Influence of density and location on degradation of sustained-release boluses given to cattle.

To better understand the factors involved in erosion of sustained-release ruminal boluses, studies were conducted to determine the relationship between density of the bolus and location in the forestomachs and the influence of these factors on bolus erosion. Boluses with densities of 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, and 2.4 g/cm3 were produced from inert materials and administered to 6 fistulated Hereford heifers. A minimum density of 1.6 g/cm3 was required to prevent regurgitation from the ruminoreticulum and a minimum of 2.0 g/cm3 for retention in the reticulum. Release of oxytetracycline from 2 boluses placed in the reticulum or in the rumen was measured in 12 fistulated Hereford heifers. Boluses retained in the reticulum had higher rates of release (P less than 0.05) than those in the rumen. The smaller reticular compartment apparently caused greater contact between individual boluses and resulted in more rapid erosion.

Chemoprophylaxis of vector-borne anaplasmosis with sustained-release boluses.

Sustained-release oxytetracycline boluses (20%) delivering 145 to 150 mg/bolus/day were administered to complement-fixation test-negative cattle at dosages of 2.0, 2.5, and 3.0 mg/kg of body weight. Subsequent challenge exposure of cattle with Dermacentor andersoni Stiles infected with Anaplasma marginale Theiler indicated that treatment with the dosage of 2.5 mg/kg prevented clinical anaplasmosis and that treatment with the dosage of 3.0 mg/kg prevented disease infection.

Transmission of Anaplasma marginale Theiler by Dermacentor andersoni Stiles and Dermacentor variabilis (Say).

Cattle were inoculated with a Virginia isolate of Anaplasma marginale Theiler and served as an infective source for laboratory-reared Dermacentor andersoni Stiles and D variabilis (Say) nymphs. Following a molt and subsequent feeding of adult ticks on susceptible cows, transstadial transmission of A marginale occurred from cattle with parasitemias ranging from undetectable (in a carrier cow) to a peak of 27% (in an acutely ill cow). Homogenates of gut tissue from unfed, incubated, and feeding adult ticks that were infected as nymphs were all infective; however, the prepatent period varied according to treatment of ticks after they had molted to the adult stage. Prepatent periods of infections in calves resulting from injection of homogenated tissue from unfed adult ticks was 29 and 34 days longer than the prepatent periods that developed in calves exposed to homogenated tissue from ticks that were feeding or incubated at 37 C for 3 days. Transovarial transmission did not occur when F1 larvae, hatched from eggs produced by female ticks known to be infective, fed on susceptible cattle.

A study of Klebsiella pneumoniae infection in the uterus of the mare.

Two experiments incorporating 13 mares were conducted for the purpose of producing and monitoring intrauterine infection with Klebsiella pneumoniae. In the pilot study, the infection was produced with strains of K pneumoniae type 68 and type 10 isolated from the genital tract of stallions with a history of breeding problems. In the principal study, K pneumoniae type 68 was used to produce the infection. Tampons and guarded culture swabs were used to obtain uterine samples in the pilot study. In comparing the efficacies of isolation of K pneumoniae with the tampons and isolation with standard guarded culture swab, the tampon proved to be a more reliable means with which to isolate K pneumoniae and was used in the principal study. In both studies, inoculated mares became infected and remained infected at least until the postinoculation estrous cycle was initiated or was completed. Some of the inoculated mares remained infected through more than one estrous cycle. The numbers of K pneumoniae decreased in the uterus of mares after completing the estrous cycle after inoculation. Klebsiella pneumoniae was not demonstrable in frozen tissue sections of uterine biopsy specimens stained by fluorescent antibody technique. Postinoculation sera antibody titers to K pneumoniae, as determined, using the capsule swelling technique, were no higher than 1:8.

Isolation of Klebsiella pneumoniae from the urogenital tract of experimentally infected mares.

K. pneumoniae capsule type 68 infused into the uterus of 4 mares was recovered up to 15 weeks after inoculation. The insertion of a tampon for 10 min was more effective than a swab technique in detecting the organism in the uterus. The clitoral fossa and the urethral orifice when sampled by the swab technique were also found to be infected for a comparable period. K. pneumoniae was isolated from the clitoral specimens more often and more consistently than from either urethral or uterine specimens.