Sonographic findings in horses with mediastinal lymphosarcoma: 13 cases (1985-1992).

Sonographic findings correlated with necropsy findings in 8 of 9 horses in which the cranial portion of the mediastinum was evaluated by use of both methods. Cranial mediastinal masses were imaged as multilobular and homogeneously hypoechoic; a complex echogenic pattern was observed with necrosis within the mass. Pleural effusion was a common finding in horses with mediastinal lymphosarcoma. Cytologic evaluation of pleural fluid samples was useful in diagnosis of lymphosarcoma in 10 of 12 horses that had thoracentesis. Sonographic examination of the thorax and cranial portion of the mediastinum can aid in the diagnosis of mediastinal lymphosarcoma in horses. Such examination should be performed in horses with clinical signs of cranial vena cava obstruction in which pleural effusion is detected, or when thoracic lymphosarcoma is suspected.

Effect of oxytetracycline on metacarpophalangeal and distal interphalangeal joint angles in newborn foals.

Thirty-five newborn foals were assigned to 1 of 3 groups and treated with 0.9% NaCl solution (saline; group 1; n = 12), oxytetracycline (44 mg/kg of body weight; group 2; n = 12), or 2-pyrrolidone (oxytetracycline vehicle; group 3; n = 11) in saline solution during the first 36 hours after birth. Serum biochemical analyses were performed on samples obtained from group-1 and group-2 foals before treatment and 24 and 96 hours after treatment. Lateral to medial radiographic views of the forelimbs were obtained before treatment and 24 and 96 hours after treatment in all foals. Metacarpophalangeal and distal interphalangeal joint angles were measured from the radiographic images. Significant changes in blood chemistry values, other than those typically observed in newborn foals, were not detected. A significant decrease in mean metacarpophalangeal joint angle was observed in foals 24 hours after treatment with oxytetracycline, compared with that in foals of groups 1 and 3. The mean metacarpophalangeal joint angle returned to pretreatment values by 96 hours. Oxytetracycline appears to be an effective method for obtaining a short-term moderate decrease in metacarpophalangeal joint angle in newborn foals.

Pharmacokinetics of metronidazole after rectal administration in horses.

Five healthy adult mares and 1 gelding were given a single dose (15 mg/kg of body weight) of metronidazole per rectum. After manual evacuation of feces from the rectum, a suspension of crushed tablets and water (40 ml) was administered via a 28-F catheter advanced 30 cm into the rectum. Blood samples were obtained by jugular venipuncture, and metronidazole concentration was measured serially for the 14 hours after drug administration. Mean serum concentration of metronidazole peaked at 4.5 micrograms/ml, 0.83 hour after administration, and decreased to 0.38 microgram/ml, 14 hours after administration. Mean elimination rate constant was 0.23/h, and the harmonic mean elimination half-life was 3.04 hours. Further study is necessary to determine a therapeutic dose regimen for metronidazole administered per rectum.

Postsurgical ventricular tachycardia in a horse.

A 2-year-old Thoroughbred racehorse developed ventricular tachycardia after elective laryngoplasty and ventriculectomy were performed while anesthesia was maintained with halothane. During surgery, the horse became febrile and developed transient mild hypercarbia. The horse was treated with an IV infusion of quinidine gluconate. Continuous electrocardiographic monitoring was used to evaluate cardiac rhythm during treatment, and conversion was achieved after 12 hours of IV infusion. The inciting cause for the arrhythmia was not determined.

Signs of abdominal pain caused by disruption of the small intestinal mesentery in three postparturient cows.

Three Holstein cows were admitted on postpartum day 3 with signs of abdominal pain, inappetence, and decreased milk production. All 3 were depressed, tachycardic, and dehydrated. Right paralumbar fossa laparotomy was performed on each cow. At surgery, a rent in the proximal portion of the jejunal mesentery, with perforation of the jejunum adjacent to the mesenteric rent, was found in all 3 cows. All had evidence of severe peritonitis and gross contamination of the abdomen with digesta. Because of severe peritonitis and inability to exteriorize the affected segment of jejunum, all 3 cows were euthanatized. We postulate that the mesenteric rent occurred at the time of parturition, resulting in ischemia and jejunal perforation in the segment of jejunum adjacent to the rent.