A 2-year-old primiparous miniature Scottish Highland cow was evaluated at a veterinary medical teaching hospital for suspected hydrops. The breeding date was unknown. On examination, the cow had rapid, shallow breathing (60 breaths/min) and a large, distended abdomen (Figure 1). Transabdominal and transrectal ultrasonographic evaluation revealed a large amount of hypoechoic fluid within an enlarged uterus; the fetus was not visualized at this time. Because of the severely distended uterus and the associated health risks to the cow, labor was induced with dinoprost tromethamine (25 mg [standard luteolytic dose for an adult cow]) and dexamethasone (20 mg [standard dose to induce parturition in an adult cow]), IM. The cow was monitored continuously over the next 36 hours for signs of parturition. General health was monitored by evaluating respiratory and heart rates, rectal temperature, mentation, mucous membrane color, and abdominal distension. Blood samples were collected from a jugular or coccygeal vein at 4-hour intervals for measurement of Hct and serum total protein concentration.
Photograph (caudocranial view) of a 2-year-old primiparous miniature Scottish Highland cow with an unknown breeding date that was evaluated for suspected hydrops. Notice the large, distended abdomen.
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.552
Following expulsion of a large volume of fluid from the uterus approximately 30 hours after treatment with dinoprost and dexamethasone, the cow was administered IV fluids (5 L of a balanced electrolyte solutiona delivered at 1 mL/kg/h [0.45 mL/lb/h]) for stabilization; monitoring was continued, and a plasma transfusion (total dose, 1 L [approx 4 mL/kg {2 mL/lb}], IV) was administered because of a decrease in serum total protein concentration (from 7.4 to 4.8 g/dL [reference range, 6.5 to 8.5 g/dL]) over a 12-hour period. The Hct remained within the reference range. Owing to lack of further progress in parturition, ultrasonographic examination was repeated 48 hours after the induction treatment, and abnormal, hyperechoic placentomes and a nonviable fetus were visualized. Vaginal examination revealed an open but not completely dilated cervix; palpation per vagina revealed that the fetus was abnormally shaped and too large to deliver vaginally. Anesthesia was induced with diazepam (0.1 mg/kg [0.045 mg/lb]) and ketamine (2 mg/kg [0.91 mg/lb]), IV, and maintained with isoflurane in oxygen. Flunixin meglumine (1.1 mg/kg [0.5 mg/lb], IV) was administered during surgery. The cow was positioned in right lateral recumbency, and a cesarean section was performed through an oblique incision in the left flank. A dead, malformed bull calf was delivered, and the cadaver was submitted for necropsy. The uterus and abdominal wall were closed routinely, and oxytetracycline (10 mg/kg [4.5 mg/lb], IV) was administered. The cow recovered uneventfully from surgery and was discharged from the hospital on the following day with an additional dose of oxytetracycline (20 mg/kg [9.1 mg/lb], SQ). Instructions were provided for postoperative monitoring of the patient, and a meat withdrawal time of 38 days from the last dose of the antimicrobial was advised.
On gross examination, the fetus had a large defect in the ventral aspect of the abdominal wall, through which a portion of the gastrointestinal tract, liver, spleen, and 1 kidney were herniated (Figure 2). Several malformations involving the skull, axial skeleton, and appendicular skeleton were evident. Craniofacial abnormalities included marked shortening of the muzzle resulting in protrusion of the tongue from the mouth, cleft hard and soft palates, and a domed skull. The vertebral column was severely shortened and markedly bowed, with the thoracic and lumbar segments bending ventrally and the cervical, sacral, and coccygeal segments bending dorsally. The ribs and thoracic limbs were abnormally short, and the appendicular long bones were pliable and composed predominantly of cartilage. There was no gross evidence of pelvic limb bones or hooves, although 2 outpouchings of skin were present in the pelvic region.
Photographs of a stillborn bull calf delivered by cesarean section from the cow in Figure 1, showing abnormalities consistent with severe chondrodystrophy (so-called bulldog calf malformations). A—In the right lateral view, notice the severely shortened thoracic limbs, apparent lack of pelvic limbs, evidence of shortened ribs and a markedly shortened and bowed vertebral column, and herniation of abdominal organs through the ventral aspect of the body wall. B—In the rostrocaudal view, notice the domed skull and shortening of the muzzle causing protrusion of the tongue. C—In the image of the oral cavity after the tongue has been removed, cleft hard and soft palates are evident.
