Embryonic loss is the greatest economic loss in the beef cow/calf industry. Therefore, your management decisions around breeding time should consider factors that may influence embryonic mortality and calf survivability. In this article, Sarah Fields, a previous Graduate Research Assistant in Beef Production, and Dr. George Perry, Beef Reproduction & Management Specialist with SDSU Animal & Range Sciences, help you better understand the effects of stress on embryonic mortality so you can make management decisions that minimize its impact.
In order to understand how stress may increase embryonic mortality, you must first understand the development of the embryo (Table 1).
Just like the estrous cycle, embryo development begins on day 0, or the day of standing estrus. This is the day the female is receptive to the male and insemination occurs. Ovulation occurs on day 1 or about 30 hours after the first standing mount (Wiltbank et al., 2000). If viable sperm is present, fertilization occurs inside the oviduct shortly after ovulation. The first cell division occurs on day 2, and by day 3 the embryo has reached the 8-cell stage (Shea, 1981). Between days 5 and 6 the embryo migrates into the uterine horn and by day 7 to 8 it forms into a blastocyst (Shea, 1981; Flechon and Renard, 1978; Peters, 1996). At this stage two distinct parts of the embryo can be seen: 1) the inner cell mass, which will become the fetus and 2) the trophoblast, which become the placenta.
Between days 9 and 11 the embryo hatches from the zona pellucida, a protective shell that has surrounded the embryo to this point (Shea, 1981; Peters, 1996). Then, on days 15 to 17, the embryo sends a signal to the cow to tell her she is pregnant (Peters, 1996). This is the first signal the cow receives to know she is pregnant. The embryo attaches to the uterus beginning on day 19, and around day 25, placentation, an intricate cellular interface between the cow and the calf, begins. By day 42 the embryo has fully attached to the uterus of the cow (Peters, 1996).
Shipping Stress and Embryonic Mortality
With knowledge of the critical time points in embryonic development, it becomes easier to understand how stress from shipping can result in increased embryonic mortality in cows (Table 2).
When you load your animals on a trailer and haul them to a new location, they become stressed and release hormones related to stress. These hormones lead to a release of different hormones that change the uterine environment where the embryo is developing. During blastocyst formation, hatching, maternal recognition of pregnancy, and attachment to the uterus, the embryo is vulnerable to these changes.
These most critical time points are between days 5 and 42 after insemination. Before day 5, the embryo is in the oviduct and is not subject to changes in the uterine environment. Therefore, stress does not influence embryo survivability at this time.
The greater the length of time after day 42, the less severe the influence of shipping stress on embryonic loss appears to be. At the time of complete attachment of the embryo to the uterus the embryo is supported by the mother and appears to be not as easily affected by changes in its environment. On the other hand, between these time points (5-42 days), the embryo is at greatest risk.
When Should Cows Not be Shipping?
Shipping cows between days 5 and 42 can be detrimental to embryo survival and cause around a 10% decrease in pregnancy rates (Table 2). Research has also demonstrated that shipping cattle 45 to 60 days after insemination can result in 6% of embryos being lost. Therefore, even shipping cattle 45 to 60 days after insemination may increase embryonic mortality.
Critical time points such as blastocyst formation, hatching, maternal recognition of pregnancy and adhesion to the uterus take place during the time of pregnancy. If these events are disturbed, it leads to increased embryonic mortality and decreased pregnancy rates. Therefore, it is important for you to transport cattle before the breeding season or immediately after insemination.
When Can Cows be Shipped?
Shipping between days 1-4 is best. The embryo is still in the oviduct during this time and therefore likely not subjected to uterine changes.
After day 45, the embryo is well established and fully attached with the placenta. Therefore, it is less susceptible to the changes resulting from stress as well. Shipping at this point is less risky; however, embryonic loss from shipping has been reported up to 60 days after insemination. Take care to reduce the stress involved when animals are shipped. Do not overcrowd trailers. Handle cattle as gently and calmly as possible.
Heat Stress and Embryonic Mortality
The best time to ship cattle is during early stages of embryonic development. However, this is also when the embryo is most susceptible to increased temperatures. Temperature, humidity, radiant heat and wind all affect heat stress in cows.
The rectal temperature of cattle is normally 102.2°F. An increase in rectal temperature as little as 2°F can result in decreased embryonic development (Ulberg and Berfening, 1967). When those temperatures reach 105.8°F for as little as 9 hours on the day of insemination, embryonic development can be compromised (Rivera and Hansen, 2001).
