Background Disturbances in lipid metabolism are usually associated with hyperlipidemia, which is commonly
observed in donkeys with inappetence or anorexia. The diagnostic utility of ultrasound measurements of croup fat
thickness (CFT) and relative liver echogenicity for lipomobilization in donkeys with fasting-induced hyperlipidemia
was investigated. A prospective observational control study involving 25 donkeys was conducted, and the animals
were randomly assigned to a fasting group (FG, n = 20) and a control group (CG, n = 5). In the FG, the experiment
period (10 days) consisted of two stages, the fasting stage (4 days) and the post-fasting stage (6 days).
Results On six occasions, the following were evaluated: body weight (BW), body condition score (BCS), ultrasound
subcutaneous CFT, ultrasound gluteal muscle thickness, liver ultrasonography, and blood metabolites. The ultrasound
CFT was significantly reduced at 4 days of fasting (P < 0.05). Donkeys with ≥ 7 mm of CFT before fasting were 6 times
more likely to develop hyperlipidemia post-fasting (P < 0.01). Hepatic ultrasonography showed no hepatomegaly.
Decrements of the portal vein (PV) diameter were noticed during fasting. The hepatic relative echogenicity (RE)
significantly increased after 4 days of fasting, and then decreased after fasting (P < 0.05). The RE of ≥ 78 is a critical
threshold for diagnosing hyperlipidemia (P < 0.001). The serum concentrations of triglycerides, total cholesterol, very
low-density lipoproteins, high-density lipoproteins, and low-density lipoproteins peaked at 4 days of fasting (P < 0.05).
The serum concentrations of FFA increased during fasting (P < 0.05) and then dropped after fasting.
Conclusion Fasting-induced hyperlipidemia is associated with reductions in CFT with concurrent increased RE,
suggesting lipomobilization. CFT and RE could be used as diagnostic tools for hyperlipidemia. Reversible variations
in serum metabolites could be noticed in donkeys as complications of fasting-induced hyperlipidemia; therefore,
therapy may be unnecessary especially in less severe cases.