CALLING "CARD" - on AI Research
This article was originally printed in the October / November 2000 issue of Tracking The Industry. . .
This article is written in grateful acknowledgment of the contributions by Dr. Murray Woodbury, Specialized Livestock Chair, Rosewood Game Farm and clients of the Western college of Veterinary Medicine.
The White-tailed deer (WTD) industry continues to be a source of agricultural diversification in Saskatchewan. In order to maintain economic health, the WTD industry should seek to improve its profitability through improvements in management practices and economically valuable genetic traits.
Planned breeding and artificial insemination (also called AI) are the main means of advancing genetic progress in WTD. Artificial insemination allows the introduction of new genes into a herd without the addition of new animals. It also expands the number of does a buck may breed, and serves as means of preserving the genes of animals with exceptional value. It is a form of genetic insurance in case of accidental death and injury. The main disadvantage of AI is the fact that it is an emerging technology and not all of the bugs have been worked out of the system. This is evident in the difficulties encountered in semen collection from bucks, and the variable pregnancy rates with AI. We have a lot to learn about the biology of WTD. AI in WTD right now is a bumpy road, and those of you in the business are still pioneers. Pioneers seem to suffer a lot from drought, insect pestilence, and wild fires.
Regarding the synchronization of female receptivity, also called heat or estrus, the starting date of the synchronization is probably one of the factors in the success of AI. In other deer species and small ruminants like sheep and goats, the farther the starting date is from the natural breeding season the lower the success rate. The peak of the WTD breeding season seems to be close to the full moon of November (mid to late November), hence if the synchronization technique fails, the natural system may kick in to bring the animal into the receptive phase breeding. At this point in time I would not recommend starting a synchronization program before the first week in November.
In the future as we gain more knowledge and compare data on the true success of a synchronization program, the effect of the starting date will need to be sorted out. It is easy to attribute success to a treatment when does are coming in on their own anyway. The end result would be that you would be spending money and manpower on something that is not really working. Therefore more studies on lots of deer are needed.
The other main factor that needs to be investigated in WTD is the so-called "Buck effect." In many deer species such as red deer, this effect is used to the producers advantage and it is common for them to turn in a vasectomized animal for about a month before the start of a synchronization program. The recent introduction of a buck that has been out of the group for 1-2 months, significantly influences on the onset and synchrony of female receptivity and fertility. The odors and presence of the buck in rut sends chemical signals, called pheromones, to impact the does physiology. Most commonly in the deer species that have been studied, the introduction of the buck into a group of does near or at the onset of the breeding season induces a fairly synchronized silent heat through pheromonal signals 5 to 7 days after the introduction of the buck. A silent heat is a heat where eggs are released from the ovary, but no behavioral signs of breeding receptivity are shown. After this silent heat most of the does will come back into heat early (in under 10 days) and have a fertile estrus, others will have another silent heat and again return quickly to estrus. The later in the season the buck is introduced the more likely he is to induce a fertile heat with behavioral receptivity.
Why do the does return to receptivity or heat so soon in the early part of the breeding season? Basically the system is still warming up and is not fully functional. The early return to heat is related to the fact that the structure that forms on the ovary after ovulation, which is called a corpus luteum, gives out early. The corpus luteum secretes the steroid hormone progesterone. Progesterone or derivatives of it are the main compounds in vaginal sponges, CIDR s, and ear implants. The giving out of the corpus luteum is linked to inadequate secretion of another hormone (luterizing hormone or LH) which is necessary to support the function of the corpus luteum. Sometimes when the progesterone source (implant, sponge CIDR) goes in, the doe s system is tricked into thinking that she has had a silent ovulation. When the progesterone is taken away, it may act somewhat like a silent heat, the doe may become receptive and eggs may be released, but if the rest of the system is still warming up the corpus luteum will fail and she will come back into heat early. This may explain why we think the normal duration of pregnancy is so broad in WTD. We are probably missing some of these early returns to heat. The quick return to heat keeps giving the doe a chance to get pregnant and helps to group fawning in the spring. We need to learn a lot more about how to use the buck effect to our advantage in AI.
A vasectomized buck works as well as an intact buck for this effect. Therefore if a vasectomized buck is introduced early in the season about a month before AI, the shenanigans that occur in the early part of season that cause the variability are usually over in about a month. Many breeders of red deer in New Zealand breed or start synchronization after the third expected heat following turn-in with a vasectomized buck.
A major unanswered question is, "When do I turn in the back-up buck after AI?" Right now the answer is that we do not know. We do know that frozen semen should not survive longer than 3 days in the female system. But we do not know if a buck turned in with females can "short circuit" them with a "buck effect". In essence the buck effect may interfere with the survival of the corpus luteum (that makes progesterone which is essential for pregnancy) after AI breeding. It is probably best to wait to turn the buck in 10 days after AI. This is the current recommendation for Elk AI as well. In this 10 day period, the embryos that are in the doe grow to a point where they can signal their mother. Prior to this time I believe that she may be more susceptible to a buck effect. Part of this signaling process by the embryo results in a rescue of the corpus luteum, which is why pregnant does do not come back into heat. The date of recognition of the pregnancy by the doe s system is probably about day 10 post AI (day 0 is the AI day). This is the rationale for this 10 day hold out period. The nonpregnant does will probably be brought into heat by a buck effect in 5-10 days after turn in. Until we can study deer more closely this question will be unanswered.
