Protection of cattle against heartwater in Botswana: comparative efficacy of different methods against natural and blood-derived challenges.

Five groups of Tswana-cross castrated male cattle between 20 and 30 months of age (a total of 158 animals) were transported from a ranch in a heartwater-free area of south Botswana to a feedlot near Gaborone in the east of Botswana where heartwater is endemic. On arrival, one group was vaccinated intravenously with the Onderstepoort sheep blood heartwater vaccine, one group was vaccinated intravenously with the new Onderstepoort tick-derived heartwater vaccine and a third group was vaccinated subcutaneously with this tick-derived vaccine. Vaccine reactions were blocked with long acting oxytetracycline on the first day of fever. A fourth group had a series of injections of long acting oxytetracycline on days 0, 7, 14 and 21 after arrival, and a fifth served as untreated controls. The animals remained at the feedlot for 65 days during which time they faced a low level of challenge by Amblyomma hebraeum ticks. None contracted heartwater and so they were then challenged, together with a further group of control cattle, with a dose of the sheep blood vaccine. Some animals in all groups had severe heartwater reactions and died despite therapy, but 76.7 per cent, 64.5 per cent and 74.3 per cent of the cattle in the blood vaccine, intravenous tick vaccine and long acting oxytetracycline groups respectively were resistant to challenge, compared with 48.3 per cent of the subcutaneous tick vaccine group and 36.4 per cent of the controls. It was concluded that intravenous vaccination of susceptible adult cattle with either the blood or the tick-derived vaccine needs careful monitoring in the month after vaccination and does not necessarily result in immune animals.(ABSTRACT TRUNCATED AT 250 WORDS)

An excitatory body-antral reflex in the sheep abomasum.

This paper describes an abomasal body-antral excitatory reflex in acute experiments in sheep anaesthetized with chloralose. The abomasum was either surgically intact or acutely transected to form separate compartments of the abomasal body and antrum. Inflation of a balloon situated in the abomasal body and active contraction of the abomasal body increased the amplitude of antral contraction. In the intact preparation, inflation of the abomasal body increased the amplitude of antral contraction before and after extrinsic denervation. The antral response was reduced by 75% after extrinsic denervation. In the acutely transected preparation, inflation of the abomasal body and electrically induced contraction of the abomasal body also increased antral contraction amplitude. The antral response was abolished by bilateral section of the cervical vagus nerves in five of six experiments. Selective extrinsic neurotomy of either compartment abolished all responses. It was concluded that the neural mechanisms controlling abomasal motility in the sheep resemble those found in species with simple stomachs: excitation of in-series tension receptors of the abomasal body causes an increase in antral contraction amplitude by vago-vagal reflex pathways. Antral motility is also modulated by changes of tension in the abomasal body by intrinsic reflex pathways and reflexes involving abdominal preganglia may also be present. In a restricted number of experiments the splanchnic nerve was shown to play an important role.