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Pregnancy Detection in Elk

by R. Garth Sasser, Ph.D., Nancy S. Sasser, Ed. D., Fan Huang, M.S. reprinted with permission

   The elk breeder often would like to know if an animal is pregnant. Valuable animals become even more so if the manager or buyer has this information. Knowing pregnancy status can also provide a means for selection of alternate feeding, breeding and calving management schemes for the herd. A cow that has not delivered a calf the previous year or so may be permanently sterile. Waiting to cull until the next calving season wastes valuable resources. The value in knowing her current pregnancy status is obvious. Extended calving seasons are always a concern because elk cows require special attention during calving. One hopes to get through the season without calling the veterinarian. If a cow is expected to calve and hasn't, the question of whether she is just a late calving cow or is not pregnant comes up. A pregnancy test at this time is often desired since it will determine the degree of observation required.

   Pregnancy testing can be of greater value in the young female. Pregnancy rates are considerably less in the yearling than in 2-year-old or older animals. The yearling herd is not as capable a reproducing group as older animals. Here is where one's skill in reproductive management can be applied. The skilled manager has an opportunity to increase profit by working with these animals. Young elk in poor body condition will not reach puberty in time for the fall breeding season and will not become pregnant. Those in good condition and with adequate growth can do so; however, as a group it will be at a lower pregnancy rate than the older cow herd. Even so, puberty and conception are often late in the breeding season. Here is where pregnancy testing is desirable. Testing could be applied during any part of pregnancy. During the calving season, worry about whether or not the young animal is pregnant can be reduced. Likewise, the manager can concentrate attention on those known to be pregnant and eliminate concern for others.

   BioTracking provides a service by testing blood for presence of the placental protein named pregnancy-specific protein B. Managers or veterinarians can send a blood serum sample to the laboratory for testing. Samples received by Tuesday of each weed will be cultured for three days; written test results are available by Saturday. The written report can be used as third-party testament that the animal is pregnant or not pregnant. This and certain other means for testing for pregnancy are discussed below.

PREGNANCY DETECTION TECHNIQUES

   There are several ways for testing for pregnancy. These include rectal palpation of the fetus or fetal membranes within the uterus, ultrasonography, measurement of blood progesterone, measurement of fecal steroid hormone metabolites, and measurement of blood pregnancy - specific protein B (PSPB).

RECTAL PALPATION

   This technique has been used by cattle managers for many years. It is used in elk and consists of inserting the hand and arm into the rectum and feeling the uterus through the rectal wall. The technician feels for presence of the fetus or fetal membranes. In cattle this can be applied at 35 or later days in pregnancy. Elk pregnancy can also be detected near this time in gestation. The technique is highly reliable at various stages of pregnancy. Error is greater at 35 days compared to 40 or 50 days after conception. The size of the rectal opening can limit ease of testing and may result in undue stress for the animal.

ULTRASONOGRAPHY

   Use of ultrasound for pregnancy detection in domestic animals is becoming very popular. It will only be discussed briefly herein. Success depends upon the skill of the operator, the type of instrument in use, and the animal to which it is applied. Real-time scanning of the uterus, in which an image is displayed on a video monitor, allows the operator to make a precise and accurate decision as to the state of pregnancy. Pregnancy can be detected in horses before 10 days of gestation. This is possible because the embryo becomes a large, fluid-filled sphere. This fluid provides the image for detection. In ruminants, including elk, the conceptus remains a filamentous structure for a considerable time and contains little fluid. Until fluid accumulates, ultrasound cannot reliably detect the conceptus. A high degree of accuracy in cattle is not obtained until the third to fourth week of gestation, when rectal probes are used to direct sound waves into the uterus. If an embryo/fetus is observed on the monitor, the animal is called pregnant and accuracy is very high. If an embryo/fetus is not observed, she is called not pregnant and accuracy is less because the probe may not have been positioned correctly for detection of the existing conceptus. Producers in New Zealand are actively using ultrasound for testing for pregnancy in red deer.