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.552
For further investigation of the abnormalities, the tissue of the head was removed with the skull left intact. A CT scanb of the skull was performed and converted to a 3-D surface model.c The resulting files were then animatedd for better evaluation. In the lateral view of the reconstructed CT image, changes to the frontal, parietal, and occipital bones, considered likely attributable to hydrocephaly, were evident (Figure 3). Severe shortening of the nasal and incisive bones was also apparent. In the craniocaudal view, the ventral nasal conchae were shortened and severe maxillary brachygnathism was present. Dorsoventral radiographs confirmed that the severely shortened thoracic limbs lacked ossification and there was no evidence of pelvic limbs; severe dysraphism of the vertebrae and bifid thoracic spinous processes were also evident (Figure 4).
Computed tomographic images (3-D reconstruction) of the skull of the calf in Figure 2. A—In the right lateral view, severe shortening of the nasal and the incisive bones is evident and the changes to the frontal, parietal, and occipital bones potentially attributable to hydrocephaly are evident. B—In the rostrocaudal view, the ventral nasal conchae are shortened and there is severe maxillary brachygnathism.
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.552
Dorsoventral radiographic view of the calf in Figure 2 after removal of the skull. There is no evidence of ossification in the abnormally short thoracic limbs, and no evidence of pelvic limbs is seen. Severe dysraphism of the vertebrae and bifid thoracic spinous processes are evident (arrow).
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.552
Gross examination of the intact and bisected skull revealed a large caudodorsal fontanelle and hydrocephalus (Figure 5). Histologic examination of the vertebrae and appendicular bones confirmed chondrodysplasia characterized by a lack of distinct physes with replacement of the normal stratified physeal cartilage by sheets of dysplastic and disorganized cartilage (Figure 6). The dysplastic cartilage consisted of densely packed chondrocytes embedded within variable amounts of chondroid matrix. The metaphyses were similarly composed of dysplastic cartilage with no obvious primary or secondary spongiosa, and the diaphyses consisted of small central segments of bone with no obvious marrow cavity.
Photograph of a sagittal view of the skull of the calf in Figure 2 revealing evidence of hydrocephaly.
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.552
Photomicrographs obtained during histologic examination of metacarpal structures of the calf in Figure 2. A—A chondrodysplastic metacarpal bone is characterized by lack of a distinct physis, replacement of the normal stratified physeal cartilage by sheets of dysplastic and disorganized cartilage, and absence of primary and secondary spongiosa in the metaphysis. A small central segment of bone with no obvious marrow cavity is present. B—The chondrodysplastic metacarpal cartilage is characterized by densely packed chondrocytes embedded within variable amounts of chondroid matrix. H&E stain; bar = 500 μm (panel A) and 50 μm (panel B).
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.552
Gross, histopathologic, and diagnostic imaging findings led to the diagnosis of chondrodystrophic dwarfism with hydrocephalus, compatible with so-called bulldog calf malformations. To investigate the presence of a genetic mutation previously associated with a similar phenotype in Dexter cattle,1 hair (including root) samples from the dam and sire of the affected fetus were subsequently submitted to the university's genetics laboratory. Following extraction of DNA by alkaline lysis methods described elsewhere,2 a PCR assay was run on a DNA analyzere with a protocol and primers designed specifically for evaluation of the aggrecan-1 (ACAN) gene on chromosome 21 in cattle.1 Both tested animals were identified as heterozygous carriers for the aggrecan-1 gene mutation previously identified as BD1.1 It was recommended that, if the dam was to be bred in the future, a bull known to test negative for the mutation should be selected to avoid producing another severely affected (homozygous for the mutant genotype) calf.
Discussion
Dwarfism has been described in multiple species, including various breeds of cattle. It is one of the most common congenital abnormalities described and has inherited and noninherited origins.3 Some of these defects have been associated with various genetic mutations, and the phenotypic characteristics may vary but always include some degree of skeletal malformation and shortening involving the skull, legs, and vertebrae.4
Common historical and clinical findings reported in association with chondrodysplasia or so-called bulldog calf malformations in Dexter calves include abortion without complications at approximately 7 months of pregnancy with the presence of a macrocephalous, short-legged fetus with a shortened vertebral column, cleft palate, retruded muzzle, protruding tongue, and abdominal hernia.3 These anatomic anomalies were all observed in the fetus of the present report. The heritability of bulldog malformations is well described in Dexter cattle,3,4 and a mutation (BD1) in the aggrecan-1 gene on chromosome 21 has been identified as the cause of this condition.1 Although homozygosity (considered lethal) causes severe defects that typically lead to fetal death and abortion, heterozygosity results in a milder form of dwarfism and is perpetuated because this yields the desired short-legged phenotype.1 Aggrecan is a proteoglycan essential for normal chondroskeletal structural development.5,6 Mutations of this gene can lead to disproportionate changes in cartilage structure, alter long bone growth and function, and have important clinical consequences.1,4
A genetic test developed for evaluation of the aggrecan-1 gene in cattle is available and can be used to identify the described mutations associated with bulldog calf malformations, thereby allowing breeders to avoid the mating of 2 carriers, which could possibly produce a calf with the homozygous lethal phenotype. Testing of hair root samples from the sire and dam of the calf of this report revealed that both carried the BD1 mutation in this gene.
