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Improving Reproductive Efficiency
by Darrel J. Kesler


  • Reproductive efficiency has declined in the dairy industry. Numerous factors have been implicated and include, but are not limited to, milk production, reproductive management practices, bST treatment, the environment, inbreeding, and reproductive diseases.
  • Reproductive indices need to be modernized. We should be more concerned with such indices such as “100-d in calf rate” or “% pregnant within 1, 2, or 3 cycles after the volunteer waiting period” combined with culling rate because the traditional indices are negatively affected by timed AI protocols even though they may improve reproductive efficiency.
  • Reproductive record management needs greater utilization.
  • Regardless of the cause, there are several reproductive technologies available to improve reproductive efficiency. These technologies include first-service synchronization and timed AI , early pregnancy detection and synchronization of the return estrus for cows that don’t conceive to the first service, embryo transfer, and CIDR treatment..


Based on a review of published data, during the past 25 to 50 years reproductive efficiency has declined in the dairy industry. Data from New York showed a decline in first-service conception rate from about 65% in 1951 to 40% in 1996. In the 1950s, typical published conception rates were about 55%. More recent journal articles report conception rates of 45% for inseminations at spontaneous estrus and approximately 35% when timed AI was used. A report from Kentucky reported an increase in services per conception of 1.62 to 2.91 from 1972 to 1996.

Is reproductive efficiency really decreasing? By selecting for milk production have we inadvertently selected for reduced fertility or are traditional reproductive indices appropriately measuring fertility? Alternatively, have dairy producers just not placed priority on reproduction? Technology exists today that can reverse this trend. It is my objective to present some of the reasons why reproductive efficiency may have declined and some approaches that can be taken to improve reproductive efficiency in dairy herds.


Milk production for U.S. dairy cows has increased approximately 20% in the last 10 years. At the same time indices of reproductive efficiency have worsened. There is a long history—even as far back as 1929—of associating greater milk production with reduced reproductive performance in dairy cattle. Based on analyses of large datasets, there is clearly an antagonistic relationship between milk production and reproduction; however, the effects of increased milk production on reproduction are relatively minor compared with the effects of other factors. Dairy cows in New Zealand, whose milk production is low compared with U.S. standards, have high first-service conception rates; however, because of their management practices improved reproductive performance has been genetically selected as well.

High milk production should not be confused with negative energy balance. Cows undergo a normal process of nutrient partitioning and adipose tissue mobilization during early lactation. Negative energy balance, weight loss, and decreased BCS occur during early lactation when nutrient requirements for maintenance and lactation exceed the ability of the cow to consume energy in feed. Several studies suggest that the effects of milk production on reproduction can only be observed in the highest-producing dairy cows. Perhaps the recent declines in reproduction simply reflect greater percentages of U.S. dairy cows within the high-producing category.

In the U.S. the number of milk cow operations is decreasing while the number of herds with more than 200 cows in increasing. First-lactation cows also represent a larger percent of milking cows. First-lactation cows have lower energy balance because they eat less and have energy requirements for growth in addition to lactation. First-lactation cows with lower energy balance have delayed intervals to first ovulation and are at greater risk for conception failure at first AI.

Traditional methods of managing reproduction including the detection of estrus may serve the modern dairy industry poorly. The average dairy cow today has 8.5 stands per estrus with an estrus duration of seven hours; however, nearly one-quarter of the cows have estrus of low intensity (<1.5 stands) and short duration (< 7 h). As herd size has increased some new reproductive management techniques have been implemented including the use of timed AI.

Traditional reproductive indices such as services per conception and conception rate are negatively affected when timed AI is implemented. Interval to first service and overall pregnancy rate may, however, be improved. Perhaps we should be reporting percent of cows pregnant by a certain period of time such as “100-d in-calf rate” or “% pregnant within 1, 2, or 3 cycles after the volunteer waiting period” combined with culling rate. In order to maintain optimal reproductive efficiency methods of managing reproduction must be modernized including remote record—records accessible in the field—keeping and utilization. Some of the decrease in reproductive efficiency may be attributed to a deficiency in simple reproductive management and utilization of records.

