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Sex-related differences in plasma chemistry reference values in stone curlews (Burhinus oedicnemus)

STONE curlews (Burhinus oedicnemus) are rare birds that live in arable land habitats, preferably open areas (Bezzel 1995). There are approximately 33,000 to 45,000 breeding pairs in Europe and 150 to 160 pairs in the UK, and their numbers are declining (Nipkow 1997). Breeding programmes have been established in numerous European zoos and by the Royal Society for the Protection of Birds in the UK. With increasing numbers of stone curlews in captivity as a result of these programmes, and because of the value of each bird, the number of these birds seen in veterinary practice is increasing, and sophisticated diagnostic techniques are required for the species. The interpretation of plasma chemistry values is a helpful diagnostic tool (Hochleithner 1994). Unfortunately, there is a lack of statistically valid reference values for the stone curlew. Reference values are only of use if they have been obtained from birds kept in similar circumstances and if they are available to veterinarians (Kraft 1998). In particular, the age and sex of the birds (Lierz and Fenske 2004), the season of sampling (Gerlach 1979), the time of feeding (Lumeij and Remple 1991), stress and the birds’ food source (Kraft 1998), or the use of other diagnostic tools before sampling (Lierz and others 1998), may affect plasma chemistry variables. Most importantly, reference values for a population can only be established if more than 20 birds are sampled (Rümke and Bezemer 1972). The aim of the present study was to establish reference plasma chemistry values for stone curlews of both sexes. Blood samples were collected from 145 male and 100 female adult stone curlews from a private breeding collection in Abu Dhabi, United Arab Emirates. All the birds were kept in an aviary containing approximately 20 to 30 birds per cage. They were fed on a homemade soft ration containing cooked eggs, carrots, shrimps, wheat and mealworms. Before blood sampling, all the birds were clinically examined and found to be clinically healthy; none received any medication before sampling. A blood sample was collected from the ulnar vein using a 0·45 x 25 mm needle (Sterican Luer-Lock; Braun Melsungen) attached to a 1 ml syringe (Braun Melsungen). Approximately 1 ml blood was collected by gentle aspiration and directly transferred into a lithium-heparin tube (Sarstedt). The plasma was separated by centrifuging the sample for 10 minutes at 4500 g and analysed using an ACE autoanalyser (Shiapparelli Biosystems) to determine 14 blood chemistry variables (Table 1) by photometric measurements. The concentration of albumin was measured using bromocresol green dye and total protein was determined using the biuret method with human protein as a standard (Shiapparelli Biosystems). All enzyme activities were measured at 30°C. The reference values were established using the inner limits of the 2·5 and 97·5 percentiles with a 95 per cent probability (Rümke and Bezemer 1972). Differences in the measured values between male and female birds were compared statistically using the Mann-Whitney U test; the level of significance was set at P=0·05. The mean (sd) measurements for each plasma chemistry variable and the reference values established are given in Table 1. The female stone curlews had significantly higher activities of aspartate aminotransferase (AST) (P=0·0012) and alanine aminotransferase