Dr Rick Last – BVSc; M.Med.Vet (Pathology)
Specialist Veterinary Pathologist
Maximizing the use of the Fetus and Placenta
The value of post mortem examination on abortions/stillbirths is often overlooked and extremely underutilized. It is a very simple and practical procedure which requires the use of simple non-expensive equipment, that is easily transportable, and so the procedure can be performed on farm or in practice. It is important to remember that the developing fetus is a growing animal that is exquisitely susceptible to the effects of nutritional imbalances, environmental influences and infectious etiologies and foetuses visibly show pathologies associated with these conditions. Therefore, one should never turn down the opportunity of performing an abortion or stillbirth investigation. A systematic approach to the post mortem procedure facilitates recognition of the abnormal. By following the same routine with each and every post mortem performed, you will start to appreciate the normal and rapidly recognize the abnormal. Practitioners frequently bemoan the apparent poor diagnostic sensitivity of the abortion investigation process, but remember, negative findings are not a “waste of time” they are extremely important and often deflect the investigation in the right direction.
By providing background data pertaining to animal information, nutrition, vaccination / treatment programs, environmental influences etc the relevance of the findings of the abortion/stillbirth investigation can be more critically evaluated and integrated to provide extremely powerful and scientifically relevant diagnostic information. Develop or use specialized abortion investigation forms where relevant questions are asked and can be answered through simple tick box selections. Such forms are easy and simple to complete and take a minimum of time, yet the information gleaned is invaluable to the investigation.
Below please find the link to example Bovine Abortion/Stillbirth Investigation and Small Ruminant Abortion/Stillbirth Investigation Submission Forms.
Bovine Abortion: https://bit.ly/2mYf9ng
Small Ruminant Abortion: https://bit.ly/2OA8zQP
The Investigation Processes
To obtain the maximum benefit out of your post mortem examination it is extremely important that you follow a very formal structured procedure to ensure that you evaluate all aspects of the investigative process and do not stop if you find what you think is a diagnostic lesion. Many abortion/stillbirth incidents are multifactorial and in addition much information can be gleaned about underlying factors that might not be the direct cause of abortion/stillbirth but have significant impact on herd/flock performance. The investigative process should always include the following 4 components.
-External examination of the foetus.
-External examination of the placenta.
-Dissection and sample collection.
External Examination of The Fetus
Take time to stand back and look, palpate and measure. Just because the animal is dead doesn’t mean you should forget your clinical skills of observation, palpation and measurement. “Fools rush in” – don’t rush in and open the carcass – there is just so much to see, feel and measure before you make your first incision. There are important occupational zoonotic hazards for veterinarians investigating abortions and stillbirths (Brucella, Q-Fever, Listeria, Rift Valley fever), so ensure that you wear protective clothing including overalls, gloves, goggles and masks. Handling aborted fetuses is the one scenario where Listeria does act as a zoonosis.
Obvious congenital abnormalities are easily visible at gross examination
Meconium staining and / or aspiration is the sign of a distressed fetus and usually occurs as a consequence of fetal hypoxia during dystochia or prolonged parturition. Meconium staining is characterized by yellow discoloration of the external surface of the fetus (figure 1 and figure 2) Hypoxia results in increased intestinal peristalsis and relaxation of the anal sphincter in the fetus resulting in release of meconium into the amniotic fluid. Meconium in the amniotic fluid can then gain access to the oropharynx of the fetus. Intra-uterine gasping with an open glottis allows aspiration of meconium contaminated amniotic fluid before delivery. Immediately after delivery meconium lodged in the nasopharynx can pass into the lung with the first breath of air. This aspirated meconial material can cause chemical (sterile) pneumonia in newborns but is also an ideal growth medium for secondary bacteria resulting in infectious pneumonia.
Figure 1: Bovine meconial staining
Figure 2: Ovine meconial staining
Evaluate mucous membranes for evidence of anemia (figure 3 – pale mucous membranes) or icterus (figure 4 – yellow discoloration of mucous membranes). On the African Continent haemoparasites (Babesia, Anaplasma, Borellia) can be significant causes of abortion. Abortion is either due to invasion of the fetus and placenta by parasites or because of maternal pyrexia. Invasion of the fetus by parasites is usually accompanied by fetal pathology including anemia and/or icterus, while in cases of maternal pyrexia no fetal pathology is evident.
