George Perry: Managing for reproductive success
May 11, 2012
BROOKINGS, SD – Fertility is influenced by many factors, and one of the best methods to look at factors that influence fertility is with the “Equation of Reproduction,” said George Perry, South Dakota state University (SDSU) Extension Beef Reproductive Management Specialist.
Perry explains that the “Equation of Reproduction” includes the following four areas:
• Percentage of animals detected in standing estrus and inseminated;
• Inseminator efficiency;
• Fertility level of the semen and;
• Fertility level of the herd.
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Each of the preceding areas will be discussed in the four-part series on managing for reproductive success by SDSU Extension.
For successful insemination of cattle to occur, animals must be detected in standing estrus, Perry says.
“Detecting standing estrus, which is also referred to as heat detection or detecting standing heat, is simply looking for the changes in animal behavior associated with a cow/heifer standing to be mounted by a bull or another cow/heifer,” he said.
Since cows not detected in estrus, and consequently not inseminated in artificial insemination (AI) programs, have no opportunity to conceive, Perry says heat detection becomes the single greatest limiting factor in managing beef cow reproductive programs.
“For successful artificial insemination of cattle to occur, the producer must take the place of the herd bull in detecting the cows/heifers that are ready to be inseminated,” Perry said. “Accurate detection of animals in standing estrus is the goal of good estrous detection and plays a vital role in the success of any AI program.”
He points to a Colorado State University study in which animals were administered an estrous synchronization protocol, then monitored for standing estrus 24-hours a day with a computer assisted estrus detection system (HeatWatch) or twice a day for 30 minutes by visual observation. By day 5, after estrous synchronization, 95 percent of animals monitored 24-hours a day, were detected in standing estrous, while only 56 percent of animals observed twice a day for 30 minutes were detected in standing estrus.
With a 95 percent estrous detection rate and a 70 percent conception rate (95% X 70% = 67%), 67 percent of the animals will be pregnant; whereas, only a 39 percent (55% X 70% = 39%) pregnancy rate will occur with a 55 percent estrus detection rate (Table 1).
“Accurate detection of estrus can be a difficult and time-consuming activity,” Perry said. “Continuous observation of over 500 animals exhibiting natural estrus in three separate studies indicated 55.9 percent of cows initiated standing estrus from 6 p.m. to 6 a.m. (Table 2),” Perry said.
Based on research, Perry encourages producers to observe cows for estrus as often as possible. The research showed that when cows were observed for standing estrus every six hours (6 a.m., noon, 6 p.m., and midnight), estrous detection increased by 10 percent with the addition of a mid-day observation and by 19 percent when observed four times daily (every six hours) compared to detecting standing estrus at 6 a.m. and 6 p.m. alone.
“Therefore, detection of standing estrus can be one of the most time-consuming chores related to artificial insemination,” he said.
With natural service, Perry says estrous detection is considered to be easy, as it is “the bulls’ job.” However, he says differences in estrous detection exist among bulls.
“Libido refers to a bull’s desire to mate. Research from Kansas State has reported that libido is highly inherited trait with heritability ranging as high as 0.59,” he said. “This is because there is more variation in libido between sons of different sires than between sons of the same sire.”
He reminds cattle producers that scrotal circumference, semen quality and physical confirmation, all traits evaluated in a Breeding Soundness Evaluations, are not related to libido.
“Libido has a direct affect on pregnancy rate and, as such, it can influence the success of an entire breeding season,” Perry said. “Libido can be practically evaluated by closely watching a bull after introducing him to a cowherd and determining his desire to detect cows in estrus.”
Although several factors are critical to the success of any well-managed beef reproductive program, estrus detection is one of the most limiting and most time consuming. Without identifying cows in estrus, cows will not have an opportunity to conceive.
Cows not detected in estrus have no opportunity to conceive. In artificial insemination systems, that opportunity to conceive when a cow is detected in estrus also depends on another limiting factor, “Inseminator Efficiency,” Perry said.
