Chapter 34 David Christiansen Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, Starkville, Mississippi, USA Pregnancy diagnosis is an invaluable tool to the cattle producer who is trying to maintain maximum profitability. In the case of the beef cattle herd, a significant portion of the cost of producing calves is related to the feeding and care of the pregnant dam particularly during the winter months. Cows that are open (not pregnant) will add to the cost of maintaining the herd while not providing income in support of the producer. Similarly in dairy cattle, a cow that fails to become pregnant in a timely fashion will ultimately produce less milk, thus adding cost but not enhancing income. A pregnancy test that would identify pregnant and open cows before they return to estrus, thus allowing intervention and rebreeding by the subsequent estrus, would help minimize the calving interval and thereby maximize profit especially in a program utilizing artificial insemination (AI). In addition, the ideal pregnancy test would be minimally invasive, simple to perform requiring little investment in equipment, supplies and time, yield quick results allowing cowside decisions to be made by the producer, and have high sensitivity and specificity. Finally, in many herds the ability to estimate the stage of gestation, the gender of the fetus, and the presence of pathologic conditions of the reproductive organs would be very helpful. Currently there are three reliable methods of diagnosing the pregnancy status of a cow: transrectal palpation, transrectal ultrasound examination, and endocrine testing. While none of these meet all the criteria for an ideal test, each has its advantages and disadvantages. The producer and veterinarian must carefully consider each test and determine which provides the most benefit for the conditions at hand. Of these methods, transrectal palpation is the most commonly utilized and meets the most criteria under the most circumstances (Table 34.1). Table 34.1 A comparison of different methods of pregnancy diagnosis. The diagnosis of pregnancy by transrectal palpation is a skill that can readily be acquired and honed to great sensitivity and specificity with good understanding of normal anatomy and physiology of the cow. A good understanding of pregnancy and fetal development also allows the palpator, with experience, to accurately estimate the stage of pregnancy. A thorough discussion of the normal anatomy and physiology and of pregnancy can be found in Chapters 21 and 25. With this understanding and practice, a palpator can achieve very consistent results approaching 100% accuracy as early as day 30–35 of pregnancy. Transrectal examination of the reproductive tract begins with identification of the cervix, which is fibrocartilagenous and firm (sometimes described as feeling somewhat like a chicken neck) and serves as the landmark for the reproductive organs. In the nongravid or early pregnant uterus, the cervix is typically found within or just at the brim of the pelvis. In multiparous cows and as pregnancy progresses, it may be found pulled (by the weight of the uterus and contents) more cranial and ventral. It is important to remember that the cervix is relatively mobile and one may have to sweep the pelvic canal and work over the brim of the pelvis until it is found. Once identified, the cervix may be grasped and used to retract the body, horns and uterus caudally to allow better access to, and examination of, these structures. In addition, the palpator can follow the cervix cranially to the body of the uterus and identify the bifurcation of the horns. At this location, the ventral intercornual ligament can be used to retract the horns and lay them along the floor of the pelvis to facilitate thorough palpation of each horn. Just beyond the tip of each horn, the ovaries can be palpated. As pregnancy progresses, the size and weight of the fetus and fetal fluids will make retraction of the cervix and uterus impossible and they will have to be examined in place. The definitive diagnosis of pregnancy is based on the identification of structures which can only occur if the cow is indeed pregnant; if none of these can be identified, the cow should be considered not pregnant or the diagnosis deferred. Four such structures can be readily palpated and are considered the cardinal signs of pregnancy: chorioallantoic (membrane) slip, the amniotic vesicle, placentomes, and the fetus. In addition, other changes in the reproductive tract can be palpated that are considered supportive of a positive diagnosis of pregnancy. These include the inability to retract the cervix, fluid within or fluctuance of