Dr. Reuben Mapletoft, professor of theriogenology with the Western College of Veterinary Medicine in Saskatoon, is among the research scientists who have been working to eliminate the major obstacle affecting the widespread use of AI — the need for observing heat.
Not only is heat detection time consuming and, therefore, costly, but it’s terribly inefficient. Only 50 to 75 per cent of estrus periods in beef cattle are detected, even with aids such as chin-ball markers, marking paint, pressure sensing devices, pedometers and, the most effective, HeatWatch electronic system.
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The major reason to detect estrus is to know when to inseminate cattle to achieve the highest pregnancy rate possible. Synchronizing estrus is a way to reduce the number of days required for heat detection, Mapletoft explains.
Fixed-time AI takes that one step further by totally eliminating the need to heat detect and the possibility of missing heats. Following a fixed-time protocol for synchronizing estrus in beef cows or heifers will result in all of the cattle ovulating on the same day. Barring any abnormalities or shortcomings, conception will occur as long as the sperm, which have a lifespan of about 24 hours, are waiting in the fallopian tube to fertilize the egg within 10 hours of its release. Artificial insemination by appointment is now a reality!
Mapletoft says that while the technology behind fixed-time AI is not new, its application could be considered new. Research scientists began working in this area about 15 years ago and the fixed-time protocols of today have evolved from discoveries made along the way.
Based on his involvement with fixed-time AI program implementation in South America, where more than four million cattle in Brazil and more than 1.5 million cattle in Argentina were bred using fixed-time AI protocols during the past year, Mapletoft would venture to guess that the Canadian beef industry is lagging behind. The depressed cattle prices through the past seven years have definitely been a factor. Accompanying that is the move toward low-cost management systems. In Canada, the biggest hurdle to the uptake of any synchronization and AI program, is the idea that they are costly, yet producers seem to underestimate the true costs of natural service, he says.
Depending on the protocol selected and price of the semen, Mapletoft estimates that fixed-time AI costs between $20 and $30 per female. This includes the cost of the required hormones and semen, hired labour for inseminating, and a charge for animal handling (weight loss and facility use). On the flip side, money is saved or earned by producing a calf crop with uniform weaning weights and superior growth and carcass traits, shortening the length and labour requirements of the calving season, reducing the incidence of dystocia in heifers and necessity for intervention during calving, resulting in more calves weaned and improved postpartum reproductive performance.
If an average bull costs $2,500 and is maintained for three years with interest, feed and other costs estimated at $600 per year, and a salvage value of $1,000, the total cost amounts to $3,300. If the bull breeds 25 females each breeding season, the annual cost works out to $44 per female. This doesn’t factor in lost opportunities for genetic improvement in light of research from the dairy industry indicating that some 80 per cent of the genetic progress in a herd is introduced through bull selection.
New discoveries
Ultrasound examination of the bovine reproductive tract on a daily basis along with analysis of the hormones that control the reproductive cycle has generated new knowledge and tools for estrus synchronization.
Attempts at synchronization began in the 1960s with the use of progestins such as melengestrol acetate (MGA). Prostaglandins to cause regression of the corpus luteum (CL) were introduced in the 1970s. Research during the 1980s revealed that the ovarian follicles that produce the eggs and CL grow in waves.
The next decade brought the discovery that the stage of follicle development at the time of treatment with prostaglandin was the reason a single injection of prostaglandin failed to consistently trigger estrus and ovulation. It was also behind the variation in the time from treatment to ovulation. If the follicle was large and growing at the time of treatment, estrus could occur within two or three days; if it was small and immature, estrus could be delayed until the fifth or sixth day following treatment.
They also learned that the growth and regression of ovarian follicles and the CL, which influences the timing of ovulation, can be controlled with estrogen or gonadotropin releasing hormone (GnRH). Either hormone can be given at the start of a protocol to eliminate the existing dominant follicles and initiate a new wave of follicles approximately two to four days later. This way, you can be confident that when progesterone is withdrawn on the seventh or eighth day, there will be a large, healthy dominant follicle that can mature and ovulate within a short, and fairly precise interval, Mapletoft explains. Unless the follicular wave is reset at the start of this protocol, an aged follicle may exist when the progesterone is withdrawn, which can result in the ovulation of an aged, sub-fertile egg and consequent low fertility.
To mimic the effect of progesterone produced by a CL, you can either feed MGA or insert a progesterone-releasing device into the vagina for a period of five to 14 days depending upon the protocol selected.
Two progesterone-releasing devices are now approved for use in beef and dairy cows and heifers in Canada: the PRID (progesterone-releasing intravaginal device) and the CIDR (controlled internal drug release). Protocols generally couple insertion and removal of the device with another step in the synchronization process. The devices are designed for single use, however, producers often reuse them at least once. Mapletoft cautions that care must be taken to ensure that venereal disease is not transmitted with reuse.
MGA-based protocols work well for heifers in a corral situation where you can mix the MGA into the ration and evenly distribute it to ensure each animal is consuming its daily requirement. It’s not recommended for cows because it is difficult to manage in a pasture situation and the calves will eat it as well.
Fixed-time protocols
The defining feature of a fixed-time protocol is the absence of heat detection. The protocol will end with AI of all synchronized cattle during a specified time period. Various regimes lead to that same end.
The ovsynch fixed-time program involves giving GnRH at the beginning of the protocol to induce ovulation, formation of a new CL and initiate a new wave of follicles. Prostaglandin is given six or seven days later, followed by a second dose of GnRH 48 to 60 hours later to induce ovulation. AI of all cattle normally takes place 12 to 16 hours after the second GnRH treatment. Mapletoft says acceptable pregnancy rates can be achieved in cows, however, the regime is less effective for heifers. The use of a CIDR or PRID inserted at the time of the first GnRH treatment on day zero and removed at the time prostaglandin is given has proven to be an effective way to achieve high pregnancy rates in heifers. It is also recommended for cows that haven’t returned to estrus following calving.
A modification of the ovsynch program, known as cosynch, is commonly used in fixed-time beef protocols. Cosynch implies that the second GnRH treatment and AI are done at the same time, thus saving a trip through the chute.
Select-synch involves the use of heat detection without a second GnRH treatment and may also include the use of a CIDR or PRID. Select-synch can be modified to accommodate an element of fixed-time AI by inseminating all cattle observed to be in heat and then giving those not showing estrus a second GnRH treatment in conjunction with AI at 72 hours after the prostaglandin treatment.
Research continues to explore ways to improve synchronization of ovulation and increase fertility, improve resynchronization and AI results, use of other hormone products (estradiol, luteinizing hormone), reduce handling, reduce costs, and increase the use of related technologies, such as sexed semen.
The new knowledge and tools are all for naught without proper nutrition, planning and attention to detail. Any AI program requires a whole lot of management in a short period of time, Mapletoft stresses. There are five steps — advance planning; match the protocol to your situation; written protocols with high compliance; skilled AI technicians; ensuring the use of highly fertile semen, a temperature-controlled water bath to thaw semen straws, and clean equipment. As little as a five per cent error in each step along the way will quickly compound to significantly affect your results.
Mapletoft reminds producers that there is no single protocol that is best for all situations. There are many factors to consider and it is essential to gain an understanding of the limitations of each protocol and what to reasonably expect as an outcome. With an understanding of the principles involved, a unique and effective protocol can be developed for almost any operation.