   The high expense of an ultrasound instrument contributes to its low use. Purchase by individual breeders for use on a limited number of animals is not practical. If one has a large number of animals, this instrument can be considered. It may be necessary to purchase equipment and offer services to several breeders or to use it in clinics within a large veterinary practice. In some countries, technicians transport equipment from farm to farm to detect pregnancy. This can be a successful business.

BIOCHEMICAL MARKERS

   This type of detection falls into two categories. One is detection of pregnancy associated substances that change in the maternal system in response to a pregnancy. Substances are from the maternal system and usually change in quantity when the female is pregnant. An example is progesterone from the ovary, which remains high during gestation.

   The other category is detection of pregnancy-specific substances. These are produced by the fetus or placenta and appear in tissues or body fluids of the mother. Examples are human chorionic gonadotropin and pregnant mare serum gonadotropin. The placentae of elk and other farm animals are not known to produce gonadotropins.

A. TESTING FOR PREGNANCY BY ANALYSIS OF PROGESTERONE

   This hormone is produced by the ovary during portions of the reproductive cycle. Since elk are seasonal breeders and have cycles only during this season, the ovary will produce progesterone only during the breeding season. Production rises and declines with each reproductive cycle. The season can run from September to March and progesterone can be high in non-pregnant animals. During each cycle, it is low for a 3- to 5-day period during heat and high the rest of the 21-day cycle. If the cow conceives, ovarian progesterone production is no longer cyclic and remains high until the end of pregnancy. The embryo/fetus stimulates the continued secretion. If pregnancy is not established or embryo death occurs, a new cycle will ensure if it is still during the breeding season.

   During pregnancy, additional progesterone comes from the placenta. One can take advantage of the high progesterone during pregnancy. For example, elk are pregnant beyond the end of the breeding season (March). If one conducts a blood progesterone test in the non-breeding season, say in April, and progesterone is high, then pregnancy is assumed. During the breeding season, if an elk is not pregnant but the sample is taken during mid-cycle, progesterone will be high. One cannot declare her pregnant or non-pregnant because she was at mid-reproductive cycle, even though we did not know that.

   In cattle, samples for progesterone are taken about 21 days after breeding. This is the time the cow is expected back in heat. (Progesterone is low if in heat.) If the sample reads a high progesterone value, the cow is presumed pregnant. This presumption is correct less than 80% of the time when pregnancy is confirmed by presence of a fetus at a later date by rectal palpation or delivery of a live calf. One reason for the poor detection rate is that the animal truly was not pregnant but had high progesterone because she returned to heat early or late and, therefore, sampling time was wrong. This sampling schedule would work in elk, too, but they are less readily sampled than are cattle.

   It is also possible that the cow is pregnant but loses the embryo before application of the follow-up tests confirming pregnancy. Embryonic death is as high as 8% from day 21 to 60 of gestation. We found an embryonic death rate near 5% from day 30 to day 60 of gestation.

   One considers the animal not pregnant if progesterone was low at 21 days after breeding. This is correct almost 100% of the time. Even if an embryo were in the uterus, it would be lost since progesterone is required to maintain pregnancy. Therefore, the confirmation test at a later time will be negative. Commercial enzyme-linked immunosorbant assay (ELISA) kits are available for cow side detection of progesterone in milk. These have been used for confirmation of estrus in bred cattle suspected as being in estrus. They are sold as estrus detection tests, not pregnancy detection tests, since they test for progesterone which is not pregnancy specific. Kits are easily used by animal managers.

   Elk are highly excitable animals, and handling them often to sample for progesterone oat the correct time during the breeding season is not practical. Bleeding for progesterone after animals have ceased having reproductive cycles in the spring can also result in false positive detection because of excess progesterone being produced by the adrenal. The adrenal gland secretes this hormone if the animal is placed under excess stress, and false positive assays could result.