Epidemiological studies suggest that disease parameter (i.e., ketosis, mastitis, retained placenta, and cystic ovarian disease) have a greater effect on herd fertility compared with non-disease parameters (i.e., milk production and BCS). Epidemiological studies evaluating the hazard ratio for conception in 13,307 New York Holstein cows demonstrated that only for the highest level of milk production was there a nonsignificant increase in hazard ratio. More important factors for conception were season of calving and postpartum disease including retained placenta, metritis, and ovarian cysts. It has been reported that moving cows into confinement housing and managing cows in larger herds increases the risk of mammary and uterine infections. Mammary and uterine infections are risk factors for infertility and such infections have been demonstrated to be a cause of ovarian cysts.

Inbreeding in U.S. Holsteins has increased dramatically since 1980. Inbreeding negatively affects reproductive traits in dairy cows, but a “safe” level of inbreeding is poorly defined. One study concluded that every 1% increase in inbreeding led to a 0.17 increase in services per conception, a 2-day increase in days open, and a 3.3 percentage-unit decrease in conception rate.

The changing global environment may be contributing to decreased reproductive efficiency as well. The decade of the 1990s was the warmest since the beginning of instrumental temperature recording. One study examined 90-day return rates throughout the calendar year and found that summer infertility was greatest in the highest milk producing dairy cows.

The administration of recombinant bST has also been implicated to be responsible for the decrease in reproductive performance. In a large study involving 28 dairy herds, recombinant bST administration to primiparous cows caused a 16-day increase in days open, but did not affect overall pregnancy rates. In the same study, days open in multiparous cows were not affected. The current period of reproductive decline began before the introduction of bST in 1994, and countries in which bST is not used (Ireland, UK, and Australia) are also experiencing reproductive problems in dairy herds. In fact, the use of bST with synchronization protocols has been shown to improve pregnancy rates (Table 1).

Table1. Effect of bST on reproduction in synchronized dairy cows.

Item Control bST
Standing Estrus 92% 42%
Silent Ovulation 0% 32%
Double Ovulations 4% 4%
Synchronized Pregnancy Rates 30% 47%


  • Ovsynch and Presynch. Reproductive tools to synchronize estrus without estrus detection can have a significant effect on reproductive efficiency. Ovsynch involves the administration of GnRH, followed by an injection of PGF 2a seven days later, and an injection of GnRH 48 hours later. The protocol is quite robust—it works in most situations (Table 1). At this time there are two alternatives for the timing of AI: AI 16 hours after the second injection of GnRH or at the time of the second injection of GnRH. Although ultrasound pregnancy rates are a bit higher for the 16 hour interval, calving rate does not differ between the two times of AI. In fact, one can expect a higher percentage of heifer calves if AI is done at the time of the second injection of GnRH (Table 2). Presynch involves the administration of PGF 2a 14 and 28 days before the first injection of GnRH for the Ovsynch protocol to cows on bST. These two injections synchronize the stage of the cycle so that pregnancy rates are increased (Table 3). Furthermore, injections of PGF 2a to postpartum cows has been demonstrated to increase fertility by improving uterine health (Table 4).

Table 2. A summary of pregnancy rates in cows administered Ovsynch.

Item Ovsynch
Mean Pregnancy Rates 34%
Number of Herds in Summary 9
Standard Error 2.4
67% Range 27 to 41%

Table 3. A summary of breeding Ovsynch treated cows at 0 or 16 hours after the second injection of GnRH.

Item 0 h (AI at time of 2 nd GnRH) 16 h (after 2 nd GnRH)
Pregnancy Rate 37% 45%
Pregnancy Loss 9% 21%
Calving Rate 31% 33%
Twinning Rate 0% 0%
Female:Male Ratio 61:39 54:46
Number Female Calves 61/100 calves born 54/100 calves born

Table 4. Pregnancy rates in cyclic cows administered Ovsynch and Presynch

Treatment Group Ovsynch Presynch
Control 34% 47%
BST at 63 d postpartum 39% 68%
BST at 73 d postpartum 51% 64%

Table 5. Postpartum PGF 2a therapy on pregnancy rate, services per conception, and days postpartum to conception.

Days Treated Control Treated
14-28Pregnancy Rate at 1 st Service 45% 62%
14-16Services/Conception 2.33 1.64
20-24Days Postpartum to Conception 115 86
20-24Services/Conception 2.3 1.8
  • Early Pregnancy Detection and Resynchronization. Because it has become so difficult, either because of management or because the reduced intensity of estrus, to detect estrus in dairy cows, it may be appropriate to eliminate estrus detection not only for the first breeding, as discussed in the previous section, but for the return estrus as well. Technology is available to routinely detect pregnancy as early as about 32 days post-breeding. Resynchronization involves the administration of synchronization products to potentially pregnant cows. A good example is briefly illustrated in Table 6.

