A working horse being treated for heat stress and dehydration in Pakistan.
Veterinarians from Bristol University and The Brooke equine welfare charity examined hydration levels in 50 working horses in Lahore during May and June 2006 at a field clinic run by The Brooke.
Dehydration is a serious welfare concern in horses working in developing countries, where they regularly work for more than eight hours a day in temperatures often exceeding 40degC.
It was hoped the study might identify a valid and practical indicator of dehydration that would enable more rapid treatment and prevention by horse owners.
The standard pinch test, or skin tent test, examines the delay in return of a fold of pinched skin to its normal position and is normally most commonly performed on the neck or point of the shoulder. Conventional wisdom is that the slower the skin's return, the more dehydrated the horse.
The researchers demonstrated that the test was an unrealiable measure.
They found the results of skin-pinch tests were affected by the side of animal where the test was undertaken, anatomical location and even coat moisture levels. Younger animals had shorter "skin tents" than older animals.
Further, there was was no significant association between the amount of water a horse drunk and the results of a skin-pinch test. Nor did the skin-pinch test correlate in any significant way with the results of accurate blood-related measures of dehydration.
"These results suggest that changes in skin tent duration may be attributable to changes in coat moisture or to other factors, such as the apparent effect of small differences in neck position and muscle movement," the authors said.
"Coat moisture had a highly significant effect on skin tent duration. Investigation of this factor was prompted by an observation, made during the preliminary testing period, that a normal (rapid) skin tent in dry horses became very prolonged when the animals were suddenly soaked with rain.
Pinch tests on the left side of animals were longer than on the right. "The assesssor's right hand was always used so, despite practice, right-handedness may have had an unintentional effect on the strength of the pinch and hence the duration of tenting.
"Alternatively, where carts are driven on the left side of the road, as in Pakistan, a difference in muscle size and/or tension on the horse's left side could cause the asymmetry of skin tent duration seen in this study."
Two of the horses involved in the trial in Pakistan.
"Offering palatable water to drink ad libitum provides both the diagnosis and the remedy for dehydration in working horses," the researchers said.
"The pattern of drinking behaviour shows that animals appeared to quench their thirst immediately on being offered water and their intake remained low for the rest of the study period," the researchers said.
"Therefore, although not ideal, water consumption appears to be the best field test for dehydration.
"Although water intake in this study did not appear to be affected by water temperature, voluntary replacement of fluid losses in working horses may be further improved by offering water at optimal temperature, flavour and salinity; this is a potential area for further research," the wrote.
The study was supported and funded by The Brooke Hospital for Animals.
Validity of indicators of dehydration in working horses: A longitudinal study of changes in skin tent duration, mucous membrane dryness and drinking behaviour.
J.C. PRITCHARD, C.C. BURN, A.R.S. BARR and H.R. WHAY. 558 EQUINE VETERINARY JOURNAL Equine vet. J. (2008) 40 (6) 558-564 doi: 10.2746/042516408X297462