Based on research, Perry says that fertilization rates don’t differ between animals following natural service or artificial insemination (AI).
He points to a study which flushed embryos following insemination. The data showed that fertilization rates following natural service or artificial insemination (AI) in cattle range from 89 to 100 percent. Furthermore, when pregnancy rates from 13,942 first-service artificial inseminations were compared to 6,310 first services by natural service, no difference was detected between artificial insemination and natural service.
“With AI, inseminator efficiency is influenced by semen handling and the ability of the technician to deposit semen in the correct location,” Perry said.
To improve semen handling, he encourages cattle producers to have a detailed inventory of semen easily accessible, so that straws may be located and removed from the tank quickly to avoid exposure of semen to ambient temperature.
“When removing a straw from a liquid nitrogen refrigerator, it is imperative that the technician keep the canister, cane and unused semen straws as low as possible in the neck of the tank,” Perry said.
He adds that it is best to keep all unused straws below the frost-line in the neck of the tank. The temperature of liquid nitrogen in a semen tank is -196 degrees Celsius (C) (-326 degrees Fahrenheit, (F)). Sperm injury (as judged by sperm motility) occurs at temperatures as warm as -79 C (-110 F), and injury to sperm cannot be corrected by returning semen to the liquid nitrogen.
Many studies have compared site of deposition on pregnancy success, says Perry.
“Some studies have reported increased conception rates when semen was deposited in the uterine horns rather than the uterine body, but other studies have reported no difference in fertility when comparing uterine body and uterine horn inseminations,” he said. “Furthermore, an inseminator and site of semen deposition interaction has been reported, with evidence of either an increase, decrease, or no effect of uterine horn deposition on conception rate for individual inseminators.”
Perry says it is not clear why some studies have shown an advantage following uterine horn insemination while others have not.
“A possible explanation for the positive effect of uterine horn inseminations may be related to the minimization or elimination of cervical semen deposition,” he said. “Studies have reported cervical insemination errors account for approximately 20 percent of attempted uterine body depositions, and cervical insemination resulted in at least a 10 percent decrease in fertility when compared with deposition of semen in the uterine body.”
Based on this information, Perry says in order to maximize conception rates, AI technicians must continue to manipulate the reproductive tract until the tip of the AI gun is past the cervix and deposition into the uterus can be accomplished.
“Clearly, all AI technicians must develop sufficient skill to recognize when the tip of the AI gun remains in the cervix,” he said.
When numerous cows must be inseminated on a given day, multiple straws of semen are routinely thawed simultaneously to facilitate AI.
Research from the University of Idaho determined simultaneous thawing and sequence of insemination (1st, 2nd, 3rd or 4th), and elapsed time from initial thaw to completion of fourth AI had no effect on conception rate within inseminator group; however average conception rate differed between groups which were treated by a professional AI technician and those serviced by a herdsman-inseminator (45% vs. 27%, respectively).
The researched looked at the following:
a) The effect of simultaneous thawing of multiple 0.5-mL straws of semen and sequence of insemination (1st, 2nd, 3rd or 4th) on conception rates;
b) Whether conception rates achieved following AI by professional AI technicians (PAI) and herdsman-inseminators (HI) differed;
c) The effect of elapsed time from initiation of thawing straws of semen to seminal deposition on conception rates.
Perry says this research reinforces the important role handling plays in conception.
He adds that conception rates are most likely maximized when personnel:
a) Follow proper procedures for thawing semen;
b) Prevent direct straw-to-straw contact during thawing of multiple straws; simultaneously to avoid decreased post-thaw sperm viability as a result of straws sticking together;
c) Use appropriate hygienic procedures;
d) Maintain thermal protection of straws during AI gun assembly and transport to the cow;
e) Deposit semen in the uterus of the cow within approximately 15 minutes after thawing.
The bull influences overall herd fertility more than any other single animal, and loss of fertility by a bull or straw of semen can cause substantial loss to a potential calf crop, Perry says.