Clinical signs observed in the pregnant cow of this report resulted in its transfer to our facility for evaluation and treatment; otherwise, abortion may have been unnoticed or may not have resulted in further evaluation or testing by the producer. Hydramnios (hydrops amnion) and hydroallantois (hydrops allantois) are rare conditions in which excessive accumulation of amniotic or allantoic fluid, respectively, can compromise the health of the dam. Complications such as uterine rupture or severe dehydration can occur, and it is usually associated with an abnormal placenta or an abnormal fetus that may have impaired capacity to swallow, renal agenesis, or both.7,8 Swallowing of the amniotic fluid by the fetus and fetal renal function are of great importance for homeostasis of the fluid8,9 and for normal architecture of the placenta.10 Possible edema of the placenta and failure of normal deglutition as a consequence of the cleft palate in the fetus may have resulted in hydramnios, hydroallantois, or both in this cow.
The BD1 mutation in aggrecan-1 identified in Dexter cattle and in the sire and dam (both miniature Scottish Highland cattle and heterozygous carriers) of the calf of this report is a cause of dwarfism in cattle; however, mutations in other genes, such as the protein kinase cGMP-dependent type II (PRKG2) gene in American Angus cattle,11 have also been associated with this condition. These mutations were not tested for, and indeed, others likely exist. The potential contribution of other genes could not be ruled out in this instance. To our knowledge, this is the first report of the BD1 mutation of aggrecan-1 in miniature Scottish Highland cattle. This is of clinical importance because the finding demonstrated that this mutation is not limited to Dexter cattle, highlighting the clinical importance of testing for known genetic diseases in breeding cattle, particularly among miniature or short-legged breeds.
Acknowledgments
The authors declare that there were no conflicts of interest.
Presented in abstract form at the Society for Theriogenology Annual Conference, Portland, Ore, August 2014.
The authors thank John Doval and Richard Barrango for technical assistance.
ABBREVIATIONS
| BDI | Bulldog dwarfism I |
Footnotes
Plasmalyte A, Baxter International Inc, Deerfield, Ill.
GE Light Speed Helical 16, Block Imaging, Holt, Mich.
Osirix, version 5.0.2, Oxiris Imaging Software, Bernex, Switzerland.
Cinema 4D R14, Maxon Computer, Friedrichsdorf, Germany.
ABI 3730, Applied Biosystems, Carlsbad, Calif.
References
1. Cavanagh JA, Tammen I, Windsor PA, et al. Bulldog dwarfism in Dexter cattle is caused by mutations in ACAN. Mamm Genome 2007; 18: 808–814.
2. Sancristobal-Gaudy M, Renand G, Amigues Y, et al. Individual traceability of bovine meat using molecular markers [in French]. Productions Animales 2000; 13: 269–276.
3. Harper PA, Latter MR, Nicholas FW, et al. Chondrodysplasia in Australian Dexter cattle. Aust Vet J 1998; 76: 199–202.
4. Whitlock BK, Kaiser L, Maxwell HS. Heritable bovine fetal abnormalities. Theriogenology 2008; 70: 535–549.
5. Cavanagh JA, Tammen I, Hayden MJ. et al. Characterisation of the bovine aggrecan gene: genomic structure and physical and linkage mapping. Anim Genet 2005; 36: 452–454.
6. Vertel BM. The ins and outs of aggrecan. Trends Cell Biol 1995; 5: 458–464.
7. Drost M. Complications during gestation in the cow. Theriogenology 2007; 68: 487–491.
8. Peek SF. Dropsical conditions affecting pregnancy. In: Youngquist RS, Threlfall WR, eds. Current therapy in large animal theriogenology. 2nd ed. St Louis: WB Saunders Co, 2007;428–431.
9. Fujino Y, Agnew CL, Schreyer P, et al. Amniotic fluid volume response to esophageal occlusion in fetal sheep. Am J Obstet Gynecol 1991; 165: 1620–1626.
10. Windsor PA, Cavanagh JA, Tammen I. Hydrops fetalis associated with pulmonary hypoplasia in Dexter calves. Aust Vet J 2006; 84: 278–281.
11. Koltes JE, Mishra BP, Kumar D, et al. A nonsense mutation in cGMP-dependent type II protein kinase (PRKG2) causes dwarfism in American Angus cattle. Proc Natl Acad Sci USA 2009;106: 19250–19255.
