Inflammatory Orbital Diseases

Orbital Cellulitis

Etiology.

Puncture wounds and lacerations of the eyelids or conjunctiva that allow opportunistic bacteria to invade orbital soft tissue are the most common cause of orbital cellulitis. Hooking the eyelid on a sharp object or stanchion lock can result in a puncture wound of the palpebral conjunctiva or eyelid. Migration of plant origin fibrous foreign bodies from the oral cavity also may result in orbital cellulitis. Severe ocular infections that progress from endophthalmitis to panophthalmitis may then infect orbital soft tissue. Chronic inflammation in the orbit from cellulitis or foreign bodies may allow orbital or retrobulbar abscess formation.

Signs.

Acute orbital cellulitis patients have rapid onset of a warm, painful swelling of the orbital region, lids, and nictitans, chemosis of the conjunctiva, and a degree of exophthalmos. Fever is usually present, and the exophthalmos may allow exposure keratitis to occur as the globe is pushed outward to such an extent that the lids no longer protect the central cornea (Figure 13-1).

Figure 13-1 Orbital cellulitis secondary to a laceration of the palpebral conjunctiva. Swelling of the orbit and lids, and conjunctival chemosis and exposure keratitis are present.

Chronic orbital cellulitis or orbital abscess results in a more insidious but painful exophthalmos with soft-tissue swelling that may be more localized. Fever is inconsistent.

Diagnosis.

Acute ophthalmic signs coupled with fever suggest acute orbital cellulitis. Definitive diagnosis is aided by the physical finding of an entry wound in the eyelid or conjunctiva. Orbital ultrasound evaluation helps rule out neoplasia or presence of a foreign body, and tissue aspirates may reveal large numbers of neutrophils. A complete blood count (CBC) is worthwhile but may be normal or show a mild neutrophilia.

Chronic orbital cellulitis or abscessation must be differentiated from orbital neoplasia and chronic frontal sinusitis (see following discussion). A complete physical examination, percussion of sinuses, orbital ultrasound, and radiographs may be required in confusing cases. Serum globulin levels may be elevated to greater than 5.7 g/dl in cases that last longer than 2 weeks, suggesting chronic inflammation or abscessation.

Treatment.

Acute orbital cellulitis is managed with systemic broad-spectrum antibiotics. Although penicillin may be effective because Arcanobacterium pyogenes is a likely causative organism, ampicillin may be a better choice. Nonsteroidal antiinflammatory agents (NSAIDs) such as aspirin (240 to 480 grains orally, twice daily) provide analgesia and mild antiinflammatory action. Warm compresses of the orbit are very helpful in reducing orbital and lid swelling, thereby lessening the degree of exophthalmos. Compresses may be applied two or three times daily for 5 minutes if labor is available. Topical antibiotic ointment or lubricant should be applied liberally to the cornea to prevent exposure keratitis. If no ulceration of the cornea has occurred, sterile ocular lubricating ointments or mastitis ointments may be used prophylactically. If exposure ulceration has occurred, the eye should be treated topically several times daily with a broad-spectrum antibiotic ointment to control infection and 1% atropine ointment to provide cycloplegia.

The prognosis for acute orbital cellulitis is good if medical and nursing care can be provided. Most cases resolve within 5 to 7 days with the aforementioned therapy.

Chronic orbital cellulitis or abscessation requires localization of the lesion to allow surgical drainage. Needle aspirates or ultrasound-guided needle aspirates confirm the location of the infection before drainage. Knowledge of the skull and orbit anatomy is helpful in avoiding injury to important structures when attempting to lance an orbital abscess (Figure 13-2). Most abscesses harbor A. pyogenes. Therefore systemic penicillin (22,000 U/kg once daily) should be used for 1 to 2 weeks following surgical drainage of the lesion. Gentle flushing of the abscess cavity should be performed once or twice daily, and warm compresses should be used if exophthalmos is severe enough to raise concern of exposure keratitis. Recurrent orbital abscesses or chronic cellulitis will dictate more intensive diagnostic work, including ultrasonography, radiographs, and culture-sensitivity testing to rule out foreign bodies and resistant organisms.

Figure 13-2 Drainage of a chronic orbital abscess in the retrobulbar region.

