Beef cow herd reproduction: Tools and tips to diagnose herd ...
Beef cow herd reproduction: Tools and tips to diagnose herd reproduction problems Bob L. Larson, DVM, PhD, ACT, ACVPM-Epi Kansas State University At fall pre-check time, I am often asked why some of the cows are open. Of course, there can be many reasons why a cow may not be pregnant after running with bulls for several weeks.
Importance of the calving distribution on the next breeding season The number of opportunities that a cow has to become pregnant in a breeding season is an important constraint to whether or not she becomes pregnant. Typically, a fertile cow has a 65% (60-70%) likelihood of a live calf being born for each ovulation and mating (estrus period) A cow that calves early enough to be cycling by the start of a 65-day breeding season will have three opportunities to become pregnant, therefore I expect that cow to have a 95% likelihood of carrying a pregnancy to term If a cow calves later in the calving season so that it does not resume cycling until the last 40 days of the breeding season (i.e. will have two opportunities to become pregnant), I expect that cow to have a 88% likelihood of carrying a pregnancy to term If a cow calves very late in the calving season so that it does not resume cycling until the last 20 days of the breeding season (i.e. will only have one opportunity to become pregnant), I expect that cow to have a 65% likelihood of carrying a pregnancy to term The maximum overall herd pregnancy percentage will determined by the number of cows in each category (3 opportunities, 2 opportunities, and 1 opportunity to become pregnant) These mathematical exercises are meant to illustrate the importance of having a high percentage of the herd calve early in the calving season so they have enough time to resume cycling before the start of the next breeding season. The average length of time to resume cycling is expected to be about 40-50 days; therefore, cows that calve later than 30 to 40 days after the start of the calving season are unlikely to be cycling at the start of the next breeding season. And, cows that calve more than 60 days after the start of the calving season are unlikely to start cycling until well into the following breeding season. Insufficient percentage of cows become pregnant early in the breeding season The reasons for low pregnancy proportion during the first 20 days of the breeding season can be placed into one of three categories: 1) An inadequate percentage of females were having fertile estrous cycles when the breeding season began
2) The bulls were not able to deliver adequate amounts of fertile semen to the female’s reproductive tract 3) Infectious or non-infectious agents prevented or ended pregnancy (Figure 1). Use of history taking, physical examination, farm record evaluation, and diagnostic laboratory testing can be used to categorize rule-outs as likely or unlikely causes of the undesired pregnancy distribution. Figure 1: Rule-outs if reproductive performance is not adequate Pregnancy rate is not adequate Inadequate % of females were having fertile estrous cycles
Bulls were not able to deliver adequate amounts of fertile semen to the female's reproductive tract
Infectious or non-infectious agents prevented or ended pregnancy
Start of breeding season
Mid- to late-breeding season
Rule-Outs
Infectious Rule-Outs
Non-Infectious Rule-Outs
Rule-Outs (Failed to initiate cycling)
Rule-Outs (Failed to initiate cycling or stopped cycling)
Semen quality / quantity problem Penile problem Musculoskeletal problem Libido problem
Venereal disease Embyonic loss Early fetal loss Bacterial, viral, fungal, & yeast
Plant toxicosis Environmental stress Genetic disorders
Inadequate postpartum period Inadequate energy reserve (BCS) Inadequate % of puberal heifers
Inadequate energy reserve (BCS)
Inadequate percentage of females were cycling when the breeding season started Sixty-five percent of the herd should be 60 days or more postpartum at the start of the breeding season If less than 55% of the herd is 60 days or more postpartum, then last year’s calving distribution or the date of the start of this year’s breeding season become likely rule-outs
In order to ensure a high proportion of cyclicity, mature cows should have a minimum Body Condition Score (BCS) of 5 (using a 9-point scale) at the start of the breeding season and heifers should have a BCS of 6
If records indicate that BCS were below these levels, then energy reserve status at the start of the breeding season becomes a likely rule-out
If farm records are inadequate to supply this information, nutritional status at the start of the breeding season remains an unknown variable in the rule-out list and veterinary involvement in capturing this data in following years is warranted