Heat stress has also been reported to change follicular waves, resulting in reduced oocyte quality (Wolfenson et al., 1995). Researchers have reported heat stress 42 days prior (Al-Katanani et al., 2001) and up to 40 days after breeding can affect pregnancy rates (Cartmill et al., 2001). This illustrates how important it is to plan ahead for the breeding season.
There are several ways to reduce the effects of heat stress. Shade, fans and misters can all reduce the effects of heat stress in natural service or artificial insemination (A.I.) programs. These methods allow animals to stay cooler during the hottest parts of the day. In humid areas, misters may not actually benefit animals. If the water cannot evaporate, it is not effective at cooling the animal.
Producers who utilize A.I. can also implement timed A.I. (T.A.I.) protocols to increase pregnancy rates during the hot summer months. Timed A.I. has increased pregnancy rates over animals inseminated 12 hours after estrus detection in conditions of heat stress (Arechiga et al., 1998; de la Sota et al., 1998). This is most likely due to fewer animals showing signs of estrus when under heat stress. When the weather is too hot, animals tend to not move around as much and do not show signs of standing estrus. Heat detection is a vital part of getting more animals pregnant. Since fewer animals are seen in heat, fewer animals can be inseminated. In this case, T.A.I. would be the best protocol to use, because it eliminates heat detection.
Using embryo transfer during times of heat stress can also increase pregnancy rates. High-quality, fresh embryos have been proven to increase pregnancy rates over A.I. in heat-stressed cows (Putney et al., 1989). Embryos at time of embryo transfer can adapt to the elevated temperatures. Therefore, use of embryo transfer during times of heat stress can improve pregnancy success.
Planning for Success
Getting cows and heifers pregnant during the breeding season - especially early in the breeding season - can have a tremendous impact on your profitability levels. You’ve already put forth the time, effort and cost to have a successful breeding season (natural service or A.I.). Ensure your management decisions lead to success too. Don’t stress animals during critical time points in embryo development. Consider heat stress and shipping stress as well. In short, planning around the breeding season becomes an important management tool for you to maximize pregnancy success.
A GENEX Beef Facebook post asked beef producers for tips in planning your next timed artificial insemination (A.I.) project. Here is a sampling of the knowledge shared by seasoned A.I. veterans, grouped into seven categories.
"Timing is cricual! We make sure our shots are done exactly on time and likewise for insemination." - Emily Smith Castine
"Luck favors the prepared." - Kate Meyer
"As cool of weather as you can get. Early morning breeding, and then let them relax." - Ryan Stoecklein
"Research your bull choices and use those that you know have good conception or PregCheck™ rankings. Is it the easiest way to boost conception." - Justine Ferguson
"A good team of people to work with! Communications is key for everything to go smoothly." - Carrie Lynch
"Good body condition and good mineral program." - James Mullens
"Handle cattle and semen carefully!" - Jeff Meyer
To help with your next beef cattle synchronization project, GENEX has compiled answers to the most frequently asked questions.
There isn't an easy answer to this question. Research does suggest some protocols perform better than others, but just because research says it's the best protocol doesn't necessarily make it the best protocol for your operation.
Instead, ask yourself these three questions before choosing a synchronization protocol:
» How many times am I willing to put the female through the chute?
» How much am I willing to spend on synchronization drugs?
» What are my expectations for results?
Once you know the answers to these questions you can objectively analyze which synchronization program best fits your operation. No matter what the research or experts tell you, the best protocol for your operation is one that aligns with your goals and one you are 100% confident you can perform perfectly from start to finish.
The answer depends if you are synchronizing heifers or cows.
Criteria for synchronizing heifers:
» Should have achieved at least 65% of mature body weight
» Minimum of 50% should have a reproductive tract score of ≥ 4 at six weeks before breeding
If you don't have a veterinarian in your area that offers reproductive tract scoring, don't panic! You can achieve the same thing by visually observing your heifers for heat in the weeks and months leading up to breeding. You want to observe that at least 50% of heifers are cycling six weeks prior to breeding.
