Congenital disorders

Chapter 1 Congenital disorders




Introduction


Congenital defects or diseases are abnormalities of structure or function that are present at birth. Not all congenital defects are caused by genetic factors. Some are due to environmental agents acting as teratogens. Examples include toxic plants (e.g., Lupinus species in crooked calf disease), prenatal viral infections (e.g., bovine virus diarrhea (BVD) resulting in cerebellar hypoplasia and hydrocephalus), and mineral deficiencies in dams of affected calves (e.g., manganese causing skeletal abnormalities).


Hereditary bovine defects are pathologically determined by mutant genes or chromosomal aberrations. Genetic defects are classified as lethal, sublethal, and subvital (including compatibility with life). Although typically occurring once or twice in every 500 births, a massive range of congenital disorders affecting different body systems has been identified in cattle, primarily as a result of records kept by artificial insemination (AI) organizations and breed societies. Economic losses are low overall, but abnormalities may cause considerable financial loss to individual pedigree breeders. Most congenital abnormalities are evident on external examination. About half of all calves with congenital defects are stillborn. Many of these stillbirths have no clearly established cause.


Examples of congenital defects are given by affected system. Some are single skeletal defects, others are systemic skeletal disorders such as chondrodysplasia. Certain congenital central nervous system (CNS) disorders may not manifest their first clinical effects until weeks or months after birth, e.g., spastic paresis and strabismus, respectively.


If several neonatal calves have similar defects, an epidemiological investigation is warranted. This should include the history of the dams (their nutrition and diseases, any drug therapy during gestation, and any movement of the dams onto premises with possible teratogens), and any possible relationship of season, newly introduced stock, as well as pedigree analysis.


Congenital ocular defects are considered elsewhere (Chapter 8), as are umbilical hernia (2.9), cryptorchidism (10.18), pseudohermaphroditism (10.4010.42), and cerebellar hypoplasia (4.1, 4.2).



Cleft lip (“harelip”, cheilognathoschisis); cleft palate (palatoschisis)







Achondroplastic dwarfism (“bulldog calf”) or dyschondroplasia




Clinical features


the Hereford calf (1.6) demonstrates brachycephalic dwarfism. The head is short and abnormally broad, the lower jaw is overshot, and the legs are very short. The abdomen was also enlarged. The calf had difficulty in standing, was dyspneic as a result of the skull deformity (“snorter dwarf”), and a cleft palate was also present. A 2-week-old Simmental crossbred suckler calf (1.7) shows severe bowing of all four legs, especially forelegs, stunting, and a slightly dished face, and euthanasia was indicated. Born in May from a winter-housed dam fed only silage, extra feed appeared to reduce the incidence of achondroplasia from 40/200 to 5/200 offspring in successive years.




Bulldog calves are often born dead (1.8). This Ayrshire has a large head and short legs, but also has extensive subcutaneous edema (anasarca). Dwarfism is inherited in several breeds, including Hereford and Angus.



A related condition is congenital joint laxity and dwarfism (CJLD), which is a distinct congenital anomaly in Canada and the UK. A severe CJLD case from Canada, the newborn calf (1.9) has a crouched appearance, short legs, metacarpophalangeal hyperextension, and sickle-shaped hind legs. Many calves are disproportionate dwarfs. The joints become stable within 2 weeks and the calves can then walk normally. Other abnormalities are not seen. In the UK in 2009/10, 70 of a group of 85 South Devon x Angus calves showed shortened limbs, joint laxity (especially of the fetlocks), dyspnea in the first days of life, and in a few cases brachygnathia. The dams had been fed straw after housing, and later straw and silage.


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Jul 8, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Congenital disorders
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