CHAPTER 139 Pregnancy Determination and Fetal Aging of Farmed Red Deer, Wapiti, and Bison
Early pregnancy detection in wapiti, red deer, and bison can be accomplished by rectal palpation, rectal ultrasound examination, serum estrone sulfate (E1S) concentrations, cross-reactivity with bovine pregnancy-specific protein (PSPB), and possibly, fecal hormone evaluation. Pregnancy diagnosis late in gestation is useful to determine if there have been fetal losses from scanning early in gestation. This may be performed by rectal manual or ultrasound examination, transabdominal ultrasound, or hormonal measurements, udder palpation, or observation. In red deer it is also possible to palpate a late-term fetus by abdominal ballottement. The principal requirement is that handling facilities and animal behavior be appropriate to ensure that the animals do not damage themselves, the operator, or the equipment while the examination is being conducted.1
MANUAL EXAMINATION
The cervix of the nulliparous red deer and wapiti is about 5 cm long and 1.5 cm in diameter. This part of the tract enlarges slightly during the first pregnancy and the cervix of multiparous wapiti females is about 5 cm in diameter and 10 cm in length.1
The uterus of nonpregnant wapiti lies almost entirely within the pelvic cavity. The yearling nonpregnant uterus is small, with a horn diameter of about 1.5 cm and a length of 8 to 10 cm. Enlargement in the pregnant horn can readily be detected manually by 42 days after conception, at which time it lies over the pelvic brim. At this time the uterus may be about 20 to 25 cm in length, and the first two of the enlarging placentomes on the dorsolateral surface of each horn can be felt. At this stage the wapiti fetus is about 24 mm in length, and can often be felt by finger-tapping of the fluid-filled uterus. The crown-rump (CR) length of the red deer fetus is about 19 mm at this stage of gestation. The fetal membrane slip technique has also been described. By 75 days of gestation the uterus has considerably enlarged, its weight has pulled it down into the abdominal cavity, and the fetus may be as much as 30 cm in length.2 By 100 days of pregnancy it may be possible to determine only that the cervix lies over the pelvic brim, and that the uterus is out of reach, as it can be difficult for the operator to insert an arm past the elbow, and for some individuals even past the middle of the forearm, even in wapiti of 300 kg body weight.
The reproductive tract of the bison female is readily examined per rectum, in which criteria used have been adopted from cattle.3,4 A small number of the animals may adopt a “dog-sitting” posture in the chutes, which delays proceedings.
ULTRASOUND
Transrectal Approach
Transrectal ultrasound examination, using a 5-MHz linear transducer on a rigid extender, has proved to be a highly reliable method of pregnancy diagnosis in red deer.5,6 Although pregnancy confirmation is by observation of the fetal membrane, placentomes or fetal anatomy, the principal challenge for the ultrasonographer is definitive identification of the nonpregnant uterus.6 A “nil diagnosis” is advised for any animal in which neither a pregnant nor a nonpregnant uterus can be detected, and these animals should be returned for repeat examination.
The fetal heartbeat can first be seen as early as 22 days of gestation in some wapiti, and by 24 days in all.7 Pregnancy should therefore not be affirmed before 24 days, although other signs, such as the presence of an amniotic vesicle, may be seen before this time.6 A cut-off of 28 days for confirmation of pregnancy by ultrasound, and a “nil diagnosis,” with a second examination to follow, has been suggested as standard procedure for any animal in which a nonpregnant uterus cannot be detected.8
For the most accurate estimation of conception date in red deer it is recommended that ultrasonographic pregnancy diagnosis be carried out between approximately 35 and 60 days of gestation. At this time, amnion dimen sions and CR length can be measured, and estimates based on these have standard errors of about 2 days.5 Although conception dates of red deer can be estimated upon measurements made after 60 days of pregnancy, the standard error of the estimate is greater. Up to 13 fetal and uterine dimensions may by used to estimate conception date.5 Note, however, that fetal aging, while providing an accurate estimation of conception date, cannot be used to accurately predict the calving date of an individual deer, because of the normal variation in gestation length described earlier. However, fetal aging can give an accurate prediction of the pattern of calving of a herd, because variation in gestation length of an individual is random about the mean. Defining the herd pattern of conception and therefore calving dates is known as “pregnancy profiling” in New Zealand.8
As pregnancy advances and the uterus moves over the pelvic brim, fetal anatomy may be difficult to scan after about 110 to 130 days in red deer. In wapiti, by 100 days, it may not be possible to determine pregnancy if the uterus has advanced into the abdominal cavity and lies between the posterior face of the rumen and the ventral abdominal muscles, where a probe, even with an extension handle attached, cannot reach it.1
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