If heifers are included in the data set, then a minimum 50-60% should have reached puberty 4-8 weeks prior to the start of the breeding season Puberal status can be determined by reproductive tract palpation to determine reproductive tract score or by observation for estrous activity
Bulls did not deliver adequate amounts of fertile semen to the female reproductive tract The cause of early breeding season failure can be due to either female or male problems. Additional information, such as the number of bulls in the pasture that passed a Breeding Soundness Examination, and the Body Condition Score of the herd at the start of the breeding season, and the vaccination and biosecurity program to control venereal disease would be helpful in narrowing the rule-outs
Age, experience, single- versus multiple-sire breeding pastures, and pasture terrain are all considered influences on the number of females that a bull can adequately service
Although, female to bull ratios average 17.5:1 for yearling bulls and 25.3:1 for mature bulls in the U.S., mature bulls that have passed a BSEB can adequately service 50 females. However, if single-sire breeding pastures are utilized, this breeding pressure has risks
Serving capacity for yearling bulls is not as great as mature bulls, therefore a decreased female:bull ratio is warranted with young bulls
If mature bulls are used following estrous synchronization, a 25:1 female:bull ratio is recommended. Yearling bulls used following estrous synchronization should not be expected to breed more than 10 females
A breeding soundness examination for bulls (BSEB) should be performed prior to the start of the breeding season on all bulls in the breeding program
Although a satisfactory BSEB does not eliminate bull sub-fertility as a ruleout for poor breeding performance, a questionable breeder as determined by BSEB may impact the female:fertile bull ratio if not replaced
Failure to obtain a BSEB on all bulls leaves bull fertility at the start of the breeding season as an unknown variable among the rule-outs
A BSEB (including a through physical examination) at the time the breeding season problem is discovered (usually at preg-check time) may supply information about penile, testicular, foot and leg or other musculoskeletal health problems during the breeding season – but lack of pathology following the breeding season does not rule-out a physical (locomotion, mounting, intromission) or semen quality problem and an associated female:fertile bull ratio inadequacy at the start of the breeding season
Infectious or non-infectious agents prevented or ended pregnancy Rule-outs for infectious pregnancy wastage detected at the time of pregnancy diagnosis (usually 17 to 25 weeks of gestation) include: Trichomoniasis, Campylobacteriosis, Bluetongue, Bovine Viral Diarrhea, Infectious Bovine Rhinotracheitis, Actinomyces pyogenes, Brucellosis, Ureaplasmosis, and Candidiasis
History of herd vaccination protocol, biosecurity management or breaks in management, disease outbreaks in other groups of livestock, and diagnostic laboratory investigation may be needed to classify these agents as likely or unlikely contributors to the undesired pregnancy distribution
Rule-outs for non-infectious early-gestation pregnancy wastage include: ingestion of highly endophyte-infested forage during periods of high environmental temperature, ingestion of toxic plants, and genetic disorders such as the presence of lethal genes.
Pregnancy percentage is not adequate during the mid- to late-breeding season If reproductive performance is poor throughout the breeding season, the rule-outs and diagnostic efforts are the same as those described for situation where pregnancy proportion is not adequate at the start of the breeding season. However, if reproductive performance is initially adequate and then deteriorates, the rule-out list is decreased (Figure 1). Because conception occurred and pregnancy was maintained early in the breeding season, one can assume that fertile bulls were turned out with fertile, cycling cows, the herd was free of pregnancy wasting disease, and the postpartum period and energy reserves, as indicated by BCS, were adequate. In herds where reproductive performance is initially good and then deteriorates, areas of investigation include: Determine if bulls developed testicular or musculoskeletal problems that prevented the production or delivery of fertile semen Explore the possibility that herd replacements brought in after the start of the breeding season introduced a venereal disease Consider whether forage or other feed became limiting after the breeding season was underway History and pasture examination to indicate forage availability or midseason BCS would determine the likelihood of nutritional shortfalls causing the poor reproductive performance If forage is adequate or abundant during the mid- to late-breeding season, then other rule-outs must be investigated.
