virus. Vet Micro.Volume 206:78-83.
- Newcomer BW, Walz PH, Givens MD, Wilson AE. (2015) Efficacy of bovine viral diarrhea virus vaccination to prevent reproductive disease: a meta-analysis. Therio Volume 83(3):360-365.
- Waldner CL, Garcia Guerra A. (2013) Cow attributes, herd management, and reproductive history events associated with the risk of nonpregnancy in cow-calf herds in Western Canada. Therio Volume 79:1083-94.
- Waldner C. (2014) Cow attributes, herd management, and reproductive history events associated with abortion in cow-calf herds from Western Canada. Therio Volume 81(6), 840-848.
- Voges H, Horner GW, Rowe S, Wellenberg GJ. (1998) Persistent bovine pestivirus infection localized in the testes of an immune-competent non-viraemic bull. Vet Microbiol Volume 61: 165-175.
- Walner CL, Kennedy RI, Palmer CW. (2010) A description of the findings from bull breeding soundness evaluations and their assocaiation with pregnancy outcomes in a study of western Canadian beef herds. Therio Volume 74:871-883
- Larson RL and White BJ. (2016) Reproductive Systems for North American Beef Cattle Herds. Vet Clin Food Anim Volume 32 249–266 http://dx.doi.org/10.1016/j.cvfa.2016.01.001
For further information on this topic, please consult with your veterinarian.
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Thanks to Dr. Cheryl Waldner, researcher and professor at the Western College of Veterinarian Medicine, University of Saskatchewan, for contributing her time and expertise in writing this page.
This topic was last revised on June 30, 2022 at 12:24 pm.