It has also been reported in red deer not exposed to a buck that many does return to heat within 10 days of CIDR withdrawal. This was a phenomenum that we also observed in WTD. This is a reason why the fawns should be parentage tested, because many does will not return at the normal time about (21 days).
In our 1999 Veramix sponge group (10 Day exposure, 2cc of prostaglandin on the day of withdrawal, AI at 60 hours) we have some incomplete data. Of the 10 animals in which sponges were inserted 5/10 (50%) retained them for 10 days. Two of the 10 animals were not bred as they did not appear to be ready at the time of AI (one of these had a sponge but did not appear to respond). Pregnancy rates for these were 2/8 bred or 2/5 that had sponges. For the 2 year period 9/20 45% became pregnant to the AI. There are 3 does that are questionable and need DNA confirmation. For the purpose of this report they are called not-pregnant to AI. If you are using sponges I suggest you synchronize more does than you need to breed. The ones where the sponges are in are more likely to get pregnant. It may be possible to improve pregnancy rates by using an agent to tighten up the ovulation window such as human chrionic gonadotrophin (hCG) 500 IU given IM (APL or Chorulon) or equine chrionic gonadotrophin (eCG or PMSG) 100 IU IM Equinex at sponge withdrawal. More multiple births are likely to occur with eCG use. If eCG or hCG is used, then AI should be backed up to 48 hours. Equine chrionic gonadotrophin induces more follicle to grow, and they grow and mature at a faster rate.
In 1999 we had a Norgestomet ear implant group with an implant period of 10 days. The fertile period should have been around Nov. 10-11. The implant was taken out (Nov. 8) and the does were bred with buck or with AI at about 60 hours post withdrawal.
In the group bred with the buck the duration of pregnancy ranged from 196-230 days, with an average of 204 days.; Seven out of 13 animals (54%) appeared to be bred close to the target date (therefore their gestation was <201 days). All but 2 of the remaining does in this group appeared to have been bred in the next 10 days. It is not known if they were not well synchronized or whether they were under the influence of the buck effect. Because most of the breeding occurred within about 10 days of buck turn out. most of the females did not come back into heat when we were observing them at 21-28 days. This protocol did not appear to cause good synchrony of heat where you would want greater than 70% responding.
In the AI group synchronized in the same way with ear implants and AI at about 60 hours, the pregnancy rates were low 1/14 (7.1%). Gestation ranged from 199-228, an average of 216 days. As none of the ear implants were lost and many of the does were observed in heat during AI, it seemed that something went wrong on the hormonal end of things. Perhaps more stimulation was necessary to cause release of the eggs, or development and support of the corpus luteum. As the semen had been used successfully and handled the same when using sponged does we had no reason to question its integrity.
This lack of great synchrony might be partially corrected by starting later in the season, holding the buck out for 10 days post AI, or using hormones to further induce egg maturation, egg release (eCG) and support of the corpus luteum (eCG or hCG). CIDR s were used with a 10 day insertion period and prostaglandin (2cc Lutalyse IM) at withdrawal with breeding at about 60 hours. In the CIDR group the average pregnancy duration was 211 days, with a range of 190-220. About a third of the does come back into heat in about a 10 day window. Data are available on 22 does and low pregnancy rates were obtained 2/22 (9%). These does were bred November 18. None of the CIDR s fell out, so it was related to the lack of progesterone exposure. Better results have been reported by using another protocol with a 14 day CIDR exposure, 100 IU of eCG at withdrawal, and Ai at 48 hours. It is not known whether 10 day insertion periods of CIDR s are better or the same as 14 days. Again in new Zealand where these were developed they will typically replace them after 1 week in red deer, because the hormone in the CIDR starts to wear out after 1 week s time. The use of eCG should help recruit more ovulations and tighten the window of ovulation. This appeared to be one of problems with the protocol we used. It may also assist with the support of the corpus ltueum as it is a long acting hormone.
In our study we had data from does where ear implants or CIDR s were used (10 day exposure, prostaglandin at withdrawal, AI at about 60 hours). Data from 21 does was available. The pregnancy rate was 4/21 (19%) overall. AI was performed on November 15th. There were 2/10 with CIDR s and 2/11 with implants that became pregnant. As others have gotten better pregnancy rates by combining CIDR s or ear implants with eCG, I would advise using eCG with the expectation that the does will have more fawns, and I would suggest backing up the AI time to 48 hours.
Sometimes being a pioneer is a tough road to follow. It is clear that more work needs to be done to increase the success and profitability of AI. Right now we are still operating on a best guess system. We would not have predicted that the pregnancy rates in our CIDR and implant groups would be lower than the sponges because the fall out rate is so high with them. The sponges also contain a more potent analogue of progesterone which may be part of their success. We also used prostaglandin in the sponged does because of the high fall out rate. Prostaglandin is a natural hormone that has only one purpose; it kills the corpus luteum. It has never been reported in any species to interfere with ovulation or pregnancy when given in the manner in which we used it (at withdrawal of the progesterone source). When considering the fawning dates, the data would have been misleading, because there appeared to be more pregnancies to AI than there actually were. The majority of pregnancies for AI appear to have a gestation length of under 204 days. The turn out of the buck 3 days after AI may have also been a strategic error on our part. We had discussed the option of the use of eCG and decided because we did not want a lot of multiple births to forego its use. In other parts of North America such as Texas, they are using the same protocol as we chose with better success without eCG. As it stands now I feel strongly that either eCG or hCG at our Northern latitude should be used to help increase the synchrony of heat and support the CL.
Dr. Claire Card
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