Stimuli of thirst in donkeys (Equus asinus).

The research evaluates the factors that stimulate thirst in donkeys and compares their thirst responses to ponies under certain conditions. It primarily found that donkeys are able to accurately compensate for fluid deficit caused by overnight water deprivation, but their latency is more and intake is less than ponies, suggesting a higher thirst threshold.

Methodology and Findings

• The study was conducted on six feral donkeys. The stimuli considered for this study were overnight water deprivation, the diuretic furosemide, and hypertonic saline infusion, all in the absence of heat stress or work.
• The donkeys were able to accurately compensate for the fluid deficit caused by overnight water deprivation. Following 19 hours without water, the donkeys drank 8.8 +/- 2.4 liters in 60 minutes. An average intake during non-deprived periods was 8.4 +/- 1.5 liters.
• The donkeys, however, had a longer latency and lower water intake than ponies under the same conditions, suggesting that donkeys have a higher thirst threshold than ponies. Further, the study found that the plasma volume fell less in donkeys, yet the osmotic changes were comparable to those reported in ponies subjected to the same deprivation.

Further Analysis and Conclusion

• When the donkeys were infused with 250 ml of 15% NaCl, they drank 0.7 +/- 0.6 liters of water within 45 mins, and osmolality increased from 287 to 297 mosmol/kg water. However, they did not drink any water during the same time period when infused with 250 ml 0.9% NaCl.
• When injected intravenously with 2 mg/kg furosemide, the donkeys drank 3.8 +/- 1.1 liters within 3 hours and their plasma protein increased from 6.9 to 7.8 g/dl. But when injected with 0.9% NaCl, they only drank 1.0 +/- 0.5 liters.
• In conclusion, donkeys demonstrated similar responses to cellular and extracellular dehydration triggers as previously demonstrated in ponies. However, the evidence reveals a less sensitive response in donkeys, while also suggesting that they offer a superior defense of blood volume compared to ponies.