Resistance to anticoagulant rodenticides in Germany and future strategies to control Rattus norvegicus

Widespread anticoagulant resistance was discovered in populations of the brown rat (Rattus norvegicus Berk.) in an area of roughly 8000 km² in north-west Germany. Resistance testing was performed by feeding tests and/or by measuring blood clotting response after intraperitoneal injection of a sublethal testing solution. A hierarchical resistance system was found with warfarin resistance at the base followed by bromadiolone/coumatetralyl resistance to difenacoum resistance at the top. Warfarin resistance was spread over the whole area with reduced incidence towards the edges. Difenacoum resistance represented the highest level found so far and was restricted to the inner zone of the resistance area where it occurred with a frequency of 6% of all individuals tested. Breeding experiments with bromadiolone-resistant rats showed that expression of the bromadiolone resistance gene differed in the two sexes, suggesting additional sex-linked modifying effects to the resistance gene. Control strategy within the resistance area with respect to prevention of further selection for resistance is discussed.     

Studies on food selection behaviour of the Norway rat (Rattus norvegicus) on farms

Measures used to control Norway rats (Rattus norvegicus Berk.) on farms are frequently unsuccessful due to poor bait uptake. In pest-control operations, rats always have the choice between the farms own food resources and the bait. In this study we analysed the individual selection behaviour in two rat colonies when the rats were offered a familiar bait which matched the food on the farm and a bait which was unknown. Bait stations equipped with video and transponder technology were installed in two differently structured areas on a farm. In four experiments, a familiar foodstuff (rolled oats) was put out for 3 days, and then at one of the stations, a test bait was put out for 4 days. The relative palatability of the test baits was known from laboratory experiments. The visits of marked individuals were registered, and the amounts consumed were estimated in the video evaluation. Location preference was determined by offering identical food in two neighbouring bait stations. Social interaction was evaluated using the video recordings. The bait stations were visited on a daily basis irrespective of the supply. Food selection patterns (and bait acceptance) observed in the two differently structured areas on the farm were different. However, the relative palatability among the four test baits was stable and agreed with the ranking in laboratory experiments. Over the days of the experiment there was no significant difference in bait acceptance. Location preference and social interaction influenced the choice of bait station. The results show that it is possible to predict bait palatability in the laboratory, which is an important prerequisite for good bait uptake. However, the bait acceptance level is ultimately determined by the prevailing living conditions in the respective area. For optimising bait uptake, the structure of the areas on the farm must be considered just as much as findings about location preferences and social interaction.     

Reactivity of cross-reacting monoclonal antibodies with canine leukocytes, platelets and erythrocytes

A panel of 380 commercially available monoclonal antibodies (mAbs) against human CD molecules from various sources was tested during the 8th Human Leukocyte Differentiation Antigen Workshop (HLDA8) for cross-reactivity on canine peripheral blood leukocytes by flow cytometry. In addition, all mAbs were used to label a 50:50 mixture of platelets and erythrocytes of the same dogs. This testing resulted in 51 cross-reacting mAbs. mAbs with specificity for CD9, CD29, CD42a, CD61, and CD41/CD61 showed cross-reactivity with canine platelets in a non-polymorphic and one mAb with the erythrocyte antigen CD235a in a polymorphic reaction pattern. Canine leukocyte-reactive mAbs included those with specificity for CD11a, CD11b, CD14, CD18, CD21, CD22, CD47, CD49d, CD49e, CD56, CD62L, CD91, CD94, and CD172a. In addition, several mAbs resulted in a staining pattern of canine cells which suggest that the canine epitope equivalents have an alternate expression pattern from that expected for humans (CD1a, CD35, CD44, CD45, CD75s, CD81). In summary, this study confirmed the reactivity of previously described cross-reactive mAbs with canine cells and resulted in the characterization of mAbs recognizing so far undetectable canine CD molecules.     

Effect of Protease Inhibitors on the Acrosome Reaction and Sperm‐Zona Pellucida Binding in Bovine Sperm

Acrosomal proteases participate in several events during fertilization process and are necessary during the acrosome reaction (AR) and sperm‐zona pellucida (ZP) binding process. In this study, the participation of sperm trypsin‐like, chymotrypsin‐like, and metalloprotease enzymes in the AR and ZP binding in cattle was investigated using protease inhibitors. Motile bovine sperm were obtained by a swim‐up method (4 × 10⁶ cells / ml) in Brackett and Oliphant medium. The sperm were capacitated and then incubated with Antithrombin III (trypsin and chymotrypsin inhibitor); N‐α‐p‐tosyl‐l ‐lysine‐chloromethyl‐ketone (trypsin inhibitor); Trypsin inhibitor (I‐S Type from soybean); N‐tosyl‐l ‐phenylalanine‐chloromethyl‐ketone (chymotrypsin inhibitor); or disodium salt from the hydrated ethylenediaminetetraacetic acid (metalloprotease inhibitor). Then, the AR was induced with lysophosphatidylcholine and evaluated with the double stain technique. Sperm‐zona binding capacity was evaluated using cumulus cell‐free oocytes. A significant decrease (p < 0.05) in the percent of true acrosome‐reacted sperm was observed only in cells incubated with trypsin (10.2 ± 1%) and chymotrypsin inhibitors (18.5 ± 1%) in relation to the control (52.2 ± 1%). Treatment with the metalloprotease inhibitor did not affect the AR percentage (51.8 ± 1%). On the contrary, there was no significant change in the number of sperm bound to the ZP with any of the inhibitors used. The results suggest a role for trypsin and chymotrypsin proteases, but not metalloproteases, in the AR in bovine sperm. In addition, these proteases do not seem to be involved in the binding of bovine sperm to the ZP.     

Influence of age on myelogram in dogs

The influence of age on the myelogram and on the different indices (ratios) was studied on bone marrow aspirates of 131 healthy dogs which were divided into different age groups (A [4-6 months] to G [> 8 years]). Myelograms were obtained by performing a differential count on 1000 cells. Age dependent differences were particularly seen in the 4 to 6 month old dogs. These dogs had significantly higher percentages of immature erythroid cells (p < 0.01) than dogs of the other age groups and, consequently, the lowest proportion of myeloid cells. This fact was also reflected by a lower quotient of number of myeloid cells/number of erythroid cells (M:E-ratio) and increased erythroid maturation index (I:ME-ratio). In addition, the proportions of monocytes and lymphocytes were increased and the number of plasma cells was decreased in juvenile dogs. The results in young dogs which were different from the values of adult animals reflect the increased requirements of red cell mass during the time of growth and ontogenesis of the immune system. These findings have to be considered in the interpretation of bone marrow films of young dogs.