Neoplastic Disease

The most common orbital tumor in dairy cattle is lymphosarcoma. Tumors may be unilateral or bilateral and cause progressive acquired exophthalmos with exposure keratitis or proptosis (Figure 13-3). Because some Jersey, Ayrshire, and Holsteins cows have relative bilateral exophthalmos (i.e., are “bug-eyed” as a normal appearance), early detection of acquired exophthalmos may be difficult for the average caretaker. Therefore severe exophthalmos and exposure damage to the globe secondary to orbital lymphosarcoma may be reported to be acute by the caretaker. This history implies a higher likelihood of orbital cellulitis than neoplasia. However, thorough physical examination to detect other neoplastic target areas and absence of fever usually allows a proper diagnosis. In fact, even though the retrobulbar lymphoid masses obviously have been present and enlarging for some time before pathologic exophthalmos, the pathology may appear very acute once the degree of exophthalmos prevents the eyelids from completely protecting the central cornea. At this point, exposure damage and desiccation of the central cornea coupled with severe blepharospasm, chemosis, and lid swelling dramatically worsen the appearance of the eye (Figure 13-4). A visual eye with moderate exophthalmos but without exposure keratopathy may change to a blind, proptosed eye with complete corneal desiccation in less than 48 hours.

Figure 13-3 Bilateral pathologic exophthalmos and chemosis caused by retrobulbar neoplasia in a cow with widespread lymphosarcoma.

Figure 13-4 Retrobulbar lymphosarcoma causing exophthalmos, chemosis, and severe exposure keratopathy.

Diagnosis depends on finding other evidence of lymphosarcoma in the patient. Enlarged lymph nodes, melena, cardiac abnormalities, uterine masses, or neurologic signs also may be present. In some patients, the retrobulbar masses are the signal lesions, and other lesions may be undetectable. In this instance, blood for a CBC and bovine leukemia virus (BLV) agar gel immunodiffusion or enzyme-linked immunosorbent assay test is indicated to add supportive data. Most cattle with clinical lymphosarcoma test positive for BLV. This test is supportive but not conclusive because most BLV-positive cattle never develop tumors. Unlike cases with an orbital abscess, serum globulins and inflammatory markers are often normal in cattle with lymphosarcoma. Aspirates from the retrobulbar region may be helpful in some affected cattle. In questionable cases, the proptosed globe should be enucleated to alleviate the cow’s pain and allow collection of tumor material from the orbit for cytology or histopathology. The lymphoid tumors can be palpated along the periorbita and in the orbital cone in most affected cattle. Although the globe usually is free of tumor, rare cases have had conjunctival, corneal, lid, or scleral involvement.

In confirmed cases, the only indication for treatment would be in extremely valuable cattle that are in the last trimester of pregnancy or candidates for embryo transfer in the near future. Enucleation is palliative to relieve the cow’s pain and reduce the possibility of panophthalmitis and orbital cellulitis. Cattle with confirmed orbital lymphosarcoma usually die within 3 to 6 months as a result of diffuse lymphosarcoma. Therefore further treatment is not warranted. Pregnant cattle with confirmed lymphosarcoma masses seldom live through more than 2 to 3 months of gestation. Those that do live to term tend to deliver small, nonviable calves. Embryo transfer attempts in cows with confirmed lymphosarcoma frequently are unsuccessful because of the cow’s catabolic state.

Squamous cell carcinoma may occur in an orbital location but usually is preceded by lid, conjunctival, or corneal squamous cell carcinoma. Orbital squamous cell carcinomas are locally invasive, tend to metastasize, and have a grave prognosis. Carcinomas of respiratory epithelial origin also have been observed in older dairy cattle (more than 8 years of age). These tumors are slow growing over months to years; cause progressive unilateral exophthalmos, inspiratory stridor, and reduced airflow in the ipsilateral nasal airway; and may cause ipsilateral Horner’s syndrome (see Figures 4-5 and 4-6). Although prognosis is poor, affected cattle may be productive for 1 to 3 years with these slow-growing tumors.

Figure 13-5 Right-sided Horner’s syndrome in a cow secondary to a perivascular reaction in the right jugular vein region. Ipsilateral ptosis and dryness of the muzzle are present.

Figure 13-6 Microphthalmia in a Guernsey calf. The calf also had congenital absence of the tail and a ventricular septal defect.

Cattle sent to slaughter with severe ocular or orbital neoplasia are condemned when the eye is destroyed, has draining pus, is obscured by neoplasia, has bony involvement, or is associated with lymph node enlargement or emaciation.