Figure 2. Pregnancy distribution in a singlebull herd following an acute onset of bull infertility
Figure 2 illustrates a problem that is seen fairly frequently in farms with one bull for each breeding pasture. The breeding season in this example starts out with a high percentage of cows cycling, good cowherd fertility and good bull fertility. Because 65% of the herd becomes pregnant in the first 20-day period, the producer can be confident that the pre-breeding feeding/supplementation program offered adequate nutrients for a high level of reproductive performance. It is also evident that the bull was able to cover the breeding pasture, find the cows displaying estrus, and successfully breed the cycling cows.
The dramatic decrease in pregnancy percentage during the second 20-day period of the breeding season is strong evidence for bull infertility
If a veterinarian only evaluated overall pregnancy percentage in the herd depicted by Figure 2, the percentage of open cows would cause some concern (especially after a 100-day breeding season), but the cause of the high open percentage would not be evident. With limited information, one could guess that nutrition or cow fertility were to blame. And, as with this example, a bull may pass a BSEB both before and after being placed in the breeding pasture without revealing that a fertility problem existed during the breeding season. By categorizing and displaying the information gained at pregnancy diagnosis or at calving, the cause of the problem becomes more obvious.
Summary High reproductive efficiency is critical for beef cowherd profitability Establishing and maintaining a management system that results in a high percentage of the herd calving in a short calving season with most of the calves born in the first 21 days requires that cows and heifers are cycling before the start of the breeding season, that bulls are fertile and physically able to mate cows, and that disease is not causing pregnancy loss Nutrition, genetics, animal husbandry, male and female reproductive soundness, and health all impact the reproductive efficiency of a herd By evaluating the herd throughout the year, veterinarians can identify strengths and weaknesses within the management system of a herd, and develop plans to maintain high reproductive efficiency.
Importance of the calving distribution on the next breeding season The number of opportunities that a cow has to become pregnant in a breeding season is an important constraint to whether or not she becomes pregnant. Typically, a fertile cow has a 65% (60-70%) likelihood of a live calf being born for each ovulation and mating (estrus period) A cow that calves early enough to be cycling by the start of a 65-day breeding season will have three opportunities to become pregnant, therefore I expect that cow to have a 95% likelihood of carrying a pregnancy to term If a cow calves later in the calving season so that it does not resume cycling until the last 40 days of the breeding season (i.e. will have two opportunities to become pregnant), I expect that cow to have a 88% likelihood of carrying a pregnancy to term If a cow calves very late in the calving season so that it does not resume cycling until the last 20 days of the breeding season (i.e. will only have one opportunity to become pregnant), I expect that cow to have a 65% likelihood of carrying a pregnancy to term The maximum overall herd pregnancy percentage will determined by the number of cows in each category (3 opportunities, 2 opportunities, and 1 opportunity to become pregnant) These mathematical exercises are meant to illustrate the importance of having a high percentage of the herd calve early in the calving season so they have enough time to resume cycling before the start of the next breeding season. The average length of time to resume cycling is expected to be about 40-50 days; therefore, cows that calve later than 30 to 40 days after the start of the calving season are unlikely to be cycling at the start of the next breeding season. And, cows that calve more than 60 days after the start of the calving season are unlikely to start cycling until well into the following breeding season. Insufficient percentage of cows become pregnant early in the breeding season The reasons for low pregnancy proportion during the first 20 days of the breeding season can be placed into one of three categories: 1) An inadequate percentage of females were having fertile estrous cycles when the breeding season began
2) The bulls were not able to deliver adequate amounts of fertile semen to the female’s reproductive tract 3) Infectious or non-infectious agents prevented or ended pregnancy (Figure 1). Use of history taking, physical examination, farm record evaluation, and diagnostic laboratory testing can be used to categorize rule-outs as likely or unlikely causes of the undesired pregnancy distribution. Figure 1: Rule-outs if reproductive performance is not adequate Pregnancy rate is not adequate Inadequate % of females were having fertile estrous cycles