the uterus, enlarged diameter and asymmetry of the uterine horn(s), and enlargement and fremitus (a buzzing sensation) of the middle uterine artery. Membrane slip can be palpated routinely by 30–32 days of pregnancy and sometimes as early as 28 days in heifers in the gravid horn and in both horns by days 50–60 of gestation. Following identification of the cervix and retraction of the uterus, each horn can be grasped gently between the fingers and thumb and lifted slightly. If pregnant, a distinct popping sensation can be felt as the membrane slips from the grasp within the uterine walls. At 32 days of pregnancy it gives the impression of a thread and by day 45 a small string slipping from the fingers in the gravid horn. By day 60, it is palpable in both horns as a somewhat larger string and by day 75 is approaching the feel of a piece of yarn slipping from the fingers. Membrane slip is most commonly used up to day 90 of gestation. The amniotic vesicle is a very turgid, fluid-filled sac surrounding and protecting the embryo proper during early gestation. It can be palpated as a small knot or bump within the uterine horn approximately 6–7 mm in diameter by 32–35 days (5 weeks) of gestation. By 6 weeks of gestation it will be 1.5 cm in diameter and at 7 weeks it will be 3.5–5 cm in diameter. By 8 weeks, the vesicle will be 6–7 cm, will be losing its turgidity, generally allowing palpation of the fetus around day 60. As this occurs, the vesicle itself will become more difficult to identify and will generally no longer be used to determine pregnancy. As the fetus becomes palpable around days 55–60, it will be approximately 5–6 cm in length and can be felt floating in the fluid of the gravid horn by carefully cupping the horn with the fingers and sliding them along the length of the pregnant horn. Alternatively, the wall of the uterus may be lightly tapped by the fingers creating a wave of fluid, and causing the fetus to bump back against the fingers (referred to as ballottement). As the pregnancy advances, fetal parts may more readily be identified such as the head, feet and legs allowing the beginner to be more comfortable with the diagnosis. By 3 months of pregnancy, the uterus and fetus will reach sufficient size and weight to cause it to drop over the brim of the pelvis and into the abdominal cavity and by 4–5 months of pregnancy the fetus may descend into the abdomen far enough to make palpation of the fetus itself difficult or impossible, particularly in large deep-bodied cows. Usually by 7 months, the fetus has grown large enough that it will be readily accessible and can once again be used to determine pregnancy status. Placentomes (occasionally referred to as “buttons” by lay personnel) are composed of the maternal caruncle and fetal cotyledon. With experience they may be palpated as early as 75–80 days of gestation as soft pea-sized swellings or bumps on the internal uterine wall, but are a bit more firm and readily palpated by day 90. At this time they are about the size of a dime and will reach about the size of a half dollar by the time the cow is pregnant 5 months. During mid gestation as the fetus becomes more difficult to reach, placentomes may become the best method to definitively diagnose pregnancy. At least three should be identified, ensuring that the ovaries are not mistaken for placentomes. As a pregnancy advances to 60 days and beyond, the weight of the fetus and fetal fluids pulls the cervix cranially over the edge of the pelvis and into the abdomen. It becomes increasingly difficult at this time to retract the uterus into the pelvic canal; thus if the cervix feels “heavy” and relatively immobile, pregnancy can immediately be suspected and the palpator can search for the cardinal signs found in more advanced pregnancy such as the fetus and placentomes. This can save time and effort that would be required to find the more subtle membrane slip or amniotic vesicle.
Pregnancy Diagnosis: Rectal Palpation
Introduction
Criteria
Endocrine testing
Ultrasound examination
Transrectal palpation
Allows intervention prior to first estrus after breeding
Yes
No
No
Minimally invasive
Minimal to moderate
Yes
Yes
Simple to perform, little investment/cost
Moderate to high
Moderate
Simple, minimal cost
Results available quickly
Minutes to days
Instant
Instant
Estimate stage of gestation
No
Yes
Yes
Gender determination
No
Yes
No
Identify pathologic conditions of reproductive tract
No
Yes
Yes
Sensitivity/specificity
Varies (Chapter 35)
Excellent
Excellent
Cardinal signs of pregnancy
Membrane slip
Amniotic vesicle
Fetus
Placentomes
Supportive signs of pregnancy
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