Neurologic Diseases

Horner’s syndrome is the most common neurologic disease of the orbit observed in dairy cattle. The features of ptosis, mild miosis, and ipsilateral facial warmth coupled with dryness of the muzzle and nares are well described. Horner’s syndrome in cattle is most commonly caused by injury to the cervical vagosympathetic trunk by carotid artery hematomas, cellulitis of the neck, or direct injury by traumatic venipuncture of the jugular vein (Figure 13-5). Other causes are rare, but the syndrome has been observed with skull tumors (e.g., squamous cell carcinoma, carcinoma, and adenocarcinoma) that invade the orbit causing upper respiratory dyspnea and decreased air flow from one or both nostrils, as well as Horner’s syndrome.

Treatment for cervical lesions is symptomatic with topical and systemic antiinflammatory drugs. Prognosis is good for return to function. Tumors have a hopeless prognosis.

Developmental Diseases of the Globe

Etiology and Signs

Developmental malformations of the globe result in megaglobus or microphthalmos (Figure 13-6). Anophthalmos, absence of all ocular tissue, is seldom an appropriate term because histologic section of orbital tissue in suspected anophthalmos cases almost always produces some evidence of ocular tissue, thus making microphthalmos the proper term. Congenital microphthalmia may be unilateral or bilateral in calves. Physical, toxic, and infectious causes have been suggested but seldom are confirmed to explain all sporadic microphthalmia. In utero infection with bovine virus diarrhea virus (BVDV) during the middle trimester occasionally has resulted in microphthalmia.

Genetic causes of microphthalmia appear common in dairy cattle. In Guernsey and Holstein calves, the defect has been linked with cardiac and tail anomalies. Most commonly these calves have a ventricular septal defect and wry tail, as well as unilateral or bilateral microphthalmia. Tail defects other than wry tail have been observed in some Guernsey and Holstein calves with microphthalmia and/or ventricular septal defect. These include absence of a tail, short tail, absence of some sacral vertebrae in addition to coccygeal vertebrae, and atresia ani coupled with absence of vertebrae (see Figure 13-6). In Guernseys, these malformations are thought to be caused by a recessive trait, but in Holsteins, the exact mode of inheritance is unknown.

Congenital megaglobus results from anterior cleavage abnormalities or multiple congenital anomalies producing glaucoma in utero. Dr. Rebhun observed several calves with anterior cleavage anomalies. The lens placode had not separated from the surface ectoderm during the development of those eyes. Subsequent influx of mesodermal tissue forming the corneal stroma, endothelium, Descemet’s membrane, and iris surrounds the lens. The resulting absence of an anterior chamber causes congenital glaucoma and buphthalmos. All cases to date have been unilateral, and the affected eye is noticeably buphthalmic at birth, with corneal edema, central dense opacity (lens in cornea), and no discernable anterior chamber (Figures 13-7 and 13-8).

Figure 13-7 Congenital buphthalmos and glaucoma in the right eye of a calf with an anterior cleavage defect.

Figure 13-8 The lens can be observed as a dense circular opacity within the cornea of a calf with an anterior cleavage anomaly. Corneal edema radiates from the lens opacity.

Convergent strabismus with or without associated relative exophthalmos has been described as an inherited trait in Jersey and Shorthorn cattle. It also has been observed occasionally in Ayrshires, Holstein, and Brown Swiss cattle (Figure 13-9). Bilateral relative exophthalmos (“bug-eyed cows”) is a condition that has been observed in several dairy breeds and probably is a genetic trait. Exophthalmos in these cows does not progress to a pathologic state or exposure keratitis because the eyelids still cover the cornea adequately. However, pigment migration occurs over the bulbar conjunctiva and peripheral cornea as a result of exposure of the globe to dust, air, or debris in some affected cattle.

Figure 13-9 Severe convergent strabismus and congenital exophthalmos in a Holstein. The temporal bulbar conjunctiva has become pigmented as a result of chronic exposure.

(Photo courtesy Dr. Kit Blackmore.)

Congenital nystagmus has been observed in several breeds and is common in Holsteins. The nystagmus is a rapid pendular nystagmus that is horizontal and constant. It persists throughout the animal’s life and does not seem to interfere significantly with vision. The heritability or mode of inheritance is unknown. The trait also has been observed commonly in a herd of purebred Guernseys.