Table 6. A method to manage the return estrus in dairy cows.

Day Activity Comment
-9 (Tu) GnRH  
-2 (Tu) PGF 2 "  
0 (Th)* GnRH and AI First Service
26 (Tu) GnRH  
33 (Tu) Ultrasound for Pregnancy—Pregnant cows Recheck on day 54
33 (Tu) Ultrasound for Pregnancy Open Cows-PGF 2a  
35 (Th) Open Cows—GnRH and AI  

*First day after the volunteer waiting period.

Based on this strategy cows would have an opportunity for two timed inseminations by 35 days postpartum. It is important to point out that PGF 2a must not be given to potentially pregnant cows as it will terminate pregnancy. GnRH, however, does not have a negative effect on pregnancy. The strategy illustrated in Table 6 can be, and is in some herds, extended so that all breeding are done on a timed basis. Another important point is that even confirmed pregnancies must be re-checked as there is an incidence of pregnancy loss in cows with early pregnancy detection; however, this pregnancy loss is not due to ultrasonography. Another option that some dairy producers include in this protocol is the management of twins. At day 33 if a twin pregnancy is detected, it may be managed as if the cow is not pregnant. Administration of PGF 2a and the termination of pregnancy.

  • Embryo Transfer. Although this is now what I would consider an older technology it has utility in today’s dairy operations. One particular value that has been demonstrated in the past several years is in regards to summer heat—a known factor to decrease reproductive efficiency or in some cases eliminate the establishment of pregnancy. Data illustrated in Table 7 suggest that embryos conceiving to AI during summer heat have a higher mortality rate than embryos transferred into the cows by ET. This study was conducted in Florida where summer heat is excessive. Therefore, one can improve summer pregnancy rates by using ET rather than AI.

Table 7. Pregnancy rates in cows administered embryos or inseminated during summer heat.

Technology Pregnancy Rate—d 22 Pregnancy Rate—d 42
AI 61% 21%
ET 60% 35%

Another value to ET is in regards to twinning. Twinning greatly increases the incidence of postpartum diseases that compromise pregnancy as discussed earlier. Cows implanted with one embryo seldom have twins. Twinning in cows after AI has increased in the dairy industry and the incidence is positively related to milk production. One study reported a 22% incidence of double ovulations in high producing dairy cows. Although not all double ovulations will result in twinning, it will still be a higher than desired incidence of twinning.

A third potential value of ET is offspring sex. Sex separated semen has been promised for a long time. The major problem with separating male and female sperm is that it is a time consuming process. This leads to significant increase in cost and a lack of availability and may not be economical for AI, particularly if conception rates are low. However, if used with donor cows, the demand is less and the cost of the sex separated semen is split among several offspring rather than just one, or possible none. Therefore, by using ET a producer can a) improve pregnancy rates particularly during summer heat, b) reduce the incidence of twinning, and c) increase the number of female offspring.

  • Estrus Synchronization, Resynchronization, and Treatment of Cystic Ovarian Disease with CIDR Protocols.

Although the CIDR has been approved by FDA, it was not approved for use in dairy cows. This, hopefully, will be changed in the near future. One protocol that has been demonstrated efficacious in dairy cows is the Ovsynch+CIDR protocol. This basically involves the insertion of the CIDR at the time of the first GnRH injection and removal at the time of PGF 2a treatment. This protocol is particularly effective in improving pregnancy rates in anestrous dairy cows as illustrated in Table 8—a multi-location study.

Table 8. Effect of CIDR on Osynch pregnancy rates.

Status N Ovsynch Ovsynch+CIDR Total
Cyclic 451 44% 49% 46%
Anestrus 182 35% 55% 45%
Total 633 41% 51% 46%

The Ovsynch protocol is similar to the treatment I created for cystic ovarian disease nearly 25 years ago. The only difference is the interval from GnRH to PGF 2a is seven days rather than the nine days I used; however, both are effective in treating cystic ovarian disease. Use of the CIDR along with the Ovsynch protocol may improve efficacy of treating cystic ovarian disease as reported in Table 9—a study we conducted.

Table 9. Efficacy of Ovsynch and Ovsynch+CIDR in cows with cystic ovarian disease.

Group Ovulation Rate Pregnancy Rate Cysts on Day +28
Normal Cows 94% 60% 6%
Cystic/Ovsynch 82% 11% 36%
Cystic/Ovsynch+CIDR 100% 33% 22%

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