Criteria for synchronizing cows:
» Body Condition Score of ≥ 5 at calving
» An average postpartum interval of ≥ 40 days at the beginning of the protocol
» A minimum of 21 days postpartum at the time of Eazi-Breed™ CIDR® insertion
» Low incidence of calving difficulty
Synchronization drugs should be given in the muscle (IM), with the exception of LUTALYSE® Hi-Con which can be administered IM or subcutaneously. When administering synchronization drugs, it is recommended to use a 1-1/2 inch, 18-gauge needle. You should also wear gloves when handling synchronization drugs to avoid contact with skin.
CIDR® inserts are labeled as a one-time use item by the manufacturer, and it is recommended that you follow this guideline. CIDR® inserts can be one of the most expensive parts of a synchronization protocol (retailing at $10 to $12) and it is tempting to cut that cost in half by using it a second time, however if tempted ask yourself what another A.I. calf is worth. It’s likely a lot more than $5 to $6.
Your pre-breeding vaccination program is an important part of an overall successful A.I. program. However, several studies have shown injection of naïve heifers with a modified live vaccine (MLV) around the time of breeding result in ovarian lesions and decreased pregnancy rates. Therefore, it is recommended that you give all pre-breeding vaccinations at least 30 days prior to breeding.
While there isn't any research that suggests administering dewormer at breeding will have a negative impact on fertility, plan to do that at least 30 days prior to breeding as well. The less stress you put on females around breeding time, the better your success. To achieve optimal results, it's best to do as little as possible to the females during the synchronization and breeding process.
The most critical time for embryonic development occurs between day five (when the embryo begins migrating from the oviduct to the uterus) and day 42 (when the embryo has made definitive attachment to the uterus). Research indicates shipping your cows during this critical time can cause a 10% decrease in pregnancy rates. The best time to move cattle is prior to insemination or days one to four post-breeding. If you can't move them within this time period, it's best to wait until after day 45.
Despite what research might say, no single synchronization protocol fits every operation. Know your operation, follow the suggestions above and trust your gut. And, if you have any questions, don’t hesitate to contact your local GENEX representative.
Historically, semen fertility has been evaluated by a trained veterinarian or lab technician who checks the semen with a microscope for percent live sperm cells, motility and morphology. In fact, every collection of semen produced by GENEX is evaluated multiple times in the lab before it's approved for use on your operation.
Lab analysis is very effective in ensuring semen has been properly processed, frozen and handled; however, lab analysis only tells part of the story. Semen from two different bulls may look very similar under the microscope yet perform very differently in cows. A better method is to let the cows tell which bull's semen is most fertile, and that's what PregCheck™ sire fertility rankings do.
Beef PregCheck™ fertility rankings use the fertility model the dairy industry has used for many years, except it is set to a beef base. This means beef sires are compared to other beef sires, not dairy sires. Many variables are statistically accounted for in the model, including technician, herd effect, age of cow, number of previous breedings and many others. This sophisticated evaluation model, along with accurate on-farm data, results in beef bull fertility data that is sound and reliable. Note that PregCheck™ rankings are not an EPD but can be read and utilized like an EPD or performance ratio.
PregCheck is set to a 100-base system, meaning a value of 100 is average. Every one point difference is equivalent to a 1% difference in conception rate. For example, if Bull A has a 104 PregCheck™ ranking and Bull B has a 100 PregCheck™ ranking, Bull A is predicted to be 4% higher in conception rate than Sire B.
PregCheck™ rankings are the result of real breedings which have shown differences between bulls.
Each bull’s ranking has an associated reliability level. Consider if Bull A has the 104 PregCheck™ ranking with 93% reliability and Bull B has the 100 PregCheck™ ranking with a 75% reliability. Bull A can be used with confidence; he routinely performs 4% above the average of his contemporaries for conception rate. At only 75% reliability, there is still some uncertainty in how Bull B will perform until he is bred to more females. However, Bull B is trending average for conception rate.
As more pregnancy data becomes available, reliability increases and the amount of change in the ranking will decrease. For a reliable evaluation, which is about 70%, a bull must have approximately 400 breedings in the database.
The true advantage is the ability to eliminate inferior fertility sires from your breeding program. When utilizing bulls with higher PregCheck™ rankings, you can expect increased conception rates resulting in more A.I. pregnancies and pounds of calf per year.
While all GENEX sires are procured with producer profitability in mind, PregCheck™ fertility rankings offer you another option to improve your bottom line.
The rankings are published in the Beef Genetic Management Guide and on individual bull pages on the website. You can also ask your local GENEX representative for a list of bulls with high PregCheck™ fertility rankings.
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