Acquired Diseases

Acquired megaglobus may follow severe intraocular inflammation of exogenous or endogenous cause. Infectious bovine keratoconjunctivitis (IBK), trauma, and uveitis are the usual causes of anterior synechiae, lens luxation, and adhesions that disturb aqueous outflow, thereby creating glaucoma. Endophthalmitis and panophthalmitis secondary to septic uveitis or ocular perforation may also cause megaglobus. If megaglobus is severe enough to cause exposure keratitis, the affected globe should be enucleated to prevent eventual perforation or panophthalmitis. Adult dairy cattle with severe megaglobus treated by enucleation become comfortable and return to anticipated production within several days (Figure 13-10). Therefore it is important that acquired megaglobus is not diagnosed erroneously as a retrobulbar neoplasia.

Figure 13-10 Acquired megaglobus following severe pinkeye in a Holstein cow. Enucleation of this eye resulted in rapid improvement in appetite and production as a result of resolution of pain and irritation caused by the enlarged globe.

Less frequently, megaglobus follows intraocular neoplasia or granulomatous infections of the uveal tract. Squamous cell carcinoma is the most frequent tumor to invade the globe, and tuberculosis must be considered when a granulomatous infection of the globe is diagnosed.

Phthisis bulbi (shrinking of the globe) follows ocular perforations, chronic uveal inflammation, and severe pinkeye complications such as corneal perforation and iris prolapse. If a phthisical globe is sterile and nonpainful, it may be ignored. However, if chronic conjunctivitis, facial dermatitis from discharges, and fly irritation affect the cow’s production, enucleation should be performed.

Congenital Diseases

Ancillary or supernumerary nasolacrimal duct openings have been reported in 13 Brown Swiss calves and 1 Holstein calf. These calves had a depigmented, hairless puncta located a few centimeters from the medial canthus in addition to the normal puncta in the upper and lower lid margins. The lesion is likely to be inherited, but this has not been proven.

Neurologic Diseases

Unilateral facial nerve palsy causing ptosis and exposure keratitis is common in calves affected with otitis media/interna and adults affected with listeriosis. Trauma may cause facial nerve injuries resulting in neuroparalytic keratitis in bovine patients of any age. The most common cause of bilateral eyelid paralysis in cattle is “stanchion trauma” wherein a cow pulls back against a stanchion until her head is trapped along the temporal ridge between the ears and orbit. The result is a bilateral traumatic palpebral nerve paralysis.

Signs of neuroparalytic keratitis include lacrimation, ptosis, absence of palpebral response, and progressive corneal exposure damage. Treatment requires therapy for primary diseases and protection of the cornea with frequent application of antibiotic ointments or tarsorrhaphy. Cattle with facial nerve paralysis appear to be much less likely to develop corneal ulcers than in many other species. Treatment of stanchion paralysis requires warm compresses, systemic antiinflammatories, and protection of the cornea with ocular lubricants or broad-spectrum antibiotic ointment if indicated.

Flashing or protrusion of the nictitans in tetanus patients is a passive rather than active movement of the nictitans. Tetany of the retractor oculi muscles pulls the globe caudally in the orbit, allowing passive prolapse of the nictitans.

Inflammatory Diseases

Neoplastic Diseases

Treatment

Fibropapillomas normally are self-limiting within 4 to 6 months and do not require treatment. Persistent or large fibropapillomas (Figure 13-11) may interfere with eyelid function or cause corneal injury and require surgical treatment via cryosurgery or sharp dissection.

Figure 13-11 Atypical large fibropapilloma growing from the upper eyelid of a Holstein heifer.

Squamous cell carcinomas tend to be locally invasive and may metastasize in some neglected cases. This tumor requires aggressive early therapy to prevent progression, or the cow will be lost. Many therapeutic options exist for early, small squamous cell carcinoma of the eyelids, whereas enucleation, radical exenteration, or culling may be required for large lid lesions. Recognition of early tumor formation when the mass is less than 2.0 cm in diameter allows consideration of cryosurgery, radiofrequency hyperthermia, radiation (if available), sharp surgery, and immunotherapy. Large lid masses (greater than 5.0 cm in diameter) are less likely to be treated successfully because destruction or removal of this much lid tissue may lead to ocular exposure damage (Figure 13-12). These large tumors also are more likely to invade adjacent adnexal tissue, orbital ligaments, periorbita, and bone of the skull. Tumors at the medial canthus are extremely dangerous because they need to advance only 2.0 cm along the medial orbital ligament before entering the bony orbit.

