The Effect of Repeated Blood Harvesting from Pregnant Mares on Haematological Variables

Studies have been carried out on the effect of large-volume blood harvesting from horses, but they were performed on nonpregnant horses of various breeds other than Icelandic horses. This study aimed to investigate the effect on the haematological variables indicating erythropoiesis of repeated blood harvesting from pregnant mares. To account for regional variation, two herds of mares were chosen, both kept under free-range conditions. Sequential EDTA blood samples were collected weekly from 160 mares and analysed for haematological variables in an automated analyser. Serum samples from 115 mares were analysed for total protein. In both herds, after three harvests, mares began to measure below the minimum value for erythrocyte numbers, and mild anaemia was present in up to 37% at one time. Mares in only one herd had moderate or marked anaemia, 14.3% of the herd. Both herds showed evidence of increased erythropoiesis, but there was a difference between the herds in the intensity of the response. In both herds, however, all mares had reached the minimum normal haematocrit value three weeks after the last harvest. It is important to investigate the causes for the differences between these herds, which might be addressed to reduce the risk of anaemia.

Haematological reference intervals for pregnant Icelandic mares on pasture

BACKGROUND

Few studies have been conducted on haematological reference intervals (RIs) in Icelandic horses. Reference intervals have been published for Icelandic horses in Austria and a preliminary study in Iceland compared haematological values in riding horses to published RIs for other breeds as well as Icelandic horses abroad. Haematological parameters can vary greatly due to factors such as breed, gender, age, reproductive status, and training, as well as feeding, prior exercise and management method. Icelandic broodmares are kept on pasture under supervision throughout the year, with haylage provided during the winter, and it is therefore of interest to establish haematological reference intervals for pregnant broodmares in Iceland. The purpose of this study was to establish haematological RIs specific to Icelandic broodmares in the first months of pregnancy, kept on pasture. Blood samples from 183 mares, stabilised in EDTA were analysed using IDEXX ProCyte Dx and total protein was analysed in serum samples from 157 of the 183 mares, using IDEXX Catalyst One analyser. The RIs were established using the guidelines of the American Society for Veterinary Clinical Pathology.

RESULTS

The RIs for red blood cell count, haematocrit and haemoglobin were higher in pasture-kept Icelandic mares in early pregnancy, most of which were lactating, than in pregnant mares of other breeds. This was also true for white blood cell count, as well as numbers of monocytes, eosinophils, and basophils, which in some instances might illustrate problems in the automated categorisation of some leukocytes.

CONCLUSIONS

As no RIs have been published for other pasture-kept Icelandic horses, future investigations should include other groups of pasture-kept Icelandic horses. Such an analysis might elucidate the effect of breed, management, and pregnancy on haematological values in pasture-kept Icelandic horses.