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The results of a direct radioimmunoassay (RIA) for porcine plasma melatonin, suggesting a relationship among plasma melatonin, feed intake and photoperiod, were investigated by comparison with the results of an extracted RIA. These findings were further examined by analysis of a small number of samples using gas chromatography-mass spectrometry (GCMS). The results identified inadequacies in the specificity of the direct RIA and failed to provide evidence for an effect of feed intake on melatonin secretion. Instead, it appeared that feed restriction exacerbated nonspecificity in the direct RIA. The cause of nonspecificity, and its effect on analysis of daily plasma melatonin profiles, were examined. The plasma component(s) responsible for nonspecificity was (were) not identified. However, the results suggest that characteristics of the antiserum used in the direct RIA are involved in the mechanism by which nonspecificity is induced. Results obtained using the extracted assay revealed that plasma melatonin concentrations in prepubertal gilts and pregnant sows exhibit a diurnal pattern, in which concentrations are low during daylight and modestly increased during darkness. Using the direct RIA, the same profiles exhibited highly variable melatonin concentrations showing little association with the light-dark cycle. Thus, assay specificity was identified as a factor contributing to inconsistencies in the literature describing plasma melatonin in the domestic pig and the importance of rigorous validation of RIAs was demonstrated. Furthermore, the results indicate that plasma melatonin concentrations in domestic pigs, as in other mammalian species, are entrained by the light-dark cycle.

Repellency is a highly desirable attribute for an acaricide that protects dogs against the Australian paralysis tick (Ixodes holocyclus). A bite from a single tick of this species can be fatal and carries the risk of transmission of vector-borne diseases. A randomised, controlled study was conducted to confirm the repellency sensu stricto and sensu lato (expellency) of a 10 % imidacloprid/4.5 % flumethrin collar (Seresto ® , Bayer) on dogs, against artificial infestations of I. holocyclus. Based on a novel protocol, dogs treated with Seresto ® , or a placebo collar, were sedated and placed in infestation chambers for 1 h at varying time points up to 6 months after treatment. Ticks were released alongside the dogs, and allowed to approach and/or attach. Treating dogs with a Seresto ® collar resulted in significantly (p < 0.001) more residual ticks being found in the infestation chambers (repellency sensu stricto) compared to the placebo treated dogs for the 168-day duration of the study (range 67.5% to 90.2 %). Repellency sensu lato (expellency) was reflected in significantly (p <0.002) fewer ticks being found attached to treated dogs throughout the study. Comparative decrease in ticks attached exceeded 95 % for 84 days, when assessed after 6 h. When assessed after 24 h, there was a > 95 % comparative decrease in ticks attached until Day 84, > 90 % on Days 112 and 140 then > 95 % to Day 168. Efficacy (killing effect) of the Seresto ® collar based on total live tick counts was > 95 % 6 h after tick challenge throughout the 6 month study period. This study demonstrated the excellent repellency effect of the Seresto ® collar against I. holocyclus in dogs. S146Ectopar asitEs