Bulls were not able to deliver adequate amounts of fertile semen to the female's reproductive tract
Infectious or non-infectious agents prevented or ended pregnancy
Start of breeding season
Mid- to late-breeding season
Rule-Outs
Infectious Rule-Outs
Non-Infectious Rule-Outs
Rule-Outs (Failed to initiate cycling)
Rule-Outs (Failed to initiate cycling or stopped cycling)
Semen quality / quantity problem Penile problem Musculoskeletal problem Libido problem
Venereal disease Embyonic loss Early fetal loss Bacterial, viral, fungal, & yeast
Plant toxicosis Environmental stress Genetic disorders
Inadequate postpartum period Inadequate energy reserve (BCS) Inadequate % of puberal heifers
Inadequate energy reserve (BCS)
Inadequate percentage of females were cycling when the breeding season started Sixty-five percent of the herd should be 60 days or more postpartum at the start of the breeding season If less than 55% of the herd is 60 days or more postpartum, then last year’s calving distribution or the date of the start of this year’s breeding season become likely rule-outs
In order to ensure a high proportion of cyclicity, mature cows should have a minimum Body Condition Score (BCS) of 5 (using a 9-point scale) at the start of the breeding season and heifers should have a BCS of 6
If records indicate that BCS were below these levels, then energy reserve status at the start of the breeding season becomes a likely rule-out
If farm records are inadequate to supply this information, nutritional status at the start of the breeding season remains an unknown variable in the rule-out list and veterinary involvement in capturing this data in following years is warranted
If heifers are included in the data set, then a minimum 50-60% should have reached puberty 4-8 weeks prior to the start of the breeding season Puberal status can be determined by reproductive tract palpation to determine reproductive tract score or by observation for estrous activity
Bulls did not deliver adequate amounts of fertile semen to the female reproductive tract The cause of early breeding season failure can be due to either female or male problems. Additional information, such as the number of bulls in the pasture that passed a Breeding Soundness Examination, and the Body Condition Score of the herd at the start of the breeding season, and the vaccination and biosecurity program to control venereal disease would be helpful in narrowing the rule-outs
Age, experience, single- versus multiple-sire breeding pastures, and pasture terrain are all considered influences on the number of females that a bull can adequately service
Although, female to bull ratios average 17.5:1 for yearling bulls and 25.3:1 for mature bulls in the U.S., mature bulls that have passed a BSEB can adequately service 50 females. However, if single-sire breeding pastures are utilized, this breeding pressure has risks
Serving capacity for yearling bulls is not as great as mature bulls, therefore a decreased female:bull ratio is warranted with young bulls
If mature bulls are used following estrous synchronization, a 25:1 female:bull ratio is recommended. Yearling bulls used following estrous synchronization should not be expected to breed more than 10 females
A breeding soundness examination for bulls (BSEB) should be performed prior to the start of the breeding season on all bulls in the breeding program
Although a satisfactory BSEB does not eliminate bull sub-fertility as a ruleout for poor breeding performance, a questionable breeder as determined by BSEB may impact the female:fertile bull ratio if not replaced
Failure to obtain a BSEB on all bulls leaves bull fertility at the start of the breeding season as an unknown variable among the rule-outs
A BSEB (including a through physical examination) at the time the breeding season problem is discovered (usually at preg-check time) may supply information about penile, testicular, foot and leg or other musculoskeletal health problems during the breeding season – but lack of pathology following the breeding season does not rule-out a physical (locomotion, mounting, intromission) or semen quality problem and an associated female:fertile bull ratio inadequacy at the start of the breeding season
Infectious or non-infectious agents prevented or ended pregnancy Rule-outs for infectious pregnancy wastage detected at the time of pregnancy diagnosis (usually 17 to 25 weeks of gestation) include: Trichomoniasis, Campylobacteriosis, Bluetongue, Bovine Viral Diarrhea, Infectious Bovine Rhinotracheitis, Actinomyces pyogenes, Brucellosis, Ureaplasmosis, and Candidiasis
History of herd vaccination protocol, biosecurity management or breaks in management, disease outbreaks in other groups of livestock, and diagnostic laboratory investigation may be needed to classify these agents as likely or unlikely contributors to the undesired pregnancy distribution
Rule-outs for non-infectious early-gestation pregnancy wastage include: ingestion of highly endophyte-infested forage during periods of high environmental temperature, ingestion of toxic plants, and genetic disorders such as the presence of lethal genes.
