Physiological responses in horses, donkeys and mules sold at livestock markets

The horse welfare at markets includes fatigue, fear, fasting, dehydration and injuries. However, the scientific literature contains no readily-available information on the physiology responses of equids sold in livestock markets. The objective of the present study was to evaluate the effect of holding in livestock markets on gas exchange, the acid-base balance, energy metabolism, and the mineral and water balance in 4 types of horses (Equus caballus), donkeys (Equus asinus) and mules ((Equus asinus × Equus caballus). To this end, a total of 1,438 equine were utilized, after classification into six groups, as follows: mules, donkeys, culled horses, charrería horses (Mexican rodeo horses), foals, and ponies. The time intervals evaluated were 1 and 5 h. During the study, the animals received only water ad libitum. The physiological blood indicators assessed were: P_vCO₂ (mm Hg) and P_vO₂ (mm Hg) pressure, pH, glucose (mg/dL), lactate (mg/dL), bicarbonate levels (mmol/L), hematocrit (%), Na⁺, K⁺ and Ca²⁺ (mmol/L). The animals that presented the most marked physiological alterations were the mules and donkeys. The mules that remained in the corrals for 1 h presented increases (P < 0.0001) in the values for pO_2, glucose, hematocrit and blood pH, compared to reference values (RV), while the donkeys had increases (P < 0.0001) in glucose and hematocrit values. By the end of the first hour at the exhibition corrals the equine were dehydrated, suffered fatigue, and suffered metabolic and compensatory problems, probably due to the combined effects of a series of factors that include transport and inadequate handling.