“The bull supplies half of the genetics to all of the calves he sires, and bull selection can be the most powerful method of genetic improvement in the herd,” Perry said. “Clearly there are differences among bulls in their ability to achieve pregnancy success.”
Perry points to research conducted at the USDA-ARS research center in Miles City, MT.
This research has shown tremendous variation in pregnancy rates between bulls when they were used either in a fixed-time artificial insemination (AI) breeding program or used following detecting cows in estrus. However, all of these bulls in this study looked normal when evaluated under a microscope for motility and morphology.
“For several decades seminal traits have been studied to try to predict reproductive success. Research is being conducted to identify characteristics of semen that influence fertility rates,” he said. “The ability of sperm to become capable of fertilizing, binding and penetrating an oocyte all influence a bull’s fertility.”
Perry says that research is underway to develop tests that will more accurately determine the fertility of individual bulls.
“Our ability to predict the fertility of individual bulls either by a semen sample or a DNA sample may eventually be possible,” he said. “Nevertheless, the only current method for determination of fertility differences between bulls requires the insemination of several thousand animals under the same management practices.”
Currently, Perry says the best method for cattle producers to acquire semen with good fertility is to buy it from a reputable source and make sure it has all been handled correctly.
With natural service, physical characteristics, such as scrotal circumference, mating ability, and semen quality play a role in a bull’s fertility,” says Perry.
He says the best way to determine these factors is through a Breeding Soundness Examination (BSE). The American Society for Theriogenology developed minimum guidelines for a bull to pass a BSE.
To successfully complete a breeding soundness evaluation, a bull must have at least 30 percent sperm motility, 70 percent normal sperm morphology, and a minimum scrotal circumference based on age. Bulls meeting the preceding minimum requirements are classified as satisfactory potential breeders. If a bull does not pass one of these tests, he is classified as a “classification deferred” animal (meaning it is recommended that the bull be tested again) or he is classified as an unsatisfactory potential breeder. Bulls should be tested approximately one month to six weeks prior to the breeding season.
“This allows for time to retest bulls if unsatisfactory results are obtained or time to find a replacement herd bull,” Perry said.
The overall purpose of the physical examination portion of a BSE is to determine a bull’s mating ability. Mating ability can be described as the physical capabilities needed to successfully breed a cow. A bull must be able to see, smell, eat and move normally to successfully breed cows. The physical examination closely scrutinizes a bull’s eyes, teeth, feet, legs and nutritional level (evaluated by body condition score). Any disease or injury that affects joints, muscles, nerves, bones, or tendons may cause a bull to be structurally unsound. In addition to structural unsoundness, diseases or injuries to the penis or prepuce can result in an inability to breed via natural service.
“These abnormalities will only be detected by careful examination or observing an attempted mating of a cow. A bull that has high-quality semen but is unable to physically breed cows is unsatisfactory for natural service,” he said.
Whether natural service or AI is used, Perry says two of the most important indicators of bull fertility currently available are sperm motility and morphology.
“With AI identifying females in estrus and proper placement of semen are critical factors for obtaining desirable pregnancy rates in the cowherd; however, compromised semen quality through semen handling will negate the attention to detail of the two factors discussed previously,” Perry said. “With natural service, structurally sound bulls with a large scrotal circumference and high semen quality should be selected as herd sires. It is important to remember that semen quality of an individual bull changes over time and, for a bull to be fertile, desire to find cows in estrus and mating ability should be evaluated periodically.
Fertility of the herd may be the most difficult factor to evaluate, Perry says.
“Accurate detection of estrus, inseminator efficiency and fertility of the semen are all vital to the success of any breeding program. However, even when these three elements are well managed, if the cowherd fertility level is compromised, pregnancy rates may not meet cattlemen’s expectations,” Perry said.
When Perry discusses herd fertility he is referring to a herd’s cycling/puberty status, compliance with protocols, embryonic mortality, body condition score (nutrition level) and disease control.
