Welcome back. Today is a continuation of the Beef Cattle Synchronization Q & A with Cliff Lamb, Ph. D., and will focus on heifer specific questions. You can view Part 1 here.
Q 1.) What % conception or success rate can herd owners anticipate on timed AI for beef heifers?
A.) A realistic goal for pregnancy rates in beef heifers is about 55%. In herds with high cycling rates and that are well managed you may be able to achieve as high as 65% (sometimes higher), but there also will be the herds that will have pregnancy rates somewhere in the 40 to 45% range. Take a look at the data that we have from 12 locations with timed AI in heifers using CO-Synch+CIDR. Notice that most herds had pregnancy rates around 55%, with a few high and a few low.
Q 2.) Which protocol for heifers has better results: one with a CIDR® or MGA?
A.) In general the 14-day CIDR protocol has had slightly better pregnancy rates than the MGA-PG protocols. However, if fed correctly and managed well, the MGA protocols work effectively, but require good feed management. Both of these protocols generally will more consistently give greater pregnancy rates than the short-term CIDR protocols, such as the 7-day CO-Synch+CIDR protocol.
Q 3.) Is pelvic scoring a good thing before breeding heifers? Should it be necessary? What if a heifer is already cycling but her pelvic score isn’t big enough, should I go ahead and still synchronize and breed her?
A.) Pelvic measurements assist in culling heifers that have excessively small pelvic areas. This is a good practice to identify those heifers that may have small pelvic areas and remove them from the breeding herd before putting resources into estrous synchronization and AI. However, it is important that a skilled technician provide the pelvic measurements to ensure that you cull the correct females.
Q 4.) If heifers are 16+ months and I haven’t observed them cycling yet, should I start them on a synchronization protocol?
A.) This depends! If the heifers are nutritionally deprived then estrous synchronization would not be a good idea. The first step would be to obtain reproductive tract scores to determine if the reproductive tracts are developed enough to respond to estrous synchronization. If more than 50% of the heifers have reproductive tracts that are sufficiently developed then estrous synchronization can be implemented; however, if the reproductive tracts are under-developed then it would be wise to consider feeding the heifers an improved diet for a period of time before initiating estrous synchronization.
Q 5.) Which protocol is best for heifers not observed cycling yet?
A.) The long-term protocols, such as the 14-day CIDR and MGA-PG protocols would be most desirable. These systems stimulate heifers to cycle at least once before AI and will ‘kick-start’ non-cycling heifers to start cycling.
Q 6.) If a heifer is of breeding age, how many days after I observe heat can I start a synchronization protocol?
A.) If you cannot AI her 12 to 16 hours after seeing her in heat then synchronization is an option. Depending on the system will be an indicator of when to start this system; however, a good rule of thumb would be to start a new system at about 6 to 8 days after she was in heat.
Q 7.) Would you heat detect and breed heifers or use a fixed time AI to get the best pregnancy rate results? If you follow the heat detection and don’t observe 100% in standing heat would you still breed the remaining with the fixed time AI protocol and shot of GnRH?
A.) In most cases I would recommend fixed-time AI (TAI) over heat detection because you will get more total females pregnant compared to only inseminating heifers that you detect in heat – whether observed or not, by breeding her you at least give her a chance to become pregnant vs. no insemination. If you use a heat detect and TAI protocol where you heat detect for 72 to 84 hours and then TAI any heifers you do not detect in heat, this would give you the greatest pregnancy rates. Therefore, it is advisable to use a clean-up TAI if you plan to heat detect.
Q 8.) Is there any benefit to giving a GnRH shot 7-10 days after finishing the MGA in that protocol?
A.) Actually it does not help with fertility to administer GnRH 7 to 10 days after MGA removal or CIDR removal in the long-term protocols. In addition, administering GnRH 7 to 10 days after AI in either protocol has not been shown to improve fertility either.
Q 9.) I have to move heifers to summer pasture post breeding – what is the best time frame after insemination to do so?
A.) Plan to move heifers between 1 and 7 days after AI, but also be sure that the heifers have dry feed (grain or hay) available when they first go onto pasture, otherwise they may experience a decrease in nutrient intake that will affect fertility.
Q 10.) I am only going to synchronize and AI one time before turning out a bull. Can I turn out a bull immediately after breeding? Wouldn’t it be better to turn the bull out immediately incase a heifer comes into heat within a day of AI, instead of waiting until her next cycle and then having calves different ages?
A.) This is not a straight forward question to answer. If it is most important to determine whether the calf is pregnant to AI (such as purebred operations) then it would be advisable to wait at least 10 days after AI; however, in most commercial operations a live calf is just as important and it would be wise to turn a clean-up bull in with the herd 12 to 24 hours after AI. In this case there may be a small percentage (< 2%) of calves that could be sired by the clean-up bull that may appear to be sired by AI. In most cases, it would be recommended to turn a bull in shortly after AI rather than waiting.
Q 11.) Is giving first calf heifer PGF a week prior to her scheduled calve date okay? Will it cause her to calve early to a lighter calf and help dystocia?
A.) No, administering PGF that late in gestating likely will have no effect on moving the calving date. At this stage of pregnancy the placenta is the organ secreting the most progesterone, not the corpus luteum (CL). Therefore, even if you eliminate the CL with PGF the placenta will continue secreting progesterone until the fetus initiates the calving process.
Q 12.) What is the best protocol if you need to abort a heifer depending on how far she is bred?
A.) This all depends on the stage of pregnancy. It is always advisable to contact a veterinarian first when considering terminating a pregnancy in heifers. Heifers pregnant for less than 150 days will likely respond to an injection of prostaglandin F2α (PGF). Heifers pregnant more than 150 days may or may not respond to PGF. Other alternatives after 150 days are available, but producers should contact a veterinarian for options.
Q 13.) Do I follow heifer or cow protocols for a 1st calf heifer?
A.) A rule of thumb is to treat anything that has given birth to a calf as a cow and anything that has not given birth as a heifer, regardless of their age. Therefore, a 1st calf heifer would be regarded as a cow when it comes to estrous synchronization.
Have more questions? There is still time to submit your question in the comments section of the blog for Dr. Lamb to answer.
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Cliff Lamb, Ph. D , is currently the Assistant Director and Professor at the University of Florida North Florida Research and Education Center in Marianna, Florida. He graduated with a B.S. in Animal Science at Middle Tennessee State University. He received his M.S in 1996 and Ph. D. in 1998 at Kansas State University. As Assistant Director of the North Florida Research and Education Center he oversees one of the largest beef cattle feed efficiency facilities in the world. Dr. Lamb oversees a research program that focuses on applied reproductive physiology in beef cattle emphasizing efficient management systems for replacement heifers and postpartum cows. A primary research focus has been on the development of practical and economical estrous synchronization protocols for beef cows and heifers. He has also published numerous research articles on the use of ultrasound technology for reproductive management of beef cattle, and has a strong research background in embryo transfer technologies. He is author of more than 60 refereed journal articles, 3 chapters in texts, and more than 200 presentations and articles in other scientific and popular press.