Use of enzyme-linked immunoassays for antibody to types C and D botulinum toxins for investigations of botulism in cattle

The development of specific enzyme-linked immunosorbent assays (ELISA) for antibody to types C and D Clostridium botulinum toxins for investigation of botulism in cattle is described. Partially purified type C and D toxins were used as antigens to develop these ELISAs. Specificity of the ELISAs was evaluated on sera from 333 adult beef and dairy cattle from areas with no history or evidence of botulism in animals or water birds. The test was also evaluated on sera from 41 herds that included herds vaccinated against botulism, confirmed botulism cases and herds from areas where the disease is considered endemic. The ELISAs detected the presence of antibody to botulinum toxins in samples from vaccinated cattle and both convalescent and clinically normal animals from unvaccinated herds with outbreaks of botulism. Antibody was also found in unvaccinated animals from herds in which there had been no diagnosed botulism cases in areas where botulism was considered endemic. Sera from some unvaccinated cattle with high ELISA reactivity was shown to be protective for mice in botulinum toxin neutralisation tests. The use of these tests in investigations of botulism in cattle is discussed.     

An evaluation of calf castration by intra-testicular injection of a lactic acid solution

This experiment evaluated intra-testicular injection of a sclerosing drug, lactic acid, for castration of bulls. Its use was compared in 58 Brahman cross calves (50 to 128kg) with the general practice of open surgical castration. Chemical castration appeared to be more painful than surgical castration, though post-operative swelling and pain appeared similar for both methods. Chemical castration took 3 times longer than surgical castration (58 sec v 20 sec; P less than 0.01). Scrotal necrosis occurred in 25% of chemically-castrated calves and appeared due to drug leakage from the testes under the high pressure of injection. Healing time for chemical castrates was approximately twice that for surgical castrates. Five chemically-castrated calves (18%) retained one testis. Though all 5 were rendered sterile, each maintained androgenesis. This led to secondary male behaviour which caused management problems. Castration method did not influence post-operative growth. It is concluded that lactic acid administration is not a suitable alternative to the open surgical technique for castration of Brahman cross calves.     

Serological evidence of widespread exposure of Grenada fruit bats to chikungunya virus

Antibody detection against selected potentially zoonotic vector‐borne alphaviruses and flaviviruses was conducted on sera from bats from all six parishes in Grenada, West Indies. Sera were tested for (i) antibodies to flaviviruses West Nile virus, St. Louis encephalitis virus, Ilhéus virus, Bussuquara virus (BSQV), Rio Bravo virus and all four serotypes of dengue virus (DENV) by plaque reduction neutralization test (PRNT); (ii) antibodies to alphaviruses western equine encephalitis virus, Venezuelan equine encephalitis virus and eastern equine encephalitis virus by epitope‐blocking enzyme‐linked immunosorbent assay (ELISA); and (iii) antibodies to the alphavirus chikungunya (CHIKV) by PRNT. Two species of fruit bats were sampled, Artibeus jamaicensis and Artibeus lituratus, all roosting in or within 1,000 m of human settlements. Fifteen (36%) of the 42 bats tested for neutralizing antibodies to CHIKV were positive. The CHIKV‐seropositive bats lived in localities spanning five of the six parishes. All 43 bats tested for epitope‐blocking ELISA antibody to the other alphaviruses were negative, except one positive for Venezuelan equine encephalitis virus. All 50 bats tested for neutralizing antibody to flaviviruses were negative, except one that had a BSQV PRNT₈₀ titre of 20. The CHIKV serology results indicate that bats living close to and within human settlements were exposed to CHIKV in multiple locations. Importantly, bats for this study were trapped a year after the introduction and peak of the human CHIKV epidemic in Grenada. Thus, our data indicate that bats were exposed to CHIKV possibly during a time of marked decline in human cases.     

Effects of increasing days of exposure to prepartum transition diets on reproduction and health in dairy cows

Objective To evaluate the effect of the number of days exposure to a prepartum transition diet on reproduction and health in dairy cows. Design A prospective cohort study. Procedures We enrolled 1008 dairy cows from three herds to examine the effects on reproduction and health of increased days exposure to prepartum transition diets that included ryegrass pasture, ryegrass silage, cereal hay, grain, by-products, oilseed meals, BioChlor®, rumen modifiers, minerals and vitamins. Diets provided 9.9 MJ metabolisable energy per kg dry matter (DM), a metabolisable protein balance of 286 g/day and a dietary cation anion difference of −150 meq/kg DM. Statistical models controlled for herd, calving day, age and gestation period. Results In two of the three herds increased days exposure to prepartum transition diets increased the hazards of submission for breeding, conception and clinical mastitis, and decreased the hazard of cow removal. The odds of pregnancy by 6 and 21 weeks after the mating start date tended to increase with increasing days of exposure to prepartum transition diets. Conclusions Increasing exposure to a prepartum transition diet improved the calving to conception interval, tended to improve the odds of pregnancy and reduced the risk of culling of cattle, but increased the hazard of clinical mastitis.