Pregnancy percentage is not adequate during the mid- to late-breeding season If reproductive performance is poor throughout the breeding season, the rule-outs and diagnostic efforts are the same as those described for situation where pregnancy proportion is not adequate at the start of the breeding season. However, if reproductive performance is initially adequate and then deteriorates, the rule-out list is decreased (Figure 1). Because conception occurred and pregnancy was maintained early in the breeding season, one can assume that fertile bulls were turned out with fertile, cycling cows, the herd was free of pregnancy wasting disease, and the postpartum period and energy reserves, as indicated by BCS, were adequate. In herds where reproductive performance is initially good and then deteriorates, areas of investigation include: Determine if bulls developed testicular or musculoskeletal problems that prevented the production or delivery of fertile semen Explore the possibility that herd replacements brought in after the start of the breeding season introduced a venereal disease Consider whether forage or other feed became limiting after the breeding season was underway History and pasture examination to indicate forage availability or midseason BCS would determine the likelihood of nutritional shortfalls causing the poor reproductive performance If forage is adequate or abundant during the mid- to late-breeding season, then other rule-outs must be investigated.
Figure 2. Pregnancy distribution in a singlebull herd following an acute onset of bull infertility
Figure 2 illustrates a problem that is seen fairly frequently in farms with one bull for each breeding pasture. The breeding season in this example starts out with a high percentage of cows cycling, good cowherd fertility and good bull fertility. Because 65% of the herd becomes pregnant in the first 20-day period, the producer can be confident that the pre-breeding feeding/supplementation program offered adequate nutrients for a high level of reproductive performance. It is also evident that the bull was able to cover the breeding pasture, find the cows displaying estrus, and successfully breed the cycling cows.
The dramatic decrease in pregnancy percentage during the second 20-day period of the breeding season is strong evidence for bull infertility
If a veterinarian only evaluated overall pregnancy percentage in the herd depicted by Figure 2, the percentage of open cows would cause some concern (especially after a 100-day breeding season), but the cause of the high open percentage would not be evident. With limited information, one could guess that nutrition or cow fertility were to blame. And, as with this example, a bull may pass a BSEB both before and after being placed in the breeding pasture without revealing that a fertility problem existed during the breeding season. By categorizing and displaying the information gained at pregnancy diagnosis or at calving, the cause of the problem becomes more obvious.
Summary High reproductive efficiency is critical for beef cowherd profitability Establishing and maintaining a management system that results in a high percentage of the herd calving in a short calving season with most of the calves born in the first 21 days requires that cows and heifers are cycling before the start of the breeding season, that bulls are fertile and physically able to mate cows, and that disease is not causing pregnancy loss Nutrition, genetics, animal husbandry, male and female reproductive soundness, and health all impact the reproductive efficiency of a herd By evaluating the herd throughout the year, veterinarians can identify strengths and weaknesses within the management system of a herd, and develop plans to maintain high reproductive efficiency.