Figure 13-12 Squamous cell carcinoma of the lower eyelid. The tumor is pink, raised, ulcerative, and has a white necrotic surface discharge. Chronic superficial keratitis is present as a result of tumor irritation of the cornea.

Treatment options include:

1. Sharp surgery: This is best performed on lesions smaller than 1.0 to 2.0 cm in diameter for which en bloc removal or wedge removal of the tumor allows complete repair of the lid margin, and it is easy to distinguish tumor margins from normal tissue. This method also is indicated for squamous cell carcinomas of the third eyelid or nictitans for which the best treatment is surgical removal of the entire third eyelid (Figure 13-13). Following sedation of the patient with xylazine, the auriculopalpebral nerve is blocked; liberal topical anesthesia (0.5% proparacaine) is applied to the eye and conjunctiva; and the nictitans then is grasped with forceps. Between 10 and 15 ml of 2% lidocaine is injected into the base of the nictitans, and the entire nictitans is removed with heavy serrated scissors. It is important to remove all of the cartilage with the nictitans, lest a sharp cartilaginous stump remains in the medial canthal region to incite further squamous cell carcinoma through chronic irritation and tissue metaplasia. Topical antibiotics are applied to the eye for 7 days, and systemic penicillin 22,000 U/kg body weight is given intramuscularly (IM), once daily for 3 days postoperatively.

2. Cryosurgery: This is perhaps the best therapy for small to moderate lesions because the “freeze” can be adjusted to the size of the tumor and cosmetic results at the lid margin tend to be good, thereby preventing subsequent exposure keratitis from loss of lid margin. The cow is sedated, restrained, and the tumor site blocked by regional anesthesia. Tissue peripheral to the lesion is shielded with petroleum jelly, and a Styrofoam wedge can be applied to the cornea to act as a protective “contact lens” if the lid margin area must be frozen. The tumor is frozen by free spray or by use of any of a number of probes or cups until the periphery of the tumor adjacent to normal skin reaches 240.0° C. The tissue is allowed to thaw and then is refrozen. Cryodestruction is maximum with a quick freeze, slow thaw, and quick freeze routine. Frozen tissue sloughs over the next 7 to 14 days and gradually is replaced by granulation tissue followed by epithelialization of the wound. Frozen tissue often may remain depigmented, and returning hair will be white in most instances. Topical protective ointments should be applied to the eye. The only complication Dr. Rebhun observed with this technique was corneal ulceration caused by a large scab that was not cleared away from the lid margin in one cow.

3. Radiofrequency hyperthermia: This is another excellent treatment for small tumors or tumors with a small base that can be debulked before application of the device. Hyperthermia only penetrates 0.5 to 1.0 cm of tissue, so large lesions are not the best candidates for this technique. Multiple applications are possible for moderate size lesions, and an impressive cure rate for beef cattle has been quoted. Instructions are available with the kit (ThermoProbe, Hach Co., Loveland, CO, or MegaTherm, Western Instrument Co., Denver, CO).

4. Radiation: Squamous cell carcinoma is a radiosensitive tumor. Very small lesions less than 2 mm in depth could be treated with 7500 to 10,000 rad (1 rad 5 1 centigy) of beta-radiation using a strontium⁹⁰ applicator, but the device does not penetrate deep lesions (Amersham Health, General Electric Health Care, Buckinghamshire, England NP7 9N UK). More radical radiation (e.g., radon seeds) has been used successfully on squamous cell carcinoma, but radiation safety laws limit the practicality of these options.

5. Immunotherapy: Many attempts at immunotherapy, including autogenous vaccines made from tumor tissue and infections of Bacillus Calmette GuÃ(c)rin (BCG) have been used to treat ocular squamous cell carcinoma. Although fair results have been reported, many questions remain regarding these techniques. The major disadvantage for dairy cattle is that injections of BCG (a mycobacterium cell wall product) may render the cow positive to tuberculin testing in the future. Recently, peritumoral injections of interleukin-2 (1 million units) for 10 days resulted in tumor regression in 69% of the cases. Tumors of the third eyelid and limbus were most responsive.