Perry says non-cycling cows at breeding time may result from a number of factors including dystocia, calving late, inadequate nutrition levels (pre- and post-calving), cow age or excessive milk production in relationship to the feed resources available or severe weather conditions. In addition, heifers not developed properly and failing to reach 55 percent to 65 percent of their mature weight by breeding time may not cycle or conceive if they do.
Synchronization protocols that utilize a progestin can help cows/heifers that have not initiated normal estrous cycles if they are almost ready to begin having normal estrous cycles.
“These protocols are the result of time-consuming research and are a valuable tool when incorporated accurately into breeding programs in conjunction with good herd management,” Perry said. “However, regimented use of them is essential for satisfactory results.”
When implementing protocols, Perry says advanced planning is important.
“Timing of prebreeding vaccinations needs to be well in advance of insemination,” he said. “Cattle producers need to plan when injections or feeding need to occur; plan access to facilities and line-up additional labor. When insemination will occur must be planned well in advance of protocol use.”
Fertilization rates are usually between 89 percent and 100 percent when semen is present at the time of ovulation. However, Perry says early embryonic mortality causes that percentage to drop to about 60 percent to 70 percent.
“Several management decisions can impact the percent of embryos lost to early embryonic mortality,” Perry said.
One factor he says is the timing of transporting cows and heifers after insemination.
“Research conducted at the USDA research center in Miles City, MT, reported transporting cows/heifers from day 5 and 42 after insemination is a very sensitive time for the embryo and can be a major factor in embryo mortality,” he said.
Another factor is changes in nutritional status.
“This can also have a tremendous influence on embryonic survival,” Perry said.
He points to research conducted at Oklahoma State University showed that severe changes in intake of energy and protein can result in heifer stopping normal estrous cycles.
“Furthermore, work done at South Dakota State University showed that moving heifers, who developed all winter in a feedlot, to pasture immediately after AI can increase early embryonic losses,” Perry said.
Body condition score (BCS) and disease are two additional causes of marginal fertility rates says Perry.
“Research recommendations suggest that cows be in a minimum BCS of 5 and heifers 6 at calving time in order for them to cycle and re-breed on an annual basis,” he said. “This allows sufficient body reserves for lactation and to initiate normal estrous cycles after calving.”
However, Perry notes, if adequate nutrition is not available after calving, body condition can be lost and may delay the return to normal estrous cycles.
Overall health of the herd can impact herd fertility says Perry.
“Cattle producers need to implement a proper pre-breeding vaccination program along with a well-managed, internal and external parasite application program. This will help limit disease occurrences in the herd and promote herd fertility,” Perry said.
He adds that special care should be taken with virgin heifers.
“Several studies have reported negative impacts on pregnancy success by vaccinating heifers that have never been vaccinated before with a modified live vaccine (MLV) for BVD or IBR around time of breeding,” he said. “Therefore, general recommendations for vaccination of replacement heifers include: before and at weaning, with both heifers and cows receiving a booster vaccine at least 30 days before breeding. If it is absolutely necessary to give a MLV vaccine less than 30 days prior to breeding, the vaccine should be administered as soon as possible and only to animals that were vaccinated both before and at weaning. Animals that have not previously been vaccinated (naïve animals) should not be vaccinated near the time of breeding.”
The “Equation of Reproduction,” which has been discussed in this four-part series, highlights management practices that are essential to any successful beef breeding program.
When “Managing for Reproductive Success,” it involves cattle producers making management decisions throughout the entire year – not just prior to the breeding season. By doing this, producers can expect to generate successful reproductive results.
“As we increase the reproductive efficiency within a herd, we can increase our management decisions on genetic improvement and other factors to increase the profitability of your herd,” Perry said.
Editor’s note: For more information contact Jim Krantz, SDSU Extension Cow/Calf Field Specialist at jim.Krantz@sdstate.edu or 605-995-7381 or Dr. George Perry, SDSU Extension Beef Reproductive Management Specialist at firstname.lastname@example.org or 605-688-5456. To listen to a recent iGrow Radio Network interview on this topic with Dr. George Perry, and to review all four articles in this four-part series released by SDSU Extension visit iGrow.org.