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

## TL;DR

This study examines how repeated blood harvesting affects pregnant mares' blood health, finding that some develop mild to moderate anemia but recover within weeks.

## Contribution

The study provides new insights into the haematological effects of repeated blood harvesting in pregnant mares under free-range conditions.

## Key findings

- Up to 14.3% of mares in one herd developed transient moderate to marked anemia.
- All mares returned to normal haematocrit levels three weeks after the last harvest.
- Differences between herds suggest nutritional factors influence anemia risk.

## Abstract

For the extraction of equine chorionic gonadotropin (eCG), mares in the first 2–4 months of pregnancy are harvested for blood. The extracted eCG has been used in pharmaceutical products for the control of reproduction in other animal species. Blood harvesting from mares has raised concerns around their welfare, such as the possibility of them developing anaemia. This study was carried out to investigate the effect on the haematological variables of repeated blood harvesting from pregnant mares in two free-range herds. Our results show that up to 14.3% of mares in one herd had transient moderate to marked anaemia, but that no mares in the other herd developed more than mild anaemia. No mares in either herd had anaemia as defined by Hct three weeks after the last blood harvest. This difference between the herds indicates that external factors such as nutrients ingested by the mares are vitally important in the response to blood loss.

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.