6. Enucleation: Enucleation in the calf or cow uses the transpalpebral approach. The cow is restrained in a chute or stanchion and sedated with xylazine (20 to 40 mg IV) before routine preparation of the orbit. The face is clipped and prepared for surgery. A circumferential infiltration of 2% lidocaine is performed approximately 3.75 to 5.00 cm from the eyelid margins, and 35 ml of 2% lidocaine is deposited in the retrobulbar cone via a 8.75-cm (3.5 in), 18-gauge needle. The orbital area is surgically prepped again and draped with a fenestrated drape that can be clamped to the halter with sharp towel clamps. (It is helpful to tape the ipsilateral ear back before draping.) A circumferential incision 1.5 cm from the eyelid margins is made through the skin but not through the palpebral conjunctiva. The incision is completed to the level of the conjunctiva with scissors, and the lid margins are clamped or sewn together. The lateral ligament of the orbit is severed, and dissection continues around the globe superficial to the conjunctiva. All muscles, the optic nerve, and retrobulbar fat are cut as traction is exerted on the globe nasally. The entire nictitans and lacrimal gland are removed. Meticulous attempts at hemostasis only serve to prolong the procedure. A subcutaneous continuous suture of 2-0 catgut closes the orbit, and nonabsorbable interrupted sutures close the skin. Preoperative and postoperative systemic antibiotics are administered for 5 days in routine cases but may be necessary for a longer period in infected globes. Drains are not used unless the orbital tissues appear infected or contaminated.

7. Exenteration: Surgical removal of all orbital tissue is recommended if any abnormal tissue is found retrobulbarly. Closure is similar to enucleation.

Figure 13-13 Squamous cell carcinoma of the nictitans in a Holstein cow.

Developmental Diseases

Dermoids of the conjunctiva cause irritation to the cornea because of hair growth on the dermoid and require surgical removal. A full-thickness wedge resection of the involved conjunctiva and lid followed by a two-layer repair has given excellent results.

Inflammatory Diseases

Etiology and Signs

Moraxella bovis, the cause of IBK (i.e., pinkeye), is the most important bacterial disease of the conjunctiva and cornea in cattle. The organisms and IBK will be discussed in the section on the cornea.

Pasteurella and other bacteria may also cause mucopurulent conjunctivitis in cattle occasionally. Pasteurella conjunctivitis occurs in conjunction with severe Pasteurella pneumonia or septicemia in calves. The organisms are normal inhabitants of the upper respiratory tract in cattle and therefore accessible to the conjunctiva. Neisseria spp. have been isolated from cattle with conjunctivitis and infectious keratitis. Atypical (winter) outbreaks of IBK-like endemics have been blamed on these other bacteria, but overwhelming evidence supports M. bovis as the most likely causative organism. Calves with respiratory infections caused by Histophilus somni may have conjunctivitis, rhinitis, laryngitis, and pneumonia. Cattle affected with bacterial conjunctivitis have a serous or mucopurulent ocular discharge, conjunctival injection, and do not appear to have ocular pain.

Mycoplasma and ureaplasma have been isolated from the eyes of cattle during herd epidemics of conjunctivitis. Affected cattle do not appear ill, but 10% to 50% of the animals have a unilateral or bilateral ocular discharge and conjunctival hyperemia. The ocular discharge is serous initially but becomes mucopurulent after 1 to 4 days. No keratitis is associated with this problem.

Infectious bovine rhinotracheitis (IBR) virus, the herpes virus 1 of cattle, may cause a severe endemic conjunctivitis in nonvaccinated cattle. The conjunctivitis may be the only lesion observed in sick cattle or may occur in conjunction with the typical respiratory form of IBR. The disease has been observed in heifers and adult cattle. Typical lesions include severe conjunctival hyperemia, heavy ocular discharge that converts from serous to mucopurulent over 48 to 72 hours, and the presence of multifocal white plaques in the palpebral conjunctiva (Figure 13-14). The lesions may be unilateral or bilateral and affect 10% to 70% of the herd. The plaque lesions are pathognomonic for IBR. Affected adult cattle have high fever (105.0 to 108.0° F/40.56 to 42.22° C), depression, and decreased milk production. Milking cattle with the conjunctival form of IBR appear ill regardless of whether the respiratory form coexists. Heifers with the conjunctival form of IBR may have fever and mild systemic illness but seldom appear as sick as adult milking cattle. The reason for this difference is not known but may be related to the stress of lactation.

Figure 13-14 Multifocal white plaques on the palpebral conjunctiva as a result of acute infectious bovine rhinotracheitis virus conjunctivitis.

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