Figure 3: Anemia
Figure 4: Icterus
Angulated limb abnormalities may be associated with in-utero viral infection, prussic acid poisoning or micronutrient imbalances. In cases of in-utero viral infection and prussic acid poisoning, these limb abnormalities are those of contracted tendons with arthrogryposis and are frequently accompanied by other skeletal abnormalities, hydranencephaly/hydrocephalus and/or ocular abnormalities (figure 5 and figure 6).
Figure 5: Arthrogryposis – contracted tendons
Figure 6: Arthrogryposis + Block vertebrae
Micronutrient imbalances on the other hand, are associated with lax tendons, but in the absence of any other conformational or anatomical abnormalities (figure 7 and figure 8).
Figure 7: Lax tendons fore + hind.
Figure 8: Lax tendons hind
Age-appropriate features are external characteristics that are matched to fetal age and can be used to determine if they are appropriate for the actual age of the fetus being examined. If features observed are inappropriate for the actual age of the fetus, this would indicate that some in-utero incident, whether that be infectious or non-infectious, has occurred and this needs to be more thoroughly investigated during your examination to ensure the relevant set of samples are collected.
Fetuses less than 6 months gestational age are usually hairless. Between 5 and 7 months color markings appear, and hair growth begins with initial hair growth points being the muzzle, distal limbs and tail. Eyelids separate at around 7 months gestation and at this stage the fetus should be well covered with body hair (figure 9). A fetus where the eyelids have separated yet is largely hairless (figure 10) would indicate an in-utero incident (infectious, nutritional, toxic).
Figure 9: Eyelids separated fully haired.
Figure 10: Eyelids separated fetal alopecia.
In-utero growth retardation (IUGR) reduces neonatal survival, has a permanent stunting effect on postnatal growth and efficacy of feed conversion, negatively affects body composition and meat quality and impairs long term health including fertility. Therefore, it is well worth your while to critically examine fetuses for evidence of in-utero growth retardation so that remedial action can be implemented as soon as possible.
Fetal growth is influenced by genetic, epigenetic (alterations of gene expression), environmental factors, nutritional factors and maternal maturity. These factors impact on placental efficiency, uteroplacental blood flow, transfer of nutrients and oxygen to the fetus, nutrient availability to the conceptus, fetal endocrine milieu and metabolic pathways. Alterations in fetal nutrition and endocrine status may result in developmental adaptions that permanently change the structure, physiology, metabolism and postnatal growth of the offspring. There is growing evidence that maternal nutritional status can alter the epigenetic state of the fetus resulting in alterations of gene expression impacting on growth, reproduction and immune function.
Causes of intra-uterine growth retardation include maternal malnutrition (protein and energy in the last trimester), micronutrient imbalances, maternal over-nutrition, in-utero viral infection, in-utero exposure to mycotoxins, uteroplacental insufficiency (small placenta, low number of cotyledons, placentitis) and maternal toxaemia.
The gross features of in-utero growth retardation include the conformational defects of shortening of the forelimbs, doming of the forehead, facial flattening, basisphenoid thickening and shortening of the maxilla (figure 11 and figure 12). The head deformities that develop as a consequence of in-utero growth retardation arise due to premature closure of the synchondroses (cartilaginous joints) of the skull. The skull is therefore unable to elongate and can only effectively grow taller and broader.
Figure 11: In-utero growth retardation
Figure 12: Age matched fetus without IUGR
This premature closure of the synchondroses results in doming of the forehead, flattening of the face, shortening of the maxilla (figure 13) and broadening of the basisphenoid bone (figure 14).
Figure 13: Head deformity IUGR
Figure 14: Broadening basisphenoid
Figure 15: Fetal oversize / dystochia
Fetal oversize/dystochia frequently characterized by facial swelling with swollen tongue, subcutaneous edema with bruising and frequently accompanied by meconium staining.
Mycotic dermatitis (figure 16 & 17)- cutaneous lesions have a site predilection for periorbital areas, shoulders, back and flanks. Occasionally the fetus may aspirate organisms from the amniotic fluid initiating a bronchopneumonia. Endometrial lesions are less severe than in the placenta and usually long-term fertility of these animals is not affected.
Figure 16: Mycotic dermatitis – shoulders
Figure 17: Mycotic dermatitis – facial
Fetal heart failure (figure 18) is associated with late stage abortion with gross external abnormalities of abdominal distention (ascites), with a fluid wave elicited on abdominal palpation. Primary differentials would include micronutrient imbalances, infectious myocarditis and mycotoxins. These findings would indicate that the fetus needs to be closely inspected for evidence of cardiac failure during the dissection and internal examination of the fetus.