B. PREGNANCY TESTING WITH PREGNANCY-SPECIFIC PROTEIN B (PSPB)

   This protein was first reported by us at the University of Idaho and has been used to develop a blood pregnancy test for ruminant animals, including elk, bison, and deer. The test is a radioimmunoassay and requires radioactive chemicals. For this reason, tests must be done in a central laboratory. The technology for the test has been licensed to BioTracking. The PSPB is a major secretory product of the placenta, once attachment to the uterus has begun. The protein appears in blood of some cattle as early as 15 days after conception, but to be reliable as a pregnancy test on a herd basis, one must wait until 28 to 30 days into gestation. The PSPB remains in the blood throughout gestation. For that reason, one does not need to know date of breeding to detect pregnancy if it is assured cows are past 30 days into gestation. Elk can also be tested for pregnancy any time after 40 days of gestation. We have been testing elk samples mailed to the laboratory from herds throughout North America. Breeders have been satisfied with the test, and we hear reports of high accuracy. Sometimes we provide false negative information; this occurs mostly in the month of November. It is suspected that in many instances, pregnancy has not progressed beyond 40 days at time of blood sampling and PSPB in the blood cannot yet be detected.

ARTIFICIAL INSEMINATION (AI) OR BACKUP BULL CONCEPTION

   A schedule for testing for PSPB has been developed to indicate to which sire the fetus was conceived. Elk breeders are actively using artificial insemination by breeding following synchronization of heat. These animals are all inseminated on the same day. Normally, 60 to 70 percent will conceive to a single breeding, and so backup bulls are placed with cows in increase herd conception rate during the breeding season. To allow for detection of AI-sire conception, the breeder must leave the backup sire out of the herd until 14 to 16 days after AI. A blood sample is then taken 40 to 42 days after AI. Since PSPB can be detected first near 40 days after conception, the test will rarely detect backup bull conceptions because they would only be 26 days old or younger, while the AI conceptions are 40 days old.

ACCURACY OF THE PSPB TEST

   To give a better idea of the accuracy of the test, Table 1 shows the results in cattle that had been bred from 0 to 60 days prior to slaughter. Blood was collected at time of slaughter and the uteri were examined for presence of an embryo or fetus. If the conceptus was not discernable by observation, the reproductive tract was flushed and fluid was searched under a microscope. Of 187 cows determined not pregnant by uterine examination, the PSPB test was 94.7 percent correct in calling cows not pregnant. Of 242 detected pregnant by uterine examination, those less than 25 days into pregnancy were detected correctly at 15.7 percent. However, if they were 25 days or more in pregnancy, the PSPB assay was 99 percent correct.

Uterine Examination

Blood Examination

STATUS

NUMBER

NUMBER

% OF UTERINE

Non-Pregnant
Pregnant
< 25 days
> 25days

187
242
51
191

177

8
189

94.7

15.7
99.0

TABLE 1. Accuracy of the PSPB blood test for pregnancy when compared to evaluation of the uterus. The 429 cattle were between 0 and 60 days of gestation; uteri and blood were colleted at slaughter.

   Examination of the reproductive tract is the sure way to know if the animal was pregnant; however, such a study is not practical in highly valued elk cows, which are rarely culled in large numbers. Accuracy in elk is only confirmed by birth of a live calf.

CAUTIONS ABOUT PREGNANCY TESTING

   It is often the opinion of breeders, researchers and practicing veterinarians that a very early test is desirable. However, embryonic death rate is high, and certain elk or cattle which test positive for pregnancy early will be non-pregnant at a later time. If one evaluates cattle, there is up to 40% loss from breeding until 30 days of gestation. Also, there is a 5% loss from 30 to 60 days. Other ruminants, including elk, have equal difficulty in maintaining a pregnancy. For the producer who pays for the animal, the importance of knowing pregnancy status, and the